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All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #ifndef V8_V8_PLATFORM_H_ #define V8_V8_PLATFORM_H_ #include #include #include // For abort. #include #include #include "v8config.h" // NOLINT(build/include_directory) namespace v8 { class Isolate; // Valid priorities supported by the task scheduling infrastructure. enum class TaskPriority : uint8_t { /** * Best effort tasks are not critical for performance of the application. The * platform implementation should preempt such tasks if higher priority tasks * arrive. */ kBestEffort, /** * User visible tasks are long running background tasks that will * improve performance and memory usage of the application upon completion. * Example: background compilation and garbage collection. */ kUserVisible, /** * User blocking tasks are highest priority tasks that block the execution * thread (e.g. major garbage collection). They must be finished as soon as * possible. */ kUserBlocking, }; /** * A Task represents a unit of work. */ class Task { public: virtual ~Task() = default; virtual void Run() = 0; }; /** * An IdleTask represents a unit of work to be performed in idle time. * The Run method is invoked with an argument that specifies the deadline in * seconds returned by MonotonicallyIncreasingTime(). * The idle task is expected to complete by this deadline. */ class IdleTask { public: virtual ~IdleTask() = default; virtual void Run(double deadline_in_seconds) = 0; }; /** * A TaskRunner allows scheduling of tasks. The TaskRunner may still be used to * post tasks after the isolate gets destructed, but these tasks may not get * executed anymore. All tasks posted to a given TaskRunner will be invoked in * sequence. Tasks can be posted from any thread. */ class TaskRunner { public: /** * Schedules a task to be invoked by this TaskRunner. The TaskRunner * implementation takes ownership of |task|. */ virtual void PostTask(std::unique_ptr task) = 0; /** * Schedules a task to be invoked by this TaskRunner. The TaskRunner * implementation takes ownership of |task|. The |task| cannot be nested * within other task executions. * * Tasks which shouldn't be interleaved with JS execution must be posted with * |PostNonNestableTask| or |PostNonNestableDelayedTask|. This is because the * embedder may process tasks in a callback which is called during JS * execution. * * In particular, tasks which execute JS must be non-nestable, since JS * execution is not allowed to nest. * * Requires that |TaskRunner::NonNestableTasksEnabled()| is true. */ virtual void PostNonNestableTask(std::unique_ptr task) {} /** * Schedules a task to be invoked by this TaskRunner. The task is scheduled * after the given number of seconds |delay_in_seconds|. The TaskRunner * implementation takes ownership of |task|. */ virtual void PostDelayedTask(std::unique_ptr task, double delay_in_seconds) = 0; /** * Schedules a task to be invoked by this TaskRunner. The task is scheduled * after the given number of seconds |delay_in_seconds|. The TaskRunner * implementation takes ownership of |task|. The |task| cannot be nested * within other task executions. * * Tasks which shouldn't be interleaved with JS execution must be posted with * |PostNonNestableTask| or |PostNonNestableDelayedTask|. This is because the * embedder may process tasks in a callback which is called during JS * execution. * * In particular, tasks which execute JS must be non-nestable, since JS * execution is not allowed to nest. * * Requires that |TaskRunner::NonNestableDelayedTasksEnabled()| is true. */ virtual void PostNonNestableDelayedTask(std::unique_ptr task, double delay_in_seconds) {} /** * Schedules an idle task to be invoked by this TaskRunner. The task is * scheduled when the embedder is idle. Requires that * |TaskRunner::IdleTasksEnabled()| is true. Idle tasks may be reordered * relative to other task types and may be starved for an arbitrarily long * time if no idle time is available. The TaskRunner implementation takes * ownership of |task|. */ virtual void PostIdleTask(std::unique_ptr task) = 0; /** * Returns true if idle tasks are enabled for this TaskRunner. */ virtual bool IdleTasksEnabled() = 0; /** * Returns true if non-nestable tasks are enabled for this TaskRunner. */ virtual bool NonNestableTasksEnabled() const { return false; } /** * Returns true if non-nestable delayed tasks are enabled for this TaskRunner. */ virtual bool NonNestableDelayedTasksEnabled() const { return false; } TaskRunner() = default; virtual ~TaskRunner() = default; TaskRunner(const TaskRunner&) = delete; TaskRunner& operator=(const TaskRunner&) = delete; }; /** * Delegate that's passed to Job's worker task, providing an entry point to * communicate with the scheduler. */ class JobDelegate { public: /** * Returns true if this thread should return from the worker task on the * current thread ASAP. Workers should periodically invoke ShouldYield (or * YieldIfNeeded()) as often as is reasonable. */ virtual bool ShouldYield() = 0; /** * Notifies the scheduler that max concurrency was increased, and the number * of worker should be adjusted accordingly. See Platform::PostJob() for more * details. */ virtual void NotifyConcurrencyIncrease() = 0; /** * Returns a task_id unique among threads currently running this job, such * that GetTaskId() < worker count. To achieve this, the same task_id may be * reused by a different thread after a worker_task returns. */ virtual uint8_t GetTaskId() = 0; /** * Returns true if the current task is called from the thread currently * running JobHandle::Join(). * TODO(etiennep): Make pure virtual once custom embedders implement it. */ virtual bool IsJoiningThread() const { return false; } }; /** * Handle returned when posting a Job. Provides methods to control execution of * the posted Job. */ class JobHandle { public: virtual ~JobHandle() = default; /** * Notifies the scheduler that max concurrency was increased, and the number * of worker should be adjusted accordingly. See Platform::PostJob() for more * details. */ virtual void NotifyConcurrencyIncrease() = 0; /** * Contributes to the job on this thread. Doesn't return until all tasks have * completed and max concurrency becomes 0. When Join() is called and max * concurrency reaches 0, it should not increase again. This also promotes * this Job's priority to be at least as high as the calling thread's * priority. */ virtual void Join() = 0; /** * Forces all existing workers to yield ASAP. Waits until they have all * returned from the Job's callback before returning. */ virtual void Cancel() = 0; /* * Forces all existing workers to yield ASAP but doesn’t wait for them. * Warning, this is dangerous if the Job's callback is bound to or has access * to state which may be deleted after this call. * TODO(etiennep): Cleanup once implemented by all embedders. */ virtual void CancelAndDetach() { Cancel(); } /** * Returns true if there's any work pending or any worker running. */ virtual bool IsActive() = 0; // TODO(etiennep): Clean up once all overrides are removed. V8_DEPRECATED("Use !IsActive() instead.") virtual bool IsCompleted() { return !IsActive(); } /** * Returns true if associated with a Job and other methods may be called. * Returns false after Join() or Cancel() was called. This may return true * even if no workers are running and IsCompleted() returns true */ virtual bool IsValid() = 0; // TODO(etiennep): Clean up once all overrides are removed. V8_DEPRECATED("Use IsValid() instead.") virtual bool IsRunning() { return IsValid(); } /** * Returns true if job priority can be changed. */ virtual bool UpdatePriorityEnabled() const { return false; } /** * Update this Job's priority. */ virtual void UpdatePriority(TaskPriority new_priority) {} }; /** * A JobTask represents work to run in parallel from Platform::PostJob(). */ class JobTask { public: virtual ~JobTask() = default; virtual void Run(JobDelegate* delegate) = 0; /** * Controls the maximum number of threads calling Run() concurrently, given * the number of threads currently assigned to this job and executing Run(). * Run() is only invoked if the number of threads previously running Run() was * less than the value returned. Since GetMaxConcurrency() is a leaf function, * it must not call back any JobHandle methods. */ virtual size_t GetMaxConcurrency(size_t worker_count) const = 0; // TODO(1114823): Clean up once all overrides are removed. V8_DEPRECATED("Use the version that takes |worker_count|.") virtual size_t GetMaxConcurrency() const { return 0; } }; /** * The interface represents complex arguments to trace events. */ class ConvertableToTraceFormat { public: virtual ~ConvertableToTraceFormat() = default; /** * Append the class info to the provided |out| string. The appended * data must be a valid JSON object. Strings must be properly quoted, and * escaped. There is no processing applied to the content after it is * appended. */ virtual void AppendAsTraceFormat(std::string* out) const = 0; }; /** * V8 Tracing controller. * * Can be implemented by an embedder to record trace events from V8. */ class TracingController { public: virtual ~TracingController() = default; // In Perfetto mode, trace events are written using Perfetto's Track Event // API directly without going through the embedder. However, it is still // possible to observe tracing being enabled and disabled. #if !defined(V8_USE_PERFETTO) /** * Called by TRACE_EVENT* macros, don't call this directly. * The name parameter is a category group for example: * TRACE_EVENT0("v8,parse", "V8.Parse") * The pointer returned points to a value with zero or more of the bits * defined in CategoryGroupEnabledFlags. **/ virtual const uint8_t* GetCategoryGroupEnabled(const char* name) { static uint8_t no = 0; return &no; } /** * Adds a trace event to the platform tracing system. These function calls are * usually the result of a TRACE_* macro from trace_event_common.h when * tracing and the category of the particular trace are enabled. It is not * advisable to call these functions on their own; they are really only meant * to be used by the trace macros. The returned handle can be used by * UpdateTraceEventDuration to update the duration of COMPLETE events. */ virtual uint64_t AddTraceEvent( char phase, const uint8_t* category_enabled_flag, const char* name, const char* scope, uint64_t id, uint64_t bind_id, int32_t num_args, const char** arg_names, const uint8_t* arg_types, const uint64_t* arg_values, std::unique_ptr* arg_convertables, unsigned int flags) { return 0; } virtual uint64_t AddTraceEventWithTimestamp( char phase, const uint8_t* category_enabled_flag, const char* name, const char* scope, uint64_t id, uint64_t bind_id, int32_t num_args, const char** arg_names, const uint8_t* arg_types, const uint64_t* arg_values, std::unique_ptr* arg_convertables, unsigned int flags, int64_t timestamp) { return 0; } /** * Sets the duration field of a COMPLETE trace event. It must be called with * the handle returned from AddTraceEvent(). **/ virtual void UpdateTraceEventDuration(const uint8_t* category_enabled_flag, const char* name, uint64_t handle) {} #endif // !defined(V8_USE_PERFETTO) class TraceStateObserver { public: virtual ~TraceStateObserver() = default; virtual void OnTraceEnabled() = 0; virtual void OnTraceDisabled() = 0; }; /** Adds tracing state change observer. */ virtual void AddTraceStateObserver(TraceStateObserver*) {} /** Removes tracing state change observer. */ virtual void RemoveTraceStateObserver(TraceStateObserver*) {} }; /** * A V8 memory page allocator. * * Can be implemented by an embedder to manage large host OS allocations. */ class PageAllocator { public: virtual ~PageAllocator() = default; /** * Gets the page granularity for AllocatePages and FreePages. Addresses and * lengths for those calls should be multiples of AllocatePageSize(). */ virtual size_t AllocatePageSize() = 0; /** * Gets the page granularity for SetPermissions and ReleasePages. Addresses * and lengths for those calls should be multiples of CommitPageSize(). */ virtual size_t CommitPageSize() = 0; /** * Sets the random seed so that GetRandomMmapAddr() will generate repeatable * sequences of random mmap addresses. */ virtual void SetRandomMmapSeed(int64_t seed) = 0; /** * Returns a randomized address, suitable for memory allocation under ASLR. * The address will be aligned to AllocatePageSize. */ virtual void* GetRandomMmapAddr() = 0; /** * Memory permissions. */ enum Permission { kNoAccess, kRead, kReadWrite, kReadWriteExecute, kReadExecute, // Set this when reserving memory that will later require kReadWriteExecute // permissions. The resulting behavior is platform-specific, currently // this is used to set the MAP_JIT flag on Apple Silicon. // TODO(jkummerow): Remove this when Wasm has a platform-independent // w^x implementation. kNoAccessWillJitLater }; /** * Allocates memory in range with the given alignment and permission. */ virtual void* AllocatePages(void* address, size_t length, size_t alignment, Permission permissions) = 0; /** * Frees memory in a range that was allocated by a call to AllocatePages. */ virtual bool FreePages(void* address, size_t length) = 0; /** * Releases memory in a range that was allocated by a call to AllocatePages. */ virtual bool ReleasePages(void* address, size_t length, size_t new_length) = 0; /** * Sets permissions on pages in an allocated range. */ virtual bool SetPermissions(void* address, size_t length, Permission permissions) = 0; /** * Frees memory in the given [address, address + size) range. address and size * should be operating system page-aligned. The next write to this * memory area brings the memory transparently back. */ virtual bool DiscardSystemPages(void* address, size_t size) { return true; } /** * INTERNAL ONLY: This interface has not been stabilised and may change * without notice from one release to another without being deprecated first. */ class SharedMemoryMapping { public: // Implementations are expected to free the shared memory mapping in the // destructor. virtual ~SharedMemoryMapping() = default; virtual void* GetMemory() const = 0; }; /** * INTERNAL ONLY: This interface has not been stabilised and may change * without notice from one release to another without being deprecated first. */ class SharedMemory { public: // Implementations are expected to free the shared memory in the destructor. virtual ~SharedMemory() = default; virtual std::unique_ptr RemapTo( void* new_address) const = 0; virtual void* GetMemory() const = 0; virtual size_t GetSize() const = 0; }; /** * INTERNAL ONLY: This interface has not been stabilised and may change * without notice from one release to another without being deprecated first. * * Reserve pages at a fixed address returning whether the reservation is * possible. The reserved memory is detached from the PageAllocator and so * should not be freed by it. It's intended for use with * SharedMemory::RemapTo, where ~SharedMemoryMapping would free the memory. */ virtual bool ReserveForSharedMemoryMapping(void* address, size_t size) { return false; } /** * INTERNAL ONLY: This interface has not been stabilised and may change * without notice from one release to another without being deprecated first. * * Allocates shared memory pages. Not all PageAllocators need support this and * so this method need not be overridden. * Allocates a new read-only shared memory region of size |length| and copies * the memory at |original_address| into it. */ virtual std::unique_ptr AllocateSharedPages( size_t length, const void* original_address) { return {}; } /** * INTERNAL ONLY: This interface has not been stabilised and may change * without notice from one release to another without being deprecated first. * * If not overridden and changed to return true, V8 will not attempt to call * AllocateSharedPages or RemapSharedPages. If overridden, AllocateSharedPages * and RemapSharedPages must also be overridden. */ virtual bool CanAllocateSharedPages() { return false; } }; /** * V8 Platform abstraction layer. * * The embedder has to provide an implementation of this interface before * initializing the rest of V8. */ class Platform { public: virtual ~Platform() = default; /** * Allows the embedder to manage memory page allocations. */ virtual PageAllocator* GetPageAllocator() { // TODO(bbudge) Make this abstract after all embedders implement this. return nullptr; } /** * Enables the embedder to respond in cases where V8 can't allocate large * blocks of memory. V8 retries the failed allocation once after calling this * method. On success, execution continues; otherwise V8 exits with a fatal * error. * Embedder overrides of this function must NOT call back into V8. */ virtual void OnCriticalMemoryPressure() { // TODO(bbudge) Remove this when embedders override the following method. // See crbug.com/634547. } /** * Enables the embedder to respond in cases where V8 can't allocate large * memory regions. The |length| parameter is the amount of memory needed. * Returns true if memory is now available. Returns false if no memory could * be made available. V8 will retry allocations until this method returns * false. * * Embedder overrides of this function must NOT call back into V8. */ virtual bool OnCriticalMemoryPressure(size_t length) { return false; } /** * Gets the number of worker threads used by * Call(BlockingTask)OnWorkerThread(). This can be used to estimate the number * of tasks a work package should be split into. A return value of 0 means * that there are no worker threads available. Note that a value of 0 won't * prohibit V8 from posting tasks using |CallOnWorkerThread|. */ virtual int NumberOfWorkerThreads() = 0; /** * Returns a TaskRunner which can be used to post a task on the foreground. * The TaskRunner's NonNestableTasksEnabled() must be true. This function * should only be called from a foreground thread. */ virtual std::shared_ptr GetForegroundTaskRunner( Isolate* isolate) = 0; /** * Schedules a task to be invoked on a worker thread. */ virtual void CallOnWorkerThread(std::unique_ptr task) = 0; /** * Schedules a task that blocks the main thread to be invoked with * high-priority on a worker thread. */ virtual void CallBlockingTaskOnWorkerThread(std::unique_ptr task) { // Embedders may optionally override this to process these tasks in a high // priority pool. CallOnWorkerThread(std::move(task)); } /** * Schedules a task to be invoked with low-priority on a worker thread. */ virtual void CallLowPriorityTaskOnWorkerThread(std::unique_ptr task) { // Embedders may optionally override this to process these tasks in a low // priority pool. CallOnWorkerThread(std::move(task)); } /** * Schedules a task to be invoked on a worker thread after |delay_in_seconds| * expires. */ virtual void CallDelayedOnWorkerThread(std::unique_ptr task, double delay_in_seconds) = 0; /** * Returns true if idle tasks are enabled for the given |isolate|. */ virtual bool IdleTasksEnabled(Isolate* isolate) { return false; } /** * Posts |job_task| to run in parallel. Returns a JobHandle associated with * the Job, which can be joined or canceled. * This avoids degenerate cases: * - Calling CallOnWorkerThread() for each work item, causing significant * overhead. * - Fixed number of CallOnWorkerThread() calls that split the work and might * run for a long time. This is problematic when many components post * "num cores" tasks and all expect to use all the cores. In these cases, * the scheduler lacks context to be fair to multiple same-priority requests * and/or ability to request lower priority work to yield when high priority * work comes in. * A canonical implementation of |job_task| looks like: * class MyJobTask : public JobTask { * public: * MyJobTask(...) : worker_queue_(...) {} * // JobTask: * void Run(JobDelegate* delegate) override { * while (!delegate->ShouldYield()) { * // Smallest unit of work. * auto work_item = worker_queue_.TakeWorkItem(); // Thread safe. * if (!work_item) return; * ProcessWork(work_item); * } * } * * size_t GetMaxConcurrency() const override { * return worker_queue_.GetSize(); // Thread safe. * } * }; * auto handle = PostJob(TaskPriority::kUserVisible, * std::make_unique(...)); * handle->Join(); * * PostJob() and methods of the returned JobHandle/JobDelegate, must never be * called while holding a lock that could be acquired by JobTask::Run or * JobTask::GetMaxConcurrency -- that could result in a deadlock. This is * because [1] JobTask::GetMaxConcurrency may be invoked while holding * internal lock (A), hence JobTask::GetMaxConcurrency can only use a lock (B) * if that lock is *never* held while calling back into JobHandle from any * thread (A=>B/B=>A deadlock) and [2] JobTask::Run or * JobTask::GetMaxConcurrency may be invoked synchronously from JobHandle * (B=>JobHandle::foo=>B deadlock). * * A sufficient PostJob() implementation that uses the default Job provided in * libplatform looks like: * std::unique_ptr PostJob( * TaskPriority priority, std::unique_ptr job_task) override { * return v8::platform::NewDefaultJobHandle( * this, priority, std::move(job_task), NumberOfWorkerThreads()); * } */ virtual std::unique_ptr PostJob( TaskPriority priority, std::unique_ptr job_task) = 0; /** * Monotonically increasing time in seconds from an arbitrary fixed point in * the past. This function is expected to return at least * millisecond-precision values. For this reason, * it is recommended that the fixed point be no further in the past than * the epoch. **/ virtual double MonotonicallyIncreasingTime() = 0; /** * Current wall-clock time in milliseconds since epoch. * This function is expected to return at least millisecond-precision values. */ virtual double CurrentClockTimeMillis() = 0; typedef void (*StackTracePrinter)(); /** * Returns a function pointer that print a stack trace of the current stack * on invocation. Disables printing of the stack trace if nullptr. */ virtual StackTracePrinter GetStackTracePrinter() { return nullptr; } /** * Returns an instance of a v8::TracingController. This must be non-nullptr. */ virtual TracingController* GetTracingController() = 0; /** * Tells the embedder to generate and upload a crashdump during an unexpected * but non-critical scenario. */ virtual void DumpWithoutCrashing() {} protected: /** * Default implementation of current wall-clock time in milliseconds * since epoch. Useful for implementing |CurrentClockTimeMillis| if * nothing special needed. */ V8_EXPORT static double SystemClockTimeMillis(); }; } // namespace v8 #endif // V8_V8_PLATFORM_H_