chromium/base/task/common/operations_controller.h

// Copyright 2018 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_COMMON_OPERATIONS_CONTROLLER_H_
#define BASE_TASK_COMMON_OPERATIONS_CONTROLLER_H_

#include <atomic>
#include <cstdint>

#include "base/base_export.h"
#include "base/memory/stack_allocated.h"
#include "base/synchronization/waitable_event.h"

namespace base {
namespace internal {

// A lock-free thread-safe controller to manage critical multi-threaded
// operations without locks.
//
// The controller is used to determine if operations are allowed, and to keep
// track of how many are currently active. Users will call TryBeginOperation()
// before starting such operations. If the call succeeds the user can run the
// operation and the controller will keep track of it until the user signals
// that the operation is completed. No operations are allowed before
// StartAcceptingOperations() is called, or after
// ShutdownAndWaitForZeroOperations() is called.
//
// There is no explicit way of telling the controller when an operation is
// completed, instead for convenience TryBeginOperation() will return a RAII
// like object that will do so on destruction.
//
// For example:
//
// OperationsController controller_;
//
// void SetUp() {
//   controller_.StartAcceptingOperations();
// }
//
// void TearDown() {
//   controller_.ShutdownAndWaitForZeroOperations();
// }
//
// void MaybeRunOperation() {
//   auto operation_token = controller_.TryBeginOperation();
//   if (operation_token) {
//     Process();
//   }
// }
//
// This class is thread-safe.
// But note that StartAcceptingOperations can never be called after
// ShutdownAndWaitForZeroOperations.
class BASE_EXPORT OperationsController { … };

}  // namespace internal
}  // namespace base

#endif  // BASE_TASK_COMMON_OPERATIONS_CONTROLLER_H_