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// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <memory>
#include <vector>
#include "base/base_export.h"
#include "base/callback.h"
#include "base/gtest_prod_util.h"
#include "base/memory/ref_counted.h"
#include "base/sequenced_task_runner.h"
#include "base/single_thread_task_runner.h"
#include "base/strings/string_piece.h"
#include "base/task/single_thread_task_runner_thread_mode.h"
#include "base/task/task_executor.h"
#include "base/task/task_scheduler/scheduler_worker_pool_params.h"
#include "base/task/task_traits.h"
#include "base/task_runner.h"
#include "base/time/time.h"
#include "build/build_config.h"
namespace gin {
class V8Platform;
namespace content {
// Can't use the FRIEND_TEST_ALL_PREFIXES macro because the test is in a
// different namespace.
class BrowserMainLoopTest_CreateThreadsInSingleProcess_Test;
} // namespace content
namespace base {
class HistogramBase;
class SchedulerWorkerObserver;
// Interface for a task scheduler and static methods to manage the instance used
// by the post_task.h API.
// The task scheduler doesn't create threads until Start() is called. Tasks can
// be posted at any time but will not run until after Start() is called.
// The instance methods of this class are thread-safe.
// Note: All TaskScheduler users should go through base/task/post_task.h instead
// of this interface except for the one callsite per process which manages the
// process's instance.
class BASE_EXPORT TaskScheduler : public TaskExecutor {
struct BASE_EXPORT InitParams {
enum class SharedWorkerPoolEnvironment {
// Use the default environment (no environment).
#if defined(OS_WIN)
// Place the worker in a COM MTA.
#endif // defined(OS_WIN)
const SchedulerWorkerPoolParams& background_worker_pool_params_in,
const SchedulerWorkerPoolParams&
const SchedulerWorkerPoolParams& foreground_worker_pool_params_in,
const SchedulerWorkerPoolParams&
SharedWorkerPoolEnvironment shared_worker_pool_environment_in =
SchedulerWorkerPoolParams background_worker_pool_params;
SchedulerWorkerPoolParams background_blocking_worker_pool_params;
SchedulerWorkerPoolParams foreground_worker_pool_params;
SchedulerWorkerPoolParams foreground_blocking_worker_pool_params;
SharedWorkerPoolEnvironment shared_worker_pool_environment;
// A ScopedExecutionFence prevents any new task from being scheduled in
// TaskScheduler within its scope. Upon its destruction, all tasks that were
// preeempted are released. Note: the constructor of ScopedExecutionFence will
// not wait for currently running tasks (as they were posted before entering
// this scope and do not violate the contract; some of them could be
// CONTINUE_ON_SHUTDOWN and waiting for them to complete is ill-advised).
class BASE_EXPORT ScopedExecutionFence {
// Destroying a TaskScheduler is not allowed in production; it is always
// leaked. In tests, it should only be destroyed after JoinForTesting() has
// returned.
~TaskScheduler() override = default;
// Allows the task scheduler to create threads and run tasks following the
// |init_params| specification.
// If specified, |scheduler_worker_observer| will be notified when a worker
// enters and exits its main function. It must not be destroyed before
// JoinForTesting() has returned (must never be destroyed in production).
// CHECKs on failure.
virtual void Start(
const InitParams& init_params,
SchedulerWorkerObserver* scheduler_worker_observer = nullptr) = 0;
#if !defined(STARBOARD)
// Returns a vector of all histograms available in this task scheduler.
virtual std::vector<const HistogramBase*> GetHistograms() const = 0;
#endif // !defined(STARBOARD)
// Synchronously shuts down the scheduler. Once this is called, only tasks
// posted with the BLOCK_SHUTDOWN behavior will be run. When this returns:
// - All SKIP_ON_SHUTDOWN tasks that were already running have completed their
// execution.
// - All posted BLOCK_SHUTDOWN tasks have completed their execution.
// - CONTINUE_ON_SHUTDOWN tasks might still be running.
// Note that an implementation can keep threads and other resources alive to
// support running CONTINUE_ON_SHUTDOWN after this returns. This can only be
// called once.
virtual void Shutdown() = 0;
// Waits until there are no pending undelayed tasks. May be called in tests
// to validate that a condition is met after all undelayed tasks have run.
// Does not wait for delayed tasks. Waits for undelayed tasks posted from
// other threads during the call. Returns immediately when shutdown completes.
virtual void FlushForTesting() = 0;
// Returns and calls |flush_callback| when there are no incomplete undelayed
// tasks. |flush_callback| may be called back on any thread and should not
// perform a lot of work. May be used when additional work on the current
// thread needs to be performed during a flush. Only one
// FlushAsyncForTesting() may be pending at any given time.
virtual void FlushAsyncForTesting(OnceClosure flush_callback) = 0;
// Joins all threads. Tasks that are already running are allowed to complete
// their execution. This can only be called once. Using this task scheduler
// instance to create task runners or post tasks is not permitted during or
// after this call.
virtual void JoinForTesting() = 0;
// CreateAndStartWithDefaultParams(), Create(), and SetInstance() register a
// TaskScheduler to handle tasks posted through the post_task.h API for this
// process.
// Processes that need to initialize TaskScheduler with custom params or that
// need to allow tasks to be posted before the TaskScheduler creates its
// threads should use Create() followed by Start(). Other processes can use
// CreateAndStartWithDefaultParams().
// A registered TaskScheduler is only deleted when a new TaskScheduler is
// registered. The last registered TaskScheduler is leaked on shutdown. The
// methods below must not be called when TaskRunners created by a previous
// TaskScheduler are still alive. The methods are not thread-safe; proper
// synchronization is required to use the post_task.h API after registering a
// new TaskScheduler.
#if !defined(OS_NACL)
// Creates and starts a task scheduler using default params. |name| is used to
// label histograms, it must not be empty. It should identify the component
// that calls this. Start() is called by this method; it is invalid to call it
// again afterwards. CHECKs on failure. For tests, prefer
// base::test::ScopedTaskEnvironment (ensures isolation).
static void CreateAndStartWithDefaultParams(StringPiece name);
// Same as CreateAndStartWithDefaultParams() but allows callers to split the
// Create() and StartWithDefaultParams() calls.
void StartWithDefaultParams();
#endif // !defined(OS_NACL)
// Creates a ready to start task scheduler. |name| is used to label
// histograms, it must not be empty. It should identify the component that
// creates the TaskScheduler. The task scheduler doesn't create threads until
// Start() is called. Tasks can be posted at any time but will not run until
// after Start() is called. For tests, prefer
// base::test::ScopedTaskEnvironment (ensures isolation).
static void Create(StringPiece name);
// Registers |task_scheduler| to handle tasks posted through the post_task.h
// API for this process. For tests, prefer base::test::ScopedTaskEnvironment
// (ensures isolation).
static void SetInstance(std::unique_ptr<TaskScheduler> task_scheduler);
// Retrieve the TaskScheduler set via SetInstance() or
// CreateAndSet(Simple|Default)TaskScheduler(). This should be used very
// rarely; most users of TaskScheduler should use the post_task.h API. In
// particular, refrain from doing
// if (!TaskScheduler::GetInstance()) {
// TaskScheduler::SetInstance(...);
// base::PostTask(...);
// }
// instead make sure to SetInstance() early in one determinstic place in the
// process' initialization phase.
// In doubt, consult with //base/task/task_scheduler/OWNERS.
static TaskScheduler* GetInstance();
friend class gin::V8Platform;
friend class content::BrowserMainLoopTest_CreateThreadsInSingleProcess_Test;
// Returns the maximum number of non-single-threaded non-blocked tasks posted
// with |traits| that can run concurrently in this TaskScheduler. |traits|
// can't contain TaskPriority::BEST_EFFORT.
// Do not use this method. To process n items, post n tasks that each process
// 1 item rather than GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated()
// tasks that each process
// n/GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated() items.
// TODO(fdoray): Remove this method.
virtual int GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated(
const TaskTraits& traits) const = 0;
// Enables/disables an execution fence that prevents tasks from running.
virtual void SetExecutionFenceEnabled(bool execution_fence_enabled) = 0;
} // namespace base