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// Copyright 2025 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_TASK_EXECUTION_FENCE_H_
#define BASE_TASK_EXECUTION_FENCE_H_
#include <memory>
#include <vector>
#include "base/base_export.h"
#include "base/task/sequence_manager/task_queue.h"
namespace base {
namespace sequence_manager {
class SequenceManager;
}
// A ScopedThreadPoolExecutionFence prevents new tasks from being scheduled in
// the ThreadPool within its scope. Multiple fences can exist at the same time.
// Upon destruction of all ScopedThreadPoolExecutionFences, tasks that were
// preeempted are released. Note: the constructor of
// ScopedThreadPoolExecutionFence 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).
// TODO(crbug.com/454908699): Remove the "Scoped" prefix. It's too verbose.
class BASE_EXPORT ScopedThreadPoolExecutionFence {
public:
ScopedThreadPoolExecutionFence();
ScopedThreadPoolExecutionFence(const ScopedThreadPoolExecutionFence&) =
delete;
ScopedThreadPoolExecutionFence& operator=(
const ScopedThreadPoolExecutionFence&) = delete;
~ScopedThreadPoolExecutionFence();
};
// ScopedBestEffortExecutionFence is similar to ScopedThreadPoolExecutionFence,
// but only prevents new tasks of BEST_EFFORT priority from being scheduled.
// See ScopedThreadPoolExecutionFence for the full semantics.
//
// By default this only applies to tasks posted to the ThreadPool, same as
// ScopedThreadPoolExecutionFence. To apply fences to other task queues, call
// AddSequenceManager.
// TODO(crbug.com/454908699): Remove the "Scoped" prefix. It's too verbose.
class BASE_EXPORT ScopedBestEffortExecutionFence {
public:
ScopedBestEffortExecutionFence();
ScopedBestEffortExecutionFence(const ScopedBestEffortExecutionFence&) =
delete;
ScopedBestEffortExecutionFence& operator=(
const ScopedBestEffortExecutionFence&) = delete;
~ScopedBestEffortExecutionFence();
// ScopedBestEffortExecutionFences created after this will also preempt
// best-effort tasks posted to the backing sequence of `sequence_manager`.
// Existing fences aren't affected. Does nothing if `sequence_manager` doesn't
// define a best-effort priority. Must be called on the thread that created
// `sequence_manager`.
// TODO(crbug.com/441949788): Currently only sequence managers bound to the
// main thread are supported.
static void AddSequenceManager(
sequence_manager::SequenceManager* sequence_manager);
// ScopedBestEffortExecutionFences created after this will no longer preempt
// best-effort tasks posted to the backing sequence of `sequence_manager`.
// Existing fences aren't affected. Must be called on the thread that called
// AddSequenceManager().
static void RemoveSequenceManager(
sequence_manager::SequenceManager* sequence_manager);
private:
// Voters used to disable additional task queues.
std::vector<std::unique_ptr<sequence_manager::TaskQueue::QueueEnabledVoter>>
task_queue_voters_;
};
} // namespace base
#endif // BASE_TASK_EXECUTION_FENCE_H_
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