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// Copyright 2019 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_MESSAGE_LOOP_WORK_ID_PROVIDER_H_
#define BASE_MESSAGE_LOOP_WORK_ID_PROVIDER_H_
#include <atomic>
#include "base/base_export.h"
#include "base/threading/thread_checker.h"
namespace base {
class MessageLoopImpl;
namespace sequence_manager {
namespace internal {
class SequenceManagerImpl;
}
} // namespace sequence_manager
// WorkIdProvider associates with the current thread (via TLS) an id state
// reflecting the current work item being executed by the message loop. The item
// is accessed lock-free from other threads to provide a snapshot of the
// currently-executing work item.
//
// The expected user is the ThreadProfiler which samples the id along with the
// thread's stack to identify cases where the same task spans multiple
// samples. The state is stored in TLS rather than on the MessageLoop or the
// ThreadProfiler because the lifetime relationship between the two classes
// varies depending on which thread is being profiled, plus the fact that
// MessageLoop doesn't have a well-defined creation point/owner on some threads.
class BASE_EXPORT WorkIdProvider {
public:
// Returns the WorkIdProvider for the current thread. Allocates a
// WorkIdProvider in TLS if not already present.
static WorkIdProvider* GetForCurrentThread();
// Returns the work id for the thread to which this WorkIdProvider
// belongs. The work id is 0 before calls to IncrementWorkId() and always
// non-zero after that point. The implementation supports being invoked while
// other threads are suspended, and thus is guaranteed to take no locks,
// directly or indirectly. May be called from any thread, as long as the
// owning thread hasn't been destroyed.
unsigned int GetWorkId();
// Public to support unique_ptr<WorkIdProvider>.
~WorkIdProvider();
void SetCurrentWorkIdForTesting(unsigned int id);
void IncrementWorkIdForTesting();
WorkIdProvider(const WorkIdProvider&) = delete;
WorkIdProvider& operator=(const WorkIdProvider&) = delete;
private:
// Friended to allow use of IncrementWorkId().
friend class MessageLoopImpl;
friend class sequence_manager::internal::SequenceManagerImpl;
WorkIdProvider();
void IncrementWorkId();
std::atomic_uint work_id_;
THREAD_CHECKER(thread_checker_);
};
} // namespace base
#endif // BASE_MESSAGE_LOOP_WORK_ID_PROVIDER_H_