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Add flow state machine extension tutorial
This commit is contained in:
Andras Slemmer
parent
ab08ce21f4
commit
80a5e7ab81
@ -5,6 +5,7 @@ import net.corda.core.concurrent.CordaFuture
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import net.corda.core.flows.FlowLogic
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import net.corda.core.serialization.CordaSerializable
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// DOCSTART FlowAsyncOperation
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/**
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* Interface for arbitrary operations that can be invoked in a flow asynchronously - the flow will suspend until the
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* operation completes. Operation parameters are expected to be injected via constructor.
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@ -14,10 +15,13 @@ interface FlowAsyncOperation<R : Any> {
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/** Performs the operation in a non-blocking fashion. */
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fun execute(): CordaFuture<R>
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}
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// DOCEND FlowAsyncOperation
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// DOCSTART executeAsync
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/** Executes the specified [operation] and suspends until operation completion. */
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@Suspendable
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fun <T, R : Any> FlowLogic<T>.executeAsync(operation: FlowAsyncOperation<R>, maySkipCheckpoint: Boolean = false): R {
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val request = FlowIORequest.ExecuteAsyncOperation(operation)
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return stateMachine.suspend(request, maySkipCheckpoint)
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}
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// DOCEND executeAsync
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@ -9,6 +9,7 @@ import net.corda.core.transactions.SignedTransaction
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import net.corda.core.utilities.NonEmptySet
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import java.time.Instant
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// DOCSTART FlowIORequest
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/**
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* A [FlowIORequest] represents an IO request of a flow when it suspends. It is persisted in checkpoints.
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*/
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@ -93,3 +94,4 @@ sealed class FlowIORequest<out R : Any> {
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// TODO: consider using an empty FlowAsyncOperation instead
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object ForceCheckpoint : FlowIORequest<Unit>()
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}
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// DOCSEND FlowIORequest
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237
docs/source/contributing-flow-state-machines.rst
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237
docs/source/contributing-flow-state-machines.rst
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@ -0,0 +1,237 @@
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.. highlight:: kotlin
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.. raw:: html
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<script type="text/javascript" src="_static/jquery.js"></script>
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<script type="text/javascript" src="_static/codesets.js"></script>
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How to extend the state machine
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===============================
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This article explains how to extend the state machine code that underlies flow execution. It is intended for Corda
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contributors.
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How to add suspending operations
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--------------------------------
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To add a suspending operation that's a simple request-response type function that perhaps involves some external IO you
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can use the internal ``FlowAsyncOperation`` interface.
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.. container:: codeset
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.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/internal/FlowAsyncOperation.kt
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:language: kotlin
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:start-after: DOCSTART FlowAsyncOperation
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:end-before: DOCEND FlowAsyncOperation
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Let's imagine we want to add a suspending operation that takes two integers and returns their sum. To do this we
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implement ``FlowAsyncOperation``:
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.. container:: codeset
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.. literalinclude:: ../../docs/source/example-code/src/main/kotlin/net/corda/docs/tutorial/flowstatemachines/TutorialFlowAsyncOperation.kt
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:language: kotlin
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:start-after: DOCSTART SummingOperation
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:end-before: DOCEND SummingOperation
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As we can see the constructor of ``SummingOperation`` takes the two numbers, and the ``execute`` function simply returns
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a future that is immediately completed by the result of summing the numbers. Note how we don't use ``@Suspendable`` on
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``execute``, this is because we'll never suspend inside this function, the suspension will happen before we're calling
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it.
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Note also how the input numbers are stored in the class as fields. This is important, because in the flow's checkpoint
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we'll store an instance of this class whenever we're suspending on such an operation. If the node fails or restarts
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while the operation is underway this class will be deserialized from the checkpoint and ``execute`` will be called
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again.
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Now we can use the internal function ``executeAsync`` to execute this operation from a flow.
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.. container:: codeset
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.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/internal/FlowAsyncOperation.kt
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:language: kotlin
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:start-after: DOCSTART executeAsync
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:end-before: DOCEND executeAsync
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It simply takes a ``FlowAsyncOperation`` and an optional flag we don't care about for now. We can use this function in a
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flow:
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.. container:: codeset
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.. literalinclude:: ../../docs/source/example-code/src/main/kotlin/net/corda/docs/tutorial/flowstatemachines/TutorialFlowAsyncOperation.kt
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:language: kotlin
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:start-after: DOCSTART ExampleSummingFlow
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:end-before: DOCEND ExampleSummingFlow
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That's it! Obviously this is a mostly useless example, but this is the basic code structure one could extend for heavier
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computations/other IO. For example the function could call into a ``CordaService`` or something similar. One thing to
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note is that the operation executed in ``execute`` must be redoable(= "idempotent") in case the node fails while the
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next checkpoint is reached.
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How to test
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-----------
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The recommended way to test flows and the state machine is using the Driver DSL. This ensures that you will test your
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flow with a full node.
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.. container:: codeset
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.. literalinclude:: ../../docs/source/example-code/src/integration-test/kotlin/net/corda/docs/TutorialFlowAsyncOperationTest.kt
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:language: kotlin
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:start-after: DOCSTART summingWorks
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:end-before: DOCEND summingWorks
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The above will spin up a node and run our example flow.
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How to debug issues
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-------------------
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Let's assume we made a mistake in our summing operation:
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.. container:: codeset
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.. literalinclude:: ../../docs/source/example-code/src/main/kotlin/net/corda/docs/tutorial/flowstatemachines/TutorialFlowAsyncOperation.kt
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:language: kotlin
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:start-after: DOCSTART SummingOperationThrowing
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:end-before: DOCEND SummingOperationThrowing
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The operation now throws a rude exception. If we modify the example flow to use this and run the same test we will get
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a lot of logs about the error condition (as we are in dev mode). The interesting bit looks like this:
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.. parsed-literal::
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[WARN ] 18:38:52,613 [Node thread-1] (DumpHistoryOnErrorInterceptor.kt:39) interceptors.DumpHistoryOnErrorInterceptor.executeTransition - Flow [03ab886e-3fd3-4667-b944-ab6a3b1f90a7] errored, dumping all transitions:
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--- Transition of flow [03ab886e-3fd3-4667-b944-ab6a3b1f90a7] ---
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Timestamp: 2018-06-01T17:38:52.426Z
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Event: DoRemainingWork
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Actions:
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CreateTransaction
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PersistCheckpoint(id=[03ab886e-3fd3-4667-b944-ab6a3b1f90a7], checkpoint=Checkpoint(invocationContext=InvocationContext(origin=RPC(actor=Actor(id=Id(value=aliceUser), serviceId=AuthServiceId(value=NODE_CONFIG), owningLegalIdentity=O=Alice Corp, L=Madrid, C=ES)), trace=Trace(invocationId=26bcf0c3-f1d8-4098-a52d-3780f4095b7a, timestamp: 2018-06-01T17:38:52.234Z, entityType: Invocation, sessionId=393d1175-3bb1-4eb1-bff0-6ba317851260, timestamp: 2018-06-01T17:38:52.169Z, entityType: Session), actor=Actor(id=Id(value=aliceUser), serviceId=AuthServiceId(value=NODE_CONFIG), owningLegalIdentity=O=Alice Corp, L=Madrid, C=ES), externalTrace=null, impersonatedActor=null), ourIdentity=O=Alice Corp, L=Madrid, C=ES, sessions={}, subFlowStack=[Inlined(flowClass=class net.corda.docs.tutorial.flowstatemachines.ExampleSummingFlow, subFlowVersion=CorDappFlow(platformVersion=1, corDappName=net.corda.docs-c6816652-f975-4fb2-aa09-ef1dddea19b3, corDappHash=F4012397D8CF97926B5998E046DBCE16D497318BB87DCED66313912D4B303BB7))], flowState=Unstarted(flowStart=Explicit, frozenFlowLogic=74BA62EC5821EBD4FC4CBE129843F9ED6509DB37E6E3C8F85E3F7A8D84083500), errorState=Clean, numberOfSuspends=0, deduplicationSeed=03ab886e-3fd3-4667-b944-ab6a3b1f90a7))
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PersistDeduplicationFacts(deduplicationHandlers=[net.corda.node.internal.FlowStarterImpl$startFlow$startFlowEvent$1@69326343])
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CommitTransaction
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AcknowledgeMessages(deduplicationHandlers=[net.corda.node.internal.FlowStarterImpl$startFlow$startFlowEvent$1@69326343])
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SignalFlowHasStarted(flowId=[03ab886e-3fd3-4667-b944-ab6a3b1f90a7])
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CreateTransaction
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Continuation: Resume(result=null)
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Diff between previous and next state:
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isAnyCheckpointPersisted:
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false
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true
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pendingDeduplicationHandlers:
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[net.corda.node.internal.FlowStarterImpl$startFlow$startFlowEvent$1@69326343]
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[]
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isFlowResumed:
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false
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true
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--- Transition of flow [03ab886e-3fd3-4667-b944-ab6a3b1f90a7] ---
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Timestamp: 2018-06-01T17:38:52.487Z
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Event: Suspend(ioRequest=ExecuteAsyncOperation(operation=net.corda.docs.tutorial.flowstatemachines.SummingOperationThrowing@40f4c23d), maySkipCheckpoint=false, fiber=15EC69204562BB396846768169AD4A339569D97AE841D805C230C513A8BA5BDE, )
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Actions:
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PersistCheckpoint(id=[03ab886e-3fd3-4667-b944-ab6a3b1f90a7], checkpoint=Checkpoint(invocationContext=InvocationContext(origin=RPC(actor=Actor(id=Id(value=aliceUser), serviceId=AuthServiceId(value=NODE_CONFIG), owningLegalIdentity=O=Alice Corp, L=Madrid, C=ES)), trace=Trace(invocationId=26bcf0c3-f1d8-4098-a52d-3780f4095b7a, timestamp: 2018-06-01T17:38:52.234Z, entityType: Invocation, sessionId=393d1175-3bb1-4eb1-bff0-6ba317851260, timestamp: 2018-06-01T17:38:52.169Z, entityType: Session), actor=Actor(id=Id(value=aliceUser), serviceId=AuthServiceId(value=NODE_CONFIG), owningLegalIdentity=O=Alice Corp, L=Madrid, C=ES), externalTrace=null, impersonatedActor=null), ourIdentity=O=Alice Corp, L=Madrid, C=ES, sessions={}, subFlowStack=[Inlined(flowClass=class net.corda.docs.tutorial.flowstatemachines.ExampleSummingFlow, subFlowVersion=CorDappFlow(platformVersion=1, corDappName=net.corda.docs-c6816652-f975-4fb2-aa09-ef1dddea19b3, corDappHash=F4012397D8CF97926B5998E046DBCE16D497318BB87DCED66313912D4B303BB7))], flowState=Started(flowIORequest=ExecuteAsyncOperation(operation=net.corda.docs.tutorial.flowstatemachines.SummingOperationThrowing@40f4c23d), frozenFiber=15EC69204562BB396846768169AD4A339569D97AE841D805C230C513A8BA5BDE), errorState=Clean, numberOfSuspends=1, deduplicationSeed=03ab886e-3fd3-4667-b944-ab6a3b1f90a7))
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PersistDeduplicationFacts(deduplicationHandlers=[])
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CommitTransaction
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AcknowledgeMessages(deduplicationHandlers=[])
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ScheduleEvent(event=DoRemainingWork)
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Continuation: ProcessEvents
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Diff between previous and next state:
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checkpoint.numberOfSuspends:
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0
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1
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checkpoint.flowState:
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Unstarted(flowStart=Explicit, frozenFlowLogic=74BA62EC5821EBD4FC4CBE129843F9ED6509DB37E6E3C8F85E3F7A8D84083500)
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Started(flowIORequest=ExecuteAsyncOperation(operation=net.corda.docs.tutorial.flowstatemachines.SummingOperationThrowing@40f4c23d), frozenFiber=15EC69204562BB396846768169AD4A339569D97AE841D805C230C513A8BA5BDE)
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isFlowResumed:
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true
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false
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--- Transition of flow [03ab886e-3fd3-4667-b944-ab6a3b1f90a7] ---
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Timestamp: 2018-06-01T17:38:52.549Z
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Event: DoRemainingWork
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Actions:
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ExecuteAsyncOperation(operation=net.corda.docs.tutorial.flowstatemachines.SummingOperationThrowing@40f4c23d)
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Continuation: ProcessEvents
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Diff between previous and intended state:
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null
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Diff between previous and next state:
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checkpoint.errorState:
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Clean
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Errored(errors=[FlowError(errorId=-8704604242619505379, exception=java.lang.IllegalStateException: You shouldn't be calling me)], propagatedIndex=0, propagating=false)
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--- Transition of flow [03ab886e-3fd3-4667-b944-ab6a3b1f90a7] ---
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Timestamp: 2018-06-01T17:38:52.555Z
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Event: DoRemainingWork
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Actions:
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Continuation: ProcessEvents
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Diff between previous and next state:
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null
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--- Transition of flow [03ab886e-3fd3-4667-b944-ab6a3b1f90a7] ---
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Timestamp: 2018-06-01T17:38:52.556Z
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Event: StartErrorPropagation
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Actions:
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ScheduleEvent(event=DoRemainingWork)
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Continuation: ProcessEvents
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Diff between previous and next state:
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checkpoint.errorState.propagating:
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false
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true
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--- Transition of flow [03ab886e-3fd3-4667-b944-ab6a3b1f90a7] ---
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Timestamp: 2018-06-01T17:38:52.606Z
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Event: DoRemainingWork
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Actions:
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PropagateErrors(errorMessages=[ErrorSessionMessage(flowException=null, errorId=-8704604242619505379)], sessions=[], senderUUID=861f07d6-4b8f-42bd-9b52-5152812db2ba)
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CreateTransaction
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RemoveCheckpoint(id=[03ab886e-3fd3-4667-b944-ab6a3b1f90a7])
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PersistDeduplicationFacts(deduplicationHandlers=[])
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ReleaseSoftLocks(uuid=03ab886e-3fd3-4667-b944-ab6a3b1f90a7)
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CommitTransaction
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AcknowledgeMessages(deduplicationHandlers=[])
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RemoveSessionBindings(sessionIds=[])
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RemoveFlow(flowId=[03ab886e-3fd3-4667-b944-ab6a3b1f90a7], removalReason=ErrorFinish(flowErrors=[FlowError(errorId=-8704604242619505379, exception=java.lang.IllegalStateException: You shouldn't be calling me)]), lastState=StateMachineState(checkpoint=Checkpoint(invocationContext=InvocationContext(origin=RPC(actor=Actor(id=Id(value=aliceUser), serviceId=AuthServiceId(value=NODE_CONFIG), owningLegalIdentity=O=Alice Corp, L=Madrid, C=ES)), trace=Trace(invocationId=26bcf0c3-f1d8-4098-a52d-3780f4095b7a, timestamp: 2018-06-01T17:38:52.234Z, entityType: Invocation, sessionId=393d1175-3bb1-4eb1-bff0-6ba317851260, timestamp: 2018-06-01T17:38:52.169Z, entityType: Session), actor=Actor(id=Id(value=aliceUser), serviceId=AuthServiceId(value=NODE_CONFIG), owningLegalIdentity=O=Alice Corp, L=Madrid, C=ES), externalTrace=null, impersonatedActor=null), ourIdentity=O=Alice Corp, L=Madrid, C=ES, sessions={}, subFlowStack=[Inlined(flowClass=class net.corda.docs.tutorial.flowstatemachines.ExampleSummingFlow, subFlowVersion=CorDappFlow(platformVersion=1, corDappName=net.corda.docs-c6816652-f975-4fb2-aa09-ef1dddea19b3, corDappHash=F4012397D8CF97926B5998E046DBCE16D497318BB87DCED66313912D4B303BB7))], flowState=Started(flowIORequest=ExecuteAsyncOperation(operation=net.corda.docs.tutorial.flowstatemachines.SummingOperationThrowing@40f4c23d), frozenFiber=15EC69204562BB396846768169AD4A339569D97AE841D805C230C513A8BA5BDE), errorState=Errored(errors=[FlowError(errorId=-8704604242619505379, exception=java.lang.IllegalStateException: You shouldn't be calling me)], propagatedIndex=1, propagating=true), numberOfSuspends=1, deduplicationSeed=03ab886e-3fd3-4667-b944-ab6a3b1f90a7), flowLogic=net.corda.docs.tutorial.flowstatemachines.ExampleSummingFlow@600b0c6c, pendingDeduplicationHandlers=[], isFlowResumed=false, isTransactionTracked=false, isAnyCheckpointPersisted=true, isStartIdempotent=false, isRemoved=true, senderUUID=861f07d6-4b8f-42bd-9b52-5152812db2ba))
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Continuation: Abort
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Diff between previous and next state:
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checkpoint.errorState.propagatedIndex:
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0
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1
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isRemoved:
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false
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true
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Whoa that's a lot of stuff. Now we get a glimpse into the bowels of the flow state machine. As we can see the flow did
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quite a few things, even though the flow code looks simple.
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What we can see here is the different transitions the flow's state machine went through that led up to the error
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condition. For each transition we see what *Event* triggered the transition, what *Action* s were taken as a consequence,
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and how the internal *State* of the state machine was modified in the process. It also prints the transition's
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*Continuation*, which indicates how the flow should proceed after the transition.
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For example in the first transition we can see that the triggering event was a ``DoRemainingWork``, this is a generic
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event that instructs the state machine to check its own state to see whether there's any work left to do, and does it if
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there's any.
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In this case the work involves persisting a checkpoint together with some deduplication data in a database transaction,
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then acknowledging any triggering messages, signalling that the flow has started, and creating a fresh database
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transaction, to be used by user code.
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The continuation is a ``Resume``, which instructs the state machine to hand control to user code. The state change is
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a simple update of bookkeeping data.
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On other words the first transition concerns initializing of the flow, which includes the creation of the
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checkpoint.
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The next transition is the suspension on our summing operation, triggered by the ``Suspend`` event. As we can see in
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this transition we aren't doing any work related to the summation yet, we're merely persisting the checkpoint that
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indicates that we want to do the summation. Had we added a ``toString`` method to our ``SummingOperationThrowing`` we
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would see a nicer message.
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The next transition is the faulty one, as we can see it was also triggered by a ``DoRemainingWork``, and executed our
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operation. We can see that there are two state "diff"s printed, one that would've happened had the transition succeeded,
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and one that actually happened, this is the marking of the flow's state as errored. The rest of the transitions involve
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error propagation (triggered by the ``FlowHospital``) and notification of failure, which ultimately raises the exception
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on the RPC ``resultFuture``.
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@ -107,6 +107,9 @@ Running the API scanner
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Your changes must also not break compatibility with existing public API. We have an API scanning tool which runs as part of the build
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process which can be used to flag up any accidental changes, which is detailed :doc:`here </api-scanner>`.
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Extending the flow state machine
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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You can find instructions on how to extend the flow state machine :doc:`here </contributing-flow-state-machines>`
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Updating the docs
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-----------------
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@ -0,0 +1,29 @@
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package net.corda.docs
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import net.corda.client.rpc.CordaRPCClient
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import net.corda.core.messaging.startFlow
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import net.corda.core.utilities.getOrThrow
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import net.corda.docs.tutorial.flowstatemachines.ExampleSummingFlow
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import net.corda.node.services.Permissions
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import net.corda.testing.core.ALICE_NAME
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import net.corda.testing.driver.DriverParameters
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import net.corda.testing.driver.driver
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import net.corda.testing.node.User
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import org.junit.Test
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import kotlin.test.assertEquals
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class TutorialFlowAsyncOperationTest {
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// DOCSTART summingWorks
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@Test
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fun summingWorks() {
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driver(DriverParameters(startNodesInProcess = true)) {
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val aliceUser = User("aliceUser", "testPassword1", permissions = setOf(Permissions.all()))
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val alice = startNode(providedName = ALICE_NAME, rpcUsers = listOf(aliceUser)).getOrThrow()
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val aliceClient = CordaRPCClient(alice.rpcAddress)
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val aliceProxy = aliceClient.start("aliceUser", "testPassword1").proxy
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val answer = aliceProxy.startFlow(::ExampleSummingFlow).returnValue.getOrThrow()
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assertEquals(3, answer)
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}
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}
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// DOCEND summingWorks
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}
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@ -0,0 +1,38 @@
|
||||
package net.corda.docs.tutorial.flowstatemachines
|
||||
|
||||
import co.paralleluniverse.fibers.Suspendable
|
||||
import net.corda.core.concurrent.CordaFuture
|
||||
import net.corda.core.flows.FlowLogic
|
||||
import net.corda.core.flows.StartableByRPC
|
||||
import net.corda.core.internal.FlowAsyncOperation
|
||||
import net.corda.core.internal.concurrent.doneFuture
|
||||
import net.corda.core.internal.concurrent.openFuture
|
||||
import net.corda.core.internal.executeAsync
|
||||
|
||||
// DOCSTART SummingOperation
|
||||
class SummingOperation(val a: Int, val b: Int) : FlowAsyncOperation<Int> {
|
||||
override fun execute(): CordaFuture<Int> {
|
||||
return doneFuture(a + b)
|
||||
}
|
||||
}
|
||||
// DOCEND SummingOperation
|
||||
|
||||
// DOCSTART SummingOperationThrowing
|
||||
class SummingOperationThrowing(val a: Int, val b: Int) : FlowAsyncOperation<Int> {
|
||||
override fun execute(): CordaFuture<Int> {
|
||||
throw IllegalStateException("You shouldn't be calling me")
|
||||
}
|
||||
}
|
||||
// DOCEND SummingOperationThrowing
|
||||
|
||||
// DOCSTART ExampleSummingFlow
|
||||
@StartableByRPC
|
||||
class ExampleSummingFlow : FlowLogic<Int>() {
|
||||
@Suspendable
|
||||
override fun call(): Int {
|
||||
val answer = executeAsync(SummingOperationThrowing(1, 2))
|
||||
return answer // hopefully 3
|
||||
}
|
||||
}
|
||||
// DOCEND ExampleSummingFlow
|
||||
|
||||
Loading…
Reference in New Issue
Block a user