gecko-dev/js/public/HeapAPI.h

390 lines
12 KiB
C++

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sts=4 et sw=4 tw=99:
* 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/. */
#ifndef js_HeapAPI_h
#define js_HeapAPI_h
#include <limits.h>
#include "js/TracingAPI.h"
#include "js/Utility.h"
/* These values are private to the JS engine. */
namespace js {
// Whether the current thread is permitted access to any part of the specified
// runtime or zone.
JS_FRIEND_API(bool)
CurrentThreadCanAccessRuntime(JSRuntime *rt);
JS_FRIEND_API(bool)
CurrentThreadCanAccessZone(JS::Zone *zone);
namespace gc {
struct Cell;
const size_t ArenaShift = 12;
const size_t ArenaSize = size_t(1) << ArenaShift;
const size_t ArenaMask = ArenaSize - 1;
#ifdef JS_GC_SMALL_CHUNK_SIZE
const size_t ChunkShift = 18;
#else
const size_t ChunkShift = 20;
#endif
const size_t ChunkSize = size_t(1) << ChunkShift;
const size_t ChunkMask = ChunkSize - 1;
const size_t CellShift = 3;
const size_t CellSize = size_t(1) << CellShift;
const size_t CellMask = CellSize - 1;
/* These are magic constants derived from actual offsets in gc/Heap.h. */
#ifdef JS_GC_SMALL_CHUNK_SIZE
const size_t ChunkMarkBitmapOffset = 258104;
const size_t ChunkMarkBitmapBits = 31744;
#else
const size_t ChunkMarkBitmapOffset = 1032352;
const size_t ChunkMarkBitmapBits = 129024;
#endif
const size_t ChunkRuntimeOffset = ChunkSize - sizeof(void*);
const size_t ChunkLocationOffset = ChunkSize - 2 * sizeof(void*) - sizeof(uint64_t);
const size_t ArenaZoneOffset = 0;
/*
* Live objects are marked black. How many other additional colors are available
* depends on the size of the GCThing. Objects marked gray are eligible for
* cycle collection.
*/
static const uint32_t BLACK = 0;
static const uint32_t GRAY = 1;
/*
* The "location" field in the Chunk trailer is a bit vector indicting various
* roles of the chunk.
*
* The value 0 for the "location" field is invalid, at least one bit must be
* set.
*
* Some bits preclude others, for example, any "nursery" bit precludes any
* "tenured" or "middle generation" bit.
*/
const uintptr_t ChunkLocationBitNursery = 1; // Standard GGC nursery
const uintptr_t ChunkLocationBitTenuredHeap = 2; // Standard GGC tenured generation
const uintptr_t ChunkLocationAnyNursery = ChunkLocationBitNursery;
#ifdef JS_DEBUG
/* When downcasting, ensure we are actually the right type. */
extern JS_FRIEND_API(void)
AssertGCThingHasType(js::gc::Cell *cell, JSGCTraceKind kind);
#else
inline void
AssertGCThingHasType(js::gc::Cell *cell, JSGCTraceKind kind) {}
#endif
MOZ_ALWAYS_INLINE bool IsInsideNursery(const js::gc::Cell *cell);
} /* namespace gc */
} /* namespace js */
namespace JS {
struct Zone;
/* Default size for the generational nursery in bytes. */
const uint32_t DefaultNurseryBytes = 16 * js::gc::ChunkSize;
/* Default maximum heap size in bytes to pass to JS_NewRuntime(). */
const uint32_t DefaultHeapMaxBytes = 32 * 1024 * 1024;
namespace shadow {
struct Zone
{
protected:
JSRuntime *const runtime_;
JSTracer *const barrierTracer_; // A pointer to the JSRuntime's |gcMarker|.
public:
bool needsIncrementalBarrier_;
Zone(JSRuntime *runtime, JSTracer *barrierTracerArg)
: runtime_(runtime),
barrierTracer_(barrierTracerArg),
needsIncrementalBarrier_(false)
{}
bool needsIncrementalBarrier() const {
return needsIncrementalBarrier_;
}
JSTracer *barrierTracer() {
MOZ_ASSERT(needsIncrementalBarrier_);
MOZ_ASSERT(js::CurrentThreadCanAccessRuntime(runtime_));
return barrierTracer_;
}
JSRuntime *runtimeFromMainThread() const {
MOZ_ASSERT(js::CurrentThreadCanAccessRuntime(runtime_));
return runtime_;
}
// Note: Unrestricted access to the zone's runtime from an arbitrary
// thread can easily lead to races. Use this method very carefully.
JSRuntime *runtimeFromAnyThread() const {
return runtime_;
}
static JS::shadow::Zone *asShadowZone(JS::Zone *zone) {
return reinterpret_cast<JS::shadow::Zone*>(zone);
}
};
} /* namespace shadow */
// A GC pointer, tagged with the trace kind.
//
// In general, a GC pointer should be stored with an exact type. This class
// is for use when that is not possible because a single pointer must point
// to several kinds of GC thing.
class JS_FRIEND_API(GCCellPtr)
{
public:
// Construction from a void* and trace kind.
GCCellPtr(void *gcthing, JSGCTraceKind traceKind) : ptr(checkedCast(gcthing, traceKind)) {}
// Construction from an explicit type.
explicit GCCellPtr(JSObject *obj) : ptr(checkedCast(obj, JSTRACE_OBJECT)) { }
explicit GCCellPtr(JSFunction *fun) : ptr(checkedCast(fun, JSTRACE_OBJECT)) { }
explicit GCCellPtr(JSString *str) : ptr(checkedCast(str, JSTRACE_STRING)) { }
explicit GCCellPtr(JSFlatString *str) : ptr(checkedCast(str, JSTRACE_STRING)) { }
explicit GCCellPtr(JSScript *script) : ptr(checkedCast(script, JSTRACE_SCRIPT)) { }
explicit GCCellPtr(const Value &v);
// Not all compilers have nullptr_t yet, so use this instead of GCCellPtr(nullptr).
static GCCellPtr NullPtr() { return GCCellPtr(nullptr, JSTRACE_NULL); }
JSGCTraceKind kind() const {
JSGCTraceKind traceKind = JSGCTraceKind(ptr & JSTRACE_OUTOFLINE);
if (traceKind != JSTRACE_OUTOFLINE)
return traceKind;
return outOfLineKind();
}
// Allow GCCellPtr to be used in a boolean context.
explicit operator bool() const {
MOZ_ASSERT(bool(asCell()) == (kind() != JSTRACE_NULL));
return asCell();
}
// Simplify checks to the kind.
bool isObject() const { return kind() == JSTRACE_OBJECT; }
bool isScript() const { return kind() == JSTRACE_SCRIPT; }
bool isString() const { return kind() == JSTRACE_STRING; }
bool isSymbol() const { return kind() == JSTRACE_SYMBOL; }
bool isShape() const { return kind() == JSTRACE_SHAPE; }
// Conversions to more specific types must match the kind. Access to
// further refined types is not allowed directly from a GCCellPtr.
JSObject *toObject() const {
MOZ_ASSERT(kind() == JSTRACE_OBJECT);
return reinterpret_cast<JSObject *>(asCell());
}
JSString *toString() const {
MOZ_ASSERT(kind() == JSTRACE_STRING);
return reinterpret_cast<JSString *>(asCell());
}
JSScript *toScript() const {
MOZ_ASSERT(kind() == JSTRACE_SCRIPT);
return reinterpret_cast<JSScript *>(asCell());
}
Symbol *toSymbol() const {
MOZ_ASSERT(kind() == JSTRACE_SYMBOL);
return reinterpret_cast<Symbol *>(asCell());
}
js::gc::Cell *asCell() const {
return reinterpret_cast<js::gc::Cell *>(ptr & ~JSTRACE_OUTOFLINE);
}
// The CC's trace logger needs an identity that is XPIDL serializable.
uint64_t unsafeAsInteger() const {
return static_cast<uint64_t>(unsafeAsUIntPtr());
}
// Inline mark bitmap access requires direct pointer arithmetic.
uintptr_t unsafeAsUIntPtr() const {
MOZ_ASSERT(asCell());
MOZ_ASSERT(!js::gc::IsInsideNursery(asCell()));
return reinterpret_cast<uintptr_t>(asCell());
}
private:
uintptr_t checkedCast(void *p, JSGCTraceKind traceKind) {
js::gc::Cell *cell = static_cast<js::gc::Cell *>(p);
MOZ_ASSERT((uintptr_t(p) & JSTRACE_OUTOFLINE) == 0);
AssertGCThingHasType(cell, traceKind);
// Note: the JSTRACE_OUTOFLINE bits are set on all out-of-line kinds
// so that we can mask instead of branching.
MOZ_ASSERT_IF(traceKind >= JSTRACE_OUTOFLINE,
(traceKind & JSTRACE_OUTOFLINE) == JSTRACE_OUTOFLINE);
return uintptr_t(p) | (traceKind & JSTRACE_OUTOFLINE);
}
JSGCTraceKind outOfLineKind() const;
uintptr_t ptr;
};
inline bool
operator==(const GCCellPtr &ptr1, const GCCellPtr &ptr2)
{
return ptr1.asCell() == ptr2.asCell();
}
inline bool
operator!=(const GCCellPtr &ptr1, const GCCellPtr &ptr2)
{
return !(ptr1 == ptr2);
}
} /* namespace JS */
namespace js {
namespace gc {
namespace detail {
static MOZ_ALWAYS_INLINE uintptr_t *
GetGCThingMarkBitmap(const uintptr_t addr)
{
MOZ_ASSERT(addr);
const uintptr_t bmap_addr = (addr & ~ChunkMask) | ChunkMarkBitmapOffset;
return reinterpret_cast<uintptr_t *>(bmap_addr);
}
static MOZ_ALWAYS_INLINE JS::shadow::Runtime *
GetGCThingRuntime(const uintptr_t addr)
{
MOZ_ASSERT(addr);
const uintptr_t rt_addr = (addr & ~ChunkMask) | ChunkRuntimeOffset;
return *reinterpret_cast<JS::shadow::Runtime **>(rt_addr);
}
static MOZ_ALWAYS_INLINE void
GetGCThingMarkWordAndMask(const uintptr_t addr, uint32_t color,
uintptr_t **wordp, uintptr_t *maskp)
{
MOZ_ASSERT(addr);
const size_t bit = (addr & js::gc::ChunkMask) / js::gc::CellSize + color;
MOZ_ASSERT(bit < js::gc::ChunkMarkBitmapBits);
uintptr_t *bitmap = GetGCThingMarkBitmap(addr);
const uintptr_t nbits = sizeof(*bitmap) * CHAR_BIT;
*maskp = uintptr_t(1) << (bit % nbits);
*wordp = &bitmap[bit / nbits];
}
static MOZ_ALWAYS_INLINE JS::Zone *
GetGCThingZone(const uintptr_t addr)
{
MOZ_ASSERT(addr);
const uintptr_t zone_addr = (addr & ~ArenaMask) | ArenaZoneOffset;
return *reinterpret_cast<JS::Zone **>(zone_addr);
}
static MOZ_ALWAYS_INLINE bool
CellIsMarkedGray(const Cell *cell)
{
MOZ_ASSERT(cell);
MOZ_ASSERT(!js::gc::IsInsideNursery(cell));
uintptr_t *word, mask;
js::gc::detail::GetGCThingMarkWordAndMask(uintptr_t(cell), js::gc::GRAY, &word, &mask);
return *word & mask;
}
} /* namespace detail */
MOZ_ALWAYS_INLINE bool
IsInsideNursery(const js::gc::Cell *cell)
{
if (!cell)
return false;
uintptr_t addr = uintptr_t(cell);
addr &= ~js::gc::ChunkMask;
addr |= js::gc::ChunkLocationOffset;
uint32_t location = *reinterpret_cast<uint32_t *>(addr);
MOZ_ASSERT(location != 0);
return location & ChunkLocationAnyNursery;
}
} /* namespace gc */
} /* namespace js */
namespace JS {
static MOZ_ALWAYS_INLINE Zone *
GetTenuredGCThingZone(void *thing)
{
MOZ_ASSERT(!js::gc::IsInsideNursery((js::gc::Cell *)thing));
return js::gc::detail::GetGCThingZone(uintptr_t(thing));
}
extern JS_PUBLIC_API(Zone *)
GetObjectZone(JSObject *obj);
static MOZ_ALWAYS_INLINE bool
ObjectIsTenured(JSObject *obj)
{
return !js::gc::IsInsideNursery(reinterpret_cast<js::gc::Cell *>(obj));
}
static MOZ_ALWAYS_INLINE bool
ObjectIsMarkedGray(JSObject *obj)
{
/*
* GC things residing in the nursery cannot be gray: they have no mark bits.
* All live objects in the nursery are moved to tenured at the beginning of
* each GC slice, so the gray marker never sees nursery things.
*/
if (js::gc::IsInsideNursery(reinterpret_cast<js::gc::Cell *>(obj)))
return false;
return js::gc::detail::CellIsMarkedGray(reinterpret_cast<js::gc::Cell *>(obj));
}
static MOZ_ALWAYS_INLINE bool
ScriptIsMarkedGray(JSScript *script)
{
return js::gc::detail::CellIsMarkedGray(reinterpret_cast<js::gc::Cell *>(script));
}
static MOZ_ALWAYS_INLINE bool
GCThingIsMarkedGray(GCCellPtr thing)
{
if (js::gc::IsInsideNursery(thing.asCell()))
return false;
return js::gc::detail::CellIsMarkedGray(thing.asCell());
}
} /* namespace JS */
namespace js {
namespace gc {
static MOZ_ALWAYS_INLINE bool
IsIncrementalBarrierNeededOnTenuredGCThing(JS::shadow::Runtime *rt, const JS::GCCellPtr thing)
{
MOZ_ASSERT(thing);
MOZ_ASSERT(!js::gc::IsInsideNursery(thing.asCell()));
if (!rt->needsIncrementalBarrier())
return false;
JS::Zone *zone = JS::GetTenuredGCThingZone(thing.asCell());
return JS::shadow::Zone::asShadowZone(zone)->needsIncrementalBarrier();
}
} /* namespace gc */
} /* namespace js */
#endif /* js_HeapAPI_h */