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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 <memory>
#include <vector>
#include "mongo/platform/atomic_word.h"
namespace mongo {
namespace executor {
struct ConnectionPoolStats;
class TaskExecutor;
/**
* Represents a pool of TaskExecutors. Work which requires a TaskExecutor can ask for an executor
* from the pool. This allows for work to be distributed across several executors.
*
* The TaskExecutor and its owned NetworkInterface can become a performance bottleneck, so this
* pooling approach provides better scalability under concurrent query workloads.
*
* Initialization and shutdown methods are not thread-safe, but getArbitraryExecutor() may be called
* concurrently by multiple threads.
*/
class TaskExecutorPool final {
public:
/**
* Based on properties of the system (e.g. the number of cores), suggests a number of executors
* to add to the pool.
*/
static size_t getSuggestedPoolSize();
/**
* Initializes the underlying executors. This method may be called at most once for the lifetime
* of an executor.
*
* May only be called after populating the pool with addExecutors().
*/
void startup();
/**
* Shuts down all underlying executors and waits for them to finish. May block.
*
* If startup() has been called, this method must eventually be called exactly once. Must be
* called after startup().
*/
void shutdownAndJoin();
/**
* Adds 'executors' and 'fixedExecutor' to the pool. May be called at most once to initialize an
* empty pool.
*/
void addExecutors(std::vector<std::unique_ptr<TaskExecutor>> executors,
std::unique_ptr<TaskExecutor> fixedExecutor);
/**
* Returns a pointer to one of the executors in the pool. Two calls to this method may return
* different executors. Invalid to call if the pool has not been initialized with
* addExecutors().
*
* Use this method if you need a TaskExecutor for performing performance-critical work.
*
* Thread-safe.
*/
TaskExecutor* getArbitraryExecutor();
/**
* Returns a pointer to the pool's fixed executor. Every call to this method will return the
* same executor. Invalid to call if the fixed executor has not been initialized with
* addExecutors().
*
* Use this method if you are *not* using the TaskExecutor for performance-critical work.
*
* Thread-safe.
*/
TaskExecutor* getFixedExecutor();
/**
* Appends connection information from all of the executors in the pool.
*
* NOTE: this method returns approximate stats. To avoid blocking operations on the
* pool, we don't lock for appendConnectionStats, so data gathered across connection pools
* will be from slightly different points in time.
*/
void appendConnectionStats(ConnectionPoolStats* stats) const;
private:
AtomicWord<unsigned> _counter;
std::vector<std::unique_ptr<TaskExecutor>> _executors;
std::unique_ptr<TaskExecutor> _fixedExecutor;
};
} // namespace executor
} // namespace mongo
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