JavaScriptCore/kjs/collector.cpp

/*
 *  Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
 *  Copyright (C) 2007 Eric Seidel <eric@webkit.org>
 *
 *  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 "ExecState.h"
#include "JSGlobalObject.h"
#include "JSString.h"
#include "JSValue.h"
#include "list.h"
#include "Machine.h"
#include <algorithm>
#include <setjmp.h>
#include <stdlib.h>
#include <wtf/FastMalloc.h>
#include <wtf/HashCountedSet.h>
#include <wtf/UnusedParam.h>

#if USE(MULTIPLE_THREADS)
#include <pthread.h>
#include <wtf/Threading.h>
#endif

#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>

#include "CollectorHeapIntrospector.h"

#elif PLATFORM(WIN_OS)

#include <windows.h>

#elif PLATFORM(UNIX)

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

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

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

#endif

#define DEBUG_COLLECTOR 0
#define COLLECT_ON_EVERY_ALLOCATION 0

using std::max;

namespace KJS {

// 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*);

Heap::Heap(Machine* machine)
    : m_markListSet(0)
    , m_machine(machine)
{
    memset(&primaryHeap, 0, sizeof(CollectorHeap));
    memset(&numberHeap, 0, sizeof(CollectorHeap));
}

Heap::~Heap()
{
    JSLock lock;

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

    ASSERT(!primaryHeap.numLiveObjects);

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

static NEVER_INLINE CollectorBlock* allocateBlock()
{
#if PLATFORM(DARWIN)    
    vm_address_t address = 0;
    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(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 USE(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

    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(WIN_OS)
    VirtualFree(block, BLOCK_SIZE, 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 <Heap::HeapType heapType> struct HeapConstants;

template <> struct HeapConstants<Heap::PrimaryHeap> {
    static const size_t cellSize = CELL_SIZE;
    static const size_t cellsPerBlock = CELLS_PER_BLOCK;
    static const size_t bitmapShift = 0;
    typedef CollectorCell Cell;
    typedef CollectorBlock Block;
};

template <> struct HeapConstants<Heap::NumberHeap> {
    static const size_t cellSize = SMALL_CELL_SIZE;
    static const size_t cellsPerBlock = SMALL_CELLS_PER_BLOCK;
    static const size_t bitmapShift = 1;
    typedef SmallCollectorCell Cell;
    typedef SmallCellCollectorBlock Block;
};

template <Heap::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(s <= HeapConstants<heapType>::cellSize);
    UNUSED_PARAM(s); // s is now only used for the above assert

    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 abort() in NDEBUG builds, which could help ensure we
    // don't spend any time debugging cases where we allocate inside an object's
    // deallocation code.

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

#if COLLECT_ON_EVERY_ALLOCATION
    collect();
#endif

    // 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 = (Block*)heap.blocks[i];
        targetBlockUsedCells = targetBlock->usedCells;
        ASSERT(targetBlockUsedCells <= HeapConstants<heapType>::cellsPerBlock);
        while (targetBlockUsedCells == HeapConstants<heapType>::cellsPerBlock) {
            if (++i == usedBlocks)
                goto collect;
            targetBlock = (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) {
            numBlocks = max(MIN_ARRAY_SIZE, numBlocks * GROWTH_FACTOR);
            heap.numBlocks = numBlocks;
            heap.blocks = static_cast<CollectorBlock**>(fastRealloc(heap.blocks, numBlocks * sizeof(CollectorBlock*)));
        }

        targetBlock = (Block*)allocateBlock();
        targetBlock->freeList = targetBlock->cells;
        targetBlock->heap = this;
        targetBlockUsedCells = 0;
        heap.blocks[usedBlocks] = (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);
}

static inline void* currentThreadStackBase()
{
#if PLATFORM(DARWIN)
    pthread_t thread = pthread_self();
    return pthread_get_stackaddr_np(thread);
#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 (void*)pTib->StackBase;
#elif PLATFORM(WIN_OS) && PLATFORM(X86_64) && COMPILER(MSVC)
    PNT_TIB64 pTib = reinterpret_cast<PNT_TIB64>(NtCurrentTeb());
    return (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 (void*)pTib->StackBase;
#elif PLATFORM(SOLARIS)
    stack_t s;
    thr_stksegment(&s);
    return s.ss_sp;
#elif PLATFORM(UNIX)
    static void* stackBase = 0;
    static size_t stackSize = 0;
    static pthread_t stackThread;
    pthread_t thread = pthread_self();
    if (stackBase == 0 || thread != stackThread) {
        pthread_attr_t sattr;
        pthread_attr_init(&sattr);
#if HAVE(PTHREAD_NP_H)
        // e.g. on FreeBSD 5.4, neundorf@kde.org
        pthread_attr_get_np(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;
#else
#error Need a way to get the stack base on this platform
#endif
}

#if USE(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

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
}

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;
};

pthread_key_t registeredThreadKey;
pthread_once_t registeredThreadKeyOnce = PTHREAD_ONCE_INIT;
Heap::Thread* registeredThreads;

static void destroyRegisteredThread(void* data) 
{
    Heap::Thread* thread = (Heap::Thread*)data;

    // Can't use JSLock convenience object here because we don't want to re-register
    // an exiting thread.
    JSLock::lock();

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

    JSLock::unlock();

    delete thread;
}

static void initializeRegisteredThreadKey()
{
    pthread_key_create(&registeredThreadKey, destroyRegisteredThread);
}

void Heap::registerThread()
{
    ASSERT(JSLock::lockCount() > 0);
    ASSERT(JSLock::currentThreadIsHoldingLock());

    pthread_once(&registeredThreadKeyOnce, initializeRegisteredThreadKey);

    if (!pthread_getspecific(registeredThreadKey)) {
        Heap::Thread* thread = new Heap::Thread(pthread_self(), getCurrentPlatformThread(), currentThreadStackBase());

        thread->next = registeredThreads;
        registeredThreads = thread;
        pthread_setspecific(registeredThreadKey, thread);
    }
}

#if PLATFORM(DARWIN)
void Heap::initializeHeapIntrospector()
{
    ASSERT(pthread_main_np());
    CollectorHeapIntrospector::init(&primaryHeap, &numberHeap);
}
#endif
#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(((char*)end - (char*)start) < 0x1000000);
    ASSERT(IS_POINTER_ALIGNED(start));
    ASSERT(IS_POINTER_ALIGNED(end));

    char** p = (char**)start;
    char** e = (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 (((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 USE(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 (void*)regs.__esp;
#elif PLATFORM(X86_64)
    return (void*)regs.__rsp;
#elif PLATFORM(PPC) || PLATFORM(PPC64)
    return (void*)regs.__r1;
#elif PLATFORM(ARM)
    return (void*)regs.__sp;
#else
#error Unknown Architecture
#endif

#else // !__DARWIN_UNIX03

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

#endif // __DARWIN_UNIX03

// end PLATFORM(DARWIN)
#elif PLATFORM(X86) && PLATFORM(WIN_OS)
    return (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)
{
    ASSERT(this == JSGlobalData::sharedInstance().heap);

    suspendThread(thread->platformThread);

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

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

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

    resumeThread(thread->platformThread);
}

#endif

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

#if USE(MULTIPLE_THREADS)

    if (this == JSGlobalData::sharedInstance().heap) {

#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
        for (Thread* thread = registeredThreads; thread != NULL; thread = thread->next) {
            if (!pthread_equal(thread->posixThread, pthread_self()))
                markOtherThreadConservatively(thread);
        }
#ifndef NDEBUG
        fastMallocAllow();
#endif
    }
#endif
}

void Heap::protect(JSValue* k)
{
    ASSERT(k);
    ASSERT(JSLock::lockCount() > 0);
    ASSERT(JSLock::currentThreadIsHoldingLock());

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

    protectedValues.add(k->asCell());
}

void Heap::unprotect(JSValue* k)
{
    ASSERT(k);
    ASSERT(JSLock::lockCount() > 0);
    ASSERT(JSLock::currentThreadIsHoldingLock());

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

    protectedValues.remove(k->asCell());
}

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

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

template <Heap::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 == Heap::PrimaryHeap ? primaryHeap : numberHeap;
    
    size_t emptyBlocks = 0;
    size_t numLiveObjects = heap.numLiveObjects;
    
    for (size_t block = 0; block < heap.usedBlocks; block++) {
        Block* curBlock = (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 != Heap::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 != Heap::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((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 = (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 (JSGlobalData::sharedInstance().heap == this) {
        ASSERT(JSLock::lockCount() > 0);
        ASSERT(JSLock::currentThreadIsHoldingLock());
    }
#endif

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

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

    markStackObjectsConservatively();
    markProtectedObjects();
    m_machine->mark(this);
    if (m_markListSet && m_markListSet->size())
        ArgList::markLists(*m_markListSet);

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

    return numLiveObjects < originalLiveObjects;
}

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

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

size_t Heap::protectedGlobalObjectCount()
{
    size_t count = 0;
    if (JSGlobalObject* head = JSGlobalData::threadInstance().head) {
        JSGlobalObject* o = head;
        do {
            if (protectedValues.contains(o))
                ++count;
            o = o->next();
        } while (o != head);
    }
    return count;
}

size_t Heap::protectedObjectCount()
{
    return protectedValues.size();
}

static const char* typeName(JSCell* val)
{
    const char* name = "???";
    switch (val->type()) {
        case UnspecifiedType:
            break;
        case UndefinedType:
            name = "undefined";
            break;
        case NullType:
            name = "null";
            break;
        case BooleanType:
            name = "boolean";
            break;
        case StringType:
            name = "string";
            break;
        case NumberType:
            name = "number";
            break;
        case ObjectType: {
            const ClassInfo* info = static_cast<JSObject*>(val)->classInfo();
            name = info ? info->className : "Object";
            break;
        }
        case GetterSetterType:
            name = "gettersetter";
            break;
    }
    return name;
}

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

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

    return counts;
}

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

} // namespace KJS