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gecko-dev/js/public/GCAPI.h

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/* -*- 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_GCAPI_h
#define js_GCAPI_h
#include "mozilla/UniquePtr.h"
#include "mozilla/Vector.h"
#include "js/HeapAPI.h"
namespace js {
namespace gc {
class GCRuntime;
}
namespace gcstats {
struct Statistics;
}
}
typedef enum JSGCMode {
/* Perform only global GCs. */
JSGC_MODE_GLOBAL = 0,
/* Perform per-compartment GCs until too much garbage has accumulated. */
JSGC_MODE_COMPARTMENT = 1,
/*
* Collect in short time slices rather than all at once. Implies
* JSGC_MODE_COMPARTMENT.
*/
JSGC_MODE_INCREMENTAL = 2
} JSGCMode;
/*
* Kinds of js_GC invocation.
*/
typedef enum JSGCInvocationKind {
/* Normal invocation. */
GC_NORMAL = 0,
/* Minimize GC triggers and release empty GC chunks right away. */
GC_SHRINK = 1
} JSGCInvocationKind;
namespace JS {
using mozilla::UniquePtr;
#define GCREASONS(D) \
/* Reasons internal to the JS engine */ \
D(API) \
D(EAGER_ALLOC_TRIGGER) \
D(DESTROY_RUNTIME) \
D(DESTROY_CONTEXT) \
D(LAST_DITCH) \
D(TOO_MUCH_MALLOC) \
D(ALLOC_TRIGGER) \
D(DEBUG_GC) \
D(COMPARTMENT_REVIVED) \
D(RESET) \
D(OUT_OF_NURSERY) \
D(EVICT_NURSERY) \
D(FULL_STORE_BUFFER) \
D(SHARED_MEMORY_LIMIT) \
D(PERIODIC_FULL_GC) \
D(INCREMENTAL_TOO_SLOW) \
D(ABORT_GC) \
\
/* These are reserved for future use. */ \
D(RESERVED0) \
D(RESERVED1) \
D(RESERVED2) \
D(RESERVED3) \
D(RESERVED4) \
D(RESERVED5) \
D(RESERVED6) \
D(RESERVED7) \
D(RESERVED8) \
D(RESERVED9) \
D(RESERVED10) \
D(RESERVED11) \
D(RESERVED12) \
D(RESERVED13) \
D(RESERVED14) \
D(RESERVED15) \
\
/* Reasons from Firefox */ \
D(DOM_WINDOW_UTILS) \
D(COMPONENT_UTILS) \
D(MEM_PRESSURE) \
D(CC_WAITING) \
D(CC_FORCED) \
D(LOAD_END) \
D(POST_COMPARTMENT) \
D(PAGE_HIDE) \
D(NSJSCONTEXT_DESTROY) \
D(SET_NEW_DOCUMENT) \
D(SET_DOC_SHELL) \
D(DOM_UTILS) \
D(DOM_IPC) \
D(DOM_WORKER) \
D(INTER_SLICE_GC) \
D(REFRESH_FRAME) \
D(FULL_GC_TIMER) \
D(SHUTDOWN_CC) \
D(FINISH_LARGE_EVALUATE) \
D(USER_INACTIVE)
namespace gcreason {
/* GCReasons will end up looking like JSGC_MAYBEGC */
enum Reason {
#define MAKE_REASON(name) name,
GCREASONS(MAKE_REASON)
#undef MAKE_REASON
NO_REASON,
NUM_REASONS,
/*
* For telemetry, we want to keep a fixed max bucket size over time so we
* don't have to switch histograms. 100 is conservative; as of this writing
* there are 52. But the cost of extra buckets seems to be low while the
* cost of switching histograms is high.
*/
NUM_TELEMETRY_REASONS = 100
};
} /* namespace gcreason */
/*
* Zone GC:
*
* SpiderMonkey's GC is capable of performing a collection on an arbitrary
* subset of the zones in the system. This allows an embedding to minimize
* collection time by only collecting zones that have run code recently,
* ignoring the parts of the heap that are unlikely to have changed.
*
* When triggering a GC using one of the functions below, it is first necessary
* to select the zones to be collected. To do this, you can call
* PrepareZoneForGC on each zone, or you can call PrepareForFullGC to select
* all zones. Failing to select any zone is an error.
*/
/*
* Schedule the given zone to be collected as part of the next GC.
*/
extern JS_PUBLIC_API(void)
PrepareZoneForGC(Zone* zone);
/*
* Schedule all zones to be collected in the next GC.
*/
extern JS_PUBLIC_API(void)
PrepareForFullGC(JSRuntime* rt);
/*
* When performing an incremental GC, the zones that were selected for the
* previous incremental slice must be selected in subsequent slices as well.
* This function selects those slices automatically.
*/
extern JS_PUBLIC_API(void)
PrepareForIncrementalGC(JSRuntime* rt);
/*
* Returns true if any zone in the system has been scheduled for GC with one of
* the functions above or by the JS engine.
*/
extern JS_PUBLIC_API(bool)
IsGCScheduled(JSRuntime* rt);
/*
* Undoes the effect of the Prepare methods above. The given zone will not be
* collected in the next GC.
*/
extern JS_PUBLIC_API(void)
SkipZoneForGC(Zone* zone);
/*
* Non-Incremental GC:
*
* The following functions perform a non-incremental GC.
*/
/*
* Performs a non-incremental collection of all selected zones.
*
* If the gckind argument is GC_NORMAL, then some objects that are unreachable
* from the program may still be alive afterwards because of internal
* references; if GC_SHRINK is passed then caches and other temporary references
* to objects will be cleared and all unreferenced objects will be removed from
* the system.
*/
extern JS_PUBLIC_API(void)
GCForReason(JSRuntime* rt, JSGCInvocationKind gckind, gcreason::Reason reason);
/*
* Incremental GC:
*
* Incremental GC divides the full mark-and-sweep collection into multiple
* slices, allowing client JavaScript code to run between each slice. This
* allows interactive apps to avoid long collection pauses. Incremental GC does
* not make collection take less time, it merely spreads that time out so that
* the pauses are less noticable.
*
* For a collection to be carried out incrementally the following conditions
* must be met:
* - The collection must be run by calling JS::IncrementalGC() rather than
* JS_GC().
* - The GC mode must have been set to JSGC_MODE_INCREMENTAL with
* JS_SetGCParameter().
* - All native objects that have their own trace hook must indicate that they
* implement read and write barriers with the JSCLASS_IMPLEMENTS_BARRIERS
* flag.
*
* Note: Even if incremental GC is enabled and working correctly,
* non-incremental collections can still happen when low on memory.
*/
/*
* Begin an incremental collection and perform one slice worth of work. When
* this function returns, the collection may not be complete.
* IncrementalGCSlice() must be called repeatedly until
* !IsIncrementalGCInProgress(rt).
*
* Note: SpiderMonkey's GC is not realtime. Slices in practice may be longer or
* shorter than the requested interval.
*/
extern JS_PUBLIC_API(void)
StartIncrementalGC(JSRuntime* rt, JSGCInvocationKind gckind, gcreason::Reason reason,
int64_t millis = 0);
/*
* Perform a slice of an ongoing incremental collection. When this function
* returns, the collection may not be complete. It must be called repeatedly
* until !IsIncrementalGCInProgress(rt).
*
* Note: SpiderMonkey's GC is not realtime. Slices in practice may be longer or
* shorter than the requested interval.
*/
extern JS_PUBLIC_API(void)
IncrementalGCSlice(JSRuntime* rt, gcreason::Reason reason, int64_t millis = 0);
/*
* If IsIncrementalGCInProgress(rt), this call finishes the ongoing collection
* by performing an arbitrarily long slice. If !IsIncrementalGCInProgress(rt),
* this is equivalent to GCForReason. When this function returns,
* IsIncrementalGCInProgress(rt) will always be false.
*/
extern JS_PUBLIC_API(void)
FinishIncrementalGC(JSRuntime* rt, gcreason::Reason reason);
/*
* If IsIncrementalGCInProgress(rt), this call aborts the ongoing collection and
* performs whatever work needs to be done to return the collector to its idle
* state. This may take an arbitrarily long time. When this function returns,
* IsIncrementalGCInProgress(rt) will always be false.
*/
extern JS_PUBLIC_API(void)
AbortIncrementalGC(JSRuntime* rt);
namespace dbg {
// The `JS::dbg::GarbageCollectionEvent` class is essentially a view of the
// `js::gcstats::Statistics` data without the uber implementation-specific bits.
// It should generally be palatable for web developers.
class GarbageCollectionEvent
{
// The major GC number of the GC cycle this data pertains to.
uint64_t majorGCNumber_;
// Reference to a non-owned, statically allocated C string. This is a very
// short reason explaining why a GC was triggered.
const char* reason;
// Reference to a nullable, non-owned, statically allocated C string. If the
// collection was forced to be non-incremental, this is a short reason of
// why the GC could not perform an incremental collection.
const char* nonincrementalReason;
// Represents a single slice of a possibly multi-slice incremental garbage
// collection.
struct Collection {
int64_t startTimestamp;
int64_t endTimestamp;
};
// The set of garbage collection slices that made up this GC cycle.
mozilla::Vector<Collection> collections;
GarbageCollectionEvent(const GarbageCollectionEvent& rhs) = delete;
GarbageCollectionEvent& operator=(const GarbageCollectionEvent& rhs) = delete;
public:
explicit GarbageCollectionEvent(uint64_t majorGCNum)
: majorGCNumber_(majorGCNum)
, reason(nullptr)
, nonincrementalReason(nullptr)
, collections()
{ }
using Ptr = UniquePtr<GarbageCollectionEvent, DeletePolicy<GarbageCollectionEvent>>;
static Ptr Create(JSRuntime* rt, ::js::gcstats::Statistics& stats, uint64_t majorGCNumber);
JSObject* toJSObject(JSContext* cx) const;
uint64_t majorGCNumber() const { return majorGCNumber_; }
};
} // namespace dbg
enum GCProgress {
/*
* During non-incremental GC, the GC is bracketed by JSGC_CYCLE_BEGIN/END
* callbacks. During an incremental GC, the sequence of callbacks is as
* follows:
* JSGC_CYCLE_BEGIN, JSGC_SLICE_END (first slice)
* JSGC_SLICE_BEGIN, JSGC_SLICE_END (second slice)
* ...
* JSGC_SLICE_BEGIN, JSGC_CYCLE_END (last slice)
*/
GC_CYCLE_BEGIN,
GC_SLICE_BEGIN,
GC_SLICE_END,
GC_CYCLE_END
};
struct JS_PUBLIC_API(GCDescription) {
bool isCompartment_;
JSGCInvocationKind invocationKind_;
GCDescription(bool isCompartment, JSGCInvocationKind kind)
: isCompartment_(isCompartment), invocationKind_(kind) {}
char16_t* formatSliceMessage(JSRuntime* rt) const;
char16_t* formatSummaryMessage(JSRuntime* rt) const;
char16_t* formatJSON(JSRuntime* rt, uint64_t timestamp) const;
JS::dbg::GarbageCollectionEvent::Ptr toGCEvent(JSRuntime* rt) const;
};
typedef void
(* GCSliceCallback)(JSRuntime* rt, GCProgress progress, const GCDescription& desc);
/*
* The GC slice callback is called at the beginning and end of each slice. This
* callback may be used for GC notifications as well as to perform additional
* marking.
*/
extern JS_PUBLIC_API(GCSliceCallback)
SetGCSliceCallback(JSRuntime* rt, GCSliceCallback callback);
/*
* Incremental GC defaults to enabled, but may be disabled for testing or in
* embeddings that have not yet implemented barriers on their native classes.
* There is not currently a way to re-enable incremental GC once it has been
* disabled on the runtime.
*/
extern JS_PUBLIC_API(void)
DisableIncrementalGC(JSRuntime* rt);
/*
* Returns true if incremental GC is enabled. Simply having incremental GC
* enabled is not sufficient to ensure incremental collections are happening.
* See the comment "Incremental GC" above for reasons why incremental GC may be
* suppressed. Inspection of the "nonincremental reason" field of the
* GCDescription returned by GCSliceCallback may help narrow down the cause if
* collections are not happening incrementally when expected.
*/
extern JS_PUBLIC_API(bool)
IsIncrementalGCEnabled(JSRuntime* rt);
/*
* Returns true while an incremental GC is ongoing, both when actively
* collecting and between slices.
*/
extern JS_PUBLIC_API(bool)
IsIncrementalGCInProgress(JSRuntime* rt);
/*
* Returns true when writes to GC things must call an incremental (pre) barrier.
* This is generally only true when running mutator code in-between GC slices.
* At other times, the barrier may be elided for performance.
*/
extern JS_PUBLIC_API(bool)
IsIncrementalBarrierNeeded(JSRuntime* rt);
extern JS_PUBLIC_API(bool)
IsIncrementalBarrierNeeded(JSContext* cx);
/*
* Notify the GC that a reference to a GC thing is about to be overwritten.
* These methods must be called if IsIncrementalBarrierNeeded.
*/
extern JS_PUBLIC_API(void)
IncrementalReferenceBarrier(GCCellPtr thing);
extern JS_PUBLIC_API(void)
IncrementalValueBarrier(const Value& v);
extern JS_PUBLIC_API(void)
IncrementalObjectBarrier(JSObject* obj);
/*
* Returns true if the most recent GC ran incrementally.
*/
extern JS_PUBLIC_API(bool)
WasIncrementalGC(JSRuntime* rt);
/*
* Generational GC:
*
* Note: Generational GC is not yet enabled by default. The following class
* is non-functional unless SpiderMonkey was configured with
* --enable-gcgenerational.
*/
/* Ensure that generational GC is disabled within some scope. */
class JS_PUBLIC_API(AutoDisableGenerationalGC)
{
js::gc::GCRuntime* gc;
public:
explicit AutoDisableGenerationalGC(JSRuntime* rt);
~AutoDisableGenerationalGC();
};
/*
* Returns true if generational allocation and collection is currently enabled
* on the given runtime.
*/
extern JS_PUBLIC_API(bool)
IsGenerationalGCEnabled(JSRuntime* rt);
/*
* Returns the GC's "number". This does not correspond directly to the number
* of GCs that have been run, but is guaranteed to be monotonically increasing
* with GC activity.
*/
extern JS_PUBLIC_API(size_t)
GetGCNumber();
/*
* The GC does not immediately return the unused memory freed by a collection
* back to the system incase it is needed soon afterwards. This call forces the
* GC to return this memory immediately.
*/
extern JS_PUBLIC_API(void)
ShrinkGCBuffers(JSRuntime* rt);
/*
* Assert if a GC occurs while this class is live. This class does not disable
* the static rooting hazard analysis.
*/
class JS_PUBLIC_API(AutoAssertOnGC)
{
#ifdef DEBUG
js::gc::GCRuntime* gc;
size_t gcNumber;
public:
AutoAssertOnGC();
explicit AutoAssertOnGC(JSRuntime* rt);
~AutoAssertOnGC();
static void VerifyIsSafeToGC(JSRuntime* rt);
#else
public:
AutoAssertOnGC() {}
explicit AutoAssertOnGC(JSRuntime* rt) {}
~AutoAssertOnGC() {}
static void VerifyIsSafeToGC(JSRuntime* rt) {}
#endif
};
/*
* Assert if an allocation of a GC thing occurs while this class is live. This
* class does not disable the static rooting hazard analysis.
*/
class JS_PUBLIC_API(AutoAssertNoAlloc)
{
#ifdef JS_DEBUG
js::gc::GCRuntime* gc;
public:
AutoAssertNoAlloc() : gc(nullptr) {}
explicit AutoAssertNoAlloc(JSRuntime* rt);
void disallowAlloc(JSRuntime* rt);
~AutoAssertNoAlloc();
#else
public:
AutoAssertNoAlloc() {}
explicit AutoAssertNoAlloc(JSRuntime* rt) {}
void disallowAlloc(JSRuntime* rt) {}
#endif
};
/*
* Disable the static rooting hazard analysis in the live region and assert if
* any allocation that could potentially trigger a GC occurs while this guard
* object is live. This is most useful to help the exact rooting hazard analysis
* in complex regions, since it cannot understand dataflow.
*
* Note: GC behavior is unpredictable even when deterministic and is generally
* non-deterministic in practice. The fact that this guard has not
* asserted is not a guarantee that a GC cannot happen in the guarded
* region. As a rule, anyone performing a GC unsafe action should
* understand the GC properties of all code in that region and ensure
* that the hazard analysis is correct for that code, rather than relying
* on this class.
*/
class JS_PUBLIC_API(AutoSuppressGCAnalysis) : public AutoAssertNoAlloc
{
public:
AutoSuppressGCAnalysis() : AutoAssertNoAlloc() {}
explicit AutoSuppressGCAnalysis(JSRuntime* rt) : AutoAssertNoAlloc(rt) {}
};
/*
* Assert that code is only ever called from a GC callback, disable the static
* rooting hazard analysis and assert if any allocation that could potentially
* trigger a GC occurs while this guard object is live.
*
* This is useful to make the static analysis ignore code that runs in GC
* callbacks.
*/
class JS_PUBLIC_API(AutoAssertGCCallback) : public AutoSuppressGCAnalysis
{
public:
explicit AutoAssertGCCallback(JSObject* obj);
};
/*
* Place AutoCheckCannotGC in scopes that you believe can never GC. These
* annotations will be verified both dynamically via AutoAssertOnGC, and
* statically with the rooting hazard analysis (implemented by making the
* analysis consider AutoCheckCannotGC to be a GC pointer, and therefore
* complain if it is live across a GC call.) It is useful when dealing with
* internal pointers to GC things where the GC thing itself may not be present
* for the static analysis: e.g. acquiring inline chars from a JSString* on the
* heap.
*/
class JS_PUBLIC_API(AutoCheckCannotGC) : public AutoAssertOnGC
{
public:
AutoCheckCannotGC() : AutoAssertOnGC() {}
explicit AutoCheckCannotGC(JSRuntime* rt) : AutoAssertOnGC(rt) {}
};
/*
* Unsets the gray bit for anything reachable from |thing|. |kind| should not be
* JS::TraceKind::Shape. |thing| should be non-null.
*/
extern JS_FRIEND_API(bool)
UnmarkGrayGCThingRecursively(GCCellPtr thing);
} /* namespace JS */
namespace js {
namespace gc {
static MOZ_ALWAYS_INLINE void
ExposeGCThingToActiveJS(JS::GCCellPtr thing)
{
MOZ_ASSERT(thing.kind() != JS::TraceKind::Shape);
/*
* 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 (IsInsideNursery(thing.asCell()))
return;
JS::shadow::Runtime* rt = detail::GetGCThingRuntime(thing.unsafeAsUIntPtr());
if (IsIncrementalBarrierNeededOnTenuredGCThing(rt, thing))
JS::IncrementalReferenceBarrier(thing);
else if (JS::GCThingIsMarkedGray(thing))
JS::UnmarkGrayGCThingRecursively(thing);
}
static MOZ_ALWAYS_INLINE void
MarkGCThingAsLive(JSRuntime* aRt, JS::GCCellPtr thing)
{
JS::shadow::Runtime* rt = JS::shadow::Runtime::asShadowRuntime(aRt);
/*
* Any object in the nursery will not be freed during any GC running at that time.
*/
if (IsInsideNursery(thing.asCell()))
return;
if (IsIncrementalBarrierNeededOnTenuredGCThing(rt, thing))
JS::IncrementalReferenceBarrier(thing);
}
} /* namespace gc */
} /* namespace js */
namespace JS {
/*
* This should be called when an object that is marked gray is exposed to the JS
* engine (by handing it to running JS code or writing it into live JS
* data). During incremental GC, since the gray bits haven't been computed yet,
* we conservatively mark the object black.
*/
static MOZ_ALWAYS_INLINE void
ExposeObjectToActiveJS(JSObject* obj)
{
js::gc::ExposeGCThingToActiveJS(GCCellPtr(obj));
}
static MOZ_ALWAYS_INLINE void
ExposeScriptToActiveJS(JSScript* script)
{
js::gc::ExposeGCThingToActiveJS(GCCellPtr(script));
}
/*
* If a GC is currently marking, mark the string black.
*/
static MOZ_ALWAYS_INLINE void
MarkStringAsLive(Zone* zone, JSString* string)
{
JSRuntime* rt = JS::shadow::Zone::asShadowZone(zone)->runtimeFromMainThread();
js::gc::MarkGCThingAsLive(rt, GCCellPtr(string));
}
/*
* Internal to Firefox.
*
* Note: this is not related to the PokeGC in nsJSEnvironment.
*/
extern JS_FRIEND_API(void)
PokeGC(JSRuntime* rt);
/*
* Internal to Firefox.
*/
extern JS_FRIEND_API(void)
NotifyDidPaint(JSRuntime* rt);
} /* namespace JS */
#endif /* js_GCAPI_h */
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