The Tor Browser: js/public/GCAPI.h@97036ab72558 (annotated)

js/public/GCAPI.h@97036ab72558 (annotated)

js/public/GCAPI.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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 */

The Tor Browser / annotate

js/public/GCAPI.h@97036ab72558 (annotated)

js/public/GCAPI.h