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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/NullPtr.h"

 #include "js/HeapAPI.h"

 #include "js/RootingAPI.h"

 #include "js/Value.h"

 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;

 namespace JS {

 #define GCREASONS(D)                            \

     /* Reasons internal to the JS engine */     \

     D(API)                                      \

     D(MAYBEGC)                                  \

     D(DESTROY_RUNTIME)                          \

     D(DESTROY_CONTEXT)                          \

     D(LAST_DITCH)                               \

     D(TOO_MUCH_MALLOC)                          \

     D(ALLOC_TRIGGER)                            \

     D(DEBUG_GC)                                 \

     D(TRANSPLANT)                               \

     D(RESET)                                    \

     D(OUT_OF_NURSERY)                           \

     D(EVICT_NURSERY)                            \

     D(FULL_STORE_BUFFER)                        \

                                                 \

     /* 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)                               \

     D(RESERVED16)                               \

     D(RESERVED17)                               \

     D(RESERVED18)                               \

     D(RESERVED19)                               \

                                                 \

     /* 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_EVALUTE)

 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 26. 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_FRIEND_API(void)

 PrepareZoneForGC(Zone *zone);

 /*

  * Schedule all zones to be collected in the next GC.

  */

 extern JS_FRIEND_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_FRIEND_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_FRIEND_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_FRIEND_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. Some objects

  * that are unreachable from the program may still be alive afterwards because

  * of internal references.

  */

 extern JS_FRIEND_API(void)

 GCForReason(JSRuntime *rt, gcreason::Reason reason);

 /*

  * Perform a non-incremental collection after clearing caches and other

  * temporary references to objects. This will remove all unreferenced objects

  * in the system.

  */

 extern JS_FRIEND_API(void)

 ShrinkingGC(JSRuntime *rt, 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 or

  * perform a slice of an ongoing incremental collection. When this function

  * returns, the collection is not complete. This function 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_FRIEND_API(void)

 IncrementalGC(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_FRIEND_API(void)

 FinishIncrementalGC(JSRuntime *rt, gcreason::Reason reason);

 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_FRIEND_API(GCDescription) {

     bool isCompartment_;

     GCDescription(bool isCompartment)

       : isCompartment_(isCompartment) {}

     jschar *formatMessage(JSRuntime *rt) const;

     jschar *formatJSON(JSRuntime *rt, uint64_t timestamp) 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_FRIEND_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_FRIEND_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_FRIEND_API(bool)

 IsIncrementalGCEnabled(JSRuntime *rt);

 /*

  * Returns true while an incremental GC is ongoing, both when actively

  * collecting and between slices.

  */

 JS_FRIEND_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_FRIEND_API(bool)

 IsIncrementalBarrierNeeded(JSRuntime *rt);

 extern JS_FRIEND_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_FRIEND_API(void)

 IncrementalReferenceBarrier(void *ptr, JSGCTraceKind kind);

 extern JS_FRIEND_API(void)

 IncrementalValueBarrier(const Value &v);

 extern JS_FRIEND_API(void)

 IncrementalObjectBarrier(JSObject *obj);

 /*

  * Returns true if the most recent GC ran incrementally.

  */

 extern JS_FRIEND_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_FRIEND_API(AutoDisableGenerationalGC)

 {

     JSRuntime *runtime;

 #if defined(JSGC_GENERATIONAL) && defined(JS_GC_ZEAL)

     bool restartVerifier;

 #endif

   public:

     AutoDisableGenerationalGC(JSRuntime *rt);

     ~AutoDisableGenerationalGC();

 };

 /*

  * Returns true if generational allocation and collection is currently enabled

  * on the given runtime.

  */

 extern JS_FRIEND_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_FRIEND_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_FRIEND_API(void)

 ShrinkGCBuffers(JSRuntime *rt);

 /*

  * Assert if any GC occured while this guard object was 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 deterministice 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(AutoAssertNoGC)

 {

 #ifdef JS_DEBUG

     JSRuntime *runtime;

     size_t gcNumber;

   public:

     AutoAssertNoGC();

     AutoAssertNoGC(JSRuntime *rt);

     ~AutoAssertNoGC();

 #else

   public:

     /* Prevent unreferenced local warnings in opt builds. */

     AutoAssertNoGC() {}

     AutoAssertNoGC(JSRuntime *) {}

 #endif

 };

 class JS_PUBLIC_API(ObjectPtr)

 {

     Heap<JSObject *> value;

   public:

     ObjectPtr() : value(nullptr) {}

     ObjectPtr(JSObject *obj) : value(obj) {}

     /* Always call finalize before the destructor. */

     ~ObjectPtr() { MOZ_ASSERT(!value); }

     void finalize(JSRuntime *rt) {

         if (IsIncrementalBarrierNeeded(rt))

             IncrementalObjectBarrier(value);

         value = nullptr;

     }

     void init(JSObject *obj) { value = obj; }

     JSObject *get() const { return value; }

     void writeBarrierPre(JSRuntime *rt) {

         IncrementalObjectBarrier(value);

     }

     bool isAboutToBeFinalized();

     ObjectPtr &operator=(JSObject *obj) {

         IncrementalObjectBarrier(value);

         value = obj;

         return *this;

     }

     void trace(JSTracer *trc, const char *name);

     JSObject &operator*() const { return *value; }

     JSObject *operator->() const { return value; }

     operator JSObject *() const { return value; }

 };

 /*

  * Unsets the gray bit for anything reachable from |thing|. |kind| should not be

  * JSTRACE_SHAPE. |thing| should be non-null.

  */

 extern JS_FRIEND_API(bool)

 UnmarkGrayGCThingRecursively(void *thing, JSGCTraceKind kind);

 /*

  * 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

 ExposeGCThingToActiveJS(void *thing, JSGCTraceKind kind)

 {

     MOZ_ASSERT(kind != JSTRACE_SHAPE);

     shadow::Runtime *rt = js::gc::GetGCThingRuntime(thing);

 #ifdef JSGC_GENERATIONAL

     /*

      * 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(rt, thing))

         return;

 #endif

     if (IsIncrementalBarrierNeededOnGCThing(rt, thing, kind))

         IncrementalReferenceBarrier(thing, kind);

     else if (GCThingIsMarkedGray(thing))

         UnmarkGrayGCThingRecursively(thing, kind);

 }

 static MOZ_ALWAYS_INLINE void

 ExposeValueToActiveJS(const Value &v)

 {

     if (v.isMarkable())

         ExposeGCThingToActiveJS(v.toGCThing(), v.gcKind());

 }

 static MOZ_ALWAYS_INLINE void

 ExposeObjectToActiveJS(JSObject *obj)

 {

     ExposeGCThingToActiveJS(obj, JSTRACE_OBJECT);

 }

 /*

  * If a GC is currently marking, mark the object black.

  */

 static MOZ_ALWAYS_INLINE void

 MarkGCThingAsLive(JSRuntime *rt_, void *thing, JSGCTraceKind kind)

 {

     shadow::Runtime *rt = shadow::Runtime::asShadowRuntime(rt_);

 #ifdef JSGC_GENERATIONAL

     /*

      * Any object in the nursery will not be freed during any GC running at that time.

      */

     if (js::gc::IsInsideNursery(rt, thing))

         return;

 #endif

     if (IsIncrementalBarrierNeededOnGCThing(rt, thing, kind))

         IncrementalReferenceBarrier(thing, kind);

 }

 static MOZ_ALWAYS_INLINE void

 MarkStringAsLive(Zone *zone, JSString *string)

 {

     JSRuntime *rt = JS::shadow::Zone::asShadowZone(zone)->runtimeFromMainThread();

     MarkGCThingAsLive(rt, string, JSTRACE_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 */