/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- * vim: set ts=8 sts=2 et sw=2 tw=80: * 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/. */ /* * High-level interface to the JS garbage collector. */ #ifndef js_GCAPI_h #define js_GCAPI_h #include "mozilla/TimeStamp.h" #include "mozilla/Vector.h" #include "js/GCAnnotations.h" #include "js/shadow/Zone.h" #include "js/SliceBudget.h" #include "js/TypeDecls.h" #include "js/UniquePtr.h" #include "js/Utility.h" class JS_PUBLIC_API JSTracer; namespace js { namespace gc { class GCRuntime; } // namespace gc class JS_PUBLIC_API SliceBudget; namespace gcstats { struct Statistics; } // namespace gcstats } // namespace js namespace JS { // Options used when starting a GC. enum class GCOptions : uint32_t { // Normal GC invocation. // // Some objects that are unreachable from the program may still be alive after // collection because of internal references Normal = 0, // A shrinking GC. // // Try to release as much memory as possible by clearing internal caches, // aggressively discarding JIT code and decommitting unused chunks. This // ensures all unreferenced objects are removed from the system. // // Finally, compact the GC heap. Shrink = 1, // A shutdown GC. // // This does more drastic cleanup as part of system shutdown, including: // - clearing WeakRef kept object sets // - not marking FinalizationRegistry roots // - repeating collection if JS::NotifyGCRootsRemoved was called // - skipping scheduling of various future work that won't be needed // // Note that this assumes that no JS will run after this point! Shutdown = 2 }; } // namespace JS typedef enum JSGCParamKey { /** * Maximum nominal heap before last ditch GC. * * Soft limit on the number of bytes we are allowed to allocate in the GC * heap. Attempts to allocate gcthings over this limit will return null and * subsequently invoke the standard OOM machinery, independent of available * physical memory. * * Pref: javascript.options.mem.max * Default: 0xffffffff */ JSGC_MAX_BYTES = 0, /** * Maximum size of the generational GC nurseries. * * This will be rounded to the nearest gc::ChunkSize. * * Pref: javascript.options.mem.nursery.max_kb * Default: JS::DefaultNurseryMaxBytes */ JSGC_MAX_NURSERY_BYTES = 2, /** Amount of bytes allocated by the GC. */ JSGC_BYTES = 3, /** Number of times GC has been invoked. Includes both major and minor GC. */ JSGC_NUMBER = 4, /** * Whether incremental GC is enabled. If not, GC will always run to * completion. * * prefs: javascript.options.mem.gc_incremental. * Default: false */ JSGC_INCREMENTAL_GC_ENABLED = 5, /** * Whether per-zone GC is enabled. If not, all zones are collected every time. * * prefs: javascript.options.mem.gc_per_zone * Default: false */ JSGC_PER_ZONE_GC_ENABLED = 6, /** Number of cached empty GC chunks. */ JSGC_UNUSED_CHUNKS = 7, /** Total number of allocated GC chunks. */ JSGC_TOTAL_CHUNKS = 8, /** * Max milliseconds to spend in an incremental GC slice. * * A value of zero means there is no maximum. * * Pref: javascript.options.mem.gc_incremental_slice_ms * Default: DefaultTimeBudgetMS. */ JSGC_SLICE_TIME_BUDGET_MS = 9, /** * Maximum size the GC mark stack can grow to. * * Pref: none * Default: MarkStack::DefaultCapacity */ JSGC_MARK_STACK_LIMIT = 10, /** * The "do we collect?" decision depends on various parameters and can be * summarised as: * * ZoneSize > Max(ThresholdBase, LastSize) * GrowthFactor * ThresholdFactor * * Where * ZoneSize: Current size of this zone. * LastSize: Heap size immediately after the most recent collection. * ThresholdBase: The JSGC_ALLOCATION_THRESHOLD parameter * GrowthFactor: A number above 1, calculated based on some of the * following parameters. * See computeZoneHeapGrowthFactorForHeapSize() in GC.cpp * ThresholdFactor: 1.0 to trigger an incremental collections or between * JSGC_SMALL_HEAP_INCREMENTAL_LIMIT and * JSGC_LARGE_HEAP_INCREMENTAL_LIMIT to trigger a * non-incremental collection. * * The RHS of the equation above is calculated and sets * zone->gcHeapThreshold.bytes(). When gcHeapSize.bytes() exeeds * gcHeapThreshold.bytes() for a zone, the zone may be scheduled for a GC. */ /** * GCs less than this far apart in milliseconds will be considered * 'high-frequency GCs'. * * Pref: javascript.options.mem.gc_high_frequency_time_limit_ms * Default: HighFrequencyThreshold */ JSGC_HIGH_FREQUENCY_TIME_LIMIT = 11, /** * Upper limit for classifying a heap as small (MB). * * Dynamic heap growth thresholds are based on whether the heap is small, * medium or large. Heaps smaller than this size are classified as small; * larger heaps are classified as medium or large. * * Pref: javascript.options.mem.gc_small_heap_size_max_mb * Default: SmallHeapSizeMaxBytes */ JSGC_SMALL_HEAP_SIZE_MAX = 12, /** * Lower limit for classifying a heap as large (MB). * * Dynamic heap growth thresholds are based on whether the heap is small, * medium or large. Heaps larger than this size are classified as large; * smaller heaps are classified as small or medium. * * Pref: javascript.options.mem.gc_large_heap_size_min_mb * Default: LargeHeapSizeMinBytes */ JSGC_LARGE_HEAP_SIZE_MIN = 13, /** * Heap growth factor for small heaps in the high-frequency GC state. * * Pref: javascript.options.mem.gc_high_frequency_small_heap_growth * Default: HighFrequencySmallHeapGrowth */ JSGC_HIGH_FREQUENCY_SMALL_HEAP_GROWTH = 14, /** * Heap growth factor for large heaps in the high-frequency GC state. * * Pref: javascript.options.mem.gc_high_frequency_large_heap_growth * Default: HighFrequencyLargeHeapGrowth */ JSGC_HIGH_FREQUENCY_LARGE_HEAP_GROWTH = 15, /** * Heap growth factor for low frequency GCs. * * This factor is applied regardless of the size of the heap when not in the * high-frequency GC state. * * Pref: javascript.options.mem.gc_low_frequency_heap_growth * Default: LowFrequencyHeapGrowth */ JSGC_LOW_FREQUENCY_HEAP_GROWTH = 16, /** * Whether balanced heap limits are enabled. * * If this is set to true then heap limits are calculated in a way designed to * balance memory usage optimally between many heaps. * * Otherwise, heap limits are set based on a linear multiple of the retained * size after the last collection. * * Pref: javascript.options.mem.gc_balanced_heap_limits * Default: BalancedHeapLimitsEnabled */ JSGC_BALANCED_HEAP_LIMITS_ENABLED = 17, /** * Heap growth parameter for balanced heap limit calculation. * * This parameter trades off GC time for memory usage. Smaller values result * in lower memory use and larger values result in less time spent collecting. * * Heap limits are set to the heap's retained size plus some extra space. The * extra space is calculated based on several factors but is scaled * proportionally to this parameter. * * Pref: javascript.options.mem.gc_heap_growth_factor * Default: HeapGrowthFactor */ JSGC_HEAP_GROWTH_FACTOR = 18, /** * Lower limit for collecting a zone (MB). * * Zones smaller than this size will not normally be collected. * * Pref: javascript.options.mem.gc_allocation_threshold_mb * Default GCZoneAllocThresholdBase */ JSGC_ALLOCATION_THRESHOLD = 19, /** * We try to keep at least this many unused chunks in the free chunk pool at * all times, even after a shrinking GC. * * Pref: javascript.options.mem.gc_min_empty_chunk_count * Default: MinEmptyChunkCount */ JSGC_MIN_EMPTY_CHUNK_COUNT = 21, /** * We never keep more than this many unused chunks in the free chunk * pool. * * Pref: javascript.options.mem.gc_min_empty_chunk_count * Default: MinEmptyChunkCount */ JSGC_MAX_EMPTY_CHUNK_COUNT = 22, /** * Whether compacting GC is enabled. * * Pref: javascript.options.mem.gc_compacting * Default: CompactingEnabled */ JSGC_COMPACTING_ENABLED = 23, /** * Limit of how far over the incremental trigger threshold we allow the heap * to grow before finishing a collection non-incrementally, for small heaps. * * We trigger an incremental GC when a trigger threshold is reached but the * collection may not be fast enough to keep up with the mutator. At some * point we finish the collection non-incrementally. * * Default: SmallHeapIncrementalLimit * Pref: javascript.options.mem.gc_small_heap_incremental_limit */ JSGC_SMALL_HEAP_INCREMENTAL_LIMIT = 25, /** * Limit of how far over the incremental trigger threshold we allow the heap * to grow before finishing a collection non-incrementally, for large heaps. * * Default: LargeHeapIncrementalLimit * Pref: javascript.options.mem.gc_large_heap_incremental_limit */ JSGC_LARGE_HEAP_INCREMENTAL_LIMIT = 26, /** * Attempt to run a minor GC in the idle time if the free space falls * below this number of bytes. * * Default: NurseryChunkUsableSize / 4 * Pref: None */ JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION = 27, /** * If this percentage of the nursery is tenured and the nursery is at least * 4MB, then proceed to examine which groups we should pretenure. * * Default: PretenureThreshold * Pref: None */ JSGC_PRETENURE_THRESHOLD = 28, /** * If the above condition is met, then any object group that tenures more than * this number of objects will be pretenured (if it can be). * * Default: PretenureGroupThreshold * Pref: None */ JSGC_PRETENURE_GROUP_THRESHOLD = 29, /** * Attempt to run a minor GC in the idle time if the free space falls * below this percentage (from 0 to 99). * * Default: 25 * Pref: None */ JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION_PERCENT = 30, /** * Minimum size of the generational GC nurseries. * * This value will be rounded to the nearest Nursery::SubChunkStep if below * gc::ChunkSize, otherwise it'll be rounded to the nearest gc::ChunkSize. * * Default: Nursery::SubChunkLimit * Pref: javascript.options.mem.nursery.min_kb */ JSGC_MIN_NURSERY_BYTES = 31, /** * The minimum time to allow between triggering last ditch GCs in seconds. * * Default: 60 seconds * Pref: None */ JSGC_MIN_LAST_DITCH_GC_PERIOD = 32, /** * The delay (in heapsize kilobytes) between slices of an incremental GC. * * Default: ZoneAllocDelayBytes */ JSGC_ZONE_ALLOC_DELAY_KB = 33, /* * The current size of the nursery. * * This parameter is read-only. */ JSGC_NURSERY_BYTES = 34, /** * Retained size base value for calculating malloc heap threshold. * * Default: MallocThresholdBase */ JSGC_MALLOC_THRESHOLD_BASE = 35, /** * Whether incremental weakmap marking is enabled. * * Pref: javascript.options.mem.incremental_weakmap * Default: IncrementalWeakMarkEnabled */ JSGC_INCREMENTAL_WEAKMAP_ENABLED = 37, /** * The chunk size in bytes for this system. * * This parameter is read-only. */ JSGC_CHUNK_BYTES = 38, /** * The number of background threads to use for parallel GC work for each CPU * core, expressed as an integer percentage. * * Pref: javascript.options.mem.gc_helper_thread_ratio */ JSGC_HELPER_THREAD_RATIO = 39, /** * The maximum number of background threads to use for parallel GC work. * * Pref: javascript.options.mem.gc_max_helper_threads */ JSGC_MAX_HELPER_THREADS = 40, /** * The number of background threads to use for parallel GC work. * * This parameter is read-only and is set based on the * JSGC_HELPER_THREAD_RATIO and JSGC_MAX_HELPER_THREADS parameters. */ JSGC_HELPER_THREAD_COUNT = 41, /** * If the percentage of the tenured strings exceeds this threshold, string * will be allocated in tenured heap instead. (Default is allocated in * nursery.) */ JSGC_PRETENURE_STRING_THRESHOLD = 42, /** * If the finalization rate of the tenured strings exceeds this threshold, * string will be allocated in nursery. */ JSGC_STOP_PRETENURE_STRING_THRESHOLD = 43, /** * A number that is incremented on every major GC slice. */ JSGC_MAJOR_GC_NUMBER = 44, /** * A number that is incremented on every minor GC. */ JSGC_MINOR_GC_NUMBER = 45, /** * JS::MaybeRunNurseryCollection will collect the nursery if it hasn't been * collected in this many milliseconds. * * Default: 5000 * Pref: None */ JSGC_NURSERY_TIMEOUT_FOR_IDLE_COLLECTION_MS = 46, /** * The system page size in KB. * * This parameter is read-only. */ JSGC_SYSTEM_PAGE_SIZE_KB = 47, /** * In an incremental GC, this determines the point at which to start * increasing the slice budget and frequency of allocation triggered slices to * try to avoid reaching the incremental limit and finishing the collection * synchronously. * * The threshold is calculated by subtracting this value from the heap's * incremental limit. */ JSGC_URGENT_THRESHOLD_MB = 48, } JSGCParamKey; /* * Generic trace operation that calls JS::TraceEdge on each traceable thing's * location reachable from data. */ typedef void (*JSTraceDataOp)(JSTracer* trc, void* data); /* * Trace hook used to trace gray roots incrementally. * * This should return whether tracing is finished. It will be called repeatedly * in subsequent GC slices until it returns true. * * While tracing this should check the budget and return false if it has been * exceeded. When passed an unlimited budget it should always return true. */ typedef bool (*JSGrayRootsTracer)(JSTracer* trc, js::SliceBudget& budget, void* data); typedef enum JSGCStatus { JSGC_BEGIN, JSGC_END } JSGCStatus; typedef void (*JSObjectsTenuredCallback)(JSContext* cx, void* data); typedef enum JSFinalizeStatus { /** * Called when preparing to sweep a group of zones, before anything has been * swept. The collector will not yield to the mutator before calling the * callback with JSFINALIZE_GROUP_START status. */ JSFINALIZE_GROUP_PREPARE, /** * Called after preparing to sweep a group of zones. Weak references to * unmarked things have been removed at this point, but no GC things have * been swept. The collector may yield to the mutator after this point. */ JSFINALIZE_GROUP_START, /** * Called after sweeping a group of zones. All dead GC things have been * swept at this point. */ JSFINALIZE_GROUP_END, /** * Called at the end of collection when everything has been swept. */ JSFINALIZE_COLLECTION_END } JSFinalizeStatus; typedef void (*JSFinalizeCallback)(JS::GCContext* gcx, JSFinalizeStatus status, void* data); typedef void (*JSWeakPointerZonesCallback)(JSTracer* trc, void* data); typedef void (*JSWeakPointerCompartmentCallback)(JSTracer* trc, JS::Compartment* comp, void* data); /* * This is called to tell the embedding that a FinalizationRegistry object has * cleanup work, and that the engine should be called back at an appropriate * later time to perform this cleanup, by calling the function |doCleanup|. * * This callback must not do anything that could cause GC. */ using JSHostCleanupFinalizationRegistryCallback = void (*)(JSFunction* doCleanup, JSObject* incumbentGlobal, void* data); /** * Each external string has a pointer to JSExternalStringCallbacks. Embedders * can use this to implement custom finalization or memory reporting behavior. */ struct JSExternalStringCallbacks { /** * Finalizes external strings created by JS_NewExternalString. The finalizer * can be called off the main thread. */ virtual void finalize(char16_t* chars) const = 0; /** * Callback used by memory reporting to ask the embedder how much memory an * external string is keeping alive. The embedder is expected to return a * value that corresponds to the size of the allocation that will be released * by the finalizer callback above. * * Implementations of this callback MUST NOT do anything that can cause GC. */ virtual size_t sizeOfBuffer(const char16_t* chars, mozilla::MallocSizeOf mallocSizeOf) const = 0; }; namespace JS { #define GCREASONS(D) \ /* Reasons internal to the JS engine. */ \ D(API, 0) \ D(EAGER_ALLOC_TRIGGER, 1) \ D(DESTROY_RUNTIME, 2) \ D(ROOTS_REMOVED, 3) \ D(LAST_DITCH, 4) \ D(TOO_MUCH_MALLOC, 5) \ D(ALLOC_TRIGGER, 6) \ D(DEBUG_GC, 7) \ D(COMPARTMENT_REVIVED, 8) \ D(RESET, 9) \ D(OUT_OF_NURSERY, 10) \ D(EVICT_NURSERY, 11) \ D(SHARED_MEMORY_LIMIT, 13) \ D(EAGER_NURSERY_COLLECTION, 14) \ D(BG_TASK_FINISHED, 15) \ D(ABORT_GC, 16) \ D(FULL_WHOLE_CELL_BUFFER, 17) \ D(FULL_GENERIC_BUFFER, 18) \ D(FULL_VALUE_BUFFER, 19) \ D(FULL_CELL_PTR_OBJ_BUFFER, 20) \ D(FULL_SLOT_BUFFER, 21) \ D(FULL_SHAPE_BUFFER, 22) \ D(TOO_MUCH_WASM_MEMORY, 23) \ D(DISABLE_GENERATIONAL_GC, 24) \ D(FINISH_GC, 25) \ D(PREPARE_FOR_TRACING, 26) \ D(UNUSED4, 27) \ D(FULL_CELL_PTR_STR_BUFFER, 28) \ D(TOO_MUCH_JIT_CODE, 29) \ D(FULL_CELL_PTR_BIGINT_BUFFER, 30) \ D(UNUSED5, 31) \ D(NURSERY_MALLOC_BUFFERS, 32) \ \ /* \ * Reasons from Firefox. \ * \ * The JS engine attaches special meanings to some of these reasons. \ */ \ D(DOM_WINDOW_UTILS, FIRST_FIREFOX_REASON) \ D(COMPONENT_UTILS, 34) \ D(MEM_PRESSURE, 35) \ D(CC_FINISHED, 36) \ D(CC_FORCED, 37) \ D(LOAD_END, 38) \ D(UNUSED3, 39) \ D(PAGE_HIDE, 40) \ D(NSJSCONTEXT_DESTROY, 41) \ D(WORKER_SHUTDOWN, 42) \ D(SET_DOC_SHELL, 43) \ D(DOM_UTILS, 44) \ D(DOM_IPC, 45) \ D(DOM_WORKER, 46) \ D(INTER_SLICE_GC, 47) \ D(UNUSED1, 48) \ D(FULL_GC_TIMER, 49) \ D(SHUTDOWN_CC, 50) \ D(UNUSED2, 51) \ D(USER_INACTIVE, 52) \ D(XPCONNECT_SHUTDOWN, 53) \ D(DOCSHELL, 54) \ D(HTML_PARSER, 55) \ D(DOM_TESTUTILS, 56) \ \ /* Reasons reserved for embeddings. */ \ D(RESERVED1, FIRST_RESERVED_REASON) \ D(RESERVED2, 91) \ D(RESERVED3, 92) \ D(RESERVED4, 93) \ D(RESERVED5, 94) \ D(RESERVED6, 95) \ D(RESERVED7, 96) \ D(RESERVED8, 97) \ D(RESERVED9, 98) enum class GCReason { FIRST_FIREFOX_REASON = 33, FIRST_RESERVED_REASON = 90, #define MAKE_REASON(name, val) name = val, 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; but the cost of extra * buckets seems to be low while the cost of switching histograms is high. */ NUM_TELEMETRY_REASONS = 100 }; /** * Get a statically allocated C string explaining the given GC reason. */ extern JS_PUBLIC_API const char* ExplainGCReason(JS::GCReason reason); /** * Return true if the GC reason is internal to the JS engine. */ extern JS_PUBLIC_API bool InternalGCReason(JS::GCReason reason); /* * 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(JSContext* cx, Zone* zone); /** * Schedule all zones to be collected in the next GC. */ extern JS_PUBLIC_API void PrepareForFullGC(JSContext* cx); /** * 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(JSContext* cx); /** * 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(JSContext* cx); /** * 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(JSContext* cx, Zone* zone); /* * Non-Incremental GC: * * The following functions perform a non-incremental GC. */ /** * Performs a non-incremental collection of all selected zones. */ extern JS_PUBLIC_API void NonIncrementalGC(JSContext* cx, JS::GCOptions options, GCReason 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 parameter JSGC_INCREMENTAL_GC_ENABLED must be true. * * 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(cx). * * 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(JSContext* cx, JS::GCOptions options, GCReason reason, const js::SliceBudget& budget); /** * 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(cx). * * 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(JSContext* cx, GCReason reason, const js::SliceBudget& budget); /** * Return whether an incremental GC has work to do on the foreground thread and * would make progress if a slice was run now. If this returns false then the GC * is waiting for background threads to finish their work and a slice started * now would return immediately. */ extern JS_PUBLIC_API bool IncrementalGCHasForegroundWork(JSContext* cx); /** * If IsIncrementalGCInProgress(cx), this call finishes the ongoing collection * by performing an arbitrarily long slice. If !IsIncrementalGCInProgress(cx), * this is equivalent to NonIncrementalGC. When this function returns, * IsIncrementalGCInProgress(cx) will always be false. */ extern JS_PUBLIC_API void FinishIncrementalGC(JSContext* cx, GCReason reason); /** * If IsIncrementalGCInProgress(cx), 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(cx) will always be false. */ extern JS_PUBLIC_API void AbortIncrementalGC(JSContext* cx); 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 { mozilla::TimeStamp startTimestamp; mozilla::TimeStamp endTimestamp; }; // The set of garbage collection slices that made up this GC cycle. mozilla::Vector 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 = js::UniquePtr; 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 GC, the GC is bracketed by GC_CYCLE_BEGIN/END callbacks. Each * slice between those (whether an incremental or the sole non-incremental * slice) is bracketed by GC_SLICE_BEGIN/GC_SLICE_END. */ GC_CYCLE_BEGIN, GC_SLICE_BEGIN, GC_SLICE_END, GC_CYCLE_END }; struct JS_PUBLIC_API GCDescription { bool isZone_; bool isComplete_; JS::GCOptions options_; GCReason reason_; GCDescription(bool isZone, bool isComplete, JS::GCOptions options, GCReason reason) : isZone_(isZone), isComplete_(isComplete), options_(options), reason_(reason) {} char16_t* formatSliceMessage(JSContext* cx) const; char16_t* formatSummaryMessage(JSContext* cx) const; mozilla::TimeStamp startTime(JSContext* cx) const; mozilla::TimeStamp endTime(JSContext* cx) const; mozilla::TimeStamp lastSliceStart(JSContext* cx) const; mozilla::TimeStamp lastSliceEnd(JSContext* cx) const; JS::UniqueChars sliceToJSONProfiler(JSContext* cx) const; JS::UniqueChars formatJSONProfiler(JSContext* cx) const; JS::dbg::GarbageCollectionEvent::Ptr toGCEvent(JSContext* cx) const; }; extern JS_PUBLIC_API UniqueChars MinorGcToJSON(JSContext* cx); typedef void (*GCSliceCallback)(JSContext* cx, 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(JSContext* cx, GCSliceCallback callback); /** * Describes the progress of an observed nursery collection. */ enum class GCNurseryProgress { /** * The nursery collection is starting. */ GC_NURSERY_COLLECTION_START, /** * The nursery collection is ending. */ GC_NURSERY_COLLECTION_END }; /** * A nursery collection callback receives the progress of the nursery collection * and the reason for the collection. */ using GCNurseryCollectionCallback = void (*)(JSContext* cx, GCNurseryProgress progress, GCReason reason); /** * Set the nursery collection callback for the given runtime. When set, it will * be called at the start and end of every nursery collection. */ extern JS_PUBLIC_API GCNurseryCollectionCallback SetGCNurseryCollectionCallback( JSContext* cx, GCNurseryCollectionCallback callback); typedef void (*DoCycleCollectionCallback)(JSContext* cx); /** * The purge gray callback is called after any COMPARTMENT_REVIVED GC in which * the majority of compartments have been marked gray. */ extern JS_PUBLIC_API DoCycleCollectionCallback SetDoCycleCollectionCallback(JSContext* cx, DoCycleCollectionCallback callback); using CreateSliceBudgetCallback = js::SliceBudget (*)(JS::GCReason reason, int64_t millis); /** * Called when generating a GC slice budget. It allows the embedding to control * the duration of slices and potentially check an interrupt flag as well. For * internally triggered GCs, the given millis parameter is the JS engine's * internal scheduling decision, which the embedding can choose to ignore. * (Otherwise, it will be the value that was passed to eg * JS::IncrementalGCSlice()). */ extern JS_PUBLIC_API void SetCreateGCSliceBudgetCallback( JSContext* cx, CreateSliceBudgetCallback cb); /** * 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(JSContext* cx); /** * 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(JSContext* cx); /** * Returns true while an incremental GC is ongoing, both when actively * collecting and between slices. */ extern JS_PUBLIC_API bool IsIncrementalGCInProgress(JSContext* cx); /** * 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 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 { JSContext* cx; public: explicit AutoDisableGenerationalGC(JSContext* cx); ~AutoDisableGenerationalGC(); }; /** * Returns true if generational allocation and collection is currently enabled * on the given runtime. */ extern JS_PUBLIC_API bool IsGenerationalGCEnabled(JSRuntime* rt); /** * Enable or disable support for pretenuring allocations based on their * allocation site. */ extern JS_PUBLIC_API void SetSiteBasedPretenuringEnabled(bool enable); /** * Pass a subclass of this "abstract" class to callees to require that they * never GC. Subclasses can use assertions or the hazard analysis to ensure no * GC happens. */ class JS_PUBLIC_API AutoRequireNoGC { protected: AutoRequireNoGC() = default; ~AutoRequireNoGC() = default; }; /** * Diagnostic assert (see MOZ_DIAGNOSTIC_ASSERT) that GC cannot occur while this * class is live. This class does not disable the static rooting hazard * analysis. * * This works by entering a GC unsafe region, which is checked on allocation and * on GC. */ class JS_PUBLIC_API AutoAssertNoGC : public AutoRequireNoGC { #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED protected: JSContext* cx_; public: // This gets the context from TLS if it is not passed in. explicit AutoAssertNoGC(JSContext* cx = nullptr); ~AutoAssertNoGC(); #else public: explicit AutoAssertNoGC(JSContext* cx = nullptr) {} ~AutoAssertNoGC() {} #endif }; /** * Disable the static rooting hazard analysis in the live region and assert in * debug builds 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. */ #ifdef DEBUG class JS_PUBLIC_API AutoSuppressGCAnalysis : public AutoAssertNoGC { public: explicit AutoSuppressGCAnalysis(JSContext* cx = nullptr) : AutoAssertNoGC(cx) {} } JS_HAZ_GC_SUPPRESSED; #else class JS_PUBLIC_API AutoSuppressGCAnalysis : public AutoRequireNoGC { public: explicit AutoSuppressGCAnalysis(JSContext* cx = nullptr) {} } JS_HAZ_GC_SUPPRESSED; #endif /** * 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: #ifdef DEBUG AutoAssertGCCallback(); #else AutoAssertGCCallback() {} #endif }; /** * Place AutoCheckCannotGC in scopes that you believe can never GC. These * annotations will be verified both dynamically via AutoAssertNoGC, 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. * * We only do the assertion checking in DEBUG builds. */ #ifdef DEBUG class JS_PUBLIC_API AutoCheckCannotGC : public AutoAssertNoGC { public: explicit AutoCheckCannotGC(JSContext* cx = nullptr) : AutoAssertNoGC(cx) {} # ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED AutoCheckCannotGC(const AutoCheckCannotGC& other) : AutoCheckCannotGC(other.cx_) {} # else AutoCheckCannotGC(const AutoCheckCannotGC& other) : AutoCheckCannotGC() {} # endif #else class JS_PUBLIC_API AutoCheckCannotGC : public AutoRequireNoGC { public: explicit AutoCheckCannotGC(JSContext* cx = nullptr) {} AutoCheckCannotGC(const AutoCheckCannotGC& other) : AutoCheckCannotGC() {} #endif } JS_HAZ_GC_INVALIDATED; extern JS_PUBLIC_API void SetLowMemoryState(JSContext* cx, bool newState); /* * Internal to Firefox. */ extern JS_PUBLIC_API void NotifyGCRootsRemoved(JSContext* cx); } /* namespace JS */ typedef void (*JSGCCallback)(JSContext* cx, JSGCStatus status, JS::GCReason reason, void* data); /** * Register externally maintained GC roots. * * traceOp: the trace operation. For each root the implementation should call * JS::TraceEdge whenever the root contains a traceable thing. * data: the data argument to pass to each invocation of traceOp. */ extern JS_PUBLIC_API bool JS_AddExtraGCRootsTracer(JSContext* cx, JSTraceDataOp traceOp, void* data); /** Undo a call to JS_AddExtraGCRootsTracer. */ extern JS_PUBLIC_API void JS_RemoveExtraGCRootsTracer(JSContext* cx, JSTraceDataOp traceOp, void* data); extern JS_PUBLIC_API void JS_GC(JSContext* cx, JS::GCReason reason = JS::GCReason::API); extern JS_PUBLIC_API void JS_MaybeGC(JSContext* cx); extern JS_PUBLIC_API void JS_SetGCCallback(JSContext* cx, JSGCCallback cb, void* data); extern JS_PUBLIC_API void JS_SetObjectsTenuredCallback( JSContext* cx, JSObjectsTenuredCallback cb, void* data); extern JS_PUBLIC_API bool JS_AddFinalizeCallback(JSContext* cx, JSFinalizeCallback cb, void* data); extern JS_PUBLIC_API void JS_RemoveFinalizeCallback(JSContext* cx, JSFinalizeCallback cb); /* * Weak pointers and garbage collection * * Weak pointers are by their nature not marked as part of garbage collection, * but they may need to be updated in two cases after a GC: * * 1) Their referent was found not to be live and is about to be finalized * 2) Their referent has been moved by a compacting GC * * To handle this, any part of the system that maintain weak pointers to * JavaScript GC things must register a callback with * JS_(Add,Remove)WeakPointer{ZoneGroup,Compartment}Callback(). This callback * must then call JS_UpdateWeakPointerAfterGC() on all weak pointers it knows * about. * * Since sweeping is incremental, we have several callbacks to avoid repeatedly * having to visit all embedder structures. The WeakPointerZonesCallback is * called once for each strongly connected group of zones, whereas the * WeakPointerCompartmentCallback is called once for each compartment that is * visited while sweeping. Structures that cannot contain references in more * than one compartment should sweep the relevant per-compartment structures * using the latter callback to minimizer per-slice overhead. * * The argument to JS_UpdateWeakPointerAfterGC() is an in-out param. If the * referent is about to be finalized the pointer will be set to null. If the * referent has been moved then the pointer will be updated to point to the new * location. * * The return value of JS_UpdateWeakPointerAfterGC() indicates whether the * referent is still alive. If the referent is is about to be finalized, this * will return false. * * Callers of this method are responsible for updating any state that is * dependent on the object's address. For example, if the object's address is * used as a key in a hashtable, then the object must be removed and * re-inserted with the correct hash. */ extern JS_PUBLIC_API bool JS_AddWeakPointerZonesCallback( JSContext* cx, JSWeakPointerZonesCallback cb, void* data); extern JS_PUBLIC_API void JS_RemoveWeakPointerZonesCallback( JSContext* cx, JSWeakPointerZonesCallback cb); extern JS_PUBLIC_API bool JS_AddWeakPointerCompartmentCallback( JSContext* cx, JSWeakPointerCompartmentCallback cb, void* data); extern JS_PUBLIC_API void JS_RemoveWeakPointerCompartmentCallback( JSContext* cx, JSWeakPointerCompartmentCallback cb); namespace JS { template class Heap; } extern JS_PUBLIC_API bool JS_UpdateWeakPointerAfterGC( JSTracer* trc, JS::Heap* objp); extern JS_PUBLIC_API bool JS_UpdateWeakPointerAfterGCUnbarriered( JSTracer* trc, JSObject** objp); extern JS_PUBLIC_API void JS_SetGCParameter(JSContext* cx, JSGCParamKey key, uint32_t value); extern JS_PUBLIC_API void JS_ResetGCParameter(JSContext* cx, JSGCParamKey key); extern JS_PUBLIC_API uint32_t JS_GetGCParameter(JSContext* cx, JSGCParamKey key); extern JS_PUBLIC_API void JS_SetGCParametersBasedOnAvailableMemory( JSContext* cx, uint32_t availMemMB); /** * Create a new JSString whose chars member refers to external memory, i.e., * memory requiring application-specific finalization. */ extern JS_PUBLIC_API JSString* JS_NewExternalString( JSContext* cx, const char16_t* chars, size_t length, const JSExternalStringCallbacks* callbacks); /** * Create a new JSString whose chars member may refer to external memory. * If a new external string is allocated, |*allocatedExternal| is set to true. * Otherwise the returned string is either not an external string or an * external string allocated by a previous call and |*allocatedExternal| is set * to false. If |*allocatedExternal| is false, |fin| won't be called. */ extern JS_PUBLIC_API JSString* JS_NewMaybeExternalString( JSContext* cx, const char16_t* chars, size_t length, const JSExternalStringCallbacks* callbacks, bool* allocatedExternal); /** * Return the 'callbacks' arg passed to JS_NewExternalString or * JS_NewMaybeExternalString. */ extern JS_PUBLIC_API const JSExternalStringCallbacks* JS_GetExternalStringCallbacks(JSString* str); namespace JS { extern JS_PUBLIC_API GCReason WantEagerMinorGC(JSRuntime* rt); extern JS_PUBLIC_API GCReason WantEagerMajorGC(JSRuntime* rt); extern JS_PUBLIC_API void MaybeRunNurseryCollection(JSRuntime* rt, JS::GCReason reason); extern JS_PUBLIC_API void SetHostCleanupFinalizationRegistryCallback( JSContext* cx, JSHostCleanupFinalizationRegistryCallback cb, void* data); /** * Clear kept alive objects in JS WeakRef. * https://tc39.es/proposal-weakrefs/#sec-clear-kept-objects */ extern JS_PUBLIC_API void ClearKeptObjects(JSContext* cx); inline JS_PUBLIC_API bool NeedGrayRootsForZone(Zone* zoneArg) { shadow::Zone* zone = shadow::Zone::from(zoneArg); return zone->isGCMarkingBlackAndGray() || zone->isGCCompacting(); } extern JS_PUBLIC_API bool AtomsZoneIsCollecting(JSRuntime* runtime); extern JS_PUBLIC_API bool IsAtomsZone(Zone* zone); } // namespace JS namespace js { namespace gc { /** * Create an object providing access to the garbage collector's internal notion * of the current state of memory (both GC heap memory and GCthing-controlled * malloc memory. */ extern JS_PUBLIC_API JSObject* NewMemoryInfoObject(JSContext* cx); /* * Run the finalizer of a nursery-allocated JSObject that is known to be dead. * * This is a dangerous operation - only use this if you know what you're doing! * * This is used by the browser to implement nursery-allocated wrapper cached * wrappers. */ extern JS_PUBLIC_API void FinalizeDeadNurseryObject(JSContext* cx, JSObject* obj); } /* namespace gc */ } /* namespace js */ #ifdef JS_GC_ZEAL # define JS_DEFAULT_ZEAL_FREQ 100 extern JS_PUBLIC_API void JS_GetGCZealBits(JSContext* cx, uint32_t* zealBits, uint32_t* frequency, uint32_t* nextScheduled); extern JS_PUBLIC_API void JS_SetGCZeal(JSContext* cx, uint8_t zeal, uint32_t frequency); extern JS_PUBLIC_API void JS_UnsetGCZeal(JSContext* cx, uint8_t zeal); extern JS_PUBLIC_API void JS_ScheduleGC(JSContext* cx, uint32_t count); #endif #endif /* js_GCAPI_h */