/*
* Initiate garbage collection.
*
* NOTES:
* - If we don't hold gDvm.threadListLock, it's possible for a thread to
* be added to the thread list while we work. The thread should NOT
* start executing, so this is only interesting when we start chasing
* thread stacks. (Before we do so, grab the lock.)
*
* We are not allowed to GC when the debugger has suspended the VM, which
* is awkward because debugger requests can cause allocations. The easiest
* way to enforce this is to refuse to GC on an allocation made by the
* JDWP thread -- we have to expand the heap or fail.
*/
void dvmCollectGarbageInternal(const GcSpec* spec)
{
GcHeap *gcHeap = gDvm.gcHeap;
u4 gcEnd = 0;
u4 rootStart = 0 , rootEnd = 0;
u4 dirtyStart = 0, dirtyEnd = 0;
size_t numObjectsFreed, numBytesFreed;
size_t currAllocated, currFootprint;
size_t percentFree;
int oldThreadPriority = INT_MAX;
/* The heap lock must be held.
*/
if (gcHeap->gcRunning) {
LOGW_HEAP("Attempted recursive GC");
return;
}
gcHeap->gcRunning = true;
rootStart = dvmGetRelativeTimeMsec();
dvmSuspendAllThreads(SUSPEND_FOR_GC);
/*
* If we are not marking concurrently raise the priority of the
* thread performing the garbage collection.
*/
if (!spec->isConcurrent) {
oldThreadPriority = os_raiseThreadPriority();
}
if (gDvm.preVerify) {
LOGV_HEAP("Verifying roots and heap before GC");
verifyRootsAndHeap();
}
dvmMethodTraceGCBegin();
/* Set up the marking context.
*/
if (!dvmHeapBeginMarkStep(spec->isPartial)) {
LOGE_HEAP("dvmHeapBeginMarkStep failed; aborting");
dvmAbort();
}
/* Mark the set of objects that are strongly reachable from the roots.
*/
LOGD_HEAP("Marking...");
dvmHeapMarkRootSet();
/* dvmHeapScanMarkedObjects() will build the lists of known
* instances of the Reference classes.
*/
assert(gcHeap->softReferences == NULL);
assert(gcHeap->weakReferences == NULL);
assert(gcHeap->finalizerReferences == NULL);
assert(gcHeap->phantomReferences == NULL);
assert(gcHeap->clearedReferences == NULL);
if (spec->isConcurrent) {
/*
* Resume threads while tracing from the roots. We unlock the
* heap to allow mutator threads to allocate from free space.
*/
dvmClearCardTable();
dvmUnlockHeap();
dvmResumeAllThreads(SUSPEND_FOR_GC);
rootEnd = dvmGetRelativeTimeMsec();
}
/* Recursively mark any objects that marked objects point to strongly.
* If we're not collecting soft references, soft-reachable
* objects will also be marked.
*/
LOGD_HEAP("Recursing...");
dvmHeapScanMarkedObjects();
if (spec->isConcurrent) {
/*
* Re-acquire the heap lock and perform the final thread
* suspension.
*/
dirtyStart = dvmGetRelativeTimeMsec();
dvmLockHeap();
dvmSuspendAllThreads(SUSPEND_FOR_GC);
/*
* As no barrier intercepts root updates, we conservatively
* assume all roots may be gray and re-mark them.
*/
dvmHeapReMarkRootSet();
/*
* With the exception of reference objects and weak interned
* strings, all gray objects should now be on dirty cards.
*/
if (gDvm.verifyCardTable) {
dvmVerifyCardTable();
}
/*
* Recursively mark gray objects pointed to by the roots or by
* heap objects dirtied during the concurrent mark.
*/
dvmHeapReScanMarkedObjects();
}
/*
* All strongly-reachable objects have now been marked. Process
* weakly-reachable objects discovered while tracing.
*/
dvmHeapProcessReferences(&gcHeap->softReferences,
spec->doPreserve == false,
&gcHeap->weakReferences,
&gcHeap->finalizerReferences,
&gcHeap->phantomReferences);
#if defined(WITH_JIT)
/*
* Patching a chaining cell is very cheap as it only updates 4 words. It's
* the overhead of stopping all threads and synchronizing the I/D cache
* that makes it expensive.
*
* Therefore we batch those work orders in a queue and go through them
* when threads are suspended for GC.
*/
dvmCompilerPerformSafePointChecks();
#endif
LOGD_HEAP("Sweeping...");
dvmHeapSweepSystemWeaks();
/*
* Live objects have a bit set in the mark bitmap, swap the mark
* and live bitmaps. The sweep can proceed concurrently viewing
* the new live bitmap as the old mark bitmap, and vice versa.
*/
dvmHeapSourceSwapBitmaps();
if (gDvm.postVerify) {
LOGV_HEAP("Verifying roots and heap after GC");
verifyRootsAndHeap();
}
if (spec->isConcurrent) {
dvmUnlockHeap();
dvmResumeAllThreads(SUSPEND_FOR_GC);
dirtyEnd = dvmGetRelativeTimeMsec();
}
dvmHeapSweepUnmarkedObjects(spec->isPartial, spec->isConcurrent,
&numObjectsFreed, &numBytesFreed);
LOGD_HEAP("Cleaning up...");
dvmHeapFinishMarkStep();
if (spec->isConcurrent) {
dvmLockHeap();
}
LOGD_HEAP("Done.");
/* Now's a good time to adjust the heap size, since
* we know what our utilization is.
*
* This doesn't actually resize any memory;
* it just lets the heap grow more when necessary.
*/
dvmHeapSourceGrowForUtilization();
currAllocated = dvmHeapSourceGetValue(HS_BYTES_ALLOCATED, NULL, 0);
currFootprint = dvmHeapSourceGetValue(HS_FOOTPRINT, NULL, 0);
dvmMethodTraceGCEnd();
LOGV_HEAP("GC finished");
gcHeap->gcRunning = false;
LOGV_HEAP("Resuming threads");
if (spec->isConcurrent) {
/*
* Wake-up any threads that blocked after a failed allocation
* request.
*/
dvmBroadcastCond(&gDvm.gcHeapCond);
}
if (!spec->isConcurrent) {
dvmResumeAllThreads(SUSPEND_FOR_GC);
dirtyEnd = dvmGetRelativeTimeMsec();
/*
* Restore the original thread scheduling priority if it was
* changed at the start of the current garbage collection.
*/
if (oldThreadPriority != INT_MAX) {
os_lowerThreadPriority(oldThreadPriority);
}
}
/*
* Move queue of pending references back into Java.
*/
dvmEnqueueClearedReferences(&gDvm.gcHeap->clearedReferences);
gcEnd = dvmGetRelativeTimeMsec();
percentFree = 100 - (size_t)(100.0f * (float)currAllocated / currFootprint);
if (!spec->isConcurrent) {
u4 markSweepTime = dirtyEnd - rootStart;
u4 gcTime = gcEnd - rootStart;
bool isSmall = numBytesFreed > 0 && numBytesFreed < 1024;
ALOGD("%s freed %s%zdK, %d%% free %zdK/%zdK, paused %ums, total %ums",
spec->reason,
isSmall ? "<" : "",
numBytesFreed ? MAX(numBytesFreed / 1024, 1) : 0,
percentFree,
currAllocated / 1024, currFootprint / 1024,
markSweepTime, gcTime);
} else {
u4 rootTime = rootEnd - rootStart;
u4 dirtyTime = dirtyEnd - dirtyStart;
u4 gcTime = gcEnd - rootStart;
bool isSmall = numBytesFreed > 0 && numBytesFreed < 1024;
ALOGD("%s freed %s%zdK, %d%% free %zdK/%zdK, paused %ums+%ums, total %ums",
spec->reason,
isSmall ? "<" : "",
numBytesFreed ? MAX(numBytesFreed / 1024, 1) : 0,
percentFree,
currAllocated / 1024, currFootprint / 1024,
rootTime, dirtyTime, gcTime);
}
if (gcHeap->ddmHpifWhen != 0) {
LOGD_HEAP("Sending VM heap info to DDM");
dvmDdmSendHeapInfo(gcHeap->ddmHpifWhen, false);
}
if (gcHeap->ddmHpsgWhen != 0) {
LOGD_HEAP("Dumping VM heap to DDM");
dvmDdmSendHeapSegments(false, false);
}
if (gcHeap->ddmNhsgWhen != 0) {
LOGD_HEAP("Dumping native heap to DDM");
dvmDdmSendHeapSegments(false, true);
}
}
/*
* The heap worker thread sits quietly until the GC tells it there's work
* to do.
*/
static void* heapWorkerThreadStart(void* arg)
{
Thread *self = dvmThreadSelf();
UNUSED_PARAMETER(arg);
LOGV("HeapWorker thread started (threadid=%d)\n", self->threadId);
/* tell the main thread that we're ready */
lockMutex(&gDvm.heapWorkerLock);
gDvm.heapWorkerReady = true;
dvmSignalCond(&gDvm.heapWorkerCond);
dvmUnlockMutex(&gDvm.heapWorkerLock);
lockMutex(&gDvm.heapWorkerLock);
while (!gDvm.haltHeapWorker) {
struct timespec trimtime;
bool timedwait = false;
/* We're done running interpreted code for now. */
dvmChangeStatus(NULL, THREAD_VMWAIT);
/* Signal anyone who wants to know when we're done. */
dvmBroadcastCond(&gDvm.heapWorkerIdleCond);
/* Trim the heap if we were asked to. */
trimtime = gDvm.gcHeap->heapWorkerNextTrim;
if (trimtime.tv_sec != 0 && trimtime.tv_nsec != 0) {
struct timespec now;
#ifdef HAVE_TIMEDWAIT_MONOTONIC
clock_gettime(CLOCK_MONOTONIC, &now); // relative time
#else
struct timeval tvnow;
gettimeofday(&tvnow, NULL); // absolute time
now.tv_sec = tvnow.tv_sec;
now.tv_nsec = tvnow.tv_usec * 1000;
#endif
if (trimtime.tv_sec < now.tv_sec ||
(trimtime.tv_sec == now.tv_sec &&
trimtime.tv_nsec <= now.tv_nsec))
{
size_t madvisedSizes[HEAP_SOURCE_MAX_HEAP_COUNT];
/*
* Acquire the gcHeapLock. The requires releasing the
* heapWorkerLock before the gcHeapLock is acquired.
* It is possible that the gcHeapLock may be acquired
* during a concurrent GC in which case heapWorkerLock
* is held by the GC and we are unable to make forward
* progress. We avoid deadlock by releasing the
* gcHeapLock and then waiting to be signaled when the
* GC completes. There is no guarantee that the next
* time we are run will coincide with GC inactivity so
* the check and wait must be performed within a loop.
*/
dvmUnlockMutex(&gDvm.heapWorkerLock);
dvmLockHeap();
while (gDvm.gcHeap->gcRunning) {
dvmWaitForConcurrentGcToComplete();
}
dvmLockMutex(&gDvm.heapWorkerLock);
memset(madvisedSizes, 0, sizeof(madvisedSizes));
dvmHeapSourceTrim(madvisedSizes, HEAP_SOURCE_MAX_HEAP_COUNT);
dvmLogMadviseStats(madvisedSizes, HEAP_SOURCE_MAX_HEAP_COUNT);
dvmUnlockHeap();
trimtime.tv_sec = 0;
trimtime.tv_nsec = 0;
gDvm.gcHeap->heapWorkerNextTrim = trimtime;
} else {
timedwait = true;
}
}
/* sleep until signaled */
if (timedwait) {
int cc __attribute__ ((__unused__));
#ifdef HAVE_TIMEDWAIT_MONOTONIC
cc = pthread_cond_timedwait_monotonic(&gDvm.heapWorkerCond,
&gDvm.heapWorkerLock, &trimtime);
#else
cc = pthread_cond_timedwait(&gDvm.heapWorkerCond,
&gDvm.heapWorkerLock, &trimtime);
#endif
assert(cc == 0 || cc == ETIMEDOUT);
} else {
dvmWaitCond(&gDvm.heapWorkerCond, &gDvm.heapWorkerLock);
}
/*
* Return to the running state before doing heap work. This
* will block if the GC has initiated a suspend. We release
* the heapWorkerLock beforehand for the GC to make progress
* and wait to be signaled after the GC completes. There is
* no guarantee that the next time we are run will coincide
* with GC inactivity so the check and wait must be performed
* within a loop.
*/
dvmUnlockMutex(&gDvm.heapWorkerLock);
dvmChangeStatus(NULL, THREAD_RUNNING);
dvmLockHeap();
while (gDvm.gcHeap->gcRunning) {
dvmWaitForConcurrentGcToComplete();
}
dvmLockMutex(&gDvm.heapWorkerLock);
dvmUnlockHeap();
LOGV("HeapWorker is awake\n");
/* Process any events in the queue.
*/
doHeapWork(self);
}
dvmUnlockMutex(&gDvm.heapWorkerLock);
if (gDvm.verboseShutdown)
LOGD("HeapWorker thread shutting down\n");
return NULL;
}
