TaskScheduler [2/9] Scheduler Lock

base/task_scheduler/scheduler_lock.h

+// 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.
+
+#ifndef BASE_TASK_SCHEDULER_SCHEDULER_LOCK_H
+#define BASE_TASK_SCHEDULER_SCHEDULER_LOCK_H
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/synchronization/lock.h"
+#include "base/task_scheduler/scheduler_lock_impl.h"
+
+namespace base {
+namespace internal {
+
+// SchedulerLock should be used anywhere a lock would be used in the scheduler.
+// When DCHECK_IS_ON(), lock checking occurs. Otherwise, SchedulerLock is
+// equivalent to base::Lock.
+//
+// The shape of SchedulerLock is as follows:
+// SchedulerLock()
+//     Default constructor, no predecessor lock.
+//     DCHECKs
+//         On Acquisition if any scheduler lock is acquired on this thread.
+//
+// SchedulerLock(const SchedulerLock* predecessor)
+//     Constructor that specifies an allowed predecessor for that lock.
+//     DCHECKs
+//         On Construction if |predecessor| forms a predecessor lock cycle.
+//         On Acquisition if the previous lock acquired on the thread is not
+//             |predecessor|. Okay if there was no previous lock acquired.
+//
+// void Acquire()
+//     Acquires the lock.
+//
+// void Release()
+//     Releases the lock.
+//
+// void AssertAcquired().
+//     DCHECKs if the lock is not acquired.
+//
+// scoped_ptr<ConditionVariable> CreateConditionVariable()
+//     Creates a condition variable using this as a lock.
+
+#if DCHECK_IS_ON()
+class SchedulerLock : public SchedulerLockImpl {
+ public:
+  SchedulerLock() = default;
+  explicit SchedulerLock(const SchedulerLock* predecessor)
+      : SchedulerLockImpl(predecessor) {}
+};
+#else  // DCHECK_IS_ON()
+class SchedulerLock : public Lock {
+ public:
+  SchedulerLock() = default;
+  explicit SchedulerLock(const SchedulerLock*) {}
+
+  scoped_ptr<ConditionVariable> CreateConditionVariable() {
+    return scoped_ptr<ConditionVariable>(new ConditionVariable(this));
+  }
+};
+#endif  // DCHECK_IS_ON()
+
+// Provides the same functionality as base::AutoLock for SchedulerLock.
+class AutoSchedulerLock {
+ public:
+  explicit AutoSchedulerLock(SchedulerLock& lock) : lock_(lock) {
+    lock_.Acquire();
+  }
+
+  ~AutoSchedulerLock() {
+    lock_.AssertAcquired();
+    lock_.Release();
+  }
+
+ private:
+  SchedulerLock& lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(AutoSchedulerLock);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_SCHEDULER_LOCK_H