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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 <memory>
#include "mongo/base/status.h"
#include "mongo/db/service_context.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/stdx/thread.h"
#include "mongo/transport/service_executor.h"
#include "mongo/util/concurrency/thread_pool.h"
#include "mongo/util/hierarchical_acquisition.h"
namespace mongo {
namespace transport {
/**
* A service executor that uses a fixed (configurable) number of threads to execute tasks.
* This executor always yields before executing scheduled tasks, and never yields before scheduling
* new tasks (i.e., `ScheduleFlags::kMayYieldBeforeSchedule` is a no-op for this executor).
*/
class ServiceExecutorFixed : public ServiceExecutor,
public std::enable_shared_from_this<ServiceExecutorFixed> {
public:
explicit ServiceExecutorFixed(ThreadPool::Options options);
virtual ~ServiceExecutorFixed();
static ServiceExecutorFixed* get(ServiceContext* ctx);
Status start() override;
Status shutdown(Milliseconds timeout) override;
Status schedule(Task task, ScheduleFlags flags) override;
Mode transportMode() const override {
return Mode::kSynchronous;
}
void appendStats(BSONObjBuilder* bob) const override;
private:
// Maintains the execution state (e.g., recursion depth) for executor threads
class ExecutorThreadContext {
public:
ExecutorThreadContext(std::weak_ptr<ServiceExecutorFixed> serviceExecutor)
: _executor(std::move(serviceExecutor)) {
_adjustRunningExecutorThreads(1);
}
ExecutorThreadContext(ExecutorThreadContext&&) = delete;
ExecutorThreadContext(const ExecutorThreadContext&) = delete;
~ExecutorThreadContext() {
_adjustRunningExecutorThreads(-1);
}
void run(ServiceExecutor::Task task) {
// Yield here to improve concurrency, especially when there are more executor threads
// than CPU cores.
stdx::this_thread::yield();
_recursionDepth++;
task();
_recursionDepth--;
}
int getRecursionDepth() const {
return _recursionDepth;
}
private:
void _adjustRunningExecutorThreads(int adjustment) {
if (auto executor = _executor.lock()) {
executor->_numRunningExecutorThreads.fetchAndAdd(adjustment);
}
}
int _recursionDepth = 0;
std::weak_ptr<ServiceExecutorFixed> _executor;
};
private:
AtomicWord<size_t> _numRunningExecutorThreads{0};
AtomicWord<bool> _canScheduleWork{false};
mutable Mutex _mutex =
MONGO_MAKE_LATCH(HierarchicalAcquisitionLevel(0), "ServiceExecutorFixed::_mutex");
stdx::condition_variable _shutdownCondition;
/**
* State transition diagram: kNotStarted ---> kRunning ---> kStopped
* The service executor cannot be in "kRunning" when its destructor is invoked.
*/
enum State { kNotStarted, kRunning, kStopped } _state = kNotStarted;
ThreadPool::Options _options;
std::unique_ptr<ThreadPool> _threadPool;
static inline thread_local std::unique_ptr<ExecutorThreadContext> _executorContext;
};
} // namespace transport
} // namespace mongo
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