Source code

Revision control

Copy as Markdown

Other Tools

/* -*- 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 */
* Definitions for managing off-thread work using a process wide list of
* worklist items and pool of threads. Worklist items are engine internal, and
* are distinct from e.g. web workers.
#ifndef vm_HelperThreadState_h
#define vm_HelperThreadState_h
#include "mozilla/AlreadyAddRefed.h" // already_AddRefed
#include "mozilla/Assertions.h" // MOZ_ASSERT, MOZ_CRASH
#include "mozilla/Attributes.h" // MOZ_RAII
#include "mozilla/EnumeratedArray.h" // mozilla::EnumeratedArray
#include "mozilla/LinkedList.h" // mozilla::LinkedList, mozilla::LinkedListElement
#include "mozilla/MemoryReporting.h" // mozilla::MallocSizeOf
#include "mozilla/RefPtr.h" // RefPtr
#include "mozilla/TimeStamp.h" // mozilla::TimeDuration
#include <stddef.h> // size_t
#include <stdint.h> // uint32_t, uint64_t
#include <utility> // std::move
#include "ds/Fifo.h" // Fifo
#include "frontend/CompilationStencil.h" // frontend::CompilationStencil
#include "gc/GCRuntime.h" // gc::GCRuntime
#include "js/AllocPolicy.h" // SystemAllocPolicy
#include "js/CompileOptions.h" // JS::ReadOnlyCompileOptions
#include "js/experimental/CompileScript.h" // JS::CompilationStorage
#include "js/experimental/JSStencil.h" // JS::InstantiationStorage
#include "js/HelperThreadAPI.h" // JS::HelperThreadTaskCallback, JS::DispatchReason
#include "js/MemoryMetrics.h" // JS::GlobalStats
#include "js/ProfilingStack.h" // JS::RegisterThreadCallback, JS::UnregisterThreadCallback
#include "js/RootingAPI.h" // JS::Handle
#include "js/UniquePtr.h" // UniquePtr
#include "js/Utility.h" // ThreadType
#include "threading/ConditionVariable.h" // ConditionVariable
#include "threading/ProtectedData.h" // WriteOnceData
#include "vm/ConcurrentDelazification.h" // DelazificationContext
#include "vm/HelperThreads.h" // AutoLockHelperThreadState, AutoUnlockHelperThreadState
#include "vm/HelperThreadTask.h" // HelperThreadTask
#include "vm/JSContext.h" // JSContext
#include "vm/JSScript.h" // ScriptSource
#include "vm/Runtime.h" // JSRuntime
#include "vm/SharedImmutableStringsCache.h" // SharedImmutableString
#include "wasm/WasmConstants.h" // wasm::CompileMode
class JSTracer;
namespace js {
struct DelazifyTask;
struct FreeDelazifyTask;
struct PromiseHelperTask;
class PromiseObject;
namespace jit {
class IonCompileTask;
class IonFreeTask;
} // namespace jit
namespace wasm {
struct CompileTask;
typedef Fifo<CompileTask*, 0, SystemAllocPolicy> CompileTaskPtrFifo;
struct Tier2GeneratorTask : public HelperThreadTask {
virtual ~Tier2GeneratorTask() = default;
virtual void cancel() = 0;
using UniqueTier2GeneratorTask = UniquePtr<Tier2GeneratorTask>;
typedef Vector<Tier2GeneratorTask*, 0, SystemAllocPolicy>
} // namespace wasm
// Per-process state for off thread work items.
class GlobalHelperThreadState {
friend class AutoLockHelperThreadState;
friend class AutoUnlockHelperThreadState;
// A single tier-2 ModuleGenerator job spawns many compilation jobs, and we
// do not want to allow more than one such ModuleGenerator to run at a time.
static const size_t MaxTier2GeneratorTasks = 1;
// Number of CPUs to treat this machine as having when creating threads.
// May be accessed without locking.
size_t cpuCount;
// Number of threads to create. May be accessed without locking.
size_t threadCount;
// Thread stack quota to use when running tasks.
size_t stackQuota;
bool terminating_ = false;
typedef Vector<jit::IonCompileTask*, 0, SystemAllocPolicy>
using IonFreeTaskVector =
Vector<js::UniquePtr<jit::IonFreeTask>, 0, SystemAllocPolicy>;
using DelazifyTaskList = mozilla::LinkedList<DelazifyTask>;
using FreeDelazifyTaskVector =
Vector<js::UniquePtr<FreeDelazifyTask>, 1, SystemAllocPolicy>;
typedef Vector<UniquePtr<SourceCompressionTask>, 0, SystemAllocPolicy>
typedef Vector<PromiseHelperTask*, 0, SystemAllocPolicy>
// Count of running task by each threadType.
mozilla::EnumeratedArray<ThreadType, ThreadType::THREAD_TYPE_MAX, size_t>
size_t totalCountRunningTasks;
WriteOnceData<JS::RegisterThreadCallback> registerThread;
WriteOnceData<JS::UnregisterThreadCallback> unregisterThread;
// Count of helper threads 'reserved' for parallel marking. This is used to
// prevent too many runtimes trying to mark in parallel at once. Does not stop
// threads from being used for other kinds of task, including GC tasks.
HelperThreadLockData<size_t> gcParallelMarkingThreads;
// The lists below are all protected by |lock|.
// Ion compilation worklist and finished jobs.
IonCompileTaskVector ionWorklist_, ionFinishedList_;
IonFreeTaskVector ionFreeList_;
// wasm worklists.
wasm::CompileTaskPtrFifo wasmWorklist_tier1_;
wasm::CompileTaskPtrFifo wasmWorklist_tier2_;
wasm::Tier2GeneratorTaskPtrVector wasmTier2GeneratorWorklist_;
// Count of finished Tier2Generator tasks.
uint32_t wasmTier2GeneratorsFinished_;
// Async tasks that, upon completion, are dispatched back to the JSContext's
// owner thread via embedding callbacks instead of a finished list.
PromiseHelperTaskVector promiseHelperTasks_;
// Script worklist, which might still have function to delazify.
DelazifyTaskList delazifyWorklist_;
// Ideally an instance should not have a method to free it-self as, the method
// has a this pointer, which aliases the deleted instance, and that the method
// might have some of its fields aliased on the stack.
// Delazification task are complex and have a lot of fields. To reduce the
// risk of having aliased fields on the stack while deleting instances of a
// DelazifyTask, we have FreeDelazifyTask. While FreeDelazifyTask suffer from
// the same problem, the limited scope of their actions should mitigate the
// risk.
FreeDelazifyTaskVector freeDelazifyTaskVector_;
// Source compression worklist of tasks that we do not yet know can start.
SourceCompressionTaskVector compressionPendingList_;
// Source compression worklist of tasks that can start.
SourceCompressionTaskVector compressionWorklist_;
// Finished source compression tasks.
SourceCompressionTaskVector compressionFinishedList_;
// GC tasks needing to be done in parallel. These are first queued in the
// GCRuntime before being dispatched to the helper thread system.
GCParallelTaskList gcParallelWorklist_;
using HelperThreadTaskVector =
Vector<HelperThreadTask*, 0, SystemAllocPolicy>;
// Vector of running HelperThreadTask.
// This is used to get the HelperThreadTask that are currently running.
HelperThreadTaskVector helperTasks_;
// Callback to dispatch a task to a thread pool. Set by
// JS::SetHelperThreadTaskCallback. If this is not set the internal thread
// pool is used.
JS::HelperThreadTaskCallback dispatchTaskCallback = nullptr;
// The number of tasks dispatched to the thread pool that have not started
// running yet.
size_t tasksPending_ = 0;
bool isInitialized_ = false;
bool useInternalThreadPool_ = true;
void addSizeOfIncludingThis(JS::GlobalStats* stats,
const AutoLockHelperThreadState& lock) const;
size_t maxIonCompilationThreads() const;
size_t maxIonFreeThreads() const;
size_t maxWasmCompilationThreads() const;
size_t maxWasmTier2GeneratorThreads() const;
size_t maxPromiseHelperThreads() const;
size_t maxDelazifyThreads() const;
size_t maxCompressionThreads() const;
size_t maxGCParallelThreads() const;
bool isInitialized(const AutoLockHelperThreadState& lock) const {
return isInitialized_;
[[nodiscard]] bool ensureInitialized();
[[nodiscard]] bool ensureThreadCount(size_t count,
AutoLockHelperThreadState& lock);
void finish(AutoLockHelperThreadState& lock);
void finishThreads(AutoLockHelperThreadState& lock);
void setCpuCount(size_t count);
void setDispatchTaskCallback(JS::HelperThreadTaskCallback callback,
size_t threadCount, size_t stackSize,
const AutoLockHelperThreadState& lock);
void destroyHelperContexts(AutoLockHelperThreadState& lock);
#ifdef DEBUG
void assertIsLockedByCurrentThread() const;
void wait(AutoLockHelperThreadState& locked,
mozilla::TimeDuration timeout = mozilla::TimeDuration::Forever());
void notifyAll(const AutoLockHelperThreadState&);
bool useInternalThreadPool(const AutoLockHelperThreadState& lock) const {
return useInternalThreadPool_;
bool isTerminating(const AutoLockHelperThreadState& locked) const {
return terminating_;
void notifyOne(const AutoLockHelperThreadState&);
// Helper method for removing items from the vectors below while iterating
// over them.
template <typename T>
void remove(T& vector, size_t* index) {
// Self-moving is undefined behavior.
if (*index != vector.length() - 1) {
vector[*index] = std::move(vector.back());
IonCompileTaskVector& ionWorklist(const AutoLockHelperThreadState&) {
return ionWorklist_;
IonCompileTaskVector& ionFinishedList(const AutoLockHelperThreadState&) {
return ionFinishedList_;
IonFreeTaskVector& ionFreeList(const AutoLockHelperThreadState&) {
return ionFreeList_;
wasm::CompileTaskPtrFifo& wasmWorklist(const AutoLockHelperThreadState&,
wasm::CompileMode m) {
switch (m) {
case wasm::CompileMode::Once:
case wasm::CompileMode::Tier1:
return wasmWorklist_tier1_;
case wasm::CompileMode::Tier2:
return wasmWorklist_tier2_;
wasm::Tier2GeneratorTaskPtrVector& wasmTier2GeneratorWorklist(
const AutoLockHelperThreadState&) {
return wasmTier2GeneratorWorklist_;
void incWasmTier2GeneratorsFinished(const AutoLockHelperThreadState&) {
uint32_t wasmTier2GeneratorsFinished(const AutoLockHelperThreadState&) const {
return wasmTier2GeneratorsFinished_;
PromiseHelperTaskVector& promiseHelperTasks(
const AutoLockHelperThreadState&) {
return promiseHelperTasks_;
DelazifyTaskList& delazifyWorklist(const AutoLockHelperThreadState&) {
return delazifyWorklist_;
FreeDelazifyTaskVector& freeDelazifyTaskVector(
const AutoLockHelperThreadState&) {
return freeDelazifyTaskVector_;
SourceCompressionTaskVector& compressionPendingList(
const AutoLockHelperThreadState&) {
return compressionPendingList_;
SourceCompressionTaskVector& compressionWorklist(
const AutoLockHelperThreadState&) {
return compressionWorklist_;
SourceCompressionTaskVector& compressionFinishedList(
const AutoLockHelperThreadState&) {
return compressionFinishedList_;
GCParallelTaskList& gcParallelWorklist() { return gcParallelWorklist_; }
HelperThreadTaskVector& helperTasks(const AutoLockHelperThreadState&) {
return helperTasks_;
bool canStartWasmCompile(const AutoLockHelperThreadState& lock,
wasm::CompileMode mode);
bool canStartWasmTier1CompileTask(const AutoLockHelperThreadState& lock);
bool canStartWasmTier2CompileTask(const AutoLockHelperThreadState& lock);
bool canStartWasmTier2GeneratorTask(const AutoLockHelperThreadState& lock);
bool canStartPromiseHelperTask(const AutoLockHelperThreadState& lock);
bool canStartIonCompileTask(const AutoLockHelperThreadState& lock);
bool canStartIonFreeTask(const AutoLockHelperThreadState& lock);
bool canStartFreeDelazifyTask(const AutoLockHelperThreadState& lock);
bool canStartDelazifyTask(const AutoLockHelperThreadState& lock);
bool canStartCompressionTask(const AutoLockHelperThreadState& lock);
bool canStartGCParallelTask(const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetWasmCompile(const AutoLockHelperThreadState& lock,
wasm::CompileMode mode);
HelperThreadTask* maybeGetWasmTier1CompileTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetWasmTier2CompileTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetWasmTier2GeneratorTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetPromiseHelperTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetIonCompileTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetLowPrioIonCompileTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetIonFreeTask(const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetFreeDelazifyTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetDelazifyTask(const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetCompressionTask(
const AutoLockHelperThreadState& lock);
HelperThreadTask* maybeGetGCParallelTask(
const AutoLockHelperThreadState& lock);
enum class ScheduleCompressionTask { GC, API };
// Used by a major GC to signal processing enqueued compression tasks.
void startHandlingCompressionTasks(ScheduleCompressionTask schedule,
JSRuntime* maybeRuntime,
const AutoLockHelperThreadState& lock);
jit::IonCompileTask* highestPriorityPendingIonCompile(
const AutoLockHelperThreadState& lock, bool checkExecutionStatus);
void trace(JSTracer* trc);
bool hasActiveThreads(const AutoLockHelperThreadState&);
bool canStartTasks(const AutoLockHelperThreadState& locked);
void waitForAllTasks();
void waitForAllTasksLocked(AutoLockHelperThreadState&);
bool checkTaskThreadLimit(ThreadType threadType, size_t maxThreads,
bool isMaster,
const AutoLockHelperThreadState& lock) const;
bool checkTaskThreadLimit(ThreadType threadType, size_t maxThreads,
const AutoLockHelperThreadState& lock) const {
return checkTaskThreadLimit(threadType, maxThreads, /* isMaster */ false,
void triggerFreeUnusedMemory();
// Condition variable for notifiying the main thread that a helper task has
// completed some work.
js::ConditionVariable consumerWakeup;
void dispatch(JS::DispatchReason reason,
const AutoLockHelperThreadState& locked);
void runTask(HelperThreadTask* task, AutoLockHelperThreadState& lock);
bool submitTask(wasm::UniqueTier2GeneratorTask task);
bool submitTask(wasm::CompileTask* task, wasm::CompileMode mode);
bool submitTask(UniquePtr<jit::IonFreeTask>&& task,
const AutoLockHelperThreadState& lock);
bool submitTask(jit::IonCompileTask* task,
const AutoLockHelperThreadState& locked);
bool submitTask(UniquePtr<SourceCompressionTask> task,
const AutoLockHelperThreadState& locked);
void submitTask(DelazifyTask* task, const AutoLockHelperThreadState& locked);
bool submitTask(UniquePtr<FreeDelazifyTask> task,
const AutoLockHelperThreadState& locked);
bool submitTask(PromiseHelperTask* task);
bool submitTask(GCParallelTask* task,
const AutoLockHelperThreadState& locked);
void runOneTask(AutoLockHelperThreadState& lock);
void runTaskLocked(HelperThreadTask* task, AutoLockHelperThreadState& lock);
using Selector = HelperThreadTask* (
GlobalHelperThreadState::*)(const AutoLockHelperThreadState&);
static const Selector selectors[];
HelperThreadTask* findHighestPriorityTask(
const AutoLockHelperThreadState& locked);
static inline bool IsHelperThreadStateInitialized() {
extern GlobalHelperThreadState* gHelperThreadState;
return gHelperThreadState;
static inline GlobalHelperThreadState& HelperThreadState() {
extern GlobalHelperThreadState* gHelperThreadState;
return *gHelperThreadState;
// Eagerly delazify functions, and send the result back to the runtime which
// requested the stencil to be parsed, by filling the stencil cache.
// This task is scheduled multiple times, each time it is scheduled, it
// delazifies a single function. Once the function is delazified, it schedules
// the inner functions of the delazified function for delazification using the
// DelazifyStrategy. The DelazifyStrategy is responsible for ordering and
// filtering functions to be delazified.
// When no more function have to be delazified, a FreeDelazifyTask is scheduled
// to remove the memory held by the DelazifyTask.
struct DelazifyTask : public mozilla::LinkedListElement<DelazifyTask>,
public HelperThreadTask {
// HelperThreads are shared between all runtimes in the process so explicitly
// track which one we are associated with.
JSRuntime* maybeRuntime = nullptr;
DelazificationContext delazificationCx;
// Create a new DelazifyTask and initialize it.
// In case of early failure, no errors are reported, as a DelazifyTask is an
// optimization and the VM should remain working even without this
// optimization in place.
static UniquePtr<DelazifyTask> Create(
JSRuntime* maybeRuntime, const JS::ReadOnlyCompileOptions& options,
const frontend::CompilationStencil& stencil);
DelazifyTask(JSRuntime* maybeRuntime,
const JS::PrefableCompileOptions& initialPrefableOptions);
[[nodiscard]] bool init(const JS::ReadOnlyCompileOptions& options,
const frontend::CompilationStencil& stencil);
bool runtimeMatchesOrNoRuntime(JSRuntime* rt) {
return !maybeRuntime || maybeRuntime == rt;
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf);
void runHelperThreadTask(AutoLockHelperThreadState& locked) override;
[[nodiscard]] bool runTask();
ThreadType threadType() override { return ThreadType::THREAD_TYPE_DELAZIFY; }
bool done() const;
// The FreeDelazifyTask exists as this is a bad practice to `js_delete(this)`,
// as fields might be aliased across the destructor, such as with RAII guards.
// The FreeDelazifyTask limits the risk of adding these kind of issues by
// limiting the number of fields to the DelazifyTask pointer, before deleting
// it-self.
struct FreeDelazifyTask : public HelperThreadTask {
DelazifyTask* task;
explicit FreeDelazifyTask(DelazifyTask* t) : task(t) {}
void runHelperThreadTask(AutoLockHelperThreadState& locked) override;
ThreadType threadType() override {
// It is not desirable to eagerly compress: if lazy functions that are tied to
// the ScriptSource were to be executed relatively soon after parsing, they
// would need to block on decompression, which hurts responsiveness.
// To this end, compression tasks are heap allocated and enqueued in a pending
// list by ScriptSource::setSourceCopy. When a major GC occurs, we schedule
// pending compression tasks and move the ones that are ready to be compressed
// to the worklist. Currently, a compression task is considered ready 2 major
// GCs after being enqueued. Completed tasks are handled during the sweeping
// phase by AttachCompressedSourcesTask, which runs in parallel with other GC
// sweeping tasks.
class SourceCompressionTask : public HelperThreadTask {
friend class HelperThread;
friend class ScriptSource;
// The runtime that the ScriptSource is associated with, in the sense that
// it uses the runtime's immutable string cache.
JSRuntime* runtime_;
// The major GC number of the runtime when the task was enqueued.
uint64_t majorGCNumber_;
// The source to be compressed.
RefPtr<ScriptSource> source_;
// The resultant compressed string. If the compressed string is larger
// than the original, or we OOM'd during compression, or nothing else
// except the task is holding the ScriptSource alive when scheduled to
// compress, this will remain None upon completion.
SharedImmutableString resultString_;
// The majorGCNumber is used for scheduling tasks.
SourceCompressionTask(JSRuntime* rt, ScriptSource* source)
: runtime_(rt), majorGCNumber_(rt->gc.majorGCCount()), source_(source) {
virtual ~SourceCompressionTask() = default;
bool runtimeMatches(JSRuntime* runtime) const { return runtime == runtime_; }
bool shouldStart() const {
// We wait 2 major GCs to start compressing, in order to avoid
// immediate compression.
return runtime_->gc.majorGCCount() > majorGCNumber_ + 1;
bool shouldCancel() const {
// If the refcount is exactly 1, then nothing else is holding on to the
// ScriptSource, so no reason to compress it and we should cancel the task.
return source_->refs == 1;
void runTask();
void runHelperThreadTask(AutoLockHelperThreadState& locked) override;
void complete();
ThreadType threadType() override { return ThreadType::THREAD_TYPE_COMPRESS; }
struct PerformTaskWork;
friend struct PerformTaskWork;
// The work algorithm, aware whether it's compressing one-byte UTF-8 source
// text or UTF-16, for CharT either Utf8Unit or char16_t. Invoked by
// work() after doing a type-test of the ScriptSource*.
template <typename CharT>
void workEncodingSpecific();
// A PromiseHelperTask is an OffThreadPromiseTask that executes a single job on
// a helper thread. Call js::StartOffThreadPromiseHelperTask to submit a
// PromiseHelperTask for execution.
// Concrete subclasses must implement execute and OffThreadPromiseTask::resolve.
// The helper thread will call execute() to do the main work. Then, the thread
// of the JSContext used to create the PromiseHelperTask will call resolve() to
// resolve promise according to those results.
struct PromiseHelperTask : OffThreadPromiseTask, public HelperThreadTask {
PromiseHelperTask(JSContext* cx, JS::Handle<PromiseObject*> promise)
: OffThreadPromiseTask(cx, promise) {}
// To be called on a helper thread and implemented by the derived class.
virtual void execute() = 0;
// May be called in the absence of helper threads or off-thread promise
// support to synchronously execute and resolve a PromiseTask.
// Warning: After this function returns, 'this' can be deleted at any time, so
// the caller must immediately return from the stream callback.
void executeAndResolveAndDestroy(JSContext* cx);
void runHelperThreadTask(AutoLockHelperThreadState& locked) override;
ThreadType threadType() override { return THREAD_TYPE_PROMISE_TASK; }
} /* namespace js */
#endif /* vm_HelperThreadState_h */