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/**
* Copyright (C) 2020-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 "mongo/platform/atomic_word.h"
namespace mongo {
class ThreadSafetyContextTest;
/**
* Provides a singleton object that allows enforcing a single-threaded context at startup.
*
* This class, currently, intercepts `stdx::thread` creations and aborts the process if a single
* threaded context is expected.
*
* You should avoid using the interfaces that specify single-threaded context (i.e.,
* `forbidMultiThreading()` and `allowMultiThreading()`) outside the main function.
*
* If using other APIs for spawning threads (e.g., `pthread_create()`), make sure to precede the
* API call with `onThreadCreate()`.
*/
class ThreadSafetyContext final {
public:
ThreadSafetyContext(const ThreadSafetyContext&) = delete;
ThreadSafetyContext(ThreadSafetyContext&&) noexcept = delete;
ThreadSafetyContext& operator=(const ThreadSafetyContext&) = delete;
ThreadSafetyContext& operator=(ThreadSafetyContext&&) = delete;
static ThreadSafetyContext* getThreadSafetyContext() noexcept;
// Prevents a multi-threaded context -- aborts the process on thread creation.
// If the program is already multi-threaded, it will abort the program.
void forbidMultiThreading() noexcept;
// Allows a multi-threaded context by lifting the limit enforced by `forbidMultiThreading()`.
void allowMultiThreading() noexcept;
// Allows detecting thread creation, and thus a multi-threaded context.
// If not using `stdx::thread`, you must always call this method before spawning a new thread.
void onThreadCreate() noexcept;
// Returns "true" if no threads have been created throughout the lifetime of the process.
bool isSingleThreaded() const noexcept {
return _isSingleThreaded.load();
}
// Restricts the ability of resetting the context to the unit-test fixture.
friend class ThreadSafetyContextTest;
private:
// Prevents creating any instance of the object (other than the singleton).
ThreadSafetyContext() = default;
// An indicator on whether the program is single-threaded.
AtomicWord<bool> _isSingleThreaded{true};
// If set to "false", it will prevent creation of new threads.
AtomicWord<bool> _safeToCreateThreads{true};
};
} // namespace mongo
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