path: root/src/3rdparty/webkit/JavaScriptCore/runtime/Collector.cpp

/*
 *  Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
 *  Copyright (C) 2007 Eric Seidel <eric@webkit.org>
 *  Copyright (C) 2008 Torch Mobile, Inc.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#include "config.h"
#include "Collector.h"

#include "ArgList.h"
#include "CollectorHeapIterator.h"
#include "CallFrame.h"
#include "JSGlobalObject.h"
#include "JSLock.h"
#include "JSString.h"
#include "JSValue.h"
#include "Interpreter.h"
#include "Tracing.h"
#include <algorithm>
#include <setjmp.h>
#include <stdlib.h>
#include <wtf/FastMalloc.h>
#include <wtf/HashCountedSet.h>
#include <wtf/UnusedParam.h>

#if PLATFORM(DARWIN)

#include <mach/mach_port.h>
#include <mach/mach_init.h>
#include <mach/task.h>
#include <mach/thread_act.h>
#include <mach/vm_map.h>

#elif PLATFORM(WIN_OS)

#include <windows.h>

#elif PLATFORM(UNIX)

#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

#if defined(QT_LINUXBASE)
#include <dlfcn.h>
#endif

#if defined(__UCLIBC__)
// versions of uClibc 0.9.28 and below do not have
// pthread_getattr_np or pthread_attr_getstack.
#if __UCLIBC_MAJOR__ == 0 && \
    (__UCLIBC_MINOR__ < 9 || \
    (__UCLIBC_MINOR__ == 9 && __UCLIBC_SUBLEVEL__ <= 30))
#define UCLIBC_USE_PROC_SELF_MAPS 1
#include <stdio_ext.h>
extern int *__libc_stack_end;
#endif
#endif

#if PLATFORM(SOLARIS)
#include <thread.h>
#endif

#if PLATFORM(OPENBSD)
#include <pthread.h>
#endif

#if HAVE(PTHREAD_NP_H)
#include <pthread_np.h>
#endif

#endif

#define DEBUG_COLLECTOR 0
#define COLLECT_ON_EVERY_ALLOCATION 0

using std::max;

namespace JSC {

// tunable parameters

const size_t SPARE_EMPTY_BLOCKS = 2;
const size_t GROWTH_FACTOR = 2;
const size_t LOW_WATER_FACTOR = 4;
const size_t ALLOCATIONS_PER_COLLECTION = 4000;
// This value has to be a macro to be used in max() without introducing
// a PIC branch in Mach-O binaries, see <rdar://problem/5971391>.
#define MIN_ARRAY_SIZE (static_cast<size_t>(14))

static void freeHeap(CollectorHeap*);

#if ENABLE(JSC_MULTIPLE_THREADS)

#if PLATFORM(DARWIN)
typedef mach_port_t PlatformThread;
#elif PLATFORM(WIN_OS)
struct PlatformThread {
    PlatformThread(DWORD _id, HANDLE _handle) : id(_id), handle(_handle) {}
    DWORD id;
    HANDLE handle;
};
#endif

class Heap::Thread {
public:
    Thread(pthread_t pthread, const PlatformThread& platThread, void* base) 
        : posixThread(pthread)
        , platformThread(platThread)
        , stackBase(base)
    {
    }

    Thread* next;
    pthread_t posixThread;
    PlatformThread platformThread;
    void* stackBase;
};

#endif

Heap::Heap(JSGlobalData* globalData)
    : m_markListSet(0)
#if ENABLE(JSC_MULTIPLE_THREADS)
    , m_registeredThreads(0)
    , m_currentThreadRegistrar(0)
#endif
    , m_globalData(globalData)
{
    ASSERT(globalData);

    memset(&primaryHeap, 0, sizeof(CollectorHeap));
    memset(&numberHeap, 0, sizeof(CollectorHeap));
}

Heap::~Heap()
{
    // The destroy function must already have been called, so assert this.
    ASSERT(!m_globalData);
}

void Heap::destroy()
{
    JSLock lock(false);

    if (!m_globalData)
        return;

    // The global object is not GC protected at this point, so sweeping may delete it
    // (and thus the global data) before other objects that may use the global data.
    RefPtr<JSGlobalData> protect(m_globalData);

    delete m_markListSet;
    m_markListSet = 0;

    sweep<PrimaryHeap>();
    // No need to sweep number heap, because the JSNumber destructor doesn't do anything.

    ASSERT(!primaryHeap.numLiveObjects);

    freeHeap(&primaryHeap);
    freeHeap(&numberHeap);

#if ENABLE(JSC_MULTIPLE_THREADS)
    if (m_currentThreadRegistrar) {
        int error = pthread_key_delete(m_currentThreadRegistrar);
        ASSERT_UNUSED(error, !error);
    }

    MutexLocker registeredThreadsLock(m_registeredThreadsMutex);
    for (Heap::Thread* t = m_registeredThreads; t;) {
        Heap::Thread* next = t->next;
        delete t;
        t = next;
    }
#endif

    m_globalData = 0;
}

template <HeapType heapType>
static NEVER_INLINE CollectorBlock* allocateBlock()
{
#if PLATFORM(DARWIN)
    vm_address_t address = 0;
    // FIXME: tag the region as a JavaScriptCore heap when we get a registered VM tag: <rdar://problem/6054788>.
    vm_map(current_task(), &address, BLOCK_SIZE, BLOCK_OFFSET_MASK, VM_FLAGS_ANYWHERE, MEMORY_OBJECT_NULL, 0, FALSE, VM_PROT_DEFAULT, VM_PROT_DEFAULT, VM_INHERIT_DEFAULT);
#elif PLATFORM(SYMBIAN)
    // no memory map in symbian, need to hack with fastMalloc
    void* address = fastMalloc(BLOCK_SIZE);
    memset(reinterpret_cast<void*>(address), 0, BLOCK_SIZE);
#elif PLATFORM(WIN_OS)
     // windows virtual address granularity is naturally 64k
    LPVOID address = VirtualAlloc(NULL, BLOCK_SIZE, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
#elif HAVE(POSIX_MEMALIGN)
    void* address;
    posix_memalign(&address, BLOCK_SIZE, BLOCK_SIZE);
    memset(address, 0, BLOCK_SIZE);
#else

#if ENABLE(JSC_MULTIPLE_THREADS)
#error Need to initialize pagesize safely.
#endif
    static size_t pagesize = getpagesize();

    size_t extra = 0;
    if (BLOCK_SIZE > pagesize)
        extra = BLOCK_SIZE - pagesize;

    void* mmapResult = mmap(NULL, BLOCK_SIZE + extra, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
    uintptr_t address = reinterpret_cast<uintptr_t>(mmapResult);

    size_t adjust = 0;
    if ((address & BLOCK_OFFSET_MASK) != 0)
        adjust = BLOCK_SIZE - (address & BLOCK_OFFSET_MASK);

    if (adjust > 0)
        munmap(reinterpret_cast<char*>(address), adjust);

    if (adjust < extra)
        munmap(reinterpret_cast<char*>(address + adjust + BLOCK_SIZE), extra - adjust);

    address += adjust;
    memset(reinterpret_cast<void*>(address), 0, BLOCK_SIZE);
#endif
    reinterpret_cast<CollectorBlock*>(address)->type = heapType;
    return reinterpret_cast<CollectorBlock*>(address);
}

static void freeBlock(CollectorBlock* block)
{
#if PLATFORM(DARWIN)    
    vm_deallocate(current_task(), reinterpret_cast<vm_address_t>(block), BLOCK_SIZE);
#elif PLATFORM(SYMBIAN)
    fastFree(block);
#elif PLATFORM(WIN_OS)
    VirtualFree(block, 0, MEM_RELEASE);
#elif HAVE(POSIX_MEMALIGN)
    free(block);
#else
    munmap(reinterpret_cast<char*>(block), BLOCK_SIZE);
#endif
}

static void freeHeap(CollectorHeap* heap)
{
    for (size_t i = 0; i < heap->usedBlocks; ++i)
        if (heap->blocks[i])
            freeBlock(heap->blocks[i]);
    fastFree(heap->blocks);
    memset(heap, 0, sizeof(CollectorHeap));
}

void Heap::recordExtraCost(size_t cost)
{
    // Our frequency of garbage collection tries to balance memory use against speed
    // by collecting based on the number of newly created values. However, for values
    // that hold on to a great deal of memory that's not in the form of other JS values,
    // that is not good enough - in some cases a lot of those objects can pile up and
    // use crazy amounts of memory without a GC happening. So we track these extra
    // memory costs. Only unusually large objects are noted, and we only keep track
    // of this extra cost until the next GC. In garbage collected languages, most values
    // are either very short lived temporaries, or have extremely long lifetimes. So
    // if a large value survives one garbage collection, there is not much point to
    // collecting more frequently as long as it stays alive.
    // NOTE: we target the primaryHeap unconditionally as JSNumber doesn't modify cost 

    primaryHeap.extraCost += cost;
}

template <HeapType heapType> ALWAYS_INLINE void* Heap::heapAllocate(size_t s)
{
    typedef typename HeapConstants<heapType>::Block Block;
    typedef typename HeapConstants<heapType>::Cell Cell;

    CollectorHeap& heap = heapType == PrimaryHeap ? primaryHeap : numberHeap;
    ASSERT(JSLock::lockCount() > 0);
    ASSERT(JSLock::currentThreadIsHoldingLock());
    ASSERT_UNUSED(s, s <= HeapConstants<heapType>::cellSize);

    ASSERT(heap.operationInProgress == NoOperation);
    ASSERT(heapType == PrimaryHeap || heap.extraCost == 0);
    // FIXME: If another global variable access here doesn't hurt performance
    // too much, we could CRASH() in NDEBUG builds, which could help ensure we
    // don't spend any time debugging cases where we allocate inside an object's
    // deallocation code.

#if COLLECT_ON_EVERY_ALLOCATION
    collect();
#endif

    size_t numLiveObjects = heap.numLiveObjects;
    size_t usedBlocks = heap.usedBlocks;
    size_t i = heap.firstBlockWithPossibleSpace;

    // if we have a huge amount of extra cost, we'll try to collect even if we still have
    // free cells left.
    if (heapType == PrimaryHeap && heap.extraCost > ALLOCATIONS_PER_COLLECTION) {
        size_t numLiveObjectsAtLastCollect = heap.numLiveObjectsAtLastCollect;
        size_t numNewObjects = numLiveObjects - numLiveObjectsAtLastCollect;
        const size_t newCost = numNewObjects + heap.extraCost;
        if (newCost >= ALLOCATIONS_PER_COLLECTION && newCost >= numLiveObjectsAtLastCollect)
            goto collect;
    }

    ASSERT(heap.operationInProgress == NoOperation);
#ifndef NDEBUG
    // FIXME: Consider doing this in NDEBUG builds too (see comment above).
    heap.operationInProgress = Allocation;
#endif

scan:
    Block* targetBlock;
    size_t targetBlockUsedCells;
    if (i != usedBlocks) {
        targetBlock = reinterpret_cast<Block*>(heap.blocks[i]);
        targetBlockUsedCells = targetBlock->usedCells;
        ASSERT(targetBlockUsedCells <= HeapConstants<heapType>::cellsPerBlock);
        while (targetBlockUsedCells == HeapConstants<heapType>::cellsPerBlock) {
            if (++i == usedBlocks)
                goto collect;
            targetBlock = reinterpret_cast<Block*>(heap.blocks[i]);
            targetBlockUsedCells = targetBlock->usedCells;
            ASSERT(targetBlockUsedCells <= HeapConstants<heapType>::cellsPerBlock);
        }
        heap.firstBlockWithPossibleSpace = i;
    } else {

collect:
        size_t numLiveObjectsAtLastCollect = heap.numLiveObjectsAtLastCollect;
        size_t numNewObjects = numLiveObjects - numLiveObjectsAtLastCollect;
        const size_t newCost = numNewObjects + heap.extraCost;

        if (newCost >= ALLOCATIONS_PER_COLLECTION && newCost >= numLiveObjectsAtLastCollect) {
#ifndef NDEBUG
            heap.operationInProgress = NoOperation;
#endif
            bool collected = collect();
#ifndef NDEBUG
            heap.operationInProgress = Allocation;
#endif
            if (collected) {
                numLiveObjects = heap.numLiveObjects;
                usedBlocks = heap.usedBlocks;
                i = heap.firstBlockWithPossibleSpace;
                goto scan;
            }
        }
  
        // didn't find a block, and GC didn't reclaim anything, need to allocate a new block
        size_t numBlocks = heap.numBlocks;
        if (usedBlocks == numBlocks) {
            static const size_t maxNumBlocks = ULONG_MAX / sizeof(CollectorBlock*) / GROWTH_FACTOR;
            if (numBlocks > maxNumBlocks)
                CRASH();
            numBlocks = max(MIN_ARRAY_SIZE, numBlocks * GROWTH_FACTOR);
            heap.numBlocks = numBlocks;
            heap.blocks = static_cast<CollectorBlock**>(fastRealloc(heap.blocks, numBlocks * sizeof(CollectorBlock*)));
        }

        targetBlock = reinterpret_cast<Block*>(allocateBlock<heapType>());
        targetBlock->freeList = targetBlock->cells;
        targetBlock->heap = this;
        targetBlockUsedCells = 0;
        heap.blocks[usedBlocks] = reinterpret_cast<CollectorBlock*>(targetBlock);
        heap.usedBlocks = usedBlocks + 1;
        heap.firstBlockWithPossibleSpace = usedBlocks;
    }
  
    // find a free spot in the block and detach it from the free list
    Cell* newCell = targetBlock->freeList;

    // "next" field is a cell offset -- 0 means next cell, so a zeroed block is already initialized
    targetBlock->freeList = (newCell + 1) + newCell->u.freeCell.next;

    targetBlock->usedCells = static_cast<uint32_t>(targetBlockUsedCells + 1);
    heap.numLiveObjects = numLiveObjects + 1;

#ifndef NDEBUG
    // FIXME: Consider doing this in NDEBUG builds too (see comment above).
    heap.operationInProgress = NoOperation;
#endif

    return newCell;
}

void* Heap::allocate(size_t s)
{
    return heapAllocate<PrimaryHeap>(s);
}

void* Heap::allocateNumber(size_t s)
{
    return heapAllocate<NumberHeap>(s);
}

#if PLATFORM(WIN_CE)
// Return the number of bytes that are writable starting at p.
// The pointer p is assumed to be page aligned.
static inline DWORD numberOfWritableBytes(void* p)
{
    MEMORY_BASIC_INFORMATION buf;
    DWORD result = VirtualQuery(p, &buf, sizeof(buf));
    ASSERT(result == sizeof(buf));
    DWORD protect = (buf.Protect & ~(PAGE_GUARD | PAGE_NOCACHE));

    // check if the page is writable
    if (protect != PAGE_READWRITE && protect != PAGE_WRITECOPY &&
        protect != PAGE_EXECUTE_READWRITE && protect != PAGE_EXECUTE_WRITECOPY)
        return 0;

    if (buf.State != MEM_COMMIT)
        return 0;

    return buf.RegionSize;
}

static DWORD systemPageSize()
 {
    SYSTEM_INFO sysInfo;
    GetSystemInfo(&sysInfo);
    return sysInfo.dwPageSize;
}

static inline void* currentThreadStackBaseWinCE()
{
    static DWORD pageSize = systemPageSize();
    int dummy;
    void* sp = &dummy;
    char* alignedStackPtr = reinterpret_cast<char*>((DWORD)sp & ~(pageSize - 1));
    DWORD size = 0;
    while (size = numberOfWritableBytes(alignedStackPtr))
        alignedStackPtr += size;
    return alignedStackPtr;
}
#endif // PLATFORM(WIN_CE)

static inline void* currentThreadStackBase()
{
#if PLATFORM(DARWIN)
    pthread_t thread = pthread_self();
    return pthread_get_stackaddr_np(thread);
#elif PLATFORM(WIN_CE)
    return currentThreadStackBaseWinCE();
#elif PLATFORM(WIN_OS) && PLATFORM(X86) && COMPILER(MSVC)
    // offset 0x18 from the FS segment register gives a pointer to
    // the thread information block for the current thread
    NT_TIB* pTib;
    __asm {
        MOV EAX, FS:[18h]
        MOV pTib, EAX
    }
    return static_cast<void*>(pTib->StackBase);
#elif PLATFORM(WIN_OS) && PLATFORM(X86_64) && COMPILER(MSVC)
    PNT_TIB64 pTib = reinterpret_cast<PNT_TIB64>(NtCurrentTeb());
    return reinterpret_cast<void*>(pTib->StackBase);
#elif PLATFORM(WIN_OS) && PLATFORM(X86) && COMPILER(GCC)
    // offset 0x18 from the FS segment register gives a pointer to
    // the thread information block for the current thread
    NT_TIB* pTib;
    asm ( "movl %%fs:0x18, %0\n"
          : "=r" (pTib)
        );
    return static_cast<void*>(pTib->StackBase);
#elif PLATFORM(SOLARIS)
    stack_t s;
    thr_stksegment(&s);
    return s.ss_sp;
#elif PLATFORM(OPENBSD)
    pthread_t thread = pthread_self();
    stack_t stack;
    pthread_stackseg_np(thread, &stack);
    return stack.ss_sp;
#elif PLATFORM(UNIX)
#ifdef UCLIBC_USE_PROC_SELF_MAPS
    // Read /proc/self/maps and locate the line whose address
    // range contains __libc_stack_end.
    FILE *file = fopen("/proc/self/maps", "r");
    if (!file)
        return 0;
    __fsetlocking(file, FSETLOCKING_BYCALLER);
    char *line = NULL;
    size_t lineLen = 0;
    while (!feof_unlocked(file)) {
        if (getdelim(&line, &lineLen, '\n', file) <= 0)
            break;

        long from;
        long to;
        if (sscanf (line, "%lx-%lx", &from, &to) != 2)
            continue;
        if (from <= (long)__libc_stack_end && (long)__libc_stack_end < to) {
            fclose(file);
            free(line);
#ifdef _STACK_GROWS_UP
            return (void *)from;
#else
            return (void *)to;
#endif
        }
    }
    fclose(file);
    free(line);
    return 0;
#else
    static void* stackBase = 0;
    static size_t stackSize = 0;
    static pthread_t stackThread;
    pthread_t thread = pthread_self();
    if (stackBase == 0 || thread != stackThread) {
#if defined(QT_LINUXBASE)
        // LinuxBase is missing pthread_getattr_np - resolve it once at runtime instead
        // see http://bugs.linuxbase.org/show_bug.cgi?id=2364
        typedef int (*GetAttrPtr)(pthread_t, pthread_attr_t *);
        static int (*pthread_getattr_np_ptr)(pthread_t, pthread_attr_t *) = 0;
        if (!pthread_getattr_np_ptr)
            *(void **)&pthread_getattr_np_ptr = dlsym(RTLD_DEFAULT, "pthread_getattr_np");
#endif
        pthread_attr_t sattr;
        pthread_attr_init(&sattr);
#if HAVE(PTHREAD_NP_H) || PLATFORM(NETBSD)
        // e.g. on FreeBSD 5.4, neundorf@kde.org
        pthread_attr_get_np(thread, &sattr);
#elif defined(QT_LINUXBASE)
        if (pthread_getattr_np_ptr)
            pthread_getattr_np_ptr(thread, &sattr);
#else
        // FIXME: this function is non-portable; other POSIX systems may have different np alternatives
        pthread_getattr_np(thread, &sattr);
#endif
        int rc = pthread_attr_getstack(&sattr, &stackBase, &stackSize);
        (void)rc; // FIXME: Deal with error code somehow? Seems fatal.
        ASSERT(stackBase);
        pthread_attr_destroy(&sattr);
        stackThread = thread;
    }
    return static_cast<char*>(stackBase) + stackSize;
#endif
#elif PLATFORM(SYMBIAN)
    static void* stackBase = 0;
    if (stackBase == 0) {
        TThreadStackInfo info;
        RThread thread;
        thread.StackInfo(info);
        stackBase = (void*)info.iBase;
    }
    return (void*)stackBase;
#else
#error Need a way to get the stack base on this platform
#endif
}

#if ENABLE(JSC_MULTIPLE_THREADS)

static inline PlatformThread getCurrentPlatformThread()
{
#if PLATFORM(DARWIN)
    return pthread_mach_thread_np(pthread_self());
#elif PLATFORM(WIN_OS)
    HANDLE threadHandle = pthread_getw32threadhandle_np(pthread_self());
    return PlatformThread(GetCurrentThreadId(), threadHandle);
#endif
}

void Heap::makeUsableFromMultipleThreads()
{
    if (m_currentThreadRegistrar)
        return;

    int error = pthread_key_create(&m_currentThreadRegistrar, unregisterThread);
    if (error)
        CRASH();
}

void Heap::registerThread()
{
    if (!m_currentThreadRegistrar || pthread_getspecific(m_currentThreadRegistrar))
        return;

    pthread_setspecific(m_currentThreadRegistrar, this);
    Heap::Thread* thread = new Heap::Thread(pthread_self(), getCurrentPlatformThread(), currentThreadStackBase());

    MutexLocker lock(m_registeredThreadsMutex);

    thread->next = m_registeredThreads;
    m_registeredThreads = thread;
}

void Heap::unregisterThread(void* p)
{
    if (p)
        static_cast<Heap*>(p)->unregisterThread();
}

void Heap::unregisterThread()
{
    pthread_t currentPosixThread = pthread_self();

    MutexLocker lock(m_registeredThreadsMutex);

    if (pthread_equal(currentPosixThread, m_registeredThreads->posixThread)) {
        Thread* t = m_registeredThreads;
        m_registeredThreads = m_registeredThreads->next;
        delete t;
    } else {
        Heap::Thread* last = m_registeredThreads;
        Heap::Thread* t;
        for (t = m_registeredThreads->next; t; t = t->next) {
            if (pthread_equal(t->posixThread, currentPosixThread)) {
                last->next = t->next;
                break;
            }
            last = t;
        }
        ASSERT(t); // If t is NULL, we never found ourselves in the list.
        delete t;
    }
}

#else // ENABLE(JSC_MULTIPLE_THREADS)

void Heap::registerThread()
{
}

#endif

#define IS_POINTER_ALIGNED(p) (((intptr_t)(p) & (sizeof(char*) - 1)) == 0)

// cell size needs to be a power of two for this to be valid
#define IS_HALF_CELL_ALIGNED(p) (((intptr_t)(p) & (CELL_MASK >> 1)) == 0)

void Heap::markConservatively(void* start, void* end)
{
    if (start > end) {
        void* tmp = start;
        start = end;
        end = tmp;
    }

    ASSERT((static_cast<char*>(end) - static_cast<char*>(start)) < 0x1000000);
    ASSERT(IS_POINTER_ALIGNED(start));
    ASSERT(IS_POINTER_ALIGNED(end));

    char** p = static_cast<char**>(start);
    char** e = static_cast<char**>(end);

    size_t usedPrimaryBlocks = primaryHeap.usedBlocks;
    size_t usedNumberBlocks = numberHeap.usedBlocks;
    CollectorBlock** primaryBlocks = primaryHeap.blocks;
    CollectorBlock** numberBlocks = numberHeap.blocks;

    const size_t lastCellOffset = sizeof(CollectorCell) * (CELLS_PER_BLOCK - 1);

    while (p != e) {
        char* x = *p++;
        if (IS_HALF_CELL_ALIGNED(x) && x) {
            uintptr_t xAsBits = reinterpret_cast<uintptr_t>(x);
            xAsBits &= CELL_ALIGN_MASK;
            uintptr_t offset = xAsBits & BLOCK_OFFSET_MASK;
            CollectorBlock* blockAddr = reinterpret_cast<CollectorBlock*>(xAsBits - offset);
            // Mark the the number heap, we can mark these Cells directly to avoid the virtual call cost
            for (size_t block = 0; block < usedNumberBlocks; block++) {
                if ((numberBlocks[block] == blockAddr) & (offset <= lastCellOffset)) {
                    Heap::markCell(reinterpret_cast<JSCell*>(xAsBits));
                    goto endMarkLoop;
                }
            }
          
            // Mark the primary heap
            for (size_t block = 0; block < usedPrimaryBlocks; block++) {
                if ((primaryBlocks[block] == blockAddr) & (offset <= lastCellOffset)) {
                    if (reinterpret_cast<CollectorCell*>(xAsBits)->u.freeCell.zeroIfFree != 0) {
                        JSCell* imp = reinterpret_cast<JSCell*>(xAsBits);
                        if (!imp->marked())
                            imp->mark();
                    }
                    break;
                }
            }
        endMarkLoop:
            ;
        }
    }
}

void NEVER_INLINE Heap::markCurrentThreadConservativelyInternal()
{
    void* dummy;
    void* stackPointer = &dummy;
    void* stackBase = currentThreadStackBase();
    markConservatively(stackPointer, stackBase);
}

void Heap::markCurrentThreadConservatively()
{
    // setjmp forces volatile registers onto the stack
    jmp_buf registers;
#if COMPILER(MSVC)
#pragma warning(push)
#pragma warning(disable: 4611)
#endif
    setjmp(registers);
#if COMPILER(MSVC)
#pragma warning(pop)
#endif

    markCurrentThreadConservativelyInternal();
}

#if ENABLE(JSC_MULTIPLE_THREADS)

static inline void suspendThread(const PlatformThread& platformThread)
{
#if PLATFORM(DARWIN)
    thread_suspend(platformThread);
#elif PLATFORM(WIN_OS)
    SuspendThread(platformThread.handle);
#else
#error Need a way to suspend threads on this platform
#endif
}

static inline void resumeThread(const PlatformThread& platformThread)
{
#if PLATFORM(DARWIN)
    thread_resume(platformThread);
#elif PLATFORM(WIN_OS)
    ResumeThread(platformThread.handle);
#else
#error Need a way to resume threads on this platform
#endif
}

typedef unsigned long usword_t; // word size, assumed to be either 32 or 64 bit

#if PLATFORM(DARWIN)

#if PLATFORM(X86)
typedef i386_thread_state_t PlatformThreadRegisters;
#elif PLATFORM(X86_64)
typedef x86_thread_state64_t PlatformThreadRegisters;
#elif PLATFORM(PPC)
typedef ppc_thread_state_t PlatformThreadRegisters;
#elif PLATFORM(PPC64)
typedef ppc_thread_state64_t PlatformThreadRegisters;
#elif PLATFORM(ARM)
typedef arm_thread_state_t PlatformThreadRegisters;
#else
#error Unknown Architecture
#endif

#elif PLATFORM(WIN_OS)&& PLATFORM(X86)
typedef CONTEXT PlatformThreadRegisters;
#else
#error Need a thread register struct for this platform
#endif

size_t getPlatformThreadRegisters(const PlatformThread& platformThread, PlatformThreadRegisters& regs)
{
#if PLATFORM(DARWIN)

#if PLATFORM(X86)
    unsigned user_count = sizeof(regs)/sizeof(int);
    thread_state_flavor_t flavor = i386_THREAD_STATE;
#elif PLATFORM(X86_64)
    unsigned user_count = x86_THREAD_STATE64_COUNT;
    thread_state_flavor_t flavor = x86_THREAD_STATE64;
#elif PLATFORM(PPC) 
    unsigned user_count = PPC_THREAD_STATE_COUNT;
    thread_state_flavor_t flavor = PPC_THREAD_STATE;
#elif PLATFORM(PPC64)
    unsigned user_count = PPC_THREAD_STATE64_COUNT;
    thread_state_flavor_t flavor = PPC_THREAD_STATE64;
#elif PLATFORM(ARM)
    unsigned user_count = ARM_THREAD_STATE_COUNT;
    thread_state_flavor_t flavor = ARM_THREAD_STATE;
#else
#error Unknown Architecture
#endif

    kern_return_t result = thread_get_state(platformThread, flavor, (thread_state_t)&regs, &user_count);
    if (result != KERN_SUCCESS) {
        WTFReportFatalError(__FILE__, __LINE__, WTF_PRETTY_FUNCTION, 
                            "JavaScript garbage collection failed because thread_get_state returned an error (%d). This is probably the result of running inside Rosetta, which is not supported.", result);
        CRASH();
    }
    return user_count * sizeof(usword_t);
// end PLATFORM(DARWIN)

#elif PLATFORM(WIN_OS) && PLATFORM(X86)
    regs.ContextFlags = CONTEXT_INTEGER | CONTEXT_CONTROL | CONTEXT_SEGMENTS;
    GetThreadContext(platformThread.handle, &regs);
    return sizeof(CONTEXT);
#else
#error Need a way to get thread registers on this platform
#endif
}

static inline void* otherThreadStackPointer(const PlatformThreadRegisters& regs)
{
#if PLATFORM(DARWIN)

#if __DARWIN_UNIX03

#if PLATFORM(X86)
    return reinterpret_cast<void*>(regs.__esp);
#elif PLATFORM(X86_64)
    return reinterpret_cast<void*>(regs.__rsp);
#elif PLATFORM(PPC) || PLATFORM(PPC64)
    return reinterpret_cast<void*>(regs.__r1);
#elif PLATFORM(ARM)
    return reinterpret_cast<void*>(regs.__sp);
#else
#error Unknown Architecture
#endif

#else // !__DARWIN_UNIX03

#if PLATFORM(X86)
    return reinterpret_cast<void*>(regs.esp);
#elif PLATFORM(X86_64)
    return reinterpret_cast<void*>(regs.rsp);
#elif (PLATFORM(PPC) || PLATFORM(PPC64))
    return reinterpret_cast<void*>(regs.r1);
#else
#error Unknown Architecture
#endif

#endif // __DARWIN_UNIX03

// end PLATFORM(DARWIN)
#elif PLATFORM(X86) && PLATFORM(WIN_OS)
    return reinterpret_cast<void*>((uintptr_t) regs.Esp);
#else
#error Need a way to get the stack pointer for another thread on this platform
#endif
}

void Heap::markOtherThreadConservatively(Thread* thread)
{
    suspendThread(thread->platformThread);

    PlatformThreadRegisters regs;
    size_t regSize = getPlatformThreadRegisters(thread->platformThread, regs);

    // mark the thread's registers
    markConservatively(static_cast<void*>(&regs), static_cast<void*>(reinterpret_cast<char*>(&regs) + regSize));

    void* stackPointer = otherThreadStackPointer(regs);
    markConservatively(stackPointer, thread->stackBase);

    resumeThread(thread->platformThread);
}

#endif

void Heap::markStackObjectsConservatively()
{
    markCurrentThreadConservatively();

#if ENABLE(JSC_MULTIPLE_THREADS)

    if (m_currentThreadRegistrar) {

        MutexLocker lock(m_registeredThreadsMutex);

#ifndef NDEBUG
        // Forbid malloc during the mark phase. Marking a thread suspends it, so 
        // a malloc inside mark() would risk a deadlock with a thread that had been 
        // suspended while holding the malloc lock.
        fastMallocForbid();
#endif
        // It is safe to access the registeredThreads list, because we earlier asserted that locks are being held,
        // and since this is a shared heap, they are real locks.
        for (Thread* thread = m_registeredThreads; thread; thread = thread->next) {
            if (!pthread_equal(thread->posixThread, pthread_self()))
                markOtherThreadConservatively(thread);
        }
#ifndef NDEBUG
        fastMallocAllow();
#endif
    }
#endif
}

void Heap::setGCProtectNeedsLocking()
{
    // Most clients do not need to call this, with the notable exception of WebCore.
    // Clients that use shared heap have JSLock protection, while others are supposed
    // to do explicit locking. WebCore violates this contract in Database code,
    // which calls gcUnprotect from a secondary thread.
    if (!m_protectedValuesMutex)
        m_protectedValuesMutex.set(new Mutex);
}

void Heap::protect(JSValuePtr k)
{
    ASSERT(k);
    ASSERT(JSLock::currentThreadIsHoldingLock() || !m_globalData->isSharedInstance);

    if (JSImmediate::isImmediate(k))
        return;

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    m_protectedValues.add(k->asCell());

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();
}

void Heap::unprotect(JSValuePtr k)
{
    ASSERT(k);
    ASSERT(JSLock::currentThreadIsHoldingLock() || !m_globalData->isSharedInstance);

    if (JSImmediate::isImmediate(k))
        return;

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    m_protectedValues.remove(k->asCell());

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();
}

Heap* Heap::heap(JSValuePtr v)
{
    if (JSImmediate::isImmediate(v))
        return 0;
    return Heap::cellBlock(v->asCell())->heap;
}

void Heap::markProtectedObjects()
{
    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    ProtectCountSet::iterator end = m_protectedValues.end();
    for (ProtectCountSet::iterator it = m_protectedValues.begin(); it != end; ++it) {
        JSCell* val = it->first;
        if (!val->marked())
            val->mark();
    }

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();
}

template <HeapType heapType> size_t Heap::sweep()
{
    typedef typename HeapConstants<heapType>::Block Block;
    typedef typename HeapConstants<heapType>::Cell Cell;

    // SWEEP: delete everything with a zero refcount (garbage) and unmark everything else
    CollectorHeap& heap = heapType == PrimaryHeap ? primaryHeap : numberHeap;
    
    size_t emptyBlocks = 0;
    size_t numLiveObjects = heap.numLiveObjects;
    
    for (size_t block = 0; block < heap.usedBlocks; block++) {
        Block* curBlock = reinterpret_cast<Block*>(heap.blocks[block]);
        
        size_t usedCells = curBlock->usedCells;
        Cell* freeList = curBlock->freeList;
        
        if (usedCells == HeapConstants<heapType>::cellsPerBlock) {
            // special case with a block where all cells are used -- testing indicates this happens often
            for (size_t i = 0; i < HeapConstants<heapType>::cellsPerBlock; i++) {
                if (!curBlock->marked.get(i >> HeapConstants<heapType>::bitmapShift)) {
                    Cell* cell = curBlock->cells + i;
                    
                    if (heapType != NumberHeap) {
                        JSCell* imp = reinterpret_cast<JSCell*>(cell);
                        // special case for allocated but uninitialized object
                        // (We don't need this check earlier because nothing prior this point 
                        // assumes the object has a valid vptr.)
                        if (cell->u.freeCell.zeroIfFree == 0)
                            continue;
                        
                        imp->~JSCell();
                    }
                    
                    --usedCells;
                    --numLiveObjects;
                    
                    // put cell on the free list
                    cell->u.freeCell.zeroIfFree = 0;
                    cell->u.freeCell.next = freeList - (cell + 1);
                    freeList = cell;
                }
            }
        } else {
            size_t minimumCellsToProcess = usedCells;
            for (size_t i = 0; (i < minimumCellsToProcess) & (i < HeapConstants<heapType>::cellsPerBlock); i++) {
                Cell* cell = curBlock->cells + i;
                if (cell->u.freeCell.zeroIfFree == 0) {
                    ++minimumCellsToProcess;
                } else {
                    if (!curBlock->marked.get(i >> HeapConstants<heapType>::bitmapShift)) {
                        if (heapType != NumberHeap) {
                            JSCell* imp = reinterpret_cast<JSCell*>(cell);
                            imp->~JSCell();
                        }
                        --usedCells;
                        --numLiveObjects;
                        
                        // put cell on the free list
                        cell->u.freeCell.zeroIfFree = 0;
                        cell->u.freeCell.next = freeList - (cell + 1); 
                        freeList = cell;
                    }
                }
            }
        }
        
        curBlock->usedCells = static_cast<uint32_t>(usedCells);
        curBlock->freeList = freeList;
        curBlock->marked.clearAll();
        
        if (usedCells == 0) {
            emptyBlocks++;
            if (emptyBlocks > SPARE_EMPTY_BLOCKS) {
#if !DEBUG_COLLECTOR
                freeBlock(reinterpret_cast<CollectorBlock*>(curBlock));
#endif
                // swap with the last block so we compact as we go
                heap.blocks[block] = heap.blocks[heap.usedBlocks - 1];
                heap.usedBlocks--;
                block--; // Don't move forward a step in this case
                
                if (heap.numBlocks > MIN_ARRAY_SIZE && heap.usedBlocks < heap.numBlocks / LOW_WATER_FACTOR) {
                    heap.numBlocks = heap.numBlocks / GROWTH_FACTOR; 
                    heap.blocks = static_cast<CollectorBlock**>(fastRealloc(heap.blocks, heap.numBlocks * sizeof(CollectorBlock*)));
                }
            }
        }
    }
    
    if (heap.numLiveObjects != numLiveObjects)
        heap.firstBlockWithPossibleSpace = 0;
        
    heap.numLiveObjects = numLiveObjects;
    heap.numLiveObjectsAtLastCollect = numLiveObjects;
    heap.extraCost = 0;
    return numLiveObjects;
}
    
bool Heap::collect()
{
#ifndef NDEBUG
    if (m_globalData->isSharedInstance) {
        ASSERT(JSLock::lockCount() > 0);
        ASSERT(JSLock::currentThreadIsHoldingLock());
    }
#endif

    ASSERT((primaryHeap.operationInProgress == NoOperation) | (numberHeap.operationInProgress == NoOperation));
    if ((primaryHeap.operationInProgress != NoOperation) | (numberHeap.operationInProgress != NoOperation))
        CRASH();

    JAVASCRIPTCORE_GC_BEGIN();
    primaryHeap.operationInProgress = Collection;
    numberHeap.operationInProgress = Collection;

    // MARK: first mark all referenced objects recursively starting out from the set of root objects

    markStackObjectsConservatively();
    markProtectedObjects();
    if (m_markListSet && m_markListSet->size())
        ArgList::markLists(*m_markListSet);
    if (m_globalData->exception && !m_globalData->exception->marked())
        m_globalData->exception->mark();
    m_globalData->interpreter->registerFile().markCallFrames(this);
    m_globalData->smallStrings.mark();

    JAVASCRIPTCORE_GC_MARKED();

    size_t originalLiveObjects = primaryHeap.numLiveObjects + numberHeap.numLiveObjects;
    size_t numLiveObjects = sweep<PrimaryHeap>();
    numLiveObjects += sweep<NumberHeap>();

    primaryHeap.operationInProgress = NoOperation;
    numberHeap.operationInProgress = NoOperation;
    JAVASCRIPTCORE_GC_END(originalLiveObjects, numLiveObjects);

    return numLiveObjects < originalLiveObjects;
}

size_t Heap::objectCount() 
{
    return primaryHeap.numLiveObjects + numberHeap.numLiveObjects; 
}

template <HeapType heapType> 
static void addToStatistics(Heap::Statistics& statistics, const CollectorHeap& heap)
{
    typedef HeapConstants<heapType> HC;
    for (size_t i = 0; i < heap.usedBlocks; ++i) {
        if (heap.blocks[i]) {
            statistics.size += BLOCK_SIZE;
            statistics.free += (HC::cellsPerBlock - heap.blocks[i]->usedCells) * HC::cellSize;
        }
    }
}

Heap::Statistics Heap::statistics() const
{
    Statistics statistics = { 0, 0 };
    JSC::addToStatistics<PrimaryHeap>(statistics, primaryHeap);
    JSC::addToStatistics<NumberHeap>(statistics, numberHeap);
    return statistics;
}

size_t Heap::globalObjectCount()
{
    size_t count = 0;
    if (JSGlobalObject* head = m_globalData->head) {
        JSGlobalObject* o = head;
        do {
            ++count;
            o = o->next();
        } while (o != head);
    }
    return count;
}

size_t Heap::protectedGlobalObjectCount()
{
    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    size_t count = 0;
    if (JSGlobalObject* head = m_globalData->head) {
        JSGlobalObject* o = head;
        do {
            if (m_protectedValues.contains(o))
                ++count;
            o = o->next();
        } while (o != head);
    }

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();

    return count;
}

size_t Heap::protectedObjectCount()
{
    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    size_t result = m_protectedValues.size();

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();

    return result;
}

static const char* typeName(JSCell* val)
{
    if (val->isString())
        return "string";
    if (val->isNumber())
        return "number";
    if (val->isGetterSetter())
        return "gettersetter";
    ASSERT(val->isObject());
    const ClassInfo* info = static_cast<JSObject*>(val)->classInfo();
    return info ? info->className : "Object";
}

HashCountedSet<const char*>* Heap::protectedObjectTypeCounts()
{
    HashCountedSet<const char*>* counts = new HashCountedSet<const char*>;

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->lock();

    ProtectCountSet::iterator end = m_protectedValues.end();
    for (ProtectCountSet::iterator it = m_protectedValues.begin(); it != end; ++it)
        counts->add(typeName(it->first));

    if (m_protectedValuesMutex)
        m_protectedValuesMutex->unlock();

    return counts;
}

bool Heap::isBusy()
{
    return (primaryHeap.operationInProgress != NoOperation) | (numberHeap.operationInProgress != NoOperation);
}

Heap::iterator Heap::primaryHeapBegin()
{
    return iterator(primaryHeap.blocks, primaryHeap.blocks + primaryHeap.usedBlocks);
}

Heap::iterator Heap::primaryHeapEnd()
{
    return iterator(primaryHeap.blocks + primaryHeap.usedBlocks, primaryHeap.blocks + primaryHeap.usedBlocks);
}

} // namespace JSC