mirror of
https://github.com/mozilla/gecko-dev.git
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381 lines
12 KiB
C++
381 lines
12 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=8 sts=4 et sw=4 tw=99:
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef js_HeapAPI_h
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#define js_HeapAPI_h
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#include <limits.h>
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#include "js/TracingAPI.h"
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#include "js/Utility.h"
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/* These values are private to the JS engine. */
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namespace js {
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// Whether the current thread is permitted access to any part of the specified
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// runtime or zone.
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JS_FRIEND_API(bool)
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CurrentThreadCanAccessRuntime(JSRuntime *rt);
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JS_FRIEND_API(bool)
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CurrentThreadCanAccessZone(JS::Zone *zone);
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namespace gc {
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struct Cell;
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const size_t ArenaShift = 12;
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const size_t ArenaSize = size_t(1) << ArenaShift;
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const size_t ArenaMask = ArenaSize - 1;
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#ifdef JS_GC_SMALL_CHUNK_SIZE
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const size_t ChunkShift = 18;
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#else
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const size_t ChunkShift = 20;
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#endif
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const size_t ChunkSize = size_t(1) << ChunkShift;
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const size_t ChunkMask = ChunkSize - 1;
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const size_t CellShift = 3;
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const size_t CellSize = size_t(1) << CellShift;
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const size_t CellMask = CellSize - 1;
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/* These are magic constants derived from actual offsets in gc/Heap.h. */
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#ifdef JS_GC_SMALL_CHUNK_SIZE
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const size_t ChunkMarkBitmapOffset = 258104;
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const size_t ChunkMarkBitmapBits = 31744;
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#else
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const size_t ChunkMarkBitmapOffset = 1032352;
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const size_t ChunkMarkBitmapBits = 129024;
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#endif
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const size_t ChunkRuntimeOffset = ChunkSize - sizeof(void*);
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const size_t ChunkLocationOffset = ChunkSize - 2 * sizeof(void*) - sizeof(uint64_t);
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const size_t ArenaZoneOffset = 0;
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/*
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* Live objects are marked black. How many other additional colors are available
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* depends on the size of the GCThing. Objects marked gray are eligible for
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* cycle collection.
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*/
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static const uint32_t BLACK = 0;
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static const uint32_t GRAY = 1;
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/*
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* The "location" field in the Chunk trailer is a bit vector indicting various
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* roles of the chunk.
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*
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* The value 0 for the "location" field is invalid, at least one bit must be
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* set.
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*
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* Some bits preclude others, for example, any "nursery" bit precludes any
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* "tenured" or "middle generation" bit.
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*/
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const uintptr_t ChunkLocationBitNursery = 1; // Standard GGC nursery
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const uintptr_t ChunkLocationBitTenuredHeap = 2; // Standard GGC tenured generation
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const uintptr_t ChunkLocationAnyNursery = ChunkLocationBitNursery;
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#ifdef JS_DEBUG
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/* When downcasting, ensure we are actually the right type. */
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extern JS_FRIEND_API(void)
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AssertGCThingHasType(js::gc::Cell *cell, JSGCTraceKind kind);
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#else
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inline void
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AssertGCThingHasType(js::gc::Cell *cell, JSGCTraceKind kind) {}
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#endif
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MOZ_ALWAYS_INLINE bool IsInsideNursery(const js::gc::Cell *cell);
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} /* namespace gc */
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} /* namespace js */
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namespace JS {
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struct Zone;
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/* Default size for the generational nursery in bytes. */
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const uint32_t DefaultNurseryBytes = 16 * js::gc::ChunkSize;
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/* Default maximum heap size in bytes to pass to JS_NewRuntime(). */
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const uint32_t DefaultHeapMaxBytes = 32 * 1024 * 1024;
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namespace shadow {
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struct Zone
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{
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protected:
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JSRuntime *const runtime_;
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JSTracer *const barrierTracer_; // A pointer to the JSRuntime's |gcMarker|.
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public:
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bool needsIncrementalBarrier_;
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Zone(JSRuntime *runtime, JSTracer *barrierTracerArg)
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: runtime_(runtime),
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barrierTracer_(barrierTracerArg),
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needsIncrementalBarrier_(false)
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{}
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bool needsIncrementalBarrier() const {
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return needsIncrementalBarrier_;
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}
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JSTracer *barrierTracer() {
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MOZ_ASSERT(needsIncrementalBarrier_);
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MOZ_ASSERT(js::CurrentThreadCanAccessRuntime(runtime_));
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return barrierTracer_;
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}
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JSRuntime *runtimeFromMainThread() const {
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MOZ_ASSERT(js::CurrentThreadCanAccessRuntime(runtime_));
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return runtime_;
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}
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// Note: Unrestricted access to the zone's runtime from an arbitrary
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// thread can easily lead to races. Use this method very carefully.
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JSRuntime *runtimeFromAnyThread() const {
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return runtime_;
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}
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static JS::shadow::Zone *asShadowZone(JS::Zone *zone) {
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return reinterpret_cast<JS::shadow::Zone*>(zone);
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}
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};
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} /* namespace shadow */
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// A GC pointer, tagged with the trace kind.
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//
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// In general, a GC pointer should be stored with an exact type. This class
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// is for use when that is not possible because a single pointer must point
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// to several kinds of GC thing.
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class JS_FRIEND_API(GCCellPtr)
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{
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typedef void (GCCellPtr::* ConvertibleToBool)();
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void nonNull() {}
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public:
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// Construction from a void* and trace kind.
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GCCellPtr(void *gcthing, JSGCTraceKind traceKind) : ptr(checkedCast(gcthing, traceKind)) {}
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// Construction from an explicit type.
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explicit GCCellPtr(JSObject *obj) : ptr(checkedCast(obj, JSTRACE_OBJECT)) { }
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explicit GCCellPtr(JSFunction *fun) : ptr(checkedCast(fun, JSTRACE_OBJECT)) { }
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explicit GCCellPtr(JSString *str) : ptr(checkedCast(str, JSTRACE_STRING)) { }
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explicit GCCellPtr(JSFlatString *str) : ptr(checkedCast(str, JSTRACE_STRING)) { }
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explicit GCCellPtr(JSScript *script) : ptr(checkedCast(script, JSTRACE_SCRIPT)) { }
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explicit GCCellPtr(const Value &v);
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// Not all compilers have nullptr_t yet, so use this instead of GCCellPtr(nullptr).
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static GCCellPtr NullPtr() { return GCCellPtr(nullptr, JSTRACE_NULL); }
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JSGCTraceKind kind() const {
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JSGCTraceKind traceKind = JSGCTraceKind(ptr & JSTRACE_OUTOFLINE);
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if (traceKind != JSTRACE_OUTOFLINE)
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return traceKind;
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return outOfLineKind();
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}
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// Allow GCCellPtr to be used in a boolean context.
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operator ConvertibleToBool() const {
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MOZ_ASSERT(bool(asCell()) == (kind() != JSTRACE_NULL));
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return asCell() ? &GCCellPtr::nonNull : 0;
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}
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// Simplify checks to the kind.
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bool isObject() const { return kind() == JSTRACE_OBJECT; }
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bool isScript() const { return kind() == JSTRACE_SCRIPT; }
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bool isString() const { return kind() == JSTRACE_STRING; }
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bool isSymbol() const { return kind() == JSTRACE_SYMBOL; }
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bool isShape() const { return kind() == JSTRACE_SHAPE; }
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// Conversions to more specific types must match the kind. Access to
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// further refined types is not allowed directly from a GCCellPtr.
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JSObject *toObject() const {
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MOZ_ASSERT(kind() == JSTRACE_OBJECT);
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return reinterpret_cast<JSObject *>(asCell());
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}
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JSString *toString() const {
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MOZ_ASSERT(kind() == JSTRACE_STRING);
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return reinterpret_cast<JSString *>(asCell());
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}
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JSScript *toScript() const {
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MOZ_ASSERT(kind() == JSTRACE_SCRIPT);
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return reinterpret_cast<JSScript *>(asCell());
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}
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Symbol *toSymbol() const {
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MOZ_ASSERT(kind() == JSTRACE_SYMBOL);
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return reinterpret_cast<Symbol *>(asCell());
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}
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js::gc::Cell *asCell() const {
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return reinterpret_cast<js::gc::Cell *>(ptr & ~JSTRACE_OUTOFLINE);
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}
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// The CC's trace logger needs an identity that is XPIDL serializable.
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uint64_t unsafeAsInteger() const {
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return static_cast<uint64_t>(unsafeAsUIntPtr());
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}
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// Inline mark bitmap access requires direct pointer arithmetic.
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uintptr_t unsafeAsUIntPtr() const {
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MOZ_ASSERT(asCell());
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MOZ_ASSERT(!js::gc::IsInsideNursery(asCell()));
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return reinterpret_cast<uintptr_t>(asCell());
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}
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private:
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uintptr_t checkedCast(void *p, JSGCTraceKind traceKind) {
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js::gc::Cell *cell = static_cast<js::gc::Cell *>(p);
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MOZ_ASSERT((uintptr_t(p) & JSTRACE_OUTOFLINE) == 0);
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AssertGCThingHasType(cell, traceKind);
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// Note: the JSTRACE_OUTOFLINE bits are set on all out-of-line kinds
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// so that we can mask instead of branching.
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MOZ_ASSERT_IF(traceKind >= JSTRACE_OUTOFLINE,
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(traceKind & JSTRACE_OUTOFLINE) == JSTRACE_OUTOFLINE);
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return uintptr_t(p) | (traceKind & JSTRACE_OUTOFLINE);
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}
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JSGCTraceKind outOfLineKind() const;
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uintptr_t ptr;
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};
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} /* namespace JS */
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namespace js {
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namespace gc {
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namespace detail {
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static MOZ_ALWAYS_INLINE uintptr_t *
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GetGCThingMarkBitmap(const uintptr_t addr)
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{
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MOZ_ASSERT(addr);
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const uintptr_t bmap_addr = (addr & ~ChunkMask) | ChunkMarkBitmapOffset;
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return reinterpret_cast<uintptr_t *>(bmap_addr);
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}
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static MOZ_ALWAYS_INLINE JS::shadow::Runtime *
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GetGCThingRuntime(const uintptr_t addr)
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{
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MOZ_ASSERT(addr);
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const uintptr_t rt_addr = (addr & ~ChunkMask) | ChunkRuntimeOffset;
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return *reinterpret_cast<JS::shadow::Runtime **>(rt_addr);
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}
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static MOZ_ALWAYS_INLINE void
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GetGCThingMarkWordAndMask(const uintptr_t addr, uint32_t color,
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uintptr_t **wordp, uintptr_t *maskp)
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{
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MOZ_ASSERT(addr);
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const size_t bit = (addr & js::gc::ChunkMask) / js::gc::CellSize + color;
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MOZ_ASSERT(bit < js::gc::ChunkMarkBitmapBits);
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uintptr_t *bitmap = GetGCThingMarkBitmap(addr);
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const uintptr_t nbits = sizeof(*bitmap) * CHAR_BIT;
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*maskp = uintptr_t(1) << (bit % nbits);
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*wordp = &bitmap[bit / nbits];
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}
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static MOZ_ALWAYS_INLINE JS::Zone *
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GetGCThingZone(const uintptr_t addr)
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{
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MOZ_ASSERT(addr);
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const uintptr_t zone_addr = (addr & ~ArenaMask) | ArenaZoneOffset;
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return *reinterpret_cast<JS::Zone **>(zone_addr);
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}
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static MOZ_ALWAYS_INLINE bool
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CellIsMarkedGray(const Cell *cell)
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{
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MOZ_ASSERT(cell);
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MOZ_ASSERT(!js::gc::IsInsideNursery(cell));
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uintptr_t *word, mask;
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js::gc::detail::GetGCThingMarkWordAndMask(uintptr_t(cell), js::gc::GRAY, &word, &mask);
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return *word & mask;
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}
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} /* namespace detail */
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MOZ_ALWAYS_INLINE bool
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IsInsideNursery(const js::gc::Cell *cell)
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{
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if (!cell)
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return false;
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uintptr_t addr = uintptr_t(cell);
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addr &= ~js::gc::ChunkMask;
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addr |= js::gc::ChunkLocationOffset;
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uint32_t location = *reinterpret_cast<uint32_t *>(addr);
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MOZ_ASSERT(location != 0);
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return location & ChunkLocationAnyNursery;
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}
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} /* namespace gc */
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} /* namespace js */
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namespace JS {
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static MOZ_ALWAYS_INLINE Zone *
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GetTenuredGCThingZone(void *thing)
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{
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MOZ_ASSERT(!js::gc::IsInsideNursery((js::gc::Cell *)thing));
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return js::gc::detail::GetGCThingZone(uintptr_t(thing));
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}
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extern JS_PUBLIC_API(Zone *)
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GetObjectZone(JSObject *obj);
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static MOZ_ALWAYS_INLINE bool
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ObjectIsTenured(JSObject *obj)
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{
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return !js::gc::IsInsideNursery(reinterpret_cast<js::gc::Cell *>(obj));
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}
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static MOZ_ALWAYS_INLINE bool
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ObjectIsMarkedGray(JSObject *obj)
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{
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/*
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* GC things residing in the nursery cannot be gray: they have no mark bits.
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* All live objects in the nursery are moved to tenured at the beginning of
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* each GC slice, so the gray marker never sees nursery things.
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*/
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if (js::gc::IsInsideNursery(reinterpret_cast<js::gc::Cell *>(obj)))
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return false;
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return js::gc::detail::CellIsMarkedGray(reinterpret_cast<js::gc::Cell *>(obj));
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}
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static MOZ_ALWAYS_INLINE bool
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ScriptIsMarkedGray(JSScript *script)
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{
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return js::gc::detail::CellIsMarkedGray(reinterpret_cast<js::gc::Cell *>(script));
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}
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static MOZ_ALWAYS_INLINE bool
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GCThingIsMarkedGray(GCCellPtr thing)
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{
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if (js::gc::IsInsideNursery(thing.asCell()))
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return false;
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return js::gc::detail::CellIsMarkedGray(thing.asCell());
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}
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} /* namespace JS */
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namespace js {
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namespace gc {
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static MOZ_ALWAYS_INLINE bool
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IsIncrementalBarrierNeededOnTenuredGCThing(JS::shadow::Runtime *rt, const JS::GCCellPtr thing)
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{
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MOZ_ASSERT(thing);
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MOZ_ASSERT(!js::gc::IsInsideNursery(thing.asCell()));
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if (!rt->needsIncrementalBarrier())
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return false;
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JS::Zone *zone = JS::GetTenuredGCThingZone(thing.asCell());
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return JS::shadow::Zone::asShadowZone(zone)->needsIncrementalBarrier();
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}
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} /* namespace gc */
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} /* namespace js */
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#endif /* js_HeapAPI_h */
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