You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
177 lines
6.7 KiB
177 lines
6.7 KiB
// Copyright (c) 2012 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.
|
|
|
|
#ifndef BASE_SEQUENCED_TASK_RUNNER_H_
|
|
#define BASE_SEQUENCED_TASK_RUNNER_H_
|
|
|
|
#include <memory>
|
|
|
|
#include "base/base_export.h"
|
|
#include "base/callback.h"
|
|
#include "base/sequenced_task_runner_helpers.h"
|
|
#include "base/task_runner.h"
|
|
|
|
namespace base {
|
|
|
|
// A SequencedTaskRunner is a subclass of TaskRunner that provides
|
|
// additional guarantees on the order that tasks are started, as well
|
|
// as guarantees on when tasks are in sequence, i.e. one task finishes
|
|
// before the other one starts.
|
|
//
|
|
// Summary
|
|
// -------
|
|
// Non-nested tasks with the same delay will run one by one in FIFO
|
|
// order.
|
|
//
|
|
// Detailed guarantees
|
|
// -------------------
|
|
//
|
|
// SequencedTaskRunner also adds additional methods for posting
|
|
// non-nestable tasks. In general, an implementation of TaskRunner
|
|
// may expose task-running methods which are themselves callable from
|
|
// within tasks. A non-nestable task is one that is guaranteed to not
|
|
// be run from within an already-running task. Conversely, a nestable
|
|
// task (the default) is a task that can be run from within an
|
|
// already-running task.
|
|
//
|
|
// The guarantees of SequencedTaskRunner are as follows:
|
|
//
|
|
// - Given two tasks T2 and T1, T2 will start after T1 starts if:
|
|
//
|
|
// * T2 is posted after T1; and
|
|
// * T2 has equal or higher delay than T1; and
|
|
// * T2 is non-nestable or T1 is nestable.
|
|
//
|
|
// - If T2 will start after T1 starts by the above guarantee, then
|
|
// T2 will start after T1 finishes and is destroyed if:
|
|
//
|
|
// * T2 is non-nestable, or
|
|
// * T1 doesn't call any task-running methods.
|
|
//
|
|
// - If T2 will start after T1 finishes by the above guarantee, then
|
|
// all memory changes in T1 and T1's destruction will be visible
|
|
// to T2.
|
|
//
|
|
// - If T2 runs nested within T1 via a call to the task-running
|
|
// method M, then all memory changes in T1 up to the call to M
|
|
// will be visible to T2, and all memory changes in T2 will be
|
|
// visible to T1 from the return from M.
|
|
//
|
|
// Note that SequencedTaskRunner does not guarantee that tasks are run
|
|
// on a single dedicated thread, although the above guarantees provide
|
|
// most (but not all) of the same guarantees. If you do need to
|
|
// guarantee that tasks are run on a single dedicated thread, see
|
|
// SingleThreadTaskRunner (in single_thread_task_runner.h).
|
|
//
|
|
// Some corollaries to the above guarantees, assuming the tasks in
|
|
// question don't call any task-running methods:
|
|
//
|
|
// - Tasks posted via PostTask are run in FIFO order.
|
|
//
|
|
// - Tasks posted via PostNonNestableTask are run in FIFO order.
|
|
//
|
|
// - Tasks posted with the same delay and the same nestable state
|
|
// are run in FIFO order.
|
|
//
|
|
// - A list of tasks with the same nestable state posted in order of
|
|
// non-decreasing delay is run in FIFO order.
|
|
//
|
|
// - A list of tasks posted in order of non-decreasing delay with at
|
|
// most a single change in nestable state from nestable to
|
|
// non-nestable is run in FIFO order. (This is equivalent to the
|
|
// statement of the first guarantee above.)
|
|
//
|
|
// Some theoretical implementations of SequencedTaskRunner:
|
|
//
|
|
// - A SequencedTaskRunner that wraps a regular TaskRunner but makes
|
|
// sure that only one task at a time is posted to the TaskRunner,
|
|
// with appropriate memory barriers in between tasks.
|
|
//
|
|
// - A SequencedTaskRunner that, for each task, spawns a joinable
|
|
// thread to run that task and immediately quit, and then
|
|
// immediately joins that thread.
|
|
//
|
|
// - A SequencedTaskRunner that stores the list of posted tasks and
|
|
// has a method Run() that runs each runnable task in FIFO order
|
|
// that can be called from any thread, but only if another
|
|
// (non-nested) Run() call isn't already happening.
|
|
class BASE_EXPORT SequencedTaskRunner : public TaskRunner {
|
|
public:
|
|
// The two PostNonNestable*Task methods below are like their
|
|
// nestable equivalents in TaskRunner, but they guarantee that the
|
|
// posted task will not run nested within an already-running task.
|
|
//
|
|
// A simple corollary is that posting a task as non-nestable can
|
|
// only delay when the task gets run. That is, posting a task as
|
|
// non-nestable may not affect when the task gets run, or it could
|
|
// make it run later than it normally would, but it won't make it
|
|
// run earlier than it normally would.
|
|
|
|
// TODO(akalin): Get rid of the boolean return value for the methods
|
|
// below.
|
|
|
|
bool PostNonNestableTask(const Location& from_here, OnceClosure task);
|
|
|
|
virtual bool PostNonNestableDelayedTask(const Location& from_here,
|
|
OnceClosure task,
|
|
base::TimeDelta delay) = 0;
|
|
|
|
// Submits a non-nestable task to delete the given object. Returns
|
|
// true if the object may be deleted at some point in the future,
|
|
// and false if the object definitely will not be deleted.
|
|
template <class T>
|
|
bool DeleteSoon(const Location& from_here, const T* object) {
|
|
return DeleteOrReleaseSoonInternal(from_here, &DeleteHelper<T>::DoDelete,
|
|
object);
|
|
}
|
|
|
|
template <class T>
|
|
bool DeleteSoon(const Location& from_here, std::unique_ptr<T> object) {
|
|
return DeleteSoon(from_here, object.release());
|
|
}
|
|
|
|
// Submits a non-nestable task to release the given object. Returns
|
|
// true if the object may be released at some point in the future,
|
|
// and false if the object definitely will not be released.
|
|
template <class T>
|
|
bool ReleaseSoon(const Location& from_here, const T* object) {
|
|
return DeleteOrReleaseSoonInternal(from_here, &ReleaseHelper<T>::DoRelease,
|
|
object);
|
|
}
|
|
|
|
protected:
|
|
~SequencedTaskRunner() override = default;
|
|
|
|
private:
|
|
bool DeleteOrReleaseSoonInternal(const Location& from_here,
|
|
void (*deleter)(const void*),
|
|
const void* object);
|
|
};
|
|
|
|
// Sample usage with std::unique_ptr :
|
|
// std::unique_ptr<Foo, base::OnTaskRunnerDeleter> ptr(
|
|
// new Foo, base::OnTaskRunnerDeleter(my_task_runner));
|
|
//
|
|
// For RefCounted see base::RefCountedDeleteOnSequence.
|
|
struct BASE_EXPORT OnTaskRunnerDeleter {
|
|
explicit OnTaskRunnerDeleter(scoped_refptr<SequencedTaskRunner> task_runner);
|
|
~OnTaskRunnerDeleter();
|
|
|
|
OnTaskRunnerDeleter(OnTaskRunnerDeleter&&);
|
|
OnTaskRunnerDeleter& operator=(OnTaskRunnerDeleter&&);
|
|
|
|
// For compatibility with std:: deleters.
|
|
template <typename T>
|
|
void operator()(const T* ptr) {
|
|
if (ptr)
|
|
task_runner_->DeleteSoon(FROM_HERE, ptr);
|
|
}
|
|
|
|
scoped_refptr<SequencedTaskRunner> task_runner_;
|
|
};
|
|
|
|
} // namespace base
|
|
|
|
#endif // BASE_SEQUENCED_TASK_RUNNER_H_
|