1133 lines
40 KiB
C++
1133 lines
40 KiB
C++
// Copyright 2013 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef V8_V8_PLATFORM_H_
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#define V8_V8_PLATFORM_H_
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#include <stddef.h>
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#include <stdint.h>
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#include <stdlib.h> // For abort.
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#include <memory>
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#include <string>
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#include "v8config.h" // NOLINT(build/include_directory)
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namespace v8 {
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class Isolate;
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// Valid priorities supported by the task scheduling infrastructure.
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enum class TaskPriority : uint8_t {
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/**
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* Best effort tasks are not critical for performance of the application. The
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* platform implementation should preempt such tasks if higher priority tasks
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* arrive.
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*/
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kBestEffort,
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/**
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* User visible tasks are long running background tasks that will
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* improve performance and memory usage of the application upon completion.
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* Example: background compilation and garbage collection.
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*/
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kUserVisible,
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/**
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* User blocking tasks are highest priority tasks that block the execution
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* thread (e.g. major garbage collection). They must be finished as soon as
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* possible.
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*/
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kUserBlocking,
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};
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/**
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* A Task represents a unit of work.
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*/
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class Task {
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public:
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virtual ~Task() = default;
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virtual void Run() = 0;
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};
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/**
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* An IdleTask represents a unit of work to be performed in idle time.
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* The Run method is invoked with an argument that specifies the deadline in
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* seconds returned by MonotonicallyIncreasingTime().
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* The idle task is expected to complete by this deadline.
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*/
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class IdleTask {
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public:
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virtual ~IdleTask() = default;
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virtual void Run(double deadline_in_seconds) = 0;
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};
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/**
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* A TaskRunner allows scheduling of tasks. The TaskRunner may still be used to
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* post tasks after the isolate gets destructed, but these tasks may not get
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* executed anymore. All tasks posted to a given TaskRunner will be invoked in
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* sequence. Tasks can be posted from any thread.
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*/
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class TaskRunner {
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public:
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/**
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* Schedules a task to be invoked by this TaskRunner. The TaskRunner
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* implementation takes ownership of |task|.
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*/
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virtual void PostTask(std::unique_ptr<Task> task) = 0;
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/**
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* Schedules a task to be invoked by this TaskRunner. The TaskRunner
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* implementation takes ownership of |task|. The |task| cannot be nested
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* within other task executions.
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*
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* Tasks which shouldn't be interleaved with JS execution must be posted with
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* |PostNonNestableTask| or |PostNonNestableDelayedTask|. This is because the
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* embedder may process tasks in a callback which is called during JS
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* execution.
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*
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* In particular, tasks which execute JS must be non-nestable, since JS
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* execution is not allowed to nest.
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*
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* Requires that |TaskRunner::NonNestableTasksEnabled()| is true.
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*/
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virtual void PostNonNestableTask(std::unique_ptr<Task> task) {}
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/**
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* Schedules a task to be invoked by this TaskRunner. The task is scheduled
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* after the given number of seconds |delay_in_seconds|. The TaskRunner
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* implementation takes ownership of |task|.
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*/
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virtual void PostDelayedTask(std::unique_ptr<Task> task,
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double delay_in_seconds) = 0;
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/**
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* Schedules a task to be invoked by this TaskRunner. The task is scheduled
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* after the given number of seconds |delay_in_seconds|. The TaskRunner
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* implementation takes ownership of |task|. The |task| cannot be nested
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* within other task executions.
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*
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* Tasks which shouldn't be interleaved with JS execution must be posted with
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* |PostNonNestableTask| or |PostNonNestableDelayedTask|. This is because the
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* embedder may process tasks in a callback which is called during JS
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* execution.
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*
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* In particular, tasks which execute JS must be non-nestable, since JS
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* execution is not allowed to nest.
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*
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* Requires that |TaskRunner::NonNestableDelayedTasksEnabled()| is true.
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*/
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virtual void PostNonNestableDelayedTask(std::unique_ptr<Task> task,
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double delay_in_seconds) {}
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/**
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* Schedules an idle task to be invoked by this TaskRunner. The task is
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* scheduled when the embedder is idle. Requires that
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* |TaskRunner::IdleTasksEnabled()| is true. Idle tasks may be reordered
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* relative to other task types and may be starved for an arbitrarily long
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* time if no idle time is available. The TaskRunner implementation takes
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* ownership of |task|.
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*/
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virtual void PostIdleTask(std::unique_ptr<IdleTask> task) = 0;
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/**
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* Returns true if idle tasks are enabled for this TaskRunner.
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*/
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virtual bool IdleTasksEnabled() = 0;
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/**
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* Returns true if non-nestable tasks are enabled for this TaskRunner.
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*/
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virtual bool NonNestableTasksEnabled() const { return false; }
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/**
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* Returns true if non-nestable delayed tasks are enabled for this TaskRunner.
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*/
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virtual bool NonNestableDelayedTasksEnabled() const { return false; }
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TaskRunner() = default;
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virtual ~TaskRunner() = default;
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TaskRunner(const TaskRunner&) = delete;
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TaskRunner& operator=(const TaskRunner&) = delete;
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virtual void PostSignalTask(std::unique_ptr<Task> task) = 0;
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};
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/**
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* Delegate that's passed to Job's worker task, providing an entry point to
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* communicate with the scheduler.
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*/
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class JobDelegate {
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public:
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/**
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* Returns true if this thread *must* return from the worker task on the
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* current thread ASAP. Workers should periodically invoke ShouldYield (or
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* YieldIfNeeded()) as often as is reasonable.
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* After this method returned true, ShouldYield must not be called again.
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*/
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virtual bool ShouldYield() = 0;
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/**
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* Notifies the scheduler that max concurrency was increased, and the number
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* of worker should be adjusted accordingly. See Platform::PostJob() for more
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* details.
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*/
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virtual void NotifyConcurrencyIncrease() = 0;
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/**
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* Returns a task_id unique among threads currently running this job, such
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* that GetTaskId() < worker count. To achieve this, the same task_id may be
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* reused by a different thread after a worker_task returns.
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*/
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virtual uint8_t GetTaskId() = 0;
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/**
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* Returns true if the current task is called from the thread currently
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* running JobHandle::Join().
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*/
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virtual bool IsJoiningThread() const = 0;
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};
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/**
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* Handle returned when posting a Job. Provides methods to control execution of
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* the posted Job.
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*/
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class JobHandle {
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public:
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virtual ~JobHandle() = default;
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/**
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* Notifies the scheduler that max concurrency was increased, and the number
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* of worker should be adjusted accordingly. See Platform::PostJob() for more
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* details.
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*/
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virtual void NotifyConcurrencyIncrease() = 0;
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/**
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* Contributes to the job on this thread. Doesn't return until all tasks have
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* completed and max concurrency becomes 0. When Join() is called and max
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* concurrency reaches 0, it should not increase again. This also promotes
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* this Job's priority to be at least as high as the calling thread's
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* priority.
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*/
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virtual void Join() = 0;
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/**
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* Forces all existing workers to yield ASAP. Waits until they have all
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* returned from the Job's callback before returning.
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*/
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virtual void Cancel() = 0;
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/*
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* Forces all existing workers to yield ASAP but doesn’t wait for them.
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* Warning, this is dangerous if the Job's callback is bound to or has access
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* to state which may be deleted after this call.
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*/
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virtual void CancelAndDetach() = 0;
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/**
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* Returns true if there's any work pending or any worker running.
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*/
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virtual bool IsActive() = 0;
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/**
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* Returns true if associated with a Job and other methods may be called.
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* Returns false after Join() or Cancel() was called. This may return true
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* even if no workers are running and IsCompleted() returns true
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*/
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virtual bool IsValid() = 0;
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/**
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* Returns true if job priority can be changed.
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*/
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virtual bool UpdatePriorityEnabled() const { return false; }
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/**
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* Update this Job's priority.
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*/
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virtual void UpdatePriority(TaskPriority new_priority) {}
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};
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/**
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* A JobTask represents work to run in parallel from Platform::PostJob().
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*/
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class JobTask {
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public:
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virtual ~JobTask() = default;
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virtual void Run(JobDelegate* delegate) = 0;
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/**
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* Controls the maximum number of threads calling Run() concurrently, given
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* the number of threads currently assigned to this job and executing Run().
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* Run() is only invoked if the number of threads previously running Run() was
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* less than the value returned. Since GetMaxConcurrency() is a leaf function,
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* it must not call back any JobHandle methods.
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*/
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virtual size_t GetMaxConcurrency(size_t worker_count) const = 0;
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};
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/**
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* The interface represents complex arguments to trace events.
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*/
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class ConvertableToTraceFormat {
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public:
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virtual ~ConvertableToTraceFormat() = default;
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/**
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* Append the class info to the provided |out| string. The appended
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* data must be a valid JSON object. Strings must be properly quoted, and
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* escaped. There is no processing applied to the content after it is
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* appended.
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*/
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virtual void AppendAsTraceFormat(std::string* out) const = 0;
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};
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/**
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* V8 Tracing controller.
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*
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* Can be implemented by an embedder to record trace events from V8.
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*
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* Will become obsolete in Perfetto SDK build (v8_use_perfetto = true).
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*/
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class TracingController {
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public:
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virtual ~TracingController() = default;
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// In Perfetto mode, trace events are written using Perfetto's Track Event
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// API directly without going through the embedder. However, it is still
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// possible to observe tracing being enabled and disabled.
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#if !defined(V8_USE_PERFETTO)
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/**
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* Called by TRACE_EVENT* macros, don't call this directly.
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* The name parameter is a category group for example:
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* TRACE_EVENT0("v8,parse", "V8.Parse")
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* The pointer returned points to a value with zero or more of the bits
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* defined in CategoryGroupEnabledFlags.
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**/
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virtual const uint8_t* GetCategoryGroupEnabled(const char* name) {
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static uint8_t no = 0;
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return &no;
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}
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/**
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* Adds a trace event to the platform tracing system. These function calls are
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* usually the result of a TRACE_* macro from trace_event_common.h when
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* tracing and the category of the particular trace are enabled. It is not
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* advisable to call these functions on their own; they are really only meant
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* to be used by the trace macros. The returned handle can be used by
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* UpdateTraceEventDuration to update the duration of COMPLETE events.
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*/
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virtual uint64_t AddTraceEvent(
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char phase, const uint8_t* category_enabled_flag, const char* name,
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const char* scope, uint64_t id, uint64_t bind_id, int32_t num_args,
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const char** arg_names, const uint8_t* arg_types,
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const uint64_t* arg_values,
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std::unique_ptr<ConvertableToTraceFormat>* arg_convertables,
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unsigned int flags) {
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return 0;
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}
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virtual uint64_t AddTraceEventWithTimestamp(
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char phase, const uint8_t* category_enabled_flag, const char* name,
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const char* scope, uint64_t id, uint64_t bind_id, int32_t num_args,
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const char** arg_names, const uint8_t* arg_types,
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const uint64_t* arg_values,
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std::unique_ptr<ConvertableToTraceFormat>* arg_convertables,
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unsigned int flags, int64_t timestamp) {
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return 0;
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}
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/**
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* Sets the duration field of a COMPLETE trace event. It must be called with
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* the handle returned from AddTraceEvent().
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**/
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virtual void UpdateTraceEventDuration(const uint8_t* category_enabled_flag,
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const char* name, uint64_t handle) {}
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#endif // !defined(V8_USE_PERFETTO)
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class TraceStateObserver {
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public:
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virtual ~TraceStateObserver() = default;
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virtual void OnTraceEnabled() = 0;
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virtual void OnTraceDisabled() = 0;
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};
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/**
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* Adds tracing state change observer.
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* Does nothing in Perfetto SDK build (v8_use_perfetto = true).
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*/
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virtual void AddTraceStateObserver(TraceStateObserver*) {}
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/**
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* Removes tracing state change observer.
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* Does nothing in Perfetto SDK build (v8_use_perfetto = true).
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*/
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virtual void RemoveTraceStateObserver(TraceStateObserver*) {}
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};
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/**
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* A V8 memory page allocator.
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*
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* Can be implemented by an embedder to manage large host OS allocations.
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*/
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class PageAllocator {
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public:
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virtual ~PageAllocator() = default;
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/**
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* Gets the page granularity for AllocatePages and FreePages. Addresses and
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* lengths for those calls should be multiples of AllocatePageSize().
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*/
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virtual size_t AllocatePageSize() = 0;
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/**
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* Gets the page granularity for SetPermissions and ReleasePages. Addresses
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* and lengths for those calls should be multiples of CommitPageSize().
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*/
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virtual size_t CommitPageSize() = 0;
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/**
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* Sets the random seed so that GetRandomMmapAddr() will generate repeatable
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* sequences of random mmap addresses.
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*/
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virtual void SetRandomMmapSeed(int64_t seed) = 0;
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/**
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* Returns a randomized address, suitable for memory allocation under ASLR.
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* The address will be aligned to AllocatePageSize.
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*/
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virtual void* GetRandomMmapAddr() = 0;
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/**
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* Memory permissions.
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*/
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enum Permission {
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kNoAccess,
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kRead,
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kReadWrite,
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kReadWriteExecute,
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kReadExecute,
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// Set this when reserving memory that will later require kReadWriteExecute
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// permissions. The resulting behavior is platform-specific, currently
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// this is used to set the MAP_JIT flag on Apple Silicon.
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// TODO(jkummerow): Remove this when Wasm has a platform-independent
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// w^x implementation.
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// TODO(saelo): Remove this once all JIT pages are allocated through the
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// VirtualAddressSpace API.
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kNoAccessWillJitLater
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};
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/**
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* Allocates memory in range with the given alignment and permission.
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*/
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virtual void* AllocatePages(void* address, size_t length, size_t alignment,
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Permission permissions) = 0;
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/**
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* Frees memory in a range that was allocated by a call to AllocatePages.
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*/
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virtual bool FreePages(void* address, size_t length) = 0;
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/**
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* Releases memory in a range that was allocated by a call to AllocatePages.
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*/
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virtual bool ReleasePages(void* address, size_t length,
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size_t new_length) = 0;
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/**
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* Sets permissions on pages in an allocated range.
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*/
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virtual bool SetPermissions(void* address, size_t length,
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Permission permissions) = 0;
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/**
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* Recommits discarded pages in the given range with given permissions.
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* Discarded pages must be recommitted with their original permissions
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* before they are used again.
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*/
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virtual bool RecommitPages(void* address, size_t length,
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Permission permissions) {
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// TODO(v8:12797): make it pure once it's implemented on Chromium side.
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return false;
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}
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/**
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* Frees memory in the given [address, address + size) range. address and size
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* should be operating system page-aligned. The next write to this
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* memory area brings the memory transparently back. This should be treated as
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* a hint to the OS that the pages are no longer needed. It does not guarantee
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* that the pages will be discarded immediately or at all.
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*/
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virtual bool DiscardSystemPages(void* address, size_t size) { return true; }
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|
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/**
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* Decommits any wired memory pages in the given range, allowing the OS to
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* reclaim them, and marks the region as inacessible (kNoAccess). The address
|
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* range stays reserved and can be accessed again later by changing its
|
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* permissions. However, in that case the memory content is guaranteed to be
|
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* zero-initialized again. The memory must have been previously allocated by a
|
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* call to AllocatePages. Returns true on success, false otherwise.
|
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*/
|
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virtual bool DecommitPages(void* address, size_t size) = 0;
|
||
|
||
/**
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* 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<SharedMemoryMapping> RemapTo(
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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<SharedMemory> 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; }
|
||
};
|
||
|
||
// Opaque type representing a handle to a shared memory region.
|
||
using PlatformSharedMemoryHandle = intptr_t;
|
||
static constexpr PlatformSharedMemoryHandle kInvalidSharedMemoryHandle = -1;
|
||
|
||
// Conversion routines from the platform-dependent shared memory identifiers
|
||
// into the opaque PlatformSharedMemoryHandle type. These use the underlying
|
||
// types (e.g. unsigned int) instead of the typedef'd ones (e.g. mach_port_t)
|
||
// to avoid pulling in large OS header files into this header file. Instead,
|
||
// the users of these routines are expected to include the respecitve OS
|
||
// headers in addition to this one.
|
||
#if V8_OS_DARWIN
|
||
// Convert between a shared memory handle and a mach_port_t referencing a memory
|
||
// entry object.
|
||
inline PlatformSharedMemoryHandle SharedMemoryHandleFromMachMemoryEntry(
|
||
unsigned int port) {
|
||
return static_cast<PlatformSharedMemoryHandle>(port);
|
||
}
|
||
inline unsigned int MachMemoryEntryFromSharedMemoryHandle(
|
||
PlatformSharedMemoryHandle handle) {
|
||
return static_cast<unsigned int>(handle);
|
||
}
|
||
#elif V8_OS_FUCHSIA
|
||
// Convert between a shared memory handle and a zx_handle_t to a VMO.
|
||
inline PlatformSharedMemoryHandle SharedMemoryHandleFromVMO(uint32_t handle) {
|
||
return static_cast<PlatformSharedMemoryHandle>(handle);
|
||
}
|
||
inline uint32_t VMOFromSharedMemoryHandle(PlatformSharedMemoryHandle handle) {
|
||
return static_cast<uint32_t>(handle);
|
||
}
|
||
#elif V8_OS_WIN
|
||
// Convert between a shared memory handle and a Windows HANDLE to a file mapping
|
||
// object.
|
||
inline PlatformSharedMemoryHandle SharedMemoryHandleFromFileMapping(
|
||
void* handle) {
|
||
return reinterpret_cast<PlatformSharedMemoryHandle>(handle);
|
||
}
|
||
inline void* FileMappingFromSharedMemoryHandle(
|
||
PlatformSharedMemoryHandle handle) {
|
||
return reinterpret_cast<void*>(handle);
|
||
}
|
||
#else
|
||
// Convert between a shared memory handle and a file descriptor.
|
||
inline PlatformSharedMemoryHandle SharedMemoryHandleFromFileDescriptor(int fd) {
|
||
return static_cast<PlatformSharedMemoryHandle>(fd);
|
||
}
|
||
inline int FileDescriptorFromSharedMemoryHandle(
|
||
PlatformSharedMemoryHandle handle) {
|
||
return static_cast<int>(handle);
|
||
}
|
||
#endif
|
||
|
||
/**
|
||
* Possible permissions for memory pages.
|
||
*/
|
||
enum class PagePermissions {
|
||
kNoAccess,
|
||
kRead,
|
||
kReadWrite,
|
||
kReadWriteExecute,
|
||
kReadExecute,
|
||
};
|
||
|
||
/**
|
||
* Class to manage a virtual memory address space.
|
||
*
|
||
* This class represents a contiguous region of virtual address space in which
|
||
* sub-spaces and (private or shared) memory pages can be allocated, freed, and
|
||
* modified. This interface is meant to eventually replace the PageAllocator
|
||
* interface, and can be used as an alternative in the meantime.
|
||
*
|
||
* This API is not yet stable and may change without notice!
|
||
*/
|
||
class VirtualAddressSpace {
|
||
public:
|
||
using Address = uintptr_t;
|
||
|
||
VirtualAddressSpace(size_t page_size, size_t allocation_granularity,
|
||
Address base, size_t size,
|
||
PagePermissions max_page_permissions)
|
||
: page_size_(page_size),
|
||
allocation_granularity_(allocation_granularity),
|
||
base_(base),
|
||
size_(size),
|
||
max_page_permissions_(max_page_permissions) {}
|
||
|
||
virtual ~VirtualAddressSpace() = default;
|
||
|
||
/**
|
||
* The page size used inside this space. Guaranteed to be a power of two.
|
||
* Used as granularity for all page-related operations except for allocation,
|
||
* which use the allocation_granularity(), see below.
|
||
*
|
||
* \returns the page size in bytes.
|
||
*/
|
||
size_t page_size() const { return page_size_; }
|
||
|
||
/**
|
||
* The granularity of page allocations and, by extension, of subspace
|
||
* allocations. This is guaranteed to be a power of two and a multiple of the
|
||
* page_size(). In practice, this is equal to the page size on most OSes, but
|
||
* on Windows it is usually 64KB, while the page size is 4KB.
|
||
*
|
||
* \returns the allocation granularity in bytes.
|
||
*/
|
||
size_t allocation_granularity() const { return allocation_granularity_; }
|
||
|
||
/**
|
||
* The base address of the address space managed by this instance.
|
||
*
|
||
* \returns the base address of this address space.
|
||
*/
|
||
Address base() const { return base_; }
|
||
|
||
/**
|
||
* The size of the address space managed by this instance.
|
||
*
|
||
* \returns the size of this address space in bytes.
|
||
*/
|
||
size_t size() const { return size_; }
|
||
|
||
/**
|
||
* The maximum page permissions that pages allocated inside this space can
|
||
* obtain.
|
||
*
|
||
* \returns the maximum page permissions.
|
||
*/
|
||
PagePermissions max_page_permissions() const { return max_page_permissions_; }
|
||
|
||
/**
|
||
* Sets the random seed so that GetRandomPageAddress() will generate
|
||
* repeatable sequences of random addresses.
|
||
*
|
||
* \param The seed for the PRNG.
|
||
*/
|
||
virtual void SetRandomSeed(int64_t seed) = 0;
|
||
|
||
/**
|
||
* Returns a random address inside this address space, suitable for page
|
||
* allocations hints.
|
||
*
|
||
* \returns a random address aligned to allocation_granularity().
|
||
*/
|
||
virtual Address RandomPageAddress() = 0;
|
||
|
||
/**
|
||
* Allocates private memory pages with the given alignment and permissions.
|
||
*
|
||
* \param hint If nonzero, the allocation is attempted to be placed at the
|
||
* given address first. If that fails, the allocation is attempted to be
|
||
* placed elsewhere, possibly nearby, but that is not guaranteed. Specifying
|
||
* zero for the hint always causes this function to choose a random address.
|
||
* The hint, if specified, must be aligned to the specified alignment.
|
||
*
|
||
* \param size The size of the allocation in bytes. Must be a multiple of the
|
||
* allocation_granularity().
|
||
*
|
||
* \param alignment The alignment of the allocation in bytes. Must be a
|
||
* multiple of the allocation_granularity() and should be a power of two.
|
||
*
|
||
* \param permissions The page permissions of the newly allocated pages.
|
||
*
|
||
* \returns the start address of the allocated pages on success, zero on
|
||
* failure.
|
||
*/
|
||
static constexpr Address kNoHint = 0;
|
||
virtual V8_WARN_UNUSED_RESULT Address
|
||
AllocatePages(Address hint, size_t size, size_t alignment,
|
||
PagePermissions permissions) = 0;
|
||
|
||
/**
|
||
* Frees previously allocated pages.
|
||
*
|
||
* This function will terminate the process on failure as this implies a bug
|
||
* in the client. As such, there is no return value.
|
||
*
|
||
* \param address The start address of the pages to free. This address must
|
||
* have been obtained through a call to AllocatePages.
|
||
*
|
||
* \param size The size in bytes of the region to free. This must match the
|
||
* size passed to AllocatePages when the pages were allocated.
|
||
*/
|
||
virtual void FreePages(Address address, size_t size) = 0;
|
||
|
||
/**
|
||
* Sets permissions of all allocated pages in the given range.
|
||
*
|
||
* This operation can fail due to OOM, in which case false is returned. If
|
||
* the operation fails for a reason other than OOM, this function will
|
||
* terminate the process as this implies a bug in the client.
|
||
*
|
||
* \param address The start address of the range. Must be aligned to
|
||
* page_size().
|
||
*
|
||
* \param size The size in bytes of the range. Must be a multiple
|
||
* of page_size().
|
||
*
|
||
* \param permissions The new permissions for the range.
|
||
*
|
||
* \returns true on success, false on OOM.
|
||
*/
|
||
virtual V8_WARN_UNUSED_RESULT bool SetPagePermissions(
|
||
Address address, size_t size, PagePermissions permissions) = 0;
|
||
|
||
/**
|
||
* Creates a guard region at the specified address.
|
||
*
|
||
* Guard regions are guaranteed to cause a fault when accessed and generally
|
||
* do not count towards any memory consumption limits. Further, allocating
|
||
* guard regions can usually not fail in subspaces if the region does not
|
||
* overlap with another region, subspace, or page allocation.
|
||
*
|
||
* \param address The start address of the guard region. Must be aligned to
|
||
* the allocation_granularity().
|
||
*
|
||
* \param size The size of the guard region in bytes. Must be a multiple of
|
||
* the allocation_granularity().
|
||
*
|
||
* \returns true on success, false otherwise.
|
||
*/
|
||
virtual V8_WARN_UNUSED_RESULT bool AllocateGuardRegion(Address address,
|
||
size_t size) = 0;
|
||
|
||
/**
|
||
* Frees an existing guard region.
|
||
*
|
||
* This function will terminate the process on failure as this implies a bug
|
||
* in the client. As such, there is no return value.
|
||
*
|
||
* \param address The start address of the guard region to free. This address
|
||
* must have previously been used as address parameter in a successful
|
||
* invocation of AllocateGuardRegion.
|
||
*
|
||
* \param size The size in bytes of the guard region to free. This must match
|
||
* the size passed to AllocateGuardRegion when the region was created.
|
||
*/
|
||
virtual void FreeGuardRegion(Address address, size_t size) = 0;
|
||
|
||
/**
|
||
* Allocates shared memory pages with the given permissions.
|
||
*
|
||
* \param hint Placement hint. See AllocatePages.
|
||
*
|
||
* \param size The size of the allocation in bytes. Must be a multiple of the
|
||
* allocation_granularity().
|
||
*
|
||
* \param permissions The page permissions of the newly allocated pages.
|
||
*
|
||
* \param handle A platform-specific handle to a shared memory object. See
|
||
* the SharedMemoryHandleFromX routines above for ways to obtain these.
|
||
*
|
||
* \param offset The offset in the shared memory object at which the mapping
|
||
* should start. Must be a multiple of the allocation_granularity().
|
||
*
|
||
* \returns the start address of the allocated pages on success, zero on
|
||
* failure.
|
||
*/
|
||
virtual V8_WARN_UNUSED_RESULT Address
|
||
AllocateSharedPages(Address hint, size_t size, PagePermissions permissions,
|
||
PlatformSharedMemoryHandle handle, uint64_t offset) = 0;
|
||
|
||
/**
|
||
* Frees previously allocated shared pages.
|
||
*
|
||
* This function will terminate the process on failure as this implies a bug
|
||
* in the client. As such, there is no return value.
|
||
*
|
||
* \param address The start address of the pages to free. This address must
|
||
* have been obtained through a call to AllocateSharedPages.
|
||
*
|
||
* \param size The size in bytes of the region to free. This must match the
|
||
* size passed to AllocateSharedPages when the pages were allocated.
|
||
*/
|
||
virtual void FreeSharedPages(Address address, size_t size) = 0;
|
||
|
||
/**
|
||
* Whether this instance can allocate subspaces or not.
|
||
*
|
||
* \returns true if subspaces can be allocated, false if not.
|
||
*/
|
||
virtual bool CanAllocateSubspaces() = 0;
|
||
|
||
/*
|
||
* Allocate a subspace.
|
||
*
|
||
* The address space of a subspace stays reserved in the parent space for the
|
||
* lifetime of the subspace. As such, it is guaranteed that page allocations
|
||
* on the parent space cannot end up inside a subspace.
|
||
*
|
||
* \param hint Hints where the subspace should be allocated. See
|
||
* AllocatePages() for more details.
|
||
*
|
||
* \param size The size in bytes of the subspace. Must be a multiple of the
|
||
* allocation_granularity().
|
||
*
|
||
* \param alignment The alignment of the subspace in bytes. Must be a multiple
|
||
* of the allocation_granularity() and should be a power of two.
|
||
*
|
||
* \param max_page_permissions The maximum permissions that pages allocated in
|
||
* the subspace can obtain.
|
||
*
|
||
* \returns a new subspace or nullptr on failure.
|
||
*/
|
||
virtual std::unique_ptr<VirtualAddressSpace> AllocateSubspace(
|
||
Address hint, size_t size, size_t alignment,
|
||
PagePermissions max_page_permissions) = 0;
|
||
|
||
//
|
||
// TODO(v8) maybe refactor the methods below before stabilizing the API. For
|
||
// example by combining them into some form of page operation method that
|
||
// takes a command enum as parameter.
|
||
//
|
||
|
||
/**
|
||
* Recommits discarded pages in the given range with given permissions.
|
||
* Discarded pages must be recommitted with their original permissions
|
||
* before they are used again.
|
||
*
|
||
* \param address The start address of the range. Must be aligned to
|
||
* page_size().
|
||
*
|
||
* \param size The size in bytes of the range. Must be a multiple
|
||
* of page_size().
|
||
*
|
||
* \param permissions The permissions for the range that the pages must have.
|
||
*
|
||
* \returns true on success, false otherwise.
|
||
*/
|
||
virtual V8_WARN_UNUSED_RESULT bool RecommitPages(
|
||
Address address, size_t size, PagePermissions permissions) = 0;
|
||
|
||
/**
|
||
* Frees memory in the given [address, address + size) range. address and
|
||
* size should be aligned to the page_size(). The next write to this memory
|
||
* area brings the memory transparently back. This should be treated as a
|
||
* hint to the OS that the pages are no longer needed. It does not guarantee
|
||
* that the pages will be discarded immediately or at all.
|
||
*
|
||
* \returns true on success, false otherwise. Since this method is only a
|
||
* hint, a successful invocation does not imply that pages have been removed.
|
||
*/
|
||
virtual V8_WARN_UNUSED_RESULT bool DiscardSystemPages(Address address,
|
||
size_t size) {
|
||
return true;
|
||
}
|
||
/**
|
||
* Decommits any wired memory pages in the given range, allowing the OS to
|
||
* reclaim them, and marks the region as inacessible (kNoAccess). The address
|
||
* range stays reserved and can be accessed again later by changing its
|
||
* permissions. However, in that case the memory content is guaranteed to be
|
||
* zero-initialized again. The memory must have been previously allocated by a
|
||
* call to AllocatePages.
|
||
*
|
||
* \returns true on success, false otherwise.
|
||
*/
|
||
virtual V8_WARN_UNUSED_RESULT bool DecommitPages(Address address,
|
||
size_t size) = 0;
|
||
|
||
private:
|
||
const size_t page_size_;
|
||
const size_t allocation_granularity_;
|
||
const Address base_;
|
||
const size_t size_;
|
||
const PagePermissions max_page_permissions_;
|
||
};
|
||
|
||
/**
|
||
* V8 Allocator used for allocating zone backings.
|
||
*/
|
||
class ZoneBackingAllocator {
|
||
public:
|
||
using MallocFn = void* (*)(size_t);
|
||
using FreeFn = void (*)(void*);
|
||
|
||
virtual MallocFn GetMallocFn() const { return ::malloc; }
|
||
virtual FreeFn GetFreeFn() const { return ::free; }
|
||
};
|
||
|
||
/**
|
||
* Observer used by V8 to notify the embedder about entering/leaving sections
|
||
* with high throughput of malloc/free operations.
|
||
*/
|
||
class HighAllocationThroughputObserver {
|
||
public:
|
||
virtual void EnterSection() {}
|
||
virtual void LeaveSection() {}
|
||
};
|
||
|
||
/**
|
||
* 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.
|
||
* Returning nullptr will cause V8 to use the default page allocator.
|
||
*/
|
||
virtual PageAllocator* GetPageAllocator() = 0;
|
||
|
||
/**
|
||
* Allows the embedder to specify a custom allocator used for zones.
|
||
*/
|
||
virtual ZoneBackingAllocator* GetZoneBackingAllocator() {
|
||
static ZoneBackingAllocator default_allocator;
|
||
return &default_allocator;
|
||
}
|
||
|
||
/**
|
||
* 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() {}
|
||
|
||
/**
|
||
* 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<v8::TaskRunner> GetForegroundTaskRunner(
|
||
Isolate* isolate) = 0;
|
||
|
||
/**
|
||
* Schedules a task to be invoked on a worker thread.
|
||
*/
|
||
virtual void CallOnWorkerThread(std::unique_ptr<Task> 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> 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> 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> 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<MyJobTask>(...));
|
||
* 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).
|
||
*/
|
||
virtual std::unique_ptr<JobHandle> PostJob(
|
||
TaskPriority priority, std::unique_ptr<JobTask> job_task) {
|
||
auto handle = CreateJob(priority, std::move(job_task));
|
||
handle->NotifyConcurrencyIncrease();
|
||
return handle;
|
||
}
|
||
|
||
/**
|
||
* Creates and returns a JobHandle associated with a Job. Unlike PostJob(),
|
||
* this doesn't immediately schedules |worker_task| to run; the Job is then
|
||
* scheduled by calling either NotifyConcurrencyIncrease() or Join().
|
||
*
|
||
* A sufficient CreateJob() implementation that uses the default Job provided
|
||
* in libplatform looks like:
|
||
* std::unique_ptr<JobHandle> CreateJob(
|
||
* TaskPriority priority, std::unique_ptr<JobTask> job_task) override {
|
||
* return v8::platform::NewDefaultJobHandle(
|
||
* this, priority, std::move(job_task), NumberOfWorkerThreads());
|
||
* }
|
||
*/
|
||
virtual std::unique_ptr<JobHandle> CreateJob(
|
||
TaskPriority priority, std::unique_ptr<JobTask> 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() {}
|
||
|
||
/**
|
||
* Allows the embedder to observe sections with high throughput allocation
|
||
* operations.
|
||
*/
|
||
virtual HighAllocationThroughputObserver*
|
||
GetHighAllocationThroughputObserver() {
|
||
static HighAllocationThroughputObserver default_observer;
|
||
return &default_observer;
|
||
}
|
||
|
||
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_
|