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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <functional>
#include <list>
#include "mongo/db/service_context.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/util/concurrency/thread_pool.h"
#include "mongo/util/functional.h"
namespace mongo {
class Status;
class OperationContext;
namespace repl {
class TaskRunner {
TaskRunner(const TaskRunner&) = delete;
TaskRunner& operator=(const TaskRunner&) = delete;
public:
/**
* Represents next steps of task runner.
*/
enum class NextAction {
kInvalid = 0,
kDisposeOperationContext = 1,
kKeepOperationContext = 2,
kCancel = 3,
};
using Task = unique_function<NextAction(OperationContext*, const Status&)>;
/**
* Creates a Task returning kCancel. This is useful in shutting down the task runner after
* running a series of tasks.
*
* Without a cancellation task, the client would need to coordinate the completion of the
* last task with calling cancel() on the task runner.
*/
static Task makeCancelTask();
explicit TaskRunner(ThreadPool* threadPool);
virtual ~TaskRunner();
/**
* Returns diagnostic information.
*/
std::string getDiagnosticString() const;
/**
* Returns true if there are any scheduled or actively running tasks.
*/
bool isActive() const;
/**
* Schedules a task to be run by the task runner. Tasks are run in the same order that they
* are scheduled.
*
* This transitions the task runner to an active state.
*
* The task runner creates an operation context using the current client
* prior to running a scheduled task. Depending on the NextAction returned from the
* task, operation contexts may be shared between consecutive tasks invoked by the task
* runner.
*
* On completion, each task is expected to return a NextAction to the task runner.
*
* If the task returns kDisposeOperationContext, the task runner destroys the operation
* context. The next task to be invoked will receive a new operation context.
*
* If the task returns kKeepOperationContext, the task runner will retain the operation
* context to pass to the next task in the queue.
*
* If the task returns kCancel, the task runner will destroy the operation context and
* cancel the remaining tasks (each task will be invoked with a status containing the
* code ErrorCodes::CallbackCanceled). After all the tasks have been canceled, the task
* runner will become inactive.
*
* If the task returns kInvalid, this NextAction will be handled in the same way as
* kDisposeOperationContext.
*
* If the status passed to the task is not OK, the task should not proceed and return
* immediately. This is usually the case when the task runner is canceled. Accessing the
* operation context in the task will result in undefined behavior.
*/
void schedule(Task task);
/**
* If there is a task that is already running, allows the task to run to completion.
* Cancels all scheduled tasks that have not been run. Canceled tasks will still be
* invoked with a status containing the code ErrorCodes::CallbackCanceled.
* After all active tasks have completed and unscheduled tasks have been canceled, the
* task runner will go into an inactive state.
*
* It is a no-op to call cancel() before scheduling any tasks.
*/
void cancel();
/**
* Waits for the task runner to become inactive.
*/
void join();
private:
/**
* Runs tasks in a loop.
* Loop exits when any of the tasks returns a non-kContinue next action.
*/
void _runTasks();
void _finishRunTasks_inlock();
/**
* Waits for next scheduled task to be added to queue.
* Returns null task when task runner is stopped.
*/
Task _waitForNextTask();
ThreadPool* _threadPool;
// Protects member data of this TaskRunner.
mutable Mutex _mutex = MONGO_MAKE_LATCH("TaskRunner::_mutex");
stdx::condition_variable _condition;
// _active is true when there are scheduled tasks in the task queue or
// when a task is being run by the task runner.
bool _active;
bool _cancelRequested;
// FIFO queue of scheduled tasks
std::list<Task> _tasks;
};
} // namespace repl
} // namespace mongo
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