5.0以前虚拟器GC回收垃圾

2016-11-16 10:12:32   0  举报

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在5.0版本之前，Android系统使用的是基于标记-清除算法的垃圾回收器。该算法分为两个阶段：标记和清除。首先，垃圾回收器会遍历所有的对象，标记出那些不再使用的对象。然后，它会清除所有被标记的对象，释放它们占用的内存空间。这种方式虽然简单高效，但也存在一些问题。例如，它可能会导致应用程序暂停或卡顿，因为它需要停止应用程序的执行来执行垃圾回收操作。此外，由于标记-清除算法无法处理浮动垃圾（即已经删除但仍被其他对象引用的对象），所以它可能会导致内存泄漏问题。为了解决这些问题，Android 5.0引入了新的垃圾回收器，采用了更先进的算法和技术来提高垃圾回收的效率和准确性。

Android GC

作者其他创作

大纲/内容

GcSpec结构体

bool isPartial

bool isConcurrent

bool doPreserve

const char *reason

分配内存成功的函数调用情况

void* dvmHeapSourceAlloc(size_t n)

手动GC或者收到系统GC信号

void dvmCollectGarbage()

涉及到的重要函数讲解

void dvmSuspendAllThreads(SuspendCause why)

bool dvmHeapBeginMarkStep(bool isPartial)

static bool createMarkStack(GcMarkStack *stack)

void *dvmHeapSourceGetImmuneLimit(bool isPartial)

void dvmHeapMarkRootSet()

void dvmMarkImmuneObjects(const char *immuneLimit)

void dvmVisitRoots(RootVisitor *visitor, void *arg)

visitHashTable(visitor, gDvm.loadedClasses, ROOT_STICKY_CLASS, arg);

visitPrimitiveTypes(visitor, arg);

visitHashTable(visitor, gDvm.dbgRegistry, ROOT_DEBUGGER, arg);

visitHashTable(visitor, gDvm.literalStrings, ROOT_INTERNED_STRING, arg);

visitIndirectRefTable(visitor, &gDvm.jniGlobalRefTable, 0, ROOT_JNI_GLOBAL, arg);

visitReferenceTable(visitor, &gDvm.jniPinRefTable, 0, ROOT_VM_INTERNAL, arg);

visitThreads(visitor, arg);

static void visitThread(RootVisitor *visitor, Thread *thread, void *arg)

(*visitor)(&thread->threadObj, threadId, ROOT_THREAD_OBJECT, arg);

(*visitor)(&thread->exception, threadId, ROOT_NATIVE_STACK, arg);

visitReferenceTable(visitor, &thread->internalLocalRefTable, threadId, ROOT_NATIVE_STACK, arg);

visitIndirectRefTable(visitor, &thread->jniLocalRefTable, threadId, ROOT_JNI_LOCAL, arg);

visitReferenceTable(visitor, &thread->jniMonitorRefTable, threadId, ROOT_JNI_MONITOR, arg);

visitThreadStack(visitor, thread, arg);

static void rootMarkObjectVisitor(void *addr, u4 thread, RootType type, void *arg)

static void markObjectNonNull(const Object *obj, GcMarkContext *ctx, bool checkFinger)

static long setAndReturnMarkBit(GcMarkContext *ctx, const void *obj)

static void markStackPush(GcMarkStack *stack, const Object *obj)

(*visitor)(&gDvm.outOfMemoryObj, 0, ROOT_VM_INTERNAL, arg);

(*visitor)(&gDvm.internalErrorObj, 0, ROOT_VM_INTERNAL, arg);

(*visitor)(&gDvm.noClassDefFoundErrorObj, 0, ROOT_VM_INTERNAL, arg);

void dvmClearCardTable()

void dvmResumeAllThreads(SuspendCause why)

void dvmHeapScanMarkedObjects(void)

void dvmHeapBitmapScanWalk(HeapBitmap *bitmap, BitmapScanCallback *callback, void *arg)

static void scanBitmapCallback(Object *obj, void *finger, void *arg)

static void scanObject(const Object *obj, GcMarkContext *ctx)

scanClassObject(obj, ctx);

scanArrayObject(obj, ctx);

scanDataObject(obj, ctx);

static void markObject(const Object *obj, GcMarkContext *ctx)

markObjectNonNull(obj, ctx, true);

scanFields(obj, ctx);

static void delayReferenceReferent(Object *obj, GcMarkContext *ctx)

static void processMarkStack(GcMarkContext *ctx)

void dvmHeapReMarkRootSet()

dvmVisitRoots(rootReMarkObjectVisitor, ctx);

static void rootReMarkObjectVisitor(void *addr, u4 thread, RootType type, void *arg)

void dvmHeapReScanMarkedObjects()

static void scanGrayObjects(GcMarkContext *ctx)

const u1 *scanDirtyCards(const u1 *start, const u1 *end, GcMarkContext *ctx)

static Object *nextGrayObject(const u1 *base, const u1 *limit,const HeapBitmap *markBits)

void dvmHeapProcessReferences(Object **softReferences, bool clearSoftRefs, Object **weakReferences,Object **finalizerReferences,Object **phantomReferences)

static void preserveSomeSoftReferences(Object **list)

static void clearWhiteReferences(Object **list)

static void enqueueFinalizerReferences(Object **list)

void dvmHeapSweepSystemWeaks()

void dvmHeapSourceSwapBitmaps()

void dvmHeapSweepUnmarkedObjects(bool isPartial, bool isConcurrent,size_t *numObjects, size_t *numBytes)

void dvmHeapBitmapSweepWalk(const HeapBitmap *liveHb, const HeapBitmap *markHb,uintptr_t base, uintptr_t max, BitmapSweepCallback *callback, void *callbackArg)