CORDA-3777 Reload after every checkpoint (#6494)

Enable reloading of a flow after every checkpoint is saved. This
includes reloading the checkpoint from the database and recreating the
fiber.

When a flow and its `StateMachineState` is created it checks the node's
config to see if the `reloadCheckpointAfterSuspend` is set to true. If it is
it initialises `StateMachineState.reloadCheckpointAfterSuspendCount`
with the value 0. Otherwise, it remains `null`.

This count represents how many times the flow has reloaded from its
checkpoint (not the same as retrying). It is incremented every time the
flow is reloaded.

When a flow suspends, it processes the suspend event like usual, but
it will now also check if `reloadCheckpointAfterSuspendCount` is not
`null` (that it is activated) and process a 
`ReloadFlowFromCheckpointAfterSuspend`event, if and only if 
`reloadCheckpointAfterSuspendCount` is greater than
`CheckpointState.numberOfSuspends`.

This means idempotent flows can reload from the start and not reload
again until reaching a new suspension point.

Flows that skip checkpoints can reload from a previously saved
checkpoint (or from the initial checkpoint) and will continue reloading
on reaching the next new suspension point (not the suspension point that
it skipped saving).

If the flow fails to deserialize the checkpoint from the database upon
reloading a `ReloadFlowFromCheckpointException` is throw. This causes
the flow to be kept for observation.

node/src/integration-test/kotlin/net/corda/node/flows/FlowReloadAfterCheckpointTest.kt

@@ -0,0 +1,511 @@
+package net.corda.node.flows
+
+import co.paralleluniverse.fibers.Suspendable
+import net.corda.core.flows.FlowLogic
+import net.corda.core.flows.FlowSession
+import net.corda.core.flows.HospitalizeFlowException
+import net.corda.core.flows.InitiatedBy
+import net.corda.core.flows.InitiatingFlow
+import net.corda.core.flows.StartableByRPC
+import net.corda.core.flows.StateMachineRunId
+import net.corda.core.identity.Party
+import net.corda.core.internal.FlowIORequest
+import net.corda.core.internal.IdempotentFlow
+import net.corda.core.internal.TimedFlow
+import net.corda.core.internal.concurrent.transpose
+import net.corda.core.messaging.StateMachineTransactionMapping
+import net.corda.core.messaging.startFlow
+import net.corda.core.utilities.OpaqueBytes
+import net.corda.core.utilities.getOrThrow
+import net.corda.core.utilities.seconds
+import net.corda.core.utilities.unwrap
+import net.corda.finance.DOLLARS
+import net.corda.finance.flows.CashIssueAndPaymentFlow
+import net.corda.node.services.config.NodeConfiguration
+import net.corda.node.services.statemachine.FlowStateMachineImpl
+import net.corda.node.services.statemachine.FlowTimeoutException
+import net.corda.node.services.statemachine.StaffedFlowHospital
+import net.corda.testing.core.ALICE_NAME
+import net.corda.testing.core.BOB_NAME
+import net.corda.testing.core.singleIdentity
+import net.corda.testing.driver.DriverParameters
+import net.corda.testing.driver.driver
+import net.corda.testing.node.internal.FINANCE_CORDAPPS
+import net.corda.testing.node.internal.enclosedCordapp
+import org.junit.Test
+import java.sql.SQLTransientConnectionException
+import java.util.concurrent.Semaphore
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+class FlowReloadAfterCheckpointTest {
+
+    private companion object {
+        val cordapps = listOf(enclosedCordapp())
+    }
+
+    @Test(timeout = 300_000)
+    fun `flow will reload from its checkpoint after suspending when reloadCheckpointAfterSuspend is true`() {
+        val reloadCounts = mutableMapOf<StateMachineRunId, Int>()
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { id ->
+            reloadCounts.compute(id) { _, value -> value?.plus(1) ?: 1 }
+        }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val (alice, bob) = listOf(ALICE_NAME, BOB_NAME)
+                .map {
+                    startNode(
+                        providedName = it,
+                        customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+                    )
+                }
+                .transpose()
+                .getOrThrow()
+
+            val handle = alice.rpc.startFlow(::ReloadFromCheckpointFlow, bob.nodeInfo.singleIdentity(), false, false, false)
+            val flowStartedByAlice = handle.id
+            handle.returnValue.getOrThrow()
+            assertEquals(5, reloadCounts[flowStartedByAlice])
+            assertEquals(6, reloadCounts[ReloadFromCheckpointResponder.flowId])
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `flow will not reload from its checkpoint after suspending when reloadCheckpointAfterSuspend is false`() {
+        val reloadCounts = mutableMapOf<StateMachineRunId, Int>()
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { id ->
+            reloadCounts.compute(id) { _, value -> value?.plus(1) ?: 1 }
+        }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val (alice, bob) = listOf(ALICE_NAME, BOB_NAME)
+                .map {
+                    startNode(
+                        providedName = it,
+                        customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to false)
+                    )
+                }
+                .transpose()
+                .getOrThrow()
+
+            val handle = alice.rpc.startFlow(::ReloadFromCheckpointFlow, bob.nodeInfo.singleIdentity(), false, false, false)
+            val flowStartedByAlice = handle.id
+            handle.returnValue.getOrThrow()
+            assertNull(reloadCounts[flowStartedByAlice])
+            assertNull(reloadCounts[ReloadFromCheckpointResponder.flowId])
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `flow will reload from its checkpoint after suspending when reloadCheckpointAfterSuspend is true and be kept for observation due to failed deserialization`() {
+        val reloadCounts = mutableMapOf<StateMachineRunId, Int>()
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { id ->
+            reloadCounts.compute(id) { _, value -> value?.plus(1) ?: 1 }
+        }
+        lateinit var flowKeptForObservation: StateMachineRunId
+        val lock = Semaphore(0)
+        StaffedFlowHospital.onFlowKeptForOvernightObservation.add { id, _ ->
+            flowKeptForObservation = id
+            lock.release()
+        }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val (alice, bob) = listOf(ALICE_NAME, BOB_NAME)
+                .map {
+                    startNode(
+                        providedName = it,
+                        customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+                    )
+                }
+                .transpose()
+                .getOrThrow()
+
+            val handle = alice.rpc.startFlow(::ReloadFromCheckpointFlow, bob.nodeInfo.singleIdentity(), true, false, false)
+            val flowStartedByAlice = handle.id
+            lock.acquire()
+            assertEquals(flowStartedByAlice, flowKeptForObservation)
+            assertEquals(4, reloadCounts[flowStartedByAlice])
+            assertEquals(4, reloadCounts[ReloadFromCheckpointResponder.flowId])
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `flow will reload from a previous checkpoint after calling suspending function and skipping the persisting the current checkpoint when reloadCheckpointAfterSuspend is true`() {
+        val reloadCounts = mutableMapOf<StateMachineRunId, Int>()
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { id ->
+            reloadCounts.compute(id) { _, value -> value?.plus(1) ?: 1 }
+        }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val (alice, bob) = listOf(ALICE_NAME, BOB_NAME)
+                .map {
+                    startNode(
+                        providedName = it,
+                        customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+                    )
+                }
+                .transpose()
+                .getOrThrow()
+
+            val handle = alice.rpc.startFlow(::ReloadFromCheckpointFlow, bob.nodeInfo.singleIdentity(), false, false, true)
+            val flowStartedByAlice = handle.id
+            handle.returnValue.getOrThrow()
+            assertEquals(5, reloadCounts[flowStartedByAlice])
+            assertEquals(6, reloadCounts[ReloadFromCheckpointResponder.flowId])
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `idempotent flow will reload from initial checkpoint after calling a suspending function when reloadCheckpointAfterSuspend is true`() {
+        var reloadCount = 0
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { _ -> reloadCount += 1 }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val alice = startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            alice.rpc.startFlow(::MyIdempotentFlow, false).returnValue.getOrThrow()
+            assertEquals(5, reloadCount)
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `idempotent flow will reload from initial checkpoint after calling a suspending function when reloadCheckpointAfterSuspend is true but can't throw deserialization error from objects in the call function`() {
+        var reloadCount = 0
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { _ -> reloadCount += 1 }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val alice = startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            alice.rpc.startFlow(::MyIdempotentFlow, true).returnValue.getOrThrow()
+            assertEquals(5, reloadCount)
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `timed flow will reload from initial checkpoint after calling a suspending function when reloadCheckpointAfterSuspend is true`() {
+        var reloadCount = 0
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { _ -> reloadCount += 1 }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val alice = startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            alice.rpc.startFlow(::MyTimedFlow).returnValue.getOrThrow()
+            assertEquals(5, reloadCount)
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `flow will correctly retry after an error when reloadCheckpointAfterSuspend is true`() {
+        var reloadCount = 0
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { _ -> reloadCount += 1 }
+        var timesDischarged = 0
+        StaffedFlowHospital.onFlowDischarged.add { _, _ -> timesDischarged += 1 }
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
+
+            val alice = startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            alice.rpc.startFlow(::TransientConnectionFailureFlow).returnValue.getOrThrow()
+            assertEquals(5, reloadCount)
+            assertEquals(3, timesDischarged)
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `flow continues reloading from checkpoints after node restart when reloadCheckpointAfterSuspend is true`() {
+        var reloadCount = 0
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { _ -> reloadCount += 1 }
+        driver(
+            DriverParameters(
+                inMemoryDB = false,
+                startNodesInProcess = true,
+                notarySpecs = emptyList(),
+                cordappsForAllNodes = cordapps
+            )
+        ) {
+
+            val alice = startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            alice.rpc.startFlow(::MyHospitalizingFlow)
+            Thread.sleep(10.seconds.toMillis())
+
+            alice.stop()
+
+            startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            Thread.sleep(20.seconds.toMillis())
+
+            assertEquals(5, reloadCount)
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `idempotent flow continues reloading from checkpoints after node restart when reloadCheckpointAfterSuspend is true`() {
+        var reloadCount = 0
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { _ -> reloadCount += 1 }
+        driver(
+            DriverParameters(
+                inMemoryDB = false,
+                startNodesInProcess = true,
+                notarySpecs = emptyList(),
+                cordappsForAllNodes = cordapps
+            )
+        ) {
+
+            val alice = startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            alice.rpc.startFlow(::IdempotentHospitalizingFlow)
+            Thread.sleep(10.seconds.toMillis())
+
+            alice.stop()
+
+            startNode(
+                providedName = ALICE_NAME,
+                customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+            ).getOrThrow()
+
+            Thread.sleep(20.seconds.toMillis())
+
+            // restarts completely from the beginning and forgets the in-memory reload count therefore
+            // it reloads an extra 2 times for checkpoints it had already reloaded before the node shutdown
+            assertEquals(7, reloadCount)
+        }
+    }
+
+    @Test(timeout = 300_000)
+    fun `more complicated flow will reload from its checkpoint after suspending when reloadCheckpointAfterSuspend is true`() {
+        val reloadCounts = mutableMapOf<StateMachineRunId, Int>()
+        FlowStateMachineImpl.onReloadFlowFromCheckpoint = { id ->
+            reloadCounts.compute(id) { _, value -> value?.plus(1) ?: 1 }
+        }
+        driver(DriverParameters(startNodesInProcess = true, cordappsForAllNodes = FINANCE_CORDAPPS)) {
+
+            val (alice, bob) = listOf(ALICE_NAME, BOB_NAME)
+                .map {
+                    startNode(
+                        providedName = it,
+                        customOverrides = mapOf(NodeConfiguration::reloadCheckpointAfterSuspend.name to true)
+                    )
+                }
+                .transpose()
+                .getOrThrow()
+
+            val handle = alice.rpc.startFlow(
+                ::CashIssueAndPaymentFlow,
+                500.DOLLARS,
+                OpaqueBytes.of(0x01),
+                bob.nodeInfo.singleIdentity(),
+                false,
+                defaultNotaryIdentity
+            )
+            val flowStartedByAlice = handle.id
+            handle.returnValue.getOrThrow(30.seconds)
+            val flowStartedByBob = bob.rpc.stateMachineRecordedTransactionMappingSnapshot()
+                .map(StateMachineTransactionMapping::stateMachineRunId)
+                .toSet()
+                .single()
+            Thread.sleep(10.seconds.toMillis())
+            assertEquals(7, reloadCounts[flowStartedByAlice])
+            assertEquals(6, reloadCounts[flowStartedByBob])
+        }
+    }
+
+    /**
+     * Has 4 suspension points inside the flow and 1 in [FlowStateMachineImpl.run] totaling 5.
+     * Therefore this flow should reload 5 times when completed without errors or restarts.
+     */
+    @StartableByRPC
+    @InitiatingFlow
+    class ReloadFromCheckpointFlow(
+        private val party: Party,
+        private val shouldHaveDeserializationError: Boolean,
+        private val counterPartyHasDeserializationError: Boolean,
+        private val skipCheckpoints: Boolean
+    ) : FlowLogic<Unit>() {
+
+        @Suspendable
+        override fun call() {
+            val session = initiateFlow(party)
+            session.send(counterPartyHasDeserializationError, skipCheckpoints)
+            session.receive(String::class.java, skipCheckpoints).unwrap { it }
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, skipCheckpoints)
+            val map = if (shouldHaveDeserializationError) {
+                BrokenMap(mutableMapOf("i dont want" to "this to work"))
+            } else {
+                mapOf("i dont want" to "this to work")
+            }
+            logger.info("I need to use my variable to pass the build!: $map")
+            session.sendAndReceive<String>("hey I made it this far")
+        }
+    }
+
+    /**
+     * Has 5 suspension points inside the flow and 1 in [FlowStateMachineImpl.run] totaling 6.
+     * Therefore this flow should reload 6 times when completed without errors or restarts.
+     */
+    @InitiatedBy(ReloadFromCheckpointFlow::class)
+    class ReloadFromCheckpointResponder(private val session: FlowSession) : FlowLogic<Unit>() {
+
+        companion object {
+            var flowId: StateMachineRunId? = null
+        }
+
+        @Suspendable
+        override fun call() {
+            flowId = runId
+            val counterPartyHasDeserializationError = session.receive<Boolean>().unwrap { it }
+            session.send("hello there 12312311")
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            val map = if (counterPartyHasDeserializationError) {
+                BrokenMap(mutableMapOf("i dont want" to "this to work"))
+            } else {
+                mapOf("i dont want" to "this to work")
+            }
+            logger.info("I need to use my variable to pass the build!: $map")
+            session.receive<String>().unwrap { it }
+            session.send("sending back a message")
+        }
+    }
+
+    /**
+     * Has 4 suspension points inside the flow and 1 in [FlowStateMachineImpl.run] totaling 5.
+     * Therefore this flow should reload 5 times when completed without errors or restarts.
+     */
+    @StartableByRPC
+    @InitiatingFlow
+    class MyIdempotentFlow(private val shouldHaveDeserializationError: Boolean) : FlowLogic<Unit>(), IdempotentFlow {
+
+        @Suspendable
+        override fun call() {
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            val map = if (shouldHaveDeserializationError) {
+                BrokenMap(mutableMapOf("i dont want" to "this to work"))
+            } else {
+                mapOf("i dont want" to "this to work")
+            }
+            logger.info("I need to use my variable to pass the build!: $map")
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+        }
+    }
+
+    /**
+     * Has 4 suspension points inside the flow and 1 in [FlowStateMachineImpl.run] totaling 5.
+     * Therefore this flow should reload 5 times when completed without errors or restarts.
+     */
+    @StartableByRPC
+    @InitiatingFlow
+    class MyTimedFlow : FlowLogic<Unit>(), TimedFlow {
+
+        companion object {
+            var thrown = false
+        }
+
+        override val isTimeoutEnabled: Boolean = true
+
+        @Suspendable
+        override fun call() {
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            if (!thrown) {
+                thrown = true
+                throw FlowTimeoutException()
+            }
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+        }
+    }
+
+    @StartableByRPC
+    @InitiatingFlow
+    class TransientConnectionFailureFlow : FlowLogic<Unit>() {
+
+        companion object {
+            var retryCount = 0
+        }
+
+        @Suspendable
+        override fun call() {
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            if (retryCount < 3) {
+                retryCount += 1
+                throw SQLTransientConnectionException("Connection is not available")
+
+            }
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+        }
+    }
+
+    /**
+     * Has 4 suspension points inside the flow and 1 in [FlowStateMachineImpl.run] totaling 5.
+     * Therefore this flow should reload 5 times when completed without errors or restarts.
+     */
+    @StartableByRPC
+    @InitiatingFlow
+    class MyHospitalizingFlow : FlowLogic<Unit>() {
+
+        companion object {
+            var thrown = false
+        }
+
+        @Suspendable
+        override fun call() {
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            if (!thrown) {
+                thrown = true
+                throw HospitalizeFlowException("i want to try again")
+            }
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+        }
+    }
+
+    /**
+     * Has 4 suspension points inside the flow and 1 in [FlowStateMachineImpl.run] totaling 5.
+     * Therefore this flow should reload 5 times when completed without errors or restarts.
+     */
+    @StartableByRPC
+    @InitiatingFlow
+    class IdempotentHospitalizingFlow : FlowLogic<Unit>(), IdempotentFlow {
+
+        companion object {
+            var thrown = false
+        }
+
+        @Suspendable
+        override fun call() {
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            if (!thrown) {
+                thrown = true
+                throw HospitalizeFlowException("i want to try again")
+            }
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+            stateMachine.suspend(FlowIORequest.ForceCheckpoint, false)
+        }
+    }
+}

node/src/integration-test/kotlin/net/corda/node/flows/FlowRetryTest.kt

@@ -1,10 +1,13 @@
 package net.corda.node.flows
 
 import co.paralleluniverse.fibers.Suspendable
-import net.corda.client.rpc.CordaRPCClient
-import net.corda.client.rpc.CordaRPCClientConfiguration
 import net.corda.core.CordaRuntimeException
-import net.corda.core.flows.*
+import net.corda.core.flows.FlowExternalAsyncOperation
+import net.corda.core.flows.FlowLogic
+import net.corda.core.flows.FlowSession
+import net.corda.core.flows.InitiatedBy
+import net.corda.core.flows.InitiatingFlow
+import net.corda.core.flows.StartableByRPC
 import net.corda.core.identity.Party
 import net.corda.core.internal.IdempotentFlow
 import net.corda.core.internal.concurrent.transpose
@@ -23,6 +26,7 @@ import net.corda.testing.core.singleIdentity
 import net.corda.testing.driver.DriverParameters
 import net.corda.testing.driver.driver
 import net.corda.testing.node.User
+import net.corda.testing.node.internal.enclosedCordapp
 import org.assertj.core.api.Assertions.assertThatExceptionOfType
 import org.hibernate.exception.ConstraintViolationException
 import org.junit.After
@@ -33,7 +37,8 @@ import java.sql.SQLException
 import java.sql.SQLTransientConnectionException
 import java.time.Duration
 import java.time.temporal.ChronoUnit
-import java.util.*
+import java.util.Collections
+import java.util.HashSet
 import java.util.concurrent.CompletableFuture
 import java.util.concurrent.TimeoutException
 import kotlin.test.assertEquals
@@ -41,7 +46,11 @@ import kotlin.test.assertFailsWith
 import kotlin.test.assertNotNull
 
 class FlowRetryTest {
-    val config = CordaRPCClientConfiguration.DEFAULT.copy(connectionRetryIntervalMultiplier = 1.1)
+
+    private companion object {
+        val user = User("mark", "dadada", setOf(Permissions.all()))
+        val cordapps = listOf(enclosedCordapp())
+    }
 
     @Before
     fun resetCounters() {
@@ -62,19 +71,19 @@ class FlowRetryTest {
     fun `flows continue despite errors`() {
         val numSessions = 2
         val numIterations = 10
-        val user = User("mark", "dadada", setOf(Permissions.startFlow<InitiatorFlow>()))
+        val result: Any? = driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList())) {
-        val result: Any? = driver(DriverParameters(
+
-                startNodesInProcess = isQuasarAgentSpecified(),
-                notarySpecs = emptyList()
-        )) {
             val (nodeAHandle, nodeBHandle) = listOf(ALICE_NAME, BOB_NAME)
                 .map { startNode(providedName = it, rpcUsers = listOf(user)) }
                 .transpose()
                 .getOrThrow()
 
-            val result = CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
+            val result = nodeAHandle.rpc.startFlow(
-                it.proxy.startFlow(::InitiatorFlow, numSessions, numIterations, nodeBHandle.nodeInfo.singleIdentity()).returnValue.getOrThrow()
+                ::InitiatorFlow,
-            }
+                numSessions,
+                numIterations,
+                nodeBHandle.nodeInfo.singleIdentity()
+            ).returnValue.getOrThrow()
             result
         }
         assertNotNull(result)
@@ -83,132 +92,112 @@ class FlowRetryTest {
 
     @Test(timeout = 300_000)
     fun `async operation deduplication id is stable accross retries`() {
-        val user = User("mark", "dadada", setOf(Permissions.startFlow<AsyncRetryFlow>()))
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
-        driver(DriverParameters(
-                startNodesInProcess = isQuasarAgentSpecified(),
-                notarySpecs = emptyList()
-        )) {
             val nodeAHandle = startNode(providedName = ALICE_NAME, rpcUsers = listOf(user)).getOrThrow()
-
+            nodeAHandle.rpc.startFlow(::AsyncRetryFlow).returnValue.getOrThrow()
-            CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
-                it.proxy.startFlow(::AsyncRetryFlow).returnValue.getOrThrow()
-            }
         }
     }
 
     @Test(timeout = 300_000)
     fun `flow gives up after number of exceptions, even if this is the first line of the flow`() {
-        val user = User("mark", "dadada", setOf(Permissions.startFlow<RetryFlow>()))
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
-        assertThatExceptionOfType(CordaRuntimeException::class.java).isThrownBy {
-            driver(DriverParameters(
-                    startNodesInProcess = isQuasarAgentSpecified(),
-                    notarySpecs = emptyList()
-            )) {
             val nodeAHandle = startNode(providedName = ALICE_NAME, rpcUsers = listOf(user)).getOrThrow()
-
+            assertFailsWith<CordaRuntimeException> {
-                val result = CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
+                nodeAHandle.rpc.startFlow(::RetryFlow).returnValue.getOrThrow()
-                    it.proxy.startFlow(::RetryFlow).returnValue.getOrThrow()
-                }
-                result
             }
         }
     }
 
     @Test(timeout = 300_000)
     fun `flow that throws in constructor throw for the RPC client that attempted to start them`() {
-        val user = User("mark", "dadada", setOf(Permissions.startFlow<ThrowingFlow>()))
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
-        assertThatExceptionOfType(CordaRuntimeException::class.java).isThrownBy {
-            driver(DriverParameters(
-                    startNodesInProcess = isQuasarAgentSpecified(),
-                    notarySpecs = emptyList()
-            )) {
             val nodeAHandle = startNode(providedName = ALICE_NAME, rpcUsers = listOf(user)).getOrThrow()
-
+            assertFailsWith<CordaRuntimeException> {
-                val result = CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
+                nodeAHandle.rpc.startFlow(::ThrowingFlow).returnValue.getOrThrow()
-                    it.proxy.startFlow(::ThrowingFlow).returnValue.getOrThrow()
-                }
-                result
             }
         }
     }
 
     @Test(timeout = 300_000)
     fun `SQLTransientConnectionExceptions thrown by hikari are retried 3 times and then kept in the checkpoints table`() {
-        val user = User("mark", "dadada", setOf(Permissions.all()))
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
-        driver(DriverParameters(isDebug = true, startNodesInProcess = isQuasarAgentSpecified())) {
 
             val (nodeAHandle, nodeBHandle) = listOf(ALICE_NAME, BOB_NAME)
                 .map { startNode(providedName = it, rpcUsers = listOf(user)) }
                 .transpose()
                 .getOrThrow()
-            CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
+
             assertFailsWith<TimeoutException> {
-                    it.proxy.startFlow(::TransientConnectionFailureFlow, nodeBHandle.nodeInfo.singleIdentity())
+                nodeAHandle.rpc.startFlow(::TransientConnectionFailureFlow, nodeBHandle.nodeInfo.singleIdentity())
                     .returnValue.getOrThrow(Duration.of(10, ChronoUnit.SECONDS))
             }
             assertEquals(3, TransientConnectionFailureFlow.retryCount)
-                assertEquals(1, it.proxy.startFlow(::GetCheckpointNumberOfStatusFlow, Checkpoint.FlowStatus.HOSPITALIZED).returnValue.get())
+            assertEquals(
-            }
+                1,
+                nodeAHandle.rpc.startFlow(::GetCheckpointNumberOfStatusFlow, Checkpoint.FlowStatus.HOSPITALIZED).returnValue.get()
+            )
         }
     }
 
     @Test(timeout = 300_000)
     fun `Specific exception still detected even if it is nested inside another exception`() {
-        val user = User("mark", "dadada", setOf(Permissions.all()))
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
-        driver(DriverParameters(isDebug = true, startNodesInProcess = isQuasarAgentSpecified())) {
 
             val (nodeAHandle, nodeBHandle) = listOf(ALICE_NAME, BOB_NAME)
                 .map { startNode(providedName = it, rpcUsers = listOf(user)) }
                 .transpose()
                 .getOrThrow()
-            CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
+
             assertFailsWith<TimeoutException> {
-                    it.proxy.startFlow(::WrappedTransientConnectionFailureFlow, nodeBHandle.nodeInfo.singleIdentity())
+                nodeAHandle.rpc.startFlow(::WrappedTransientConnectionFailureFlow, nodeBHandle.nodeInfo.singleIdentity())
                     .returnValue.getOrThrow(Duration.of(10, ChronoUnit.SECONDS))
             }
             assertEquals(3, WrappedTransientConnectionFailureFlow.retryCount)
-                assertEquals(1, it.proxy.startFlow(::GetCheckpointNumberOfStatusFlow, Checkpoint.FlowStatus.HOSPITALIZED).returnValue.get())
+            assertEquals(
-            }
+                1,
+                nodeAHandle.rpc.startFlow(::GetCheckpointNumberOfStatusFlow, Checkpoint.FlowStatus.HOSPITALIZED).returnValue.get()
+            )
         }
     }
 
     @Test(timeout = 300_000)
     fun `General external exceptions are not retried and propagate`() {
-        val user = User("mark", "dadada", setOf(Permissions.all()))
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
-        driver(DriverParameters(isDebug = true, startNodesInProcess = isQuasarAgentSpecified())) {
 
             val (nodeAHandle, nodeBHandle) = listOf(ALICE_NAME, BOB_NAME)
                 .map { startNode(providedName = it, rpcUsers = listOf(user)) }
                 .transpose()
                 .getOrThrow()
 
-            CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
             assertFailsWith<CordaRuntimeException> {
-                    it.proxy.startFlow(::GeneralExternalFailureFlow, nodeBHandle.nodeInfo.singleIdentity()).returnValue.getOrThrow()
+                nodeAHandle.rpc.startFlow(
+                    ::GeneralExternalFailureFlow,
+                    nodeBHandle.nodeInfo.singleIdentity()
+                ).returnValue.getOrThrow()
             }
             assertEquals(0, GeneralExternalFailureFlow.retryCount)
-                assertEquals(1, it.proxy.startFlow(::GetCheckpointNumberOfStatusFlow, Checkpoint.FlowStatus.FAILED).returnValue.get())
+            assertEquals(
-            }
+                1,
+                nodeAHandle.rpc.startFlow(::GetCheckpointNumberOfStatusFlow, Checkpoint.FlowStatus.FAILED).returnValue.get()
+            )
         }
     }
 
     @Test(timeout = 300_000)
     fun `Permission exceptions are not retried and propagate`() {
         val user = User("mark", "dadada", setOf())
-        driver(DriverParameters(isDebug = true, startNodesInProcess = isQuasarAgentSpecified())) {
+        driver(DriverParameters(startNodesInProcess = true, notarySpecs = emptyList(), cordappsForAllNodes = cordapps)) {
 
             val nodeAHandle = startNode(providedName = ALICE_NAME, rpcUsers = listOf(user)).getOrThrow()
 
-            CordaRPCClient(nodeAHandle.rpcAddress, config).start(user.username, user.password).use {
             assertThatExceptionOfType(CordaRuntimeException::class.java).isThrownBy {
-                    it.proxy.startFlow(::AsyncRetryFlow).returnValue.getOrThrow()
+                nodeAHandle.rpc.startFlow(::AsyncRetryFlow).returnValue.getOrThrow()
             }.withMessageStartingWith("User not authorized to perform RPC call")
             // This stays at -1 since the flow never even got called
             assertEquals(-1, GeneralExternalFailureFlow.retryCount)
         }
     }
 }
-}
 
 fun isQuasarAgentSpecified(): Boolean {
     val jvmArgs = ManagementFactory.getRuntimeMXBean().inputArguments
@@ -315,6 +304,10 @@ enum class Step { First, BeforeInitiate, AfterInitiate, AfterInitiateSendReceive
 
 data class Visited(val sessionNum: Int, val iterationNum: Int, val step: Step)
 
+class BrokenMap<K, V>(delegate: MutableMap<K, V> = mutableMapOf()) : MutableMap<K, V> by delegate {
+    override fun put(key: K, value: V): V? = throw IllegalStateException("Broken on purpose")
+}
+
 @StartableByRPC
 class RetryFlow() : FlowLogic<String>(), IdempotentFlow {
     companion object {
@@ -424,7 +417,8 @@ class WrappedTransientConnectionFailureFlow(private val party: Party) : FlowLogi
         retryCount += 1
         throw IllegalStateException(
             "wrapped error message",
-                IllegalStateException("another layer deep", SQLTransientConnectionException("Connection is not available")))
+            IllegalStateException("another layer deep", SQLTransientConnectionException("Connection is not available"))
+        )
     }
 }
 
@@ -465,6 +459,8 @@ class GeneralExternalFailureResponder(private val session: FlowSession) : FlowLo
 
 @StartableByRPC
 class GetCheckpointNumberOfStatusFlow(private val flowStatus: Checkpoint.FlowStatus) : FlowLogic<Long>() {
+
+    @Suspendable
     override fun call(): Long {
         val sqlStatement =
             "select count(*) " +

node/src/main/kotlin/net/corda/node/services/config/NodeConfiguration.kt

@@ -93,6 +93,8 @@ interface NodeConfiguration : ConfigurationWithOptionsContainer {
 
     val quasarExcludePackages: List<String>
 
+    val reloadCheckpointAfterSuspend: Boolean
+
     companion object {
         // default to at least 8MB and a bit extra for larger heap sizes
         val defaultTransactionCacheSize: Long = 8.MB + getAdditionalCacheMemory()
@@ -125,6 +127,10 @@ enum class JmxReporterType {
 }
 
 data class DevModeOptions(
+    @Deprecated(
+        "The checkpoint checker has been replaced by the ability to reload a checkpoint from the database after every suspend" +
+                "Use [NodeConfiguration.disableReloadCheckpointAfterSuspend] instead."
+    )
     val disableCheckpointChecker: Boolean = Defaults.disableCheckpointChecker,
     val allowCompatibilityZone: Boolean = Defaults.allowCompatibilityZone,
     val djvm: DJVMOptions? = null
@@ -140,10 +146,6 @@ data class DJVMOptions(
    val cordaSource: List<String>
 )
 
-fun NodeConfiguration.shouldCheckCheckpoints(): Boolean {
-    return this.devMode && this.devModeOptions?.disableCheckpointChecker != true
-}
-
 fun NodeConfiguration.shouldStartSSHDaemon() = this.sshd != null
 fun NodeConfiguration.shouldStartLocalShell() = !this.noLocalShell && System.console() != null && this.devMode
 fun NodeConfiguration.shouldInitCrashShell() = shouldStartLocalShell() || shouldStartSSHDaemon()

node/src/main/kotlin/net/corda/node/services/config/NodeConfigurationImpl.kt

@@ -84,7 +84,9 @@ data class NodeConfigurationImpl(
         override val blacklistedAttachmentSigningKeys: List<String> = Defaults.blacklistedAttachmentSigningKeys,
         override val configurationWithOptions: ConfigurationWithOptions,
         override val flowExternalOperationThreadPoolSize: Int = Defaults.flowExternalOperationThreadPoolSize,
-        override val quasarExcludePackages: List<String> = Defaults.quasarExcludePackages
+        override val quasarExcludePackages: List<String> = Defaults.quasarExcludePackages,
+        override val reloadCheckpointAfterSuspend: Boolean = Defaults.reloadCheckpointAfterSuspend
+
 ) : NodeConfiguration {
     internal object Defaults {
         val jmxMonitoringHttpPort: Int? = null
@@ -123,6 +125,7 @@ data class NodeConfigurationImpl(
         val blacklistedAttachmentSigningKeys: List<String> = emptyList()
         const val flowExternalOperationThreadPoolSize: Int = 1
         val quasarExcludePackages: List<String> = emptyList()
+        val reloadCheckpointAfterSuspend: Boolean = System.getProperty("reloadCheckpointAfterSuspend", "false")!!.toBoolean()
 
         fun cordappsDirectories(baseDirectory: Path) = listOf(baseDirectory / CORDAPPS_DIR_NAME_DEFAULT)
 

node/src/main/kotlin/net/corda/node/services/config/schema/v1/V1NodeConfigurationSpec.kt

@@ -8,6 +8,7 @@ import net.corda.common.validation.internal.Validated.Companion.invalid
 import net.corda.common.validation.internal.Validated.Companion.valid
 import net.corda.node.services.config.*
 import net.corda.node.services.config.NodeConfigurationImpl.Defaults
+import net.corda.node.services.config.NodeConfigurationImpl.Defaults.reloadCheckpointAfterSuspend
 import net.corda.node.services.config.schema.parsers.*
 
 internal object V1NodeConfigurationSpec : Configuration.Specification<NodeConfiguration>("NodeConfiguration") {
@@ -66,6 +67,7 @@ internal object V1NodeConfigurationSpec : Configuration.Specification<NodeConfig
             .withDefaultValue(Defaults.networkParameterAcceptanceSettings)
     private val flowExternalOperationThreadPoolSize by int().optional().withDefaultValue(Defaults.flowExternalOperationThreadPoolSize)
     private val quasarExcludePackages by string().list().optional().withDefaultValue(Defaults.quasarExcludePackages)
+    private val reloadCheckpointAfterSuspend by boolean().optional().withDefaultValue(Defaults.reloadCheckpointAfterSuspend)
     @Suppress("unused")
     private val custom by nestedObject().optional()
     @Suppress("unused")
@@ -133,7 +135,8 @@ internal object V1NodeConfigurationSpec : Configuration.Specification<NodeConfig
                     networkParameterAcceptanceSettings = config[networkParameterAcceptanceSettings],
                     configurationWithOptions = ConfigurationWithOptions(configuration, Configuration.Options.defaults),
                     flowExternalOperationThreadPoolSize = config[flowExternalOperationThreadPoolSize],
-                    quasarExcludePackages = config[quasarExcludePackages]
+                    quasarExcludePackages = config[quasarExcludePackages],
+                    reloadCheckpointAfterSuspend = config[reloadCheckpointAfterSuspend]
             ))
         } catch (e: Exception) {
             return when (e) {

node/src/main/kotlin/net/corda/node/services/statemachine/Event.kt

@@ -148,12 +148,21 @@ sealed class Event {
     data class AsyncOperationThrows(val throwable: Throwable) : Event()
 
     /**
-     * Retry a flow from the last checkpoint, or if there is no checkpoint, restart the flow with the same invocation details.
+     * Retry a flow from its last checkpoint, or if there is no checkpoint, restart the flow with the same invocation details.
      */
     object RetryFlowFromSafePoint : Event() {
         override fun toString() = "RetryFlowFromSafePoint"
     }
 
+    /**
+     * Reload a flow from its last checkpoint, or if there is no checkpoint, restart the flow with the same invocation details.
+     * This is separate from [RetryFlowFromSafePoint] which is used for error handling within the state machine.
+     * [ReloadFlowFromCheckpointAfterSuspend] is only used when [NodeConfiguration.reloadCheckpointAfterSuspend] is true.
+     */
+    object ReloadFlowFromCheckpointAfterSuspend : Event() {
+        override fun toString() = "ReloadFlowFromCheckpointAfterSuspend"
+    }
+
     /**
      * Keeps a flow for overnight observation. Overnight observation practically sends the fiber to get suspended,
      * in [FlowStateMachineImpl.processEventsUntilFlowIsResumed]. Since the fiber's channel will have no more events to process,

node/src/main/kotlin/net/corda/node/services/statemachine/FlowCreator.kt

@@ -19,6 +19,7 @@ import net.corda.core.utilities.contextLogger
 import net.corda.node.services.api.CheckpointStorage
 import net.corda.node.services.api.ServiceHubInternal
 import net.corda.node.services.messaging.DeduplicationHandler
+import net.corda.node.services.statemachine.FlowStateMachineImpl.Companion.currentStateMachine
 import net.corda.node.services.statemachine.transitions.StateMachine
 import net.corda.node.utilities.isEnabledTimedFlow
 import net.corda.nodeapi.internal.persistence.CordaPersistence
@@ -36,21 +37,23 @@ class NonResidentFlow(val runId: StateMachineRunId, val checkpoint: Checkpoint)
 }
 
 class FlowCreator(
-    val checkpointSerializationContext: CheckpointSerializationContext,
+    private val checkpointSerializationContext: CheckpointSerializationContext,
     private val checkpointStorage: CheckpointStorage,
-    val scheduler: FiberScheduler,
+    private val scheduler: FiberScheduler,
-    val database: CordaPersistence,
+    private val database: CordaPersistence,
-    val transitionExecutor: TransitionExecutor,
+    private val transitionExecutor: TransitionExecutor,
-    val actionExecutor: ActionExecutor,
+    private val actionExecutor: ActionExecutor,
-    val secureRandom: SecureRandom,
+    private val secureRandom: SecureRandom,
-    val serviceHub: ServiceHubInternal,
+    private val serviceHub: ServiceHubInternal,
-    val unfinishedFibers: ReusableLatch,
+    private val unfinishedFibers: ReusableLatch,
-    val resetCustomTimeout: (StateMachineRunId, Long) -> Unit) {
+    private val resetCustomTimeout: (StateMachineRunId, Long) -> Unit) {
 
     companion object {
         private val logger = contextLogger()
     }
 
+    private val reloadCheckpointAfterSuspend = serviceHub.configuration.reloadCheckpointAfterSuspend
+
     fun createFlowFromNonResidentFlow(nonResidentFlow: NonResidentFlow): Flow<*>? {
         // As for paused flows we don't extract the serialized flow state we need to re-extract the checkpoint from the database.
         val checkpoint = when (nonResidentFlow.checkpoint.status) {
@@ -65,13 +68,23 @@ class FlowCreator(
         return createFlowFromCheckpoint(nonResidentFlow.runId, checkpoint)
     }
 
-    fun createFlowFromCheckpoint(runId: StateMachineRunId, oldCheckpoint: Checkpoint): Flow<*>? {
+    fun createFlowFromCheckpoint(
+        runId: StateMachineRunId,
+        oldCheckpoint: Checkpoint,
+        reloadCheckpointAfterSuspendCount: Int? = null
+    ): Flow<*>? {
         val checkpoint = oldCheckpoint.copy(status = Checkpoint.FlowStatus.RUNNABLE)
         val fiber = checkpoint.getFiberFromCheckpoint(runId) ?: return null
         val resultFuture = openFuture<Any?>()
         fiber.logic.stateMachine = fiber
         verifyFlowLogicIsSuspendable(fiber.logic)
-        val state = createStateMachineState(checkpoint, fiber, true)
+        val state = createStateMachineState(
+            checkpoint = checkpoint,
+            fiber = fiber,
+            anyCheckpointPersisted = true,
+            reloadCheckpointAfterSuspendCount = reloadCheckpointAfterSuspendCount
+                ?: if (reloadCheckpointAfterSuspend) checkpoint.checkpointState.numberOfSuspends else null
+        )
         fiber.transientValues = createTransientValues(runId, resultFuture)
         fiber.transientState = state
         return Flow(fiber, resultFuture)
@@ -108,11 +121,13 @@ class FlowCreator(
         ).getOrThrow()
 
         val state = createStateMachineState(
-            checkpoint,
+            checkpoint = checkpoint,
-            flowStateMachineImpl,
+            fiber = flowStateMachineImpl,
-            existingCheckpoint != null,
+            anyCheckpointPersisted = existingCheckpoint != null,
-             deduplicationHandler,
+            reloadCheckpointAfterSuspendCount = if (reloadCheckpointAfterSuspend) 0 else null,
-             senderUUID)
+            deduplicationHandler = deduplicationHandler,
+            senderUUID = senderUUID
+        )
         flowStateMachineImpl.transientState = state
         return  Flow(flowStateMachineImpl, resultFuture)
     }
@@ -125,9 +140,7 @@ class FlowCreator(
             }
             is FlowState.Started -> tryCheckpointDeserialize(this.flowState.frozenFiber, runId) ?: return null
             // Places calling this function is rely on it to return null if the flow cannot be created from the checkpoint.
-            else -> {
+            else -> null
-                return null
-            }
         }
     }
 
@@ -136,10 +149,18 @@ class FlowCreator(
         return try {
             bytes.checkpointDeserialize(context = checkpointSerializationContext)
         } catch (e: Exception) {
+            if (reloadCheckpointAfterSuspend && currentStateMachine() != null) {
+                logger.error(
+                    "Unable to deserialize checkpoint for flow $flowId. [reloadCheckpointAfterSuspend] is turned on, throwing exception",
+                    e
+                )
+                throw ReloadFlowFromCheckpointException(e)
+            } else {
                 logger.error("Unable to deserialize checkpoint for flow $flowId. Something is very wrong and this flow will be ignored.", e)
                 null
             }
         }
+    }
 
     private fun verifyFlowLogicIsSuspendable(logic: FlowLogic<Any?>) {
         // Quasar requires (in Java 8) that at least the call method be annotated suspendable. Unfortunately, it's
@@ -169,12 +190,15 @@ class FlowCreator(
         )
     }
 
+    @Suppress("LongParameterList")
     private fun createStateMachineState(
         checkpoint: Checkpoint,
         fiber: FlowStateMachineImpl<*>,
         anyCheckpointPersisted: Boolean,
+        reloadCheckpointAfterSuspendCount: Int?,
         deduplicationHandler: DeduplicationHandler? = null,
-            senderUUID: String? = null): StateMachineState {
+        senderUUID: String? = null
+    ): StateMachineState {
         return StateMachineState(
             checkpoint = checkpoint,
             pendingDeduplicationHandlers = deduplicationHandler?.let { listOf(it) } ?: emptyList(),
@@ -186,6 +210,8 @@ class FlowCreator(
             isRemoved = false,
             isKilled = false,
             flowLogic = fiber.logic,
-            senderUUID = senderUUID)
+            senderUUID = senderUUID,
+            reloadCheckpointAfterSuspendCount = reloadCheckpointAfterSuspendCount
+        )
     }
 }

node/src/main/kotlin/net/corda/node/services/statemachine/FlowStateMachineImpl.kt

@@ -29,6 +29,7 @@ import net.corda.core.internal.DeclaredField
 import net.corda.core.internal.FlowIORequest
 import net.corda.core.internal.FlowStateMachine
 import net.corda.core.internal.IdempotentFlow
+import net.corda.core.internal.VisibleForTesting
 import net.corda.core.internal.concurrent.OpenFuture
 import net.corda.core.internal.isIdempotentFlow
 import net.corda.core.internal.isRegularFile
@@ -87,6 +88,9 @@ class FlowStateMachineImpl<R>(override val id: StateMachineRunId,
         private val log: Logger = LoggerFactory.getLogger("net.corda.flow")
 
         private val SERIALIZER_BLOCKER = Fiber::class.java.getDeclaredField("SERIALIZER_BLOCKER").apply { isAccessible = true }.get(null)
+
+        @VisibleForTesting
+        var onReloadFlowFromCheckpoint: ((id: StateMachineRunId) -> Unit)? = null
     }
 
     data class TransientValues(
@@ -529,6 +533,18 @@ class FlowStateMachineImpl<R>(override val id: StateMachineRunId,
                 unpark(SERIALIZER_BLOCKER)
             }
         }
+
+        transientState.reloadCheckpointAfterSuspendCount?.let { count ->
+            if (count < transientState.checkpoint.checkpointState.numberOfSuspends) {
+                onReloadFlowFromCheckpoint?.invoke(id)
+                processEventImmediately(
+                    Event.ReloadFlowFromCheckpointAfterSuspend,
+                    isDbTransactionOpenOnEntry = false,
+                    isDbTransactionOpenOnExit = false
+                )
+            }
+        }
+
         return uncheckedCast(processEventsUntilFlowIsResumed(
                 isDbTransactionOpenOnEntry = false,
                 isDbTransactionOpenOnExit = true

node/src/main/kotlin/net/corda/node/services/statemachine/SingleThreadedStateMachineManager.kt

@@ -30,11 +30,9 @@ import net.corda.core.utilities.debug
 import net.corda.node.internal.InitiatedFlowFactory
 import net.corda.node.services.api.CheckpointStorage
 import net.corda.node.services.api.ServiceHubInternal
-import net.corda.node.services.config.shouldCheckCheckpoints
 import net.corda.node.services.messaging.DeduplicationHandler
+import net.corda.node.services.statemachine.FlowStateMachineImpl.Companion.currentStateMachine
 import net.corda.node.services.statemachine.interceptors.DumpHistoryOnErrorInterceptor
-import net.corda.node.services.statemachine.interceptors.FiberDeserializationChecker
-import net.corda.node.services.statemachine.interceptors.FiberDeserializationCheckingInterceptor
 import net.corda.node.services.statemachine.interceptors.HospitalisingInterceptor
 import net.corda.node.services.statemachine.interceptors.PrintingInterceptor
 import net.corda.node.utilities.AffinityExecutor
@@ -89,7 +87,6 @@ internal class SingleThreadedStateMachineManager(
     private val flowMessaging: FlowMessaging = FlowMessagingImpl(serviceHub)
     private val actionFutureExecutor = ActionFutureExecutor(innerState, serviceHub, scheduledFutureExecutor)
     private val flowTimeoutScheduler = FlowTimeoutScheduler(innerState, scheduledFutureExecutor, serviceHub)
-    private val fiberDeserializationChecker = if (serviceHub.configuration.shouldCheckCheckpoints()) FiberDeserializationChecker() else null
     private val ourSenderUUID = serviceHub.networkService.ourSenderUUID
 
     private var checkpointSerializationContext: CheckpointSerializationContext? = null
@@ -97,6 +94,7 @@ internal class SingleThreadedStateMachineManager(
 
     override val flowHospital: StaffedFlowHospital = makeFlowHospital()
     private val transitionExecutor = makeTransitionExecutor()
+    private val reloadCheckpointAfterSuspend = serviceHub.configuration.reloadCheckpointAfterSuspend
 
     override val allStateMachines: List<FlowLogic<*>>
         get() = innerState.withLock { flows.values.map { it.fiber.logic } }
@@ -124,7 +122,6 @@ internal class SingleThreadedStateMachineManager(
         )
         this.checkpointSerializationContext = checkpointSerializationContext
         val actionExecutor = makeActionExecutor(checkpointSerializationContext)
-        fiberDeserializationChecker?.start(checkpointSerializationContext)
         when (startMode) {
             StateMachineManager.StartMode.ExcludingPaused -> {}
             StateMachineManager.StartMode.Safe -> markAllFlowsAsPaused()
@@ -207,10 +204,6 @@ internal class SingleThreadedStateMachineManager(
         // Account for any expected Fibers in a test scenario.
         liveFibers.countDown(allowedUnsuspendedFiberCount)
         liveFibers.await()
-        fiberDeserializationChecker?.let {
-            val foundUnrestorableFibers = it.stop()
-            check(!foundUnrestorableFibers) { "Unrestorable checkpoints were created, please check the logs for details." }
-        }
         flowHospital.close()
         scheduledFutureExecutor.shutdown()
         scheduler.shutdown()
@@ -397,7 +390,7 @@ internal class SingleThreadedStateMachineManager(
 
             val checkpoint = tryDeserializeCheckpoint(serializedCheckpoint, flowId) ?: return
             // Resurrect flow
-            flowCreator.createFlowFromCheckpoint(flowId, checkpoint) ?: return
+            flowCreator.createFlowFromCheckpoint(flowId, checkpoint, currentState.reloadCheckpointAfterSuspendCount) ?: return
         } else {
             // Just flow initiation message
             null
@@ -632,10 +625,18 @@ internal class SingleThreadedStateMachineManager(
         return try {
             serializedCheckpoint.deserialize(checkpointSerializationContext!!)
         } catch (e: Exception) {
+            if (reloadCheckpointAfterSuspend && currentStateMachine() != null) {
+                logger.error(
+                    "Unable to deserialize checkpoint for flow $flowId. [reloadCheckpointAfterSuspend] is turned on, throwing exception",
+                    e
+                )
+                throw ReloadFlowFromCheckpointException(e)
+            } else {
                 logger.error("Unable to deserialize checkpoint for flow $flowId. Something is very wrong and this flow will be ignored.", e)
                 null
             }
         }
+    }
 
     private fun addAndStartFlow(id: StateMachineRunId, flow: Flow<*>) {
         val checkpoint = flow.fiber.snapshot().checkpoint
@@ -700,9 +701,6 @@ internal class SingleThreadedStateMachineManager(
         if (serviceHub.configuration.devMode) {
             interceptors.add { DumpHistoryOnErrorInterceptor(it) }
         }
-        if (serviceHub.configuration.shouldCheckCheckpoints()) {
-            interceptors.add { FiberDeserializationCheckingInterceptor(fiberDeserializationChecker!!, it) }
-        }
         if (logger.isDebugEnabled) {
             interceptors.add { PrintingInterceptor(it) }
         }

node/src/main/kotlin/net/corda/node/services/statemachine/StaffedFlowHospital.kt

@@ -589,6 +589,7 @@ class StaffedFlowHospital(private val flowMessaging: FlowMessaging,
             return if (newError.mentionsThrowable(StateTransitionException::class.java)) {
                 when {
                     newError.mentionsThrowable(InterruptedException::class.java) -> Diagnosis.TERMINAL
+                    newError.mentionsThrowable(ReloadFlowFromCheckpointException::class.java) -> Diagnosis.OVERNIGHT_OBSERVATION
                     newError.mentionsThrowable(AsyncOperationTransitionException::class.java) -> Diagnosis.NOT_MY_SPECIALTY
                     history.notDischargedForTheSameThingMoreThan(2, this, currentState) -> Diagnosis.DISCHARGE
                     else -> Diagnosis.OVERNIGHT_OBSERVATION

node/src/main/kotlin/net/corda/node/services/statemachine/StateMachineState.kt

@@ -59,7 +59,8 @@ data class StateMachineState(
     val isRemoved: Boolean,
     @Volatile
     var isKilled: Boolean,
-    val senderUUID: String?
+    val senderUUID: String?,
+    val reloadCheckpointAfterSuspendCount: Int?
 ) : KryoSerializable {
     override fun write(kryo: Kryo?, output: Output?) {
         throw IllegalStateException("${StateMachineState::class.qualifiedName} should never be serialized")

node/src/main/kotlin/net/corda/node/services/statemachine/StateTransitionExceptions.kt

@@ -1,6 +1,6 @@
 package net.corda.node.services.statemachine
 
-import net.corda.core.CordaException
+import net.corda.core.CordaRuntimeException
 import net.corda.core.serialization.ConstructorForDeserialization
 
 // CORDA-3353 - These exceptions should not be propagated up to rpc as they suppress the real exceptions
@@ -9,12 +9,17 @@ class StateTransitionException(
     val transitionAction: Action?,
     val transitionEvent: Event?,
     val exception: Exception
-) : CordaException(exception.message, exception) {
+) : CordaRuntimeException(exception.message, exception) {
 
     @ConstructorForDeserialization
     constructor(exception: Exception): this(null, null, exception)
 }
 
-class AsyncOperationTransitionException(exception: Exception) : CordaException(exception.message, exception)
+class AsyncOperationTransitionException(exception: Exception) : CordaRuntimeException(exception.message, exception)
 
-class ErrorStateTransitionException(val exception: Exception) : CordaException(exception.message, exception)
+class ErrorStateTransitionException(val exception: Exception) : CordaRuntimeException(exception.message, exception)
+
+class ReloadFlowFromCheckpointException(cause: Exception) : CordaRuntimeException(
+    "Could not reload flow from checkpoint. This is likely due to a discrepancy " +
+            "between the serialization and deserialization of an object in the flow's checkpoint", cause
+)

node/src/main/kotlin/net/corda/node/services/statemachine/interceptors/FiberDeserializationCheckingInterceptor.kt

@@ -1,101 +0,0 @@
-package net.corda.node.services.statemachine.interceptors
-
-import co.paralleluniverse.fibers.Suspendable
-import net.corda.core.serialization.SerializedBytes
-import net.corda.core.serialization.internal.CheckpointSerializationContext
-import net.corda.core.serialization.internal.checkpointDeserialize
-import net.corda.core.utilities.contextLogger
-import net.corda.node.services.statemachine.ActionExecutor
-import net.corda.node.services.statemachine.Event
-import net.corda.node.services.statemachine.FlowFiber
-import net.corda.node.services.statemachine.FlowState
-import net.corda.node.services.statemachine.FlowStateMachineImpl
-import net.corda.node.services.statemachine.StateMachineState
-import net.corda.node.services.statemachine.TransitionExecutor
-import net.corda.node.services.statemachine.transitions.FlowContinuation
-import net.corda.node.services.statemachine.transitions.TransitionResult
-import java.util.concurrent.LinkedBlockingQueue
-import kotlin.concurrent.thread
-
-/**
- * This interceptor checks whether a checkpointed fiber state can be deserialised in a separate thread.
- */
-class FiberDeserializationCheckingInterceptor(
-        val fiberDeserializationChecker: FiberDeserializationChecker,
-        val delegate: TransitionExecutor
-) : TransitionExecutor {
-
-    @Suspendable
-    override fun executeTransition(
-            fiber: FlowFiber,
-            previousState: StateMachineState,
-            event: Event,
-            transition: TransitionResult,
-            actionExecutor: ActionExecutor
-    ): Pair<FlowContinuation, StateMachineState> {
-        val (continuation, nextState) = delegate.executeTransition(fiber, previousState, event, transition, actionExecutor)
-        val previousFlowState = previousState.checkpoint.flowState
-        val nextFlowState = nextState.checkpoint.flowState
-        if (nextFlowState is FlowState.Started) {
-            if (previousFlowState !is FlowState.Started || previousFlowState.frozenFiber != nextFlowState.frozenFiber) {
-                fiberDeserializationChecker.submitCheck(nextFlowState.frozenFiber)
-            }
-        }
-        return Pair(continuation, nextState)
-    }
-}
-
-/**
- * A fiber deserialisation checker thread. It checks the queued up serialised checkpoints to see if they can be
- * deserialised. This is only run in development mode to allow detecting of corrupt serialised checkpoints before they
- * are actually used.
- */
-class FiberDeserializationChecker {
-    companion object {
-        val log = contextLogger()
-    }
-
-    private sealed class Job {
-        class Check(val serializedFiber: SerializedBytes<FlowStateMachineImpl<*>>) : Job()
-        object Finish : Job()
-    }
-
-    private var checkerThread: Thread? = null
-    private val jobQueue = LinkedBlockingQueue<Job>()
-    private var foundUnrestorableFibers: Boolean = false
-
-    fun start(checkpointSerializationContext: CheckpointSerializationContext) {
-        require(checkerThread == null){"Checking thread must not already be started"}
-        checkerThread = thread(name = "FiberDeserializationChecker") {
-            while (true) {
-                val job = jobQueue.take()
-                when (job) {
-                    is Job.Check -> {
-                        try {
-                            job.serializedFiber.checkpointDeserialize(context = checkpointSerializationContext)
-                        } catch (exception: Exception) {
-                            log.error("Encountered unrestorable checkpoint!", exception)
-                            foundUnrestorableFibers = true
-                        }
-                    }
-                    Job.Finish -> {
-                        return@thread
-                    }
-                }
-            }
-        }
-    }
-
-    fun submitCheck(serializedFiber: SerializedBytes<FlowStateMachineImpl<*>>) {
-        jobQueue.add(Job.Check(serializedFiber))
-    }
-
-    /**
-     * Returns true if some unrestorable checkpoints were encountered, false otherwise
-     */
-    fun stop(): Boolean {
-        jobQueue.add(Job.Finish)
-        checkerThread?.join()
-        return foundUnrestorableFibers
-    }
-}

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/TopLevelTransition.kt

@@ -58,7 +58,8 @@ class TopLevelTransition(
             is Event.InitiateFlow -> initiateFlowTransition(event)
             is Event.AsyncOperationCompletion -> asyncOperationCompletionTransition(event)
             is Event.AsyncOperationThrows -> asyncOperationThrowsTransition(event)
-            is Event.RetryFlowFromSafePoint -> retryFlowFromSafePointTransition(startingState)
+            is Event.RetryFlowFromSafePoint -> retryFlowFromSafePointTransition()
+            is Event.ReloadFlowFromCheckpointAfterSuspend -> reloadFlowFromCheckpointAfterSuspendTransition()
             is Event.OvernightObservation -> overnightObservationTransition()
             is Event.WakeUpFromSleep -> wakeUpFromSleepTransition()
         }
@@ -315,10 +316,18 @@ class TopLevelTransition(
         }
     }
 
-    private fun retryFlowFromSafePointTransition(startingState: StateMachineState): TransitionResult {
+    private fun retryFlowFromSafePointTransition(): TransitionResult {
         return builder {
             // Need to create a flow from the prior checkpoint or flow initiation.
-            actions.add(Action.RetryFlowFromSafePoint(startingState))
+            actions.add(Action.RetryFlowFromSafePoint(currentState))
+            FlowContinuation.Abort
+        }
+    }
+
+    private fun reloadFlowFromCheckpointAfterSuspendTransition(): TransitionResult {
+        return builder {
+            currentState = currentState.copy(reloadCheckpointAfterSuspendCount = currentState.reloadCheckpointAfterSuspendCount!! + 1)
+            actions.add(Action.RetryFlowFromSafePoint(currentState))
             FlowContinuation.Abort
         }
     }

node/src/test/kotlin/net/corda/node/services/config/NodeConfigurationImplTest.kt

@@ -60,14 +60,6 @@ class NodeConfigurationImplTest {
         assertThat(configValidationResult.first()).contains("crlCheckSoftFail")
     }
 
-    @Test(timeout=3_000)
-	fun `check devModeOptions flag helper`() {
-        assertTrue { configDebugOptions(true, null).shouldCheckCheckpoints() }
-        assertTrue { configDebugOptions(true, DevModeOptions()).shouldCheckCheckpoints() }
-        assertTrue { configDebugOptions(true, DevModeOptions(false)).shouldCheckCheckpoints() }
-        assertFalse { configDebugOptions(true, DevModeOptions(true)).shouldCheckCheckpoints() }
-    }
-
     @Test(timeout=3_000)
 	fun `check crashShell flags helper`() {
         assertFalse { testConfiguration.copy(sshd = null).shouldStartSSHDaemon() }

testing/node-driver/src/main/kotlin/net/corda/testing/node/internal/InternalMockNetwork.kt

@@ -639,6 +639,7 @@ private fun mockNodeConfiguration(certificatesDirectory: Path): NodeConfiguratio
         doReturn(NetworkParameterAcceptanceSettings()).whenever(it).networkParameterAcceptanceSettings
         doReturn(rigorousMock<ConfigurationWithOptions>()).whenever(it).configurationWithOptions
         doReturn(2).whenever(it).flowExternalOperationThreadPoolSize
+        doReturn(false).whenever(it).reloadCheckpointAfterSuspend
     }
 }