ThreadPool.h

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/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
 
#ifndef META_OCEAN_BASE_THREAD_POOL_H
#define META_OCEAN_BASE_THREAD_POOL_H
 
#include "ocean/base/Base.h"
#include "ocean/base/Lock.h"
#include "ocean/base/Signal.h"
#include "ocean/base/Singleton.h"
#include "ocean/base/Thread.h"
 
#include <functional>
#include <queue>
 
namespace Ocean
{
 
/**
 * This class implements a pool holding re-usable thread objects for individual use.
 * This class is not a singleton, use ThreadPoolSingleton in case a singleton is sufficient.
 * @see ThreadPoolSingleton, Scheduler, TaskQueue.
 * @ingroup base
 */
class OCEAN_BASE_EXPORT ThreadPool : protected Thread
{
    public:
 
        /**
         * Definition of a caller function without return parameter.
         */
        using Function = std::function<void()>;
 
    protected:
 
        /**
         * This class implements one thread of this thread pool.
         */
        class OCEAN_BASE_EXPORT PoolThread : protected Thread
        {
            public:
 
                /**
                 * Creates a new thread object.
                 * @param name The thread name
                 */
                explicit PoolThread(const std::string& name);
 
                /**
                 * Destructs a thread object.
                 */
                ~PoolThread() override;
 
                /**
                 * Returns whether this thread is currently busy.
                 * @return True, if so
                 */
                inline bool isBusy() const;
 
                /**
                 * Sets the thread function.
                 * @param function The thread function that will be invoked in this thread
                 */
                void invoke(Function&& function);
 
            protected:
 
                /**
                 * Thread run function.
                 */
                void threadRun() override;
 
            protected:
 
                /// Internal signal handling the internal thread execution.
                Signal signal_;
 
                /// The function that is invoked in this thread.
                Function function_;
 
                /// Thread lock.
                mutable Lock lock_;
        };
 
        /**
         * Definition of a unique pointer holding a pool thread.
         */
        using UniquePoolThread = std::unique_ptr<PoolThread>;
 
        /**
         * Definition of a vector holding pool threads.
         */
        using PoolThreads = std::vector<UniquePoolThread>;
 
        /**
         * Definition of a queue holding functions.
         */
        using FunctionQueue = std::queue<Function>;
 
    public:
 
        /**
         * Creates a new thread pool object.
         */
        ThreadPool() = default;
 
        /**
         * Destructs a thread pool.
         */
        ~ThreadPool() override;
 
        /**
         * Returns the maximal number of thread objects allowed inside this pool.
         * @return Maximal thread capacity, with range [1, infinity); 2 by default
         */
        inline size_t capacity() const;
 
        /**
         * Returns the number of currently busy/active threads in this pool.
         * @return Thread number, with range [0, infinity)
         */
        inline size_t size() const;
 
        /**
         * Defines the maximal number of thread objects existing concurrently.
         * @param capacity Maximal number of thread objects to be allowed inside this pool, with range (1, infinity)
         * @return True, if succeeded
         */
        bool setCapacity(const size_t capacity);
 
        /**
         * Invokes a function on one of the free threads of this pool.
         * @param function The function that will be invoked by a free thread
         * @return True, if the function will be invoked by a free thread, otherwise no free thread was available
         */
        bool invoke(Function&& function);
 
        /**
         * Returns the number of pending functions.
         * @return The number of pending functions which have not been executed yet as the pool is at capacity, with range [0, infinity)
         */
        inline size_t pending() const;
 
    protected:
 
        /**
         * Thread run function.
         */
        void threadRun() override;
 
    protected:
 
        /// The busy pool threads.
        PoolThreads busyPoolThreads_;
 
        /// The idle pool threads.
        PoolThreads idlePoolThreads_;
 
        /// The pending functions.
        FunctionQueue pendingFunctions_;
 
        /// Maximal pool capacity, with range [1, infinity)
        size_t capacity_ = 2;
 
        /// The counter for pool thread ids.
        size_t poolThreadIdCounter_ = 0;
 
        /// Pool lock.
        mutable Lock lock_;
};
 
/**
 * This class wraps the ThreadPool into a singleton for global usage.
 * Use the standard ThreadPool in case a singleton is not sufficient.
 * @see ThreadPool.
 * @ingroup base
 */
class ThreadPoolSingleton :
    public Singleton<ThreadPoolSingleton>,
    public ThreadPool
{
    friend class Singleton<ThreadPoolSingleton>;
 
    protected:
 
        /**
         * Protected default constructor.
         */
        ThreadPoolSingleton();
};
 
inline bool ThreadPool::PoolThread::isBusy() const
{
    const ScopedLock scopedLock(lock_);
 
    return function_ != nullptr;
}
 
inline size_t ThreadPool::capacity() const
{
    const ScopedLock scopedLock(lock_);
    return capacity_;
}
 
inline size_t ThreadPool::size() const
{
    const ScopedLock scopedLock(lock_);
 
    return busyPoolThreads_.size();
}
 
inline size_t ThreadPool::pending() const
{
    const ScopedLock scopedLock(lock_);
 
    return pendingFunctions_.size();
}
 
}
 
#endif // META_OCEAN_BASE_THREAD_POOL_H