avoid calling doCollect recursively

We must not allocate heap objects from doCollect, since it might
trigger a GC while one is already in progress, which can cause trouble
when we're still queuing up objects to finalize, among other things.
To avoid this, I've added extra fields to the finalizer and cleaner
types which we can use to link instances up during GC without
allocating new memory.

src/machine.cpp

@@ -364,8 +364,18 @@ finalizerTargetUnreachable(Thread* t, Heap::Visitor* v, object* p)
 
   object finalizer = *p;
   *p = finalizerNext(t, finalizer);
-  finalizerNext(t, finalizer) = t->m->finalizeQueue;
-  t->m->finalizeQueue = finalizer;
+
+  void (*function)(Thread*, object);
+  memcpy(&function, &finalizerFinalize(t, finalizer), BytesPerWord);
+
+  if (function) {
+    finalizerNext(t, finalizer) = t->m->finalizeQueue;
+    t->m->finalizeQueue = finalizer;
+  } else {
+    set(t, finalizer, FinalizerQueueTarget, finalizerTarget(t, finalizer));
+    set(t, finalizer, FinalizerQueueNext, root(t, Machine::ObjectsToFinalize));
+    setRoot(t, Machine::ObjectsToFinalize, finalizer);
+  }
 }
 
 void
@@ -382,8 +392,9 @@ referenceTargetUnreachable(Thread* t, Heap::Visitor* v, object* p)
   if (objectClass(t, *p) == type(t, Machine::CleanerType)) {
     object reference = *p;
     *p = jreferenceVmNext(t, reference);
-    jreferenceVmNext(t, reference) = t->m->cleanerQueue;
-    t->m->cleanerQueue = reference;
+
+    set(t, reference, CleanerQueueNext, root(t, Machine::ObjectsToClean));
+    setRoot(t, Machine::ObjectsToClean, reference);
   } else {
     if (jreferenceQueue(t, *p)
         and t->m->heap->status(jreferenceQueue(t, *p)) != Heap::Unreachable)
@@ -453,7 +464,6 @@ postVisit(Thread* t, Heap::Visitor* v)
   bool major = m->heap->collectionType() == Heap::MajorCollection;
 
   assert(t, m->finalizeQueue == 0);
-  assert(t, m->cleanerQueue == 0);
 
   object firstNewTenuredFinalizer = 0;
   object lastNewTenuredFinalizer = 0;
@@ -2230,6 +2240,11 @@ class HeapClient: public Heap::Client {
 void
 doCollect(Thread* t, Heap::CollectionType type)
 {
+  expect(t, not t->m->collecting);
+
+  t->m->collecting = true;
+  THREAD_RESOURCE0(t, t->m->collecting = false);
+
 #ifdef VM_STRESS
   bool stress = (t->flags & Thread::StressFlag) != 0;
   if (not stress) atomicOr(&(t->flags), Thread::StressFlag);
@@ -2263,36 +2278,16 @@ doCollect(Thread* t, Heap::CollectionType type)
 #endif
 
   object finalizeQueue = t->m->finalizeQueue;
-  PROTECT(t, finalizeQueue);
   t->m->finalizeQueue = 0;
   for (; finalizeQueue; finalizeQueue = finalizerNext(t, finalizeQueue)) {
     void (*function)(Thread*, object);
     memcpy(&function, &finalizerFinalize(t, finalizeQueue), BytesPerWord);
-    if (function) {
-      function(t, finalizerTarget(t, finalizeQueue));
-    } else {
-      setRoot(t, Machine::ObjectsToFinalize, makeFinalizeNode
-              (t, finalizerTarget(t, finalizeQueue),
-               const_cast<char*>("finalize"),
-               root(t, Machine::ObjectsToFinalize)));
-    }
+    function(t, finalizerTarget(t, finalizeQueue));
   }
 
-  object cleanerQueue = t->m->cleanerQueue;
-  PROTECT(t, cleanerQueue);
-  t->m->cleanerQueue = 0;
-  while (cleanerQueue) {
-    setRoot(t, Machine::ObjectsToFinalize, makeFinalizeNode
-            (t, cleanerQueue,
-             const_cast<char*>("clean"),
-             root(t, Machine::ObjectsToFinalize)));
-
-    object tmp = cleanerQueue;
-    cleanerQueue = jreferenceVmNext(t, cleanerQueue);
-    jreferenceVmNext(t, tmp) = 0;
-  }
-
-  if (root(t, Machine::ObjectsToFinalize) and m->finalizeThread == 0) {
+  if ((root(t, Machine::ObjectsToFinalize) or root(t, Machine::ObjectsToClean))
+      and m->finalizeThread == 0)
+  {
     m->finalizeThread = m->processor->makeThread
       (m, root(t, Machine::FinalizerThread), m->rootThread);
     
@@ -2355,10 +2350,10 @@ Machine::Machine(System* system, Heap* heap, Finder* bootFinder,
   finalizers(0),
   tenuredFinalizers(0),
   finalizeQueue(0),
-  cleanerQueue(0),
   weakReferences(0),
   tenuredWeakReferences(0),
   unsafe(false),
+  collecting(false),
   triedBuiltinOnLoad(false),
   dumpedHeapOnOOM(false),
   heapPoolIndex(0)
@@ -3810,7 +3805,7 @@ addFinalizer(Thread* t, object target, void (*finalize)(Thread*, object))
   void* function;
   memcpy(&function, &finalize, BytesPerWord);
 
-  object f = makeFinalizer(t, 0, function, 0);
+  object f = makeFinalizer(t, 0, function, 0, 0, 0);
   finalizerTarget(t, f) = target;
   finalizerNext(t, f) = t->m->finalizers;
   t->m->finalizers = f;
@@ -4104,14 +4099,18 @@ makeTrace(Thread* t, Thread* target)
 void
 runFinalizeThread(Thread* t)
 {
-  object list = 0;
-  PROTECT(t, list);
+  object finalizeList = 0;
+  PROTECT(t, finalizeList);
+
+  object cleanList = 0;
+  PROTECT(t, cleanList);
 
   while (true) {
     { ACQUIRE(t, t->m->stateLock);
 
       while (t->m->finalizeThread
-             and root(t, Machine::ObjectsToFinalize) == 0)
+             and root(t, Machine::ObjectsToFinalize) == 0
+             and root(t, Machine::ObjectsToClean) == 0)
       {
         ENTER(t, Thread::IdleState);
         t->m->stateLock->wait(t->systemThread, 0);
@@ -4120,15 +4119,20 @@ runFinalizeThread(Thread* t)
       if (t->m->finalizeThread == 0) {
         return;
       } else {
-        list = root(t, Machine::ObjectsToFinalize);
+        finalizeList = root(t, Machine::ObjectsToFinalize);
         setRoot(t, Machine::ObjectsToFinalize, 0);
+
+        cleanList = root(t, Machine::ObjectsToClean);
+        setRoot(t, Machine::ObjectsToClean, 0);
       }
     }
 
-    for (; list; list = finalizeNodeNext(t, list)) {
-      finalizeObject
-        (t, finalizeNodeTarget(t, list),
-         static_cast<const char*>(finalizeNodeMethodName(t, list)));
+    for (; finalizeList; finalizeList = finalizerQueueNext(t, finalizeList)) {
+      finalizeObject(t, finalizerQueueTarget(t, finalizeList), "finalize");
+    }
+
+    for (; cleanList; cleanList = cleanerQueueNext(t, cleanList)) {
+      finalizeObject(t, cleanList, "clean");
     }
   }
 }

src/machine.h

@@ -1260,6 +1260,7 @@ class Machine {
     ShutdownHooks,
     FinalizerThread,
     ObjectsToFinalize,
+    ObjectsToClean,
     NullPointerException,
     ArithmeticException,
     ArrayIndexOutOfBoundsException,
@@ -1311,10 +1312,10 @@ class Machine {
   object finalizers;
   object tenuredFinalizers;
   object finalizeQueue;
-  object cleanerQueue;
   object weakReferences;
   object tenuredWeakReferences;
   bool unsafe;
+  bool collecting;
   bool triedBuiltinOnLoad;
   bool dumpedHeapOnOOM;
   JavaVMVTable javaVMVTable;

src/types.def

@@ -104,12 +104,9 @@
 (type finalizer
   (nogc object target)
   (void* finalize)
-  (nogc object next))
-
-(type finalizeNode
-  (object target)
-  (void* methodName)
-  (object next))
+  (nogc object next)
+  (object queueTarget)
+  (object queueNext))
 
 (type hashMap
   (uint32_t size)
@@ -299,7 +296,8 @@
 
 (type phantomReference java/lang/ref/PhantomReference)
 
-(type cleaner sun/misc/Cleaner)
+(type cleaner sun/misc/Cleaner
+  (object queueNext))
 
 (type byteArray [B
   (extends jobject)