gecko/js/src/jscntxt.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sw=4 et tw=78:
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* JS execution context. */

#ifndef jscntxt_h___
#define jscntxt_h___

#include "mozilla/Attributes.h"

#include <string.h>

#include "jsapi.h"
#include "jsfriendapi.h"
#include "jsprvtd.h"
#include "jsatom.h"
#include "jsclist.h"
#include "jsgc.h"
#include "jspropertycache.h"
#include "jspropertytree.h"
#include "jsprototypes.h"
#include "jsutil.h"
#include "prmjtime.h"

#include "ds/LifoAlloc.h"
#include "gc/Statistics.h"
#include "js/HashTable.h"
#include "js/Vector.h"
#include "vm/Stack.h"
#include "vm/SPSProfiler.h"

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4100) /* Silence unreferenced formal parameter warnings */
#pragma warning(push)
#pragma warning(disable:4355) /* Silence warning about "this" used in base member initializer list */
#endif

JS_BEGIN_EXTERN_C
struct DtoaState;
JS_END_EXTERN_C

extern void
js_ReportOutOfMemory(JSContext *cx);

extern void
js_ReportAllocationOverflow(JSContext *cx);

namespace js {

typedef HashSet<JSObject *> ObjectSet;

/* Detects cycles when traversing an object graph. */
class AutoCycleDetector
{
    JSContext *cx;
    JSObject *obj;
    bool cyclic;
    uint32_t hashsetGenerationAtInit;
    ObjectSet::AddPtr hashsetAddPointer;
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER

  public:
    AutoCycleDetector(JSContext *cx, JSObject *obj
                      JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : cx(cx), obj(obj), cyclic(true)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
    }

    ~AutoCycleDetector();

    bool init();

    bool foundCycle() { return cyclic; }
};

/* Updates references in the cycle detection set if the GC moves them. */
extern void
TraceCycleDetectionSet(JSTracer *trc, ObjectSet &set);

namespace mjit {
class JaegerRuntime;
}

class MathCache;

namespace ion {
class IonActivation;
}

class WeakMapBase;
class InterpreterFrames;
class DebugScopes;
class WorkerThreadState;

/*
 * GetSrcNote cache to avoid O(n^2) growth in finding a source note for a
 * given pc in a script. We use the script->code pointer to tag the cache,
 * instead of the script address itself, so that source notes are always found
 * by offset from the bytecode with which they were generated.
 */
struct GSNCache {
    typedef HashMap<jsbytecode *,
                    jssrcnote *,
                    PointerHasher<jsbytecode *, 0>,
                    SystemAllocPolicy> Map;

    jsbytecode      *code;
    Map             map;

    GSNCache() : code(NULL) { }

    void purge();
};

inline GSNCache *
GetGSNCache(JSContext *cx);

typedef Vector<ScriptAndCounts, 0, SystemAllocPolicy> ScriptAndCountsVector;

struct ConservativeGCData
{
    /*
     * The GC scans conservatively between ThreadData::nativeStackBase and
     * nativeStackTop unless the latter is NULL.
     */
    uintptr_t           *nativeStackTop;

#if defined(JSGC_ROOT_ANALYSIS) && (JS_STACK_GROWTH_DIRECTION < 0)
    /*
     * Record old contents of the native stack from the last time there was a
     * scan, to reduce the overhead involved in repeatedly rescanning the
     * native stack during root analysis. oldStackData stores words in reverse
     * order starting at oldStackEnd.
     */
    uintptr_t           *oldStackMin, *oldStackEnd;
    uintptr_t           *oldStackData;
    size_t              oldStackCapacity; // in sizeof(uintptr_t)
#endif

    union {
        jmp_buf         jmpbuf;
        uintptr_t       words[JS_HOWMANY(sizeof(jmp_buf), sizeof(uintptr_t))];
    } registerSnapshot;

    ConservativeGCData() {
        PodZero(this);
    }

    ~ConservativeGCData() {
#ifdef JS_THREADSAFE
        /*
         * The conservative GC scanner should be disabled when the thread leaves
         * the last request.
         */
        JS_ASSERT(!hasStackToScan());
#endif
    }

    JS_NEVER_INLINE void recordStackTop();

#ifdef JS_THREADSAFE
    void updateForRequestEnd() {
        nativeStackTop = NULL;
    }
#endif

    bool hasStackToScan() const {
        return !!nativeStackTop;
    }
};

class SourceDataCache
{
    typedef HashMap<ScriptSource *,
                    JSStableString *,
                    DefaultHasher<ScriptSource *>,
                    SystemAllocPolicy> Map;
    Map *map_;

  public:
    SourceDataCache() : map_(NULL) {}
    JSStableString *lookup(ScriptSource *ss);
    void put(ScriptSource *ss, JSStableString *);
    void purge();
};

struct EvalCacheLookup
{
    JSLinearString *str;
    JSFunction *caller;
    unsigned staticLevel;
    JSVersion version;
    JSCompartment *compartment;
};

struct EvalCacheHashPolicy
{
    typedef EvalCacheLookup Lookup;

    static HashNumber hash(const Lookup &l);
    static bool match(JSScript *script, const EvalCacheLookup &l);
};

typedef HashSet<JSScript *, EvalCacheHashPolicy, SystemAllocPolicy> EvalCache;

class NativeIterCache
{
    static const size_t SIZE = size_t(1) << 8;

    /* Cached native iterators. */
    PropertyIteratorObject *data[SIZE];

    static size_t getIndex(uint32_t key) {
        return size_t(key) % SIZE;
    }

  public:
    /* Native iterator most recently started. */
    PropertyIteratorObject *last;

    NativeIterCache()
      : last(NULL) {
        PodArrayZero(data);
    }

    void purge() {
        last = NULL;
        PodArrayZero(data);
    }

    PropertyIteratorObject *get(uint32_t key) const {
        return data[getIndex(key)];
    }

    void set(uint32_t key, PropertyIteratorObject *iterobj) {
        data[getIndex(key)] = iterobj;
    }
};

/*
 * Cache for speeding up repetitive creation of objects in the VM.
 * When an object is created which matches the criteria in the 'key' section
 * below, an entry is filled with the resulting object.
 */
class NewObjectCache
{
    /* Statically asserted to be equal to sizeof(JSObject_Slots16) */
    static const unsigned MAX_OBJ_SIZE = 4 * sizeof(void*) + 16 * sizeof(Value);
    static inline void staticAsserts();

    struct Entry
    {
        /* Class of the constructed object. */
        Class *clasp;

        /*
         * Key with one of three possible values:
         *
         * - Global for the object. The object must have a standard class for
         *   which the global's prototype can be determined, and the object's
         *   parent will be the global.
         *
         * - Prototype for the object (cannot be global). The object's parent
         *   will be the prototype's parent.
         *
         * - Type for the object. The object's parent will be the type's
         *   prototype's parent.
         */
        gc::Cell *key;

        /* Allocation kind for the constructed object. */
        gc::AllocKind kind;

        /* Number of bytes to copy from the template object. */
        uint32_t nbytes;

        /*
         * Template object to copy from, with the initial values of fields,
         * fixed slots (undefined) and private data (NULL).
         */
        char templateObject[MAX_OBJ_SIZE];
    };

    Entry entries[41];  // TODO: reconsider size

  public:

    typedef int EntryIndex;

    NewObjectCache() { PodZero(this); }
    void purge() { PodZero(this); }

    /*
     * Get the entry index for the given lookup, return whether there was a hit
     * on an existing entry.
     */
    inline bool lookupProto(Class *clasp, JSObject *proto, gc::AllocKind kind, EntryIndex *pentry);
    inline bool lookupGlobal(Class *clasp, js::GlobalObject *global, gc::AllocKind kind, EntryIndex *pentry);
    inline bool lookupType(Class *clasp, js::types::TypeObject *type, gc::AllocKind kind, EntryIndex *pentry);

    /*
     * Return a new object from a cache hit produced by a lookup method, or
     * NULL if returning the object could possibly trigger GC (does not
     * indicate failure).
     */
    inline JSObject *newObjectFromHit(JSContext *cx, EntryIndex entry);

    /* Fill an entry after a cache miss. */
    inline void fillProto(EntryIndex entry, Class *clasp, js::TaggedProto proto, gc::AllocKind kind, JSObject *obj);
    inline void fillGlobal(EntryIndex entry, Class *clasp, js::GlobalObject *global, gc::AllocKind kind, JSObject *obj);
    inline void fillType(EntryIndex entry, Class *clasp, js::types::TypeObject *type, gc::AllocKind kind, JSObject *obj);

    /* Invalidate any entries which might produce an object with shape/proto. */
    void invalidateEntriesForShape(JSContext *cx, Shape *shape, JSObject *proto);

  private:
    inline bool lookup(Class *clasp, gc::Cell *key, gc::AllocKind kind, EntryIndex *pentry);
    inline void fill(EntryIndex entry, Class *clasp, gc::Cell *key, gc::AllocKind kind, JSObject *obj);
    static inline void copyCachedToObject(JSObject *dst, JSObject *src);
};

/*
 * A FreeOp can do one thing: free memory. For convenience, it has delete_
 * convenience methods that also call destructors.
 *
 * FreeOp is passed to finalizers and other sweep-phase hooks so that we do not
 * need to pass a JSContext to those hooks.
 */
class FreeOp : public JSFreeOp {
    bool        shouldFreeLater_;

  public:
    static FreeOp *get(JSFreeOp *fop) {
        return static_cast<FreeOp *>(fop);
    }

    FreeOp(JSRuntime *rt, bool shouldFreeLater)
      : JSFreeOp(rt),
        shouldFreeLater_(shouldFreeLater)
    {
    }

    bool shouldFreeLater() const {
        return shouldFreeLater_;
    }

    inline void free_(void* p);

    template <class T>
    inline void delete_(T *p) {
        if (p) {
            p->~T();
            free_(p);
        }
    }

    static void staticAsserts() {
        /*
         * Check that JSFreeOp is the first base class for FreeOp and we can
         * reinterpret a pointer to JSFreeOp as a pointer to FreeOp without
         * any offset adjustments. JSClass::finalize <-> Class::finalize depends
         * on this.
         */
        JS_STATIC_ASSERT(offsetof(FreeOp, shouldFreeLater_) == sizeof(JSFreeOp));
    }
};

} /* namespace js */

namespace JS {
struct RuntimeSizes;
}

/* Various built-in or commonly-used names pinned on first context. */
struct JSAtomState
{
#define PROPERTYNAME_FIELD(idpart, id, text) js::FixedHeapPtr<js::PropertyName> id;
    FOR_EACH_COMMON_PROPERTYNAME(PROPERTYNAME_FIELD)
#undef PROPERTYNAME_FIELD
#define PROPERTYNAME_FIELD(name, code, init) js::FixedHeapPtr<js::PropertyName> name;
    JS_FOR_EACH_PROTOTYPE(PROPERTYNAME_FIELD)
#undef PROPERTYNAME_FIELD
};

#define NAME_OFFSET(name)       offsetof(JSAtomState, name)
#define OFFSET_TO_NAME(rt,off)  (*(js::FixedHeapPtr<js::PropertyName>*)((char*)&(rt)->atomState + (off)))

struct JSRuntime : js::RuntimeFriendFields
{
    /* Default compartment. */
    JSCompartment       *atomsCompartment;

    /* List of compartments (protected by the GC lock). */
    js::CompartmentVector compartments;

    /* See comment for JS_AbortIfWrongThread in jsapi.h. */
#ifdef JS_THREADSAFE
  public:
    void *ownerThread() const { return ownerThread_; }
    void clearOwnerThread();
    void setOwnerThread();
    JS_FRIEND_API(void) abortIfWrongThread() const;
    JS_FRIEND_API(void) assertValidThread() const;
  private:
    void                *ownerThread_;
  public:
#else
  public:
    void abortIfWrongThread() const {}
    void assertValidThread() const {}
#endif

    /* Keeper of the contiguous stack used by all contexts in this thread. */
    js::StackSpace stackSpace;

    /* Temporary arena pool used while compiling and decompiling. */
    static const size_t TEMP_LIFO_ALLOC_PRIMARY_CHUNK_SIZE = 4 * 1024;
    js::LifoAlloc tempLifoAlloc;

    /*
     * Free LIFO blocks are transferred to this allocator before being freed on
     * the background GC thread.
     */
    js::LifoAlloc freeLifoAlloc;

  private:
    /*
     * Both of these allocators are used for regular expression code which is shared at the
     * thread-data level.
     */
    JSC::ExecutableAllocator *execAlloc_;
    WTF::BumpPointerAllocator *bumpAlloc_;
#ifdef JS_METHODJIT
    js::mjit::JaegerRuntime *jaegerRuntime_;
#endif

    JSObject *selfHostedGlobal_;

    JSC::ExecutableAllocator *createExecutableAllocator(JSContext *cx);
    WTF::BumpPointerAllocator *createBumpPointerAllocator(JSContext *cx);
    js::mjit::JaegerRuntime *createJaegerRuntime(JSContext *cx);

  public:
    JSC::ExecutableAllocator *getExecAlloc(JSContext *cx) {
        return execAlloc_ ? execAlloc_ : createExecutableAllocator(cx);
    }
    JSC::ExecutableAllocator &execAlloc() {
        JS_ASSERT(execAlloc_);
        return *execAlloc_;
    }
    WTF::BumpPointerAllocator *getBumpPointerAllocator(JSContext *cx) {
        return bumpAlloc_ ? bumpAlloc_ : createBumpPointerAllocator(cx);
    }
#ifdef JS_METHODJIT
    js::mjit::JaegerRuntime *getJaegerRuntime(JSContext *cx) {
        return jaegerRuntime_ ? jaegerRuntime_ : createJaegerRuntime(cx);
    }
    bool hasJaegerRuntime() const {
        return jaegerRuntime_;
    }
    js::mjit::JaegerRuntime &jaegerRuntime() {
        JS_ASSERT(hasJaegerRuntime());
        return *jaegerRuntime_;
    }
#endif

    bool initSelfHosting(JSContext *cx);
    void markSelfHostedGlobal(JSTracer *trc);
    JSFunction *getSelfHostedFunction(JSContext *cx, const char *name);
    bool cloneSelfHostedValueById(JSContext *cx, jsid id, js::HandleObject holder, js::Value *vp);

    /* Base address of the native stack for the current thread. */
    uintptr_t           nativeStackBase;

    /* The native stack size limit that runtime should not exceed. */
    size_t              nativeStackQuota;

    /*
     * Frames currently running in js::Interpret. See InterpreterFrames for
     * details.
     */
    js::InterpreterFrames *interpreterFrames;

    /* Context create/destroy callback. */
    JSContextCallback   cxCallback;

    /* Compartment destroy callback. */
    JSDestroyCompartmentCallback destroyCompartmentCallback;

    /* Call this to get the name of a compartment. */
    JSCompartmentNameCallback compartmentNameCallback;

    js::ActivityCallback  activityCallback;
    void                 *activityCallbackArg;

#ifdef JS_THREADSAFE
    /* The request depth for this thread. */
    unsigned            requestDepth;

# ifdef DEBUG
    unsigned            checkRequestDepth;
# endif
#endif

    /* Garbage collector state, used by jsgc.c. */

    /*
     * Set of all GC chunks with at least one allocated thing. The
     * conservative GC uses it to quickly check if a possible GC thing points
     * into an allocated chunk.
     */
    js::GCChunkSet      gcChunkSet;

    /*
     * Doubly-linked lists of chunks from user and system compartments. The GC
     * allocates its arenas from the corresponding list and when all arenas
     * in the list head are taken, then the chunk is removed from the list.
     * During the GC when all arenas in a chunk become free, that chunk is
     * removed from the list and scheduled for release.
     */
    js::gc::Chunk       *gcSystemAvailableChunkListHead;
    js::gc::Chunk       *gcUserAvailableChunkListHead;
    js::gc::ChunkPool   gcChunkPool;

    js::RootedValueMap  gcRootsHash;
    js::GCLocks         gcLocksHash;
    unsigned            gcKeepAtoms;
    size_t              gcBytes;
    size_t              gcMaxBytes;
    size_t              gcMaxMallocBytes;

    /*
     * Number of the committed arenas in all GC chunks including empty chunks.
     * The counter is volatile as it is read without the GC lock, see comments
     * in MaybeGC.
     */
    volatile uint32_t   gcNumArenasFreeCommitted;
    js::GCMarker        gcMarker;
    void                *gcVerifyPreData;
    void                *gcVerifyPostData;
    bool                gcChunkAllocationSinceLastGC;
    int64_t             gcNextFullGCTime;
    int64_t             gcLastGCTime;
    int64_t             gcJitReleaseTime;
    JSGCMode            gcMode;
    bool                gcHighFrequencyGC;
    uint64_t            gcHighFrequencyTimeThreshold;
    uint64_t            gcHighFrequencyLowLimitBytes;
    uint64_t            gcHighFrequencyHighLimitBytes;
    double              gcHighFrequencyHeapGrowthMax;
    double              gcHighFrequencyHeapGrowthMin;
    double              gcLowFrequencyHeapGrowth;
    bool                gcDynamicHeapGrowth;
    bool                gcDynamicMarkSlice;

    /* During shutdown, the GC needs to clean up every possible object. */
    bool                gcShouldCleanUpEverything;

    /*
     * These flags must be kept separate so that a thread requesting a
     * compartment GC doesn't cancel another thread's concurrent request for a
     * full GC.
     */
    volatile uintptr_t  gcIsNeeded;

    js::WeakMapBase     *gcWeakMapList;
    js::gcstats::Statistics gcStats;

    /* Incremented on every GC slice. */
    uint64_t            gcNumber;

    /* The gcNumber at the time of the most recent GC's first slice. */
    uint64_t            gcStartNumber;

    /* Whether the currently running GC can finish in multiple slices. */
    int                 gcIsIncremental;

    /* Whether all compartments are being collected in first GC slice. */
    bool                gcIsFull;

    /* The reason that an interrupt-triggered GC should be called. */
    js::gcreason::Reason gcTriggerReason;

    /*
     * If this is true, all marked objects must belong to a compartment being
     * GCed. This is used to look for compartment bugs.
     */
    bool                gcStrictCompartmentChecking;

    /*
     * If this is 0, all cross-compartment proxies must be registered in the
     * wrapper map. This checking must be disabled temporarily while creating
     * new wrappers. When non-zero, this records the recursion depth of wrapper
     * creation.
     */
    uintptr_t           gcDisableStrictProxyCheckingCount;

    /*
     * The current incremental GC phase. This is also used internally in
     * non-incremental GC.
     */
    js::gc::State       gcIncrementalState;

    /* Indicates that the last incremental slice exhausted the mark stack. */
    bool                gcLastMarkSlice;

    /* Whether any sweeping will take place in the separate GC helper thread. */
    bool                gcSweepOnBackgroundThread;

    /* List head of compartments being swept. */
    JSCompartment       *gcSweepingCompartments;

    /*
     * Incremental sweep state.
     */
    int                 gcSweepPhase;
    ptrdiff_t           gcSweepCompartmentIndex;
    int                 gcSweepKindIndex;

    /*
     * List head of arenas allocated during the sweep phase.
     */
    js::gc::ArenaHeader *gcArenasAllocatedDuringSweep;

    /*
     * Indicates that a GC slice has taken place in the middle of an animation
     * frame, rather than at the beginning. In this case, the next slice will be
     * delayed so that we don't get back-to-back slices.
     */
    volatile uintptr_t  gcInterFrameGC;

    /* Default budget for incremental GC slice. See SliceBudget in jsgc.h. */
    int64_t             gcSliceBudget;

    /*
     * We disable incremental GC if we encounter a js::Class with a trace hook
     * that does not implement write barriers.
     */
    bool                gcIncrementalEnabled;

    /*
     * Whether exact stack scanning is enabled for this runtime. This is
     * currently only used for dynamic root analysis. Exact scanning starts out
     * enabled, and is disabled if e4x has been used.
     */
    bool                gcExactScanningEnabled;

    /*
     * We save all conservative scanned roots in this vector so that
     * conservative scanning can be "replayed" deterministically. In DEBUG mode,
     * this allows us to run a non-incremental GC after every incremental GC to
     * ensure that no objects were missed.
     */
#ifdef DEBUG
    struct SavedGCRoot {
        void *thing;
        JSGCTraceKind kind;

        SavedGCRoot(void *thing, JSGCTraceKind kind) : thing(thing), kind(kind) {}
    };
    js::Vector<SavedGCRoot, 0, js::SystemAllocPolicy> gcSavedRoots;

    bool                gcRelaxRootChecks;
    int                 gcAssertNoGCDepth;
#endif

    bool                gcPoke;

    enum HeapState {
        Idle,       // doing nothing with the GC heap
        Tracing,    // tracing the GC heap without collecting, e.g. IterateCompartments()
        Collecting  // doing a GC of the heap
    };

    HeapState           heapState;

    bool isHeapBusy() { return heapState != Idle; }

    bool isHeapCollecting() { return heapState == Collecting; }

    /*
     * These options control the zealousness of the GC. The fundamental values
     * are gcNextScheduled and gcDebugCompartmentGC. At every allocation,
     * gcNextScheduled is decremented. When it reaches zero, we do either a
     * full or a compartmental GC, based on gcDebugCompartmentGC.
     *
     * At this point, if gcZeal_ is one of the types that trigger periodic
     * collection, then gcNextScheduled is reset to the value of
     * gcZealFrequency. Otherwise, no additional GCs take place.
     *
     * You can control these values in several ways:
     *   - Pass the -Z flag to the shell (see the usage info for details)
     *   - Call gczeal() or schedulegc() from inside shell-executed JS code
     *     (see the help for details)
     *
     * If gzZeal_ == 1 then we perform GCs in select places (during MaybeGC and
     * whenever a GC poke happens). This option is mainly useful to embedders.
     *
     * We use gcZeal_ == 4 to enable write barrier verification. See the comment
     * in jsgc.cpp for more information about this.
     *
     * gcZeal_ values from 8 to 10 periodically run different types of
     * incremental GC.
     */
#ifdef JS_GC_ZEAL
    int                 gcZeal_;
    int                 gcZealFrequency;
    int                 gcNextScheduled;
    bool                gcDeterministicOnly;
    int                 gcIncrementalLimit;

    js::Vector<JSObject *, 0, js::SystemAllocPolicy> gcSelectedForMarking;

    int gcZeal() { return gcZeal_; }

    bool needZealousGC() {
        if (gcNextScheduled > 0 && --gcNextScheduled == 0) {
            if (gcZeal() == js::gc::ZealAllocValue ||
                gcZeal() == js::gc::ZealPurgeAnalysisValue ||
                (gcZeal() >= js::gc::ZealIncrementalRootsThenFinish &&
                 gcZeal() <= js::gc::ZealIncrementalMultipleSlices))
            {
                gcNextScheduled = gcZealFrequency;
            }
            return true;
        }
        return false;
    }
#else
    int gcZeal() { return 0; }
    bool needZealousGC() { return false; }
#endif

    bool                gcValidate;

    JSGCCallback        gcCallback;
    js::GCSliceCallback gcSliceCallback;
    JSFinalizeCallback  gcFinalizeCallback;

    js::AnalysisPurgeCallback analysisPurgeCallback;
    uint64_t            analysisPurgeTriggerBytes;

  private:
    /*
     * Malloc counter to measure memory pressure for GC scheduling. It runs
     * from gcMaxMallocBytes down to zero.
     */
    volatile ptrdiff_t  gcMallocBytes;

  public:
    /*
     * The trace operations to trace embedding-specific GC roots. One is for
     * tracing through black roots and the other is for tracing through gray
     * roots. The black/gray distinction is only relevant to the cycle
     * collector.
     */
    JSTraceDataOp       gcBlackRootsTraceOp;
    void                *gcBlackRootsData;
    JSTraceDataOp       gcGrayRootsTraceOp;
    void                *gcGrayRootsData;

    /* Stack of thread-stack-allocated GC roots. */
    js::AutoGCRooter   *autoGCRooters;

    /* Strong references on scripts held for PCCount profiling API. */
    js::ScriptAndCountsVector *scriptAndCountsVector;

    /* Well-known numbers held for use by this runtime's contexts. */
    js::Value           NaNValue;
    js::Value           negativeInfinityValue;
    js::Value           positiveInfinityValue;

    js::PropertyName    *emptyString;

    /* List of active contexts sharing this runtime. */
    JSCList             contextList;

    bool hasContexts() const {
        return !JS_CLIST_IS_EMPTY(&contextList);
    }

    JS_SourceHook       sourceHook;

    /* Per runtime debug hooks -- see jsprvtd.h and jsdbgapi.h. */
    JSDebugHooks        debugHooks;

    /* If true, new compartments are initially in debug mode. */
    bool                debugMode;

    /* SPS profiling metadata */
    js::SPSProfiler     spsProfiler;

    /* If true, new scripts must be created with PC counter information. */
    bool                profilingScripts;

    /* Always preserve JIT code during GCs, for testing. */
    bool                alwaysPreserveCode;

    /* Had an out-of-memory error which did not populate an exception. */
    JSBool              hadOutOfMemory;

    /*
     * Linked list of all js::Debugger objects. This may be accessed by the GC
     * thread, if any, or a thread that is in a request and holds gcLock.
     */
    JSCList             debuggerList;

    /* Bookkeeping information for debug scope objects. */
    js::DebugScopes     *debugScopes;

    /* Linked list of live array buffers with >1 view */
    JSObject            *liveArrayBuffers;

    /* Client opaque pointers */
    void                *data;

    /* These combine to interlock the GC and new requests. */
    PRLock              *gcLock;

    js::GCHelperThread  gcHelperThread;

#ifdef JS_THREADSAFE
# ifdef JS_ION
    js::WorkerThreadState *workerThreadState;
# endif

    js::SourceCompressorThread sourceCompressorThread;
#endif

  private:
    js::FreeOp          defaultFreeOp_;

  public:
    js::FreeOp *defaultFreeOp() {
        return &defaultFreeOp_;
    }

    uint32_t            debuggerMutations;

    const JSSecurityCallbacks *securityCallbacks;
    const js::DOMCallbacks *DOMcallbacks;
    JSDestroyPrincipalsOp destroyPrincipals;

    /* Structured data callbacks are runtime-wide. */
    const JSStructuredCloneCallbacks *structuredCloneCallbacks;

    /* Call this to accumulate telemetry data. */
    JSAccumulateTelemetryDataCallback telemetryCallback;

    /*
     * The propertyRemovals counter is incremented for every JSObject::clear,
     * and for each JSObject::remove method call that frees a slot in the given
     * object. See js_NativeGet and js_NativeSet in jsobj.cpp.
     */
    int32_t             propertyRemovals;

    /* Number localization, used by jsnum.c */
    const char          *thousandsSeparator;
    const char          *decimalSeparator;
    const char          *numGrouping;

    /*
     * Flag indicating that we are waiving any soft limits on the GC heap
     * because we want allocations to be infallible (except when we hit OOM).
     */
    bool                waiveGCQuota;

  private:
    js::MathCache *mathCache_;
    js::MathCache *createMathCache(JSContext *cx);
  public:
    js::MathCache *getMathCache(JSContext *cx) {
        return mathCache_ ? mathCache_ : createMathCache(cx);
    }

    js::GSNCache        gsnCache;
    js::PropertyCache   propertyCache;
    js::NewObjectCache  newObjectCache;
    js::NativeIterCache nativeIterCache;
    js::SourceDataCache sourceDataCache;
    js::EvalCache       evalCache;

    /* State used by jsdtoa.cpp. */
    DtoaState           *dtoaState;

    js::ConservativeGCData conservativeGC;

  private:
    JSPrincipals        *trustedPrincipals_;
  public:
    void setTrustedPrincipals(JSPrincipals *p) { trustedPrincipals_ = p; }
    JSPrincipals *trustedPrincipals() const { return trustedPrincipals_; }

    /* Set of all currently-living atoms. */
    js::AtomSet         atoms;

    union {
        /*
         * Cached pointers to various interned property names, initialized in
         * order from first to last via the other union arm.
         */
        JSAtomState atomState;

        js::FixedHeapPtr<js::PropertyName> firstCachedName;
    };

    /* Tables of strings that are pre-allocated in the atomsCompartment. */
    js::StaticStrings   staticStrings;

    JSWrapObjectCallback                   wrapObjectCallback;
    JSSameCompartmentWrapObjectCallback    sameCompartmentWrapObjectCallback;
    JSPreWrapCallback                      preWrapObjectCallback;
    js::PreserveWrapperCallback            preserveWrapperCallback;

    js::ScriptFilenameTable scriptFilenameTable;

#ifdef DEBUG
    size_t              noGCOrAllocationCheck;
#endif

    /*
     * To ensure that cx->malloc does not cause a GC, we set this flag during
     * OOM reporting (in js_ReportOutOfMemory). If a GC is requested while
     * reporting the OOM, we ignore it.
     */
    int32_t             inOOMReport;

    bool                jitHardening;

    // If Ion code is on the stack, and has called into C++, this will be
    // aligned to an Ion exit frame.
    uint8_t             *ionTop;
    JSContext           *ionJSContext;
    uintptr_t            ionStackLimit;

    void resetIonStackLimit() {
        ionStackLimit = nativeStackLimit;
    }

    // This points to the most recent Ion activation running on the thread.
    js::ion::IonActivation  *ionActivation;

  private:
    // In certain cases, we want to optimize certain opcodes to typed instructions,
    // to avoid carrying an extra register to feed into an unbox. Unfortunately,
    // that's not always possible. For example, a GetPropertyCacheT could return a
    // typed double, but if it takes its out-of-line path, it could return an
    // object, and trigger invalidation. The invalidation bailout will consider the
    // return value to be a double, and create a garbage Value.
    //
    // To allow the GetPropertyCacheT optimization, we allow the ability for
    // GetPropertyCache to override the return value at the top of the stack - the
    // value that will be temporarily corrupt. This special override value is set
    // only in callVM() targets that are about to return *and* have invalidated
    // their callee.
    js::Value            ionReturnOverride_;

  public:
    bool hasIonReturnOverride() const {
        return !ionReturnOverride_.isMagic();
    }
    js::Value takeIonReturnOverride() {
        js::Value v = ionReturnOverride_;
        ionReturnOverride_ = js::MagicValue(JS_ARG_POISON);
        return v;
    }
    void setIonReturnOverride(const js::Value &v) {
        JS_ASSERT(!hasIonReturnOverride());
        ionReturnOverride_ = v;
    }

    JSRuntime();
    ~JSRuntime();

    bool init(uint32_t maxbytes);

    JSRuntime *thisFromCtor() { return this; }

    /*
     * Call the system malloc while checking for GC memory pressure and
     * reporting OOM error when cx is not null. We will not GC from here.
     */
    void* malloc_(size_t bytes, JSContext *cx = NULL) {
        updateMallocCounter(cx, bytes);
        void *p = js_malloc(bytes);
        return JS_LIKELY(!!p) ? p : onOutOfMemory(NULL, bytes, cx);
    }

    /*
     * Call the system calloc while checking for GC memory pressure and
     * reporting OOM error when cx is not null. We will not GC from here.
     */
    void* calloc_(size_t bytes, JSContext *cx = NULL) {
        updateMallocCounter(cx, bytes);
        void *p = js_calloc(bytes);
        return JS_LIKELY(!!p) ? p : onOutOfMemory(reinterpret_cast<void *>(1), bytes, cx);
    }

    void* realloc_(void* p, size_t oldBytes, size_t newBytes, JSContext *cx = NULL) {
        JS_ASSERT(oldBytes < newBytes);
        updateMallocCounter(cx, newBytes - oldBytes);
        void *p2 = js_realloc(p, newBytes);
        return JS_LIKELY(!!p2) ? p2 : onOutOfMemory(p, newBytes, cx);
    }

    void* realloc_(void* p, size_t bytes, JSContext *cx = NULL) {
        /*
         * For compatibility we do not account for realloc that increases
         * previously allocated memory.
         */
        if (!p)
            updateMallocCounter(cx, bytes);
        void *p2 = js_realloc(p, bytes);
        return JS_LIKELY(!!p2) ? p2 : onOutOfMemory(p, bytes, cx);
    }

    template <class T>
    T *pod_malloc(JSContext *cx = NULL) {
        return (T *)malloc_(sizeof(T), cx);
    }

    template <class T>
    T *pod_calloc(JSContext *cx = NULL) {
        return (T *)calloc_(sizeof(T), cx);
    }

    template <class T>
    T *pod_malloc(size_t numElems, JSContext *cx = NULL) {
        if (numElems & js::tl::MulOverflowMask<sizeof(T)>::result) {
            js_ReportAllocationOverflow(cx);
            return NULL;
        }
        return (T *)malloc_(numElems * sizeof(T), cx);
    }

    template <class T>
    T *pod_calloc(size_t numElems, JSContext *cx = NULL) {
        if (numElems & js::tl::MulOverflowMask<sizeof(T)>::result) {
            js_ReportAllocationOverflow(cx);
            return NULL;
        }
        return (T *)calloc_(numElems * sizeof(T), cx);
    }

    JS_DECLARE_NEW_METHODS(new_, malloc_, JS_ALWAYS_INLINE)

    void setGCMaxMallocBytes(size_t value);

    void resetGCMallocBytes() { gcMallocBytes = ptrdiff_t(gcMaxMallocBytes); }

    /*
     * Call this after allocating memory held by GC things, to update memory
     * pressure counters or report the OOM error if necessary. If oomError and
     * cx is not null the function also reports OOM error.
     *
     * The function must be called outside the GC lock and in case of OOM error
     * the caller must ensure that no deadlock possible during OOM reporting.
     */
    void updateMallocCounter(JSContext *cx, size_t nbytes);

    bool isTooMuchMalloc() const {
        return gcMallocBytes <= 0;
    }

    /*
     * The function must be called outside the GC lock.
     */
    JS_FRIEND_API(void) onTooMuchMalloc();

    /*
     * This should be called after system malloc/realloc returns NULL to try
     * to recove some memory or to report an error. Failures in malloc and
     * calloc are signaled by p == null and p == reinterpret_cast<void *>(1).
     * Other values of p mean a realloc failure.
     *
     * The function must be called outside the GC lock.
     */
    JS_FRIEND_API(void *) onOutOfMemory(void *p, size_t nbytes, JSContext *cx);

    void triggerOperationCallback();

    void setJitHardening(bool enabled);
    bool getJitHardening() const {
        return jitHardening;
    }

    void sizeOfIncludingThis(JSMallocSizeOfFun mallocSizeOf, JS::RuntimeSizes *runtime);
    size_t sizeOfExplicitNonHeap();
};

/* Common macros to access thread-local caches in JSRuntime. */
#define JS_KEEP_ATOMS(rt)   (rt)->gcKeepAtoms++;
#define JS_UNKEEP_ATOMS(rt) (rt)->gcKeepAtoms--;

namespace js {

struct AutoResolving;

static inline bool
OptionsHasAllowXML(uint32_t options)
{
    return !!(options & JSOPTION_ALLOW_XML);
}

static inline bool
OptionsHasMoarXML(uint32_t options)
{
    return !!(options & JSOPTION_MOAR_XML);
}

static inline bool
OptionsSameVersionFlags(uint32_t self, uint32_t other)
{
    static const uint32_t mask = JSOPTION_MOAR_XML;
    return !((self & mask) ^ (other & mask));
}

/*
 * Flags accompany script version data so that a) dynamically created scripts
 * can inherit their caller's compile-time properties and b) scripts can be
 * appropriately compared in the eval cache across global option changes. An
 * example of the latter is enabling the top-level-anonymous-function-is-error
 * option: subsequent evals of the same, previously-valid script text may have
 * become invalid.
 */
namespace VersionFlags {
static const unsigned MASK      = 0x0FFF; /* see JSVersion in jspubtd.h */
static const unsigned ALLOW_XML = 0x1000; /* flag induced by JSOPTION_ALLOW_XML */
static const unsigned MOAR_XML  = 0x2000; /* flag induced by JSOPTION_MOAR_XML */
static const unsigned FULL_MASK = 0x3FFF;
} /* namespace VersionFlags */

static inline JSVersion
VersionNumber(JSVersion version)
{
    return JSVersion(uint32_t(version) & VersionFlags::MASK);
}

static inline bool
VersionHasAllowXML(JSVersion version)
{
    return !!(version & VersionFlags::ALLOW_XML);
}

static inline bool
VersionHasMoarXML(JSVersion version)
{
    return !!(version & VersionFlags::MOAR_XML);
}

/* @warning This is a distinct condition from having the XML flag set. */
static inline bool
VersionShouldParseXML(JSVersion version)
{
    return VersionHasMoarXML(version) || VersionNumber(version) >= JSVERSION_1_6;
}

static inline JSVersion
VersionExtractFlags(JSVersion version)
{
    return JSVersion(uint32_t(version) & ~VersionFlags::MASK);
}

static inline void
VersionCopyFlags(JSVersion *version, JSVersion from)
{
    *version = JSVersion(VersionNumber(*version) | VersionExtractFlags(from));
}

static inline bool
VersionHasFlags(JSVersion version)
{
    return !!VersionExtractFlags(version);
}

static inline unsigned
VersionFlagsToOptions(JSVersion version)
{
    unsigned copts = (VersionHasAllowXML(version) ? JSOPTION_ALLOW_XML : 0) |
                     (VersionHasMoarXML(version) ? JSOPTION_MOAR_XML : 0);
    JS_ASSERT((copts & JSCOMPILEOPTION_MASK) == copts);
    return copts;
}

static inline JSVersion
OptionFlagsToVersion(unsigned options, JSVersion version)
{
    uint32_t v = version;
    v &= ~(VersionFlags::ALLOW_XML | VersionFlags::MOAR_XML);
    if (OptionsHasAllowXML(options))
        v |= VersionFlags::ALLOW_XML;
    if (OptionsHasMoarXML(options))
        v |= VersionFlags::MOAR_XML;
    return JSVersion(v);
}

static inline bool
VersionIsKnown(JSVersion version)
{
    return VersionNumber(version) != JSVERSION_UNKNOWN;
}

inline void
FreeOp::free_(void* p) {
    if (shouldFreeLater()) {
        runtime()->gcHelperThread.freeLater(p);
        return;
    }
    js_free(p);
}

} /* namespace js */

struct JSContext : js::ContextFriendFields
{
    explicit JSContext(JSRuntime *rt);
    JSContext *thisDuringConstruction() { return this; }
    ~JSContext();

    /* JSRuntime contextList linkage. */
    JSCList             link;

  private:
    /* See JSContext::findVersion. */
    JSVersion           defaultVersion;      /* script compilation version */
    JSVersion           versionOverride;     /* supercedes defaultVersion when valid */
    bool                hasVersionOverride;

    /* Exception state -- the exception member is a GC root by definition. */
    JSBool              throwing;            /* is there a pending exception? */
    js::Value           exception;           /* most-recently-thrown exception */

    /* Per-context run options. */
    unsigned            runOptions;          /* see jsapi.h for JSOPTION_* */

  public:
    int32_t             reportGranularity;  /* see jsprobes.h */

    /* Locale specific callbacks for string conversion. */
    JSLocaleCallbacks   *localeCallbacks;

    js::AutoResolving   *resolvingList;

    /* True if generating an error, to prevent runaway recursion. */
    bool                generatingError;

    /* The current compartment. */
    JSCompartment       *compartment;

    inline void setCompartment(JSCompartment *c) { compartment = c; }

    /*
     * "Entering" a compartment changes cx->compartment (which changes
     * cx->global). Note that this does not push any StackFrame which means
     * that it is possible for cx->fp()->compartment() != cx->compartment.
     * This is not a problem since, in general, most places in the VM cannot
     * know that they were called from script (e.g., they may have been called
     * through the JSAPI via JS_CallFunction) and thus cannot expect fp.
     *
     * Compartments should be entered/left in a LIFO fasion. The depth of this
     * enter/leave stack is maintained by enterCompartmentDepth_ and queried by
     * hasEnteredCompartment.
     *
     * To enter a compartment, code should prefer using AutoCompartment over
     * manually calling cx->enterCompartment/leaveCompartment.
     */
  private:
    unsigned            enterCompartmentDepth_;
  public:
    bool hasEnteredCompartment() const {
        return enterCompartmentDepth_ > 0;
    }

    void enterCompartment(JSCompartment *c) {
        enterCompartmentDepth_++;
        compartment = c;
        if (throwing)
            wrapPendingException();
    }

    inline void leaveCompartment(JSCompartment *oldCompartment) {
        JS_ASSERT(hasEnteredCompartment());
        enterCompartmentDepth_--;

        /*
         * Before we entered the current compartment, 'compartment' was
         * 'oldCompartment', so we might want to simply set it back. However, we
         * currently have this terrible scheme whereby defaultCompartmentObject_
         * can be updated while enterCompartmentDepth_ > 0. In this case,
         * oldCompartment != defaultCompartmentObject_->compartment and we must
         * ignore oldCompartment.
         */
        if (hasEnteredCompartment() || !defaultCompartmentObject_)
            compartment = oldCompartment;
        else
            compartment = defaultCompartmentObject_->compartment();

        if (throwing)
            wrapPendingException();
    }

    /* See JS_SaveFrameChain/JS_RestoreFrameChain. */
  private:
    struct SavedFrameChain {
        SavedFrameChain(JSCompartment *comp, unsigned count)
          : compartment(comp), enterCompartmentCount(count) {}
        JSCompartment *compartment;
        unsigned enterCompartmentCount;
    };
    typedef js::Vector<SavedFrameChain, 1, js::SystemAllocPolicy> SaveStack;
    SaveStack           savedFrameChains_;
  public:
    bool saveFrameChain();
    void restoreFrameChain();

    /*
     * When no compartments have been explicitly entered, the context's
     * compartment will be set to the compartment of the "default compartment
     * object".
     */
  private:
    JSObject *defaultCompartmentObject_;
  public:
    inline void setDefaultCompartmentObject(JSObject *obj);
    inline void setDefaultCompartmentObjectIfUnset(JSObject *obj);
    JSObject *maybeDefaultCompartmentObject() const { return defaultCompartmentObject_; }

    /* Current execution stack. */
    js::ContextStack    stack;

    /* Current global. */
    inline js::Handle<js::GlobalObject*> global() const;

    /* ContextStack convenience functions */
    inline bool hasfp() const               { return stack.hasfp(); }
    inline js::StackFrame* fp() const       { return stack.fp(); }
    inline js::StackFrame* maybefp() const  { return stack.maybefp(); }
    inline js::FrameRegs& regs() const      { return stack.regs(); }
    inline js::FrameRegs* maybeRegs() const { return stack.maybeRegs(); }

    /* Wrap cx->exception for the current compartment. */
    void wrapPendingException();

  private:
    /* Lazily initialized pool of maps used during parse/emit. */
    js::frontend::ParseMapPool *parseMapPool_;

  public:
    /* State for object and array toSource conversion. */
    js::ObjectSet       cycleDetectorSet;

    /* Last message string and log file for debugging. */
    char                *lastMessage;

    /* Per-context optional error reporter. */
    JSErrorReporter     errorReporter;

    /* Branch callback. */
    JSOperationCallback operationCallback;

    /* Client opaque pointers. */
    void                *data;
    void                *data2;

    inline js::RegExpStatics *regExpStatics();

  public:
    js::frontend::ParseMapPool &parseMapPool() {
        JS_ASSERT(parseMapPool_);
        return *parseMapPool_;
    }

    inline bool ensureParseMapPool();

    /*
     * The default script compilation version can be set iff there is no code running.
     * This typically occurs via the JSAPI right after a context is constructed.
     */
    inline bool canSetDefaultVersion() const;

    /* Force a version for future script compilation. */
    inline void overrideVersion(JSVersion newVersion);

    /* Set the default script compilation version. */
    void setDefaultVersion(JSVersion version) {
        defaultVersion = version;
    }

    void clearVersionOverride() { hasVersionOverride = false; }
    JSVersion getDefaultVersion() const { return defaultVersion; }
    bool isVersionOverridden() const { return hasVersionOverride; }

    JSVersion getVersionOverride() const {
        JS_ASSERT(isVersionOverridden());
        return versionOverride;
    }

    /*
     * Set the default version if possible; otherwise, force the version.
     * Return whether an override occurred.
     */
    inline bool maybeOverrideVersion(JSVersion newVersion);

    /*
     * If there is no code on the stack, turn the override version into the
     * default version.
     */
    void maybeMigrateVersionOverride() {
        JS_ASSERT(stack.empty());
        if (JS_UNLIKELY(isVersionOverridden())) {
            defaultVersion = versionOverride;
            clearVersionOverride();
        }
    }

    /*
     * Return:
     * - The override version, if there is an override version.
     * - The newest scripted frame's version, if there is such a frame.
     * - The default version.
     *
     * Note: if this ever shows up in a profile, just add caching!
     */
    inline JSVersion findVersion() const;

    void setRunOptions(unsigned ropts) {
        JS_ASSERT((ropts & JSRUNOPTION_MASK) == ropts);
        runOptions = ropts;
    }

    /* Note: may override the version. */
    inline void setCompileOptions(unsigned newcopts);

    unsigned getRunOptions() const { return runOptions; }
    inline unsigned getCompileOptions() const;
    inline unsigned allOptions() const;

    bool hasRunOption(unsigned ropt) const {
        JS_ASSERT((ropt & JSRUNOPTION_MASK) == ropt);
        return !!(runOptions & ropt);
    }

    bool hasStrictOption() const { return hasRunOption(JSOPTION_STRICT); }
    bool hasWErrorOption() const { return hasRunOption(JSOPTION_WERROR); }
    bool hasAtLineOption() const { return hasRunOption(JSOPTION_ATLINE); }

    js::LifoAlloc &tempLifoAlloc() { return runtime->tempLifoAlloc; }
    inline js::LifoAlloc &analysisLifoAlloc();
    inline js::LifoAlloc &typeLifoAlloc();

    inline js::PropertyTree &propertyTree();

    js::PropertyCache &propertyCache() { return runtime->propertyCache; }

#ifdef JS_THREADSAFE
    unsigned            outstandingRequests;/* number of JS_BeginRequest calls
                                               without the corresponding
                                               JS_EndRequest. */
#endif

    /* Stored here to avoid passing it around as a parameter. */
    unsigned               resolveFlags;

    /* Random number generator state, used by jsmath.cpp. */
    int64_t             rngSeed;

    /* Location to stash the iteration value between JSOP_MOREITER and JSOP_ITERNEXT. */
    js::Value           iterValue;

#ifdef JS_METHODJIT
    bool                 methodJitEnabled;

    js::mjit::JaegerRuntime &jaegerRuntime() { return runtime->jaegerRuntime(); }
#endif

    inline bool typeInferenceEnabled() const;

    /* Caller must be holding runtime->gcLock. */
    void updateJITEnabled();

#ifdef MOZ_TRACE_JSCALLS
    /* Function entry/exit debugging callback. */
    JSFunctionCallback    functionCallback;

    void doFunctionCallback(const JSFunction *fun,
                            const JSScript *scr,
                            int entering) const
    {
        if (functionCallback)
            functionCallback(fun, scr, this, entering);
    }
#endif

    DSTOffsetCache dstOffsetCache;

    /* List of currently active non-escaping enumerators (for-in). */
    js::PropertyIteratorObject *enumerators;

  private:
    /* Innermost-executing generator or null if no generator are executing. */
    JSGenerator *innermostGenerator_;
  public:
    JSGenerator *innermostGenerator() const { return innermostGenerator_; }
    void enterGenerator(JSGenerator *gen);
    void leaveGenerator(JSGenerator *gen);

    inline void* malloc_(size_t bytes) {
        return runtime->malloc_(bytes, this);
    }

    inline void* calloc_(size_t bytes) {
        return runtime->calloc_(bytes, this);
    }

    inline void* realloc_(void* p, size_t bytes) {
        return runtime->realloc_(p, bytes, this);
    }

    inline void* realloc_(void* p, size_t oldBytes, size_t newBytes) {
        return runtime->realloc_(p, oldBytes, newBytes, this);
    }

    template <class T> T *pod_malloc() {
        return runtime->pod_malloc<T>(this);
    }

    template <class T> T *pod_calloc() {
        return runtime->pod_calloc<T>(this);
    }

    template <class T> T *pod_malloc(size_t numElems) {
        return runtime->pod_malloc<T>(numElems, this);
    }

    template <class T>
    T *pod_calloc(size_t numElems) {
        return runtime->pod_calloc<T>(numElems, this);
    }

    JS_DECLARE_NEW_METHODS(new_, malloc_, JS_ALWAYS_INLINE)

    void purge();

    bool isExceptionPending() {
        return throwing;
    }

    js::Value getPendingException() {
        JS_ASSERT(throwing);
        return exception;
    }

    void setPendingException(js::Value v);

    void clearPendingException() {
        throwing = false;
        exception.setUndefined();
    }

    JSAtomState & names() { return runtime->atomState; }

#ifdef DEBUG
    /*
     * Controls whether a quadratic-complexity assertion is performed during
     * stack iteration; defaults to true.
     */
    bool stackIterAssertionEnabled;
#endif

    /*
     * Count of currently active compilations.
     * When there are compilations active for the context, the GC must not
     * purge the ParseMapPool.
     */
    unsigned activeCompilations;

    /*
     * See JS_SetTrustedPrincipals in jsapi.h.
     * Note: !cx->compartment is treated as trusted.
     */
    bool runningWithTrustedPrincipals() const;

    JS_FRIEND_API(size_t) sizeOfIncludingThis(JSMallocSizeOfFun mallocSizeOf) const;

    static inline JSContext *fromLinkField(JSCList *link) {
        JS_ASSERT(link);
        return reinterpret_cast<JSContext *>(uintptr_t(link) - offsetof(JSContext, link));
    }

    void mark(JSTracer *trc);

  private:
    /*
     * The allocation code calls the function to indicate either OOM failure
     * when p is null or that a memory pressure counter has reached some
     * threshold when p is not null. The function takes the pointer and not
     * a boolean flag to minimize the amount of code in its inlined callers.
     */
    JS_FRIEND_API(void) checkMallocGCPressure(void *p);
}; /* struct JSContext */

namespace js {

struct AutoResolving {
  public:
    enum Kind {
        LOOKUP,
        WATCH
    };

    AutoResolving(JSContext *cx, HandleObject obj, HandleId id, Kind kind = LOOKUP
                  JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : context(cx), object(obj), id(id), kind(kind), link(cx->resolvingList)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
        JS_ASSERT(obj);
        cx->resolvingList = this;
    }

    ~AutoResolving() {
        JS_ASSERT(context->resolvingList == this);
        context->resolvingList = link;
    }

    bool alreadyStarted() const {
        return link && alreadyStartedSlow();
    }

  private:
    bool alreadyStartedSlow() const;

    JSContext           *const context;
    HandleObject        object;
    HandleId            id;
    Kind                const kind;
    AutoResolving       *const link;
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER
};

#if JS_HAS_XML_SUPPORT
class AutoXMLRooter : private AutoGCRooter {
  public:
    AutoXMLRooter(JSContext *cx, JSXML *xml
                  JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : AutoGCRooter(cx, XML), xml(xml)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
        JS_ASSERT(xml);
    }

    friend void AutoGCRooter::trace(JSTracer *trc);

  private:
    JSXML * const xml;
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER
};
#endif /* JS_HAS_XML_SUPPORT */

#ifdef JS_THREADSAFE
# define JS_LOCK_GC(rt)    PR_Lock((rt)->gcLock)
# define JS_UNLOCK_GC(rt)  PR_Unlock((rt)->gcLock)
#else
# define JS_LOCK_GC(rt)    do { } while (0)
# define JS_UNLOCK_GC(rt)  do { } while (0)
#endif

class AutoLockGC
{
  public:
    explicit AutoLockGC(JSRuntime *rt = NULL
                        MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
      : runtime(rt)
    {
        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
        // Avoid MSVC warning C4390 for non-threadsafe builds.
        if (rt)
            JS_LOCK_GC(rt);
    }

    ~AutoLockGC()
    {
        if (runtime)
            JS_UNLOCK_GC(runtime);
    }

    bool locked() const {
        return !!runtime;
    }

    void lock(JSRuntime *rt) {
        JS_ASSERT(rt);
        JS_ASSERT(!runtime);
        runtime = rt;
        JS_LOCK_GC(rt);
    }

  private:
    JSRuntime *runtime;
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

class AutoUnlockGC {
  private:
#ifdef JS_THREADSAFE
    JSRuntime *rt;
#endif
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER

  public:
    explicit AutoUnlockGC(JSRuntime *rt
                          JS_GUARD_OBJECT_NOTIFIER_PARAM)
#ifdef JS_THREADSAFE
      : rt(rt)
#endif
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
        JS_UNLOCK_GC(rt);
    }
    ~AutoUnlockGC() { JS_LOCK_GC(rt); }
};

class AutoKeepAtoms {
    JSRuntime *rt;
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER

  public:
    explicit AutoKeepAtoms(JSRuntime *rt
                           JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : rt(rt)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
        JS_KEEP_ATOMS(rt);
    }
    ~AutoKeepAtoms() { JS_UNKEEP_ATOMS(rt); }
};

class AutoReleasePtr {
    void        *ptr;
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER

    AutoReleasePtr(const AutoReleasePtr &other) MOZ_DELETE;
    AutoReleasePtr operator=(const AutoReleasePtr &other) MOZ_DELETE;

  public:
    explicit AutoReleasePtr(void *ptr
                            JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : ptr(ptr)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
    }
    void forget() { ptr = NULL; }
    ~AutoReleasePtr() { js_free(ptr); }
};

/*
 * FIXME: bug 602774: cleaner API for AutoReleaseNullablePtr
 */
class AutoReleaseNullablePtr {
    void        *ptr;
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER

    AutoReleaseNullablePtr(const AutoReleaseNullablePtr &other) MOZ_DELETE;
    AutoReleaseNullablePtr operator=(const AutoReleaseNullablePtr &other) MOZ_DELETE;

  public:
    explicit AutoReleaseNullablePtr(void *ptr
                                    JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : ptr(ptr)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
    }
    void reset(void *ptr2) {
        if (ptr)
            js_free(ptr);
        ptr = ptr2;
    }
    ~AutoReleaseNullablePtr() { if (ptr) js_free(ptr); }
};

} /* namespace js */

class JSAutoResolveFlags
{
  public:
    JSAutoResolveFlags(JSContext *cx, unsigned flags
                       JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : mContext(cx), mSaved(cx->resolveFlags)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
        cx->resolveFlags = flags;
    }

    ~JSAutoResolveFlags() { mContext->resolveFlags = mSaved; }

  private:
    JSContext *mContext;
    unsigned mSaved;
    JS_DECL_USE_GUARD_OBJECT_NOTIFIER
};

namespace js {

/*
 * Enumerate all contexts in a runtime.
 */
class ContextIter {
    JSCList *begin;
    JSCList *end;

public:
    explicit ContextIter(JSRuntime *rt) {
        end = &rt->contextList;
        begin = end->next;
    }

    bool done() const {
        return begin == end;
    }

    void next() {
        JS_ASSERT(!done());
        begin = begin->next;
    }

    JSContext *get() const {
        JS_ASSERT(!done());
        return JSContext::fromLinkField(begin);
    }

    operator JSContext *() const {
        return get();
    }

    JSContext *operator ->() const {
        return get();
    }
};

/*
 * Create and destroy functions for JSContext, which is manually allocated
 * and exclusively owned.
 */
extern JSContext *
NewContext(JSRuntime *rt, size_t stackChunkSize);

enum DestroyContextMode {
    DCM_NO_GC,
    DCM_FORCE_GC,
    DCM_NEW_FAILED
};

extern void
DestroyContext(JSContext *cx, DestroyContextMode mode);

} /* namespace js */

#ifdef va_start
extern JSBool
js_ReportErrorVA(JSContext *cx, unsigned flags, const char *format, va_list ap);

extern JSBool
js_ReportErrorNumberVA(JSContext *cx, unsigned flags, JSErrorCallback callback,
                       void *userRef, const unsigned errorNumber,
                       JSBool charArgs, va_list ap);

extern JSBool
js_ExpandErrorArguments(JSContext *cx, JSErrorCallback callback,
                        void *userRef, const unsigned errorNumber,
                        char **message, JSErrorReport *reportp,
                        bool charArgs, va_list ap);
#endif

namespace js {

/* |callee| requires a usage string provided by JS_DefineFunctionsWithHelp. */
extern void
ReportUsageError(JSContext *cx, HandleObject callee, const char *msg);

/*
 * Prints a full report and returns true if the given report is non-NULL and
 * the report doesn't have the JSREPORT_WARNING flag set or reportWarnings is
 * true.
 * Returns false otherwise, printing just the message if the report is NULL.
 */
extern bool
PrintError(JSContext *cx, FILE *file, const char *message, JSErrorReport *report,
           bool reportWarnings);
} /* namespace js */

/*
 * Report an exception using a previously composed JSErrorReport.
 * XXXbe remove from "friend" API
 */
extern JS_FRIEND_API(void)
js_ReportErrorAgain(JSContext *cx, const char *message, JSErrorReport *report);

extern void
js_ReportIsNotDefined(JSContext *cx, const char *name);

/*
 * Report an attempt to access the property of a null or undefined value (v).
 */
extern JSBool
js_ReportIsNullOrUndefined(JSContext *cx, int spindex, js::HandleValue v,
                           js::HandleString fallback);

extern void
js_ReportMissingArg(JSContext *cx, js::HandleValue v, unsigned arg);

/*
 * Report error using js_DecompileValueGenerator(cx, spindex, v, fallback) as
 * the first argument for the error message. If the error message has less
 * then 3 arguments, use null for arg1 or arg2.
 */
extern JSBool
js_ReportValueErrorFlags(JSContext *cx, unsigned flags, const unsigned errorNumber,
                         int spindex, js::HandleValue v, js::HandleString fallback,
                         const char *arg1, const char *arg2);

#define js_ReportValueError(cx,errorNumber,spindex,v,fallback)                \
    ((void)js_ReportValueErrorFlags(cx, JSREPORT_ERROR, errorNumber,          \
                                    spindex, v, fallback, NULL, NULL))

#define js_ReportValueError2(cx,errorNumber,spindex,v,fallback,arg1)          \
    ((void)js_ReportValueErrorFlags(cx, JSREPORT_ERROR, errorNumber,          \
                                    spindex, v, fallback, arg1, NULL))

#define js_ReportValueError3(cx,errorNumber,spindex,v,fallback,arg1,arg2)     \
    ((void)js_ReportValueErrorFlags(cx, JSREPORT_ERROR, errorNumber,          \
                                    spindex, v, fallback, arg1, arg2))

extern JSErrorFormatString js_ErrorFormatString[JSErr_Limit];

#ifdef JS_THREADSAFE
# define JS_ASSERT_REQUEST_DEPTH(cx)  JS_ASSERT((cx)->runtime->requestDepth >= 1)
#else
# define JS_ASSERT_REQUEST_DEPTH(cx)  ((void) 0)
#endif

/*
 * Invoke the operation callback and return false if the current execution
 * is to be terminated.
 */
extern JSBool
js_InvokeOperationCallback(JSContext *cx);

extern JSBool
js_HandleExecutionInterrupt(JSContext *cx);

extern jsbytecode*
js_GetCurrentBytecodePC(JSContext* cx);

/*
 * If the operation callback flag was set, call the operation callback.
 * This macro can run the full GC. Return true if it is OK to continue and
 * false otherwise.
 */
static MOZ_ALWAYS_INLINE bool
JS_CHECK_OPERATION_LIMIT(JSContext *cx)
{
    JS_ASSERT_REQUEST_DEPTH(cx);
    return !cx->runtime->interrupt || js_InvokeOperationCallback(cx);
}

namespace js {

#ifdef JS_METHODJIT
namespace mjit {
    void ExpandInlineFrames(JSCompartment *compartment);
}
#endif

} /* namespace js */

/* How much expansion of inlined frames to do when inspecting the stack. */
enum FrameExpandKind {
    FRAME_EXPAND_NONE = 0,
    FRAME_EXPAND_ALL = 1
};

namespace js {

/************************************************************************/

static JS_ALWAYS_INLINE void
MakeRangeGCSafe(Value *vec, size_t len)
{
    PodZero(vec, len);
}

static JS_ALWAYS_INLINE void
MakeRangeGCSafe(Value *beg, Value *end)
{
    PodZero(beg, end - beg);
}

static JS_ALWAYS_INLINE void
MakeRangeGCSafe(jsid *beg, jsid *end)
{
    for (jsid *id = beg; id != end; ++id)
        *id = INT_TO_JSID(0);
}

static JS_ALWAYS_INLINE void
MakeRangeGCSafe(jsid *vec, size_t len)
{
    MakeRangeGCSafe(vec, vec + len);
}

static JS_ALWAYS_INLINE void
MakeRangeGCSafe(Shape **beg, Shape **end)
{
    PodZero(beg, end - beg);
}

static JS_ALWAYS_INLINE void
MakeRangeGCSafe(Shape **vec, size_t len)
{
    PodZero(vec, len);
}

static JS_ALWAYS_INLINE void
SetValueRangeToUndefined(Value *beg, Value *end)
{
    for (Value *v = beg; v != end; ++v)
        v->setUndefined();
}

static JS_ALWAYS_INLINE void
SetValueRangeToUndefined(Value *vec, size_t len)
{
    SetValueRangeToUndefined(vec, vec + len);
}

static JS_ALWAYS_INLINE void
SetValueRangeToNull(Value *beg, Value *end)
{
    for (Value *v = beg; v != end; ++v)
        v->setNull();
}

static JS_ALWAYS_INLINE void
SetValueRangeToNull(Value *vec, size_t len)
{
    SetValueRangeToNull(vec, vec + len);
}

class AutoObjectVector : public AutoVectorRooter<JSObject *>
{
  public:
    explicit AutoObjectVector(JSContext *cx
                              JS_GUARD_OBJECT_NOTIFIER_PARAM)
        : AutoVectorRooter<JSObject *>(cx, OBJVECTOR)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
    }

    JS_DECL_USE_GUARD_OBJECT_NOTIFIER
};

class AutoStringVector : public AutoVectorRooter<JSString *>
{
  public:
    explicit AutoStringVector(JSContext *cx
                              JS_GUARD_OBJECT_NOTIFIER_PARAM)
        : AutoVectorRooter<JSString *>(cx, STRINGVECTOR)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
    }

    JS_DECL_USE_GUARD_OBJECT_NOTIFIER
};

class AutoShapeVector : public AutoVectorRooter<Shape *>
{
  public:
    explicit AutoShapeVector(JSContext *cx
                             JS_GUARD_OBJECT_NOTIFIER_PARAM)
        : AutoVectorRooter<Shape *>(cx, SHAPEVECTOR)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
    }

    JS_DECL_USE_GUARD_OBJECT_NOTIFIER
};

class AutoValueArray : public AutoGCRooter
{
    js::Value *start_;
    unsigned length_;
    SkipRoot skip;

  public:
    AutoValueArray(JSContext *cx, js::Value *start, unsigned length
                   JS_GUARD_OBJECT_NOTIFIER_PARAM)
      : AutoGCRooter(cx, VALARRAY), start_(start), length_(length), skip(cx, start, length)
    {
        JS_GUARD_OBJECT_NOTIFIER_INIT;
    }

    Value *start() { return start_; }
    unsigned length() const { return length_; }

    JS_DECL_USE_GUARD_OBJECT_NOTIFIER
};

/*
 * Allocation policy that uses JSRuntime::malloc_ and friends, so that
 * memory pressure is properly accounted for. This is suitable for
 * long-lived objects owned by the JSRuntime.
 *
 * Since it doesn't hold a JSContext (those may not live long enough), it
 * can't report out-of-memory conditions itself; the caller must check for
 * OOM and take the appropriate action.
 *
 * FIXME bug 647103 - replace these *AllocPolicy names.
 */
class RuntimeAllocPolicy
{
    JSRuntime *const runtime;

  public:
    RuntimeAllocPolicy(JSRuntime *rt) : runtime(rt) {}
    RuntimeAllocPolicy(JSContext *cx) : runtime(cx->runtime) {}
    void *malloc_(size_t bytes) { return runtime->malloc_(bytes); }
    void *realloc_(void *p, size_t bytes) { return runtime->realloc_(p, bytes); }
    void free_(void *p) { js_free(p); }
    void reportAllocOverflow() const {}
};

/*
 * FIXME bug 647103 - replace these *AllocPolicy names.
 */
class ContextAllocPolicy
{
    JSContext *const cx;

  public:
    ContextAllocPolicy(JSContext *cx) : cx(cx) {}
    JSContext *context() const { return cx; }
    void *malloc_(size_t bytes) { return cx->malloc_(bytes); }
    void *realloc_(void *p, size_t oldBytes, size_t bytes) { return cx->realloc_(p, oldBytes, bytes); }
    void free_(void *p) { js_free(p); }
    void reportAllocOverflow() const { js_ReportAllocationOverflow(cx); }
};

} /* namespace js */

#ifdef _MSC_VER
#pragma warning(pop)
#pragma warning(pop)
#endif

#endif /* jscntxt_h___ */