Workers.h

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2012, 2013 Ripple Labs Inc.
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#ifndef RIPPLE_CORE_WORKERS_H_INCLUDED
#define RIPPLE_CORE_WORKERS_H_INCLUDED
 
#include <ripple/core/impl/semaphore.h>
#include <ripple/beast/core/LockFreeStack.h>
#include <atomic>
#include <condition_variable>
#include <mutex>
#include <string>
#include <thread>
 
namespace ripple {
 
namespace perf
{
    class PerfLog;
}
 
class Workers
{
public:
    struct Callback
    {
        virtual ~Callback () = default;
        Callback() = default;
        Callback(Callback const&) = delete;
        Callback& operator=(Callback const&) = delete;
 
        virtual void processTask (int instance) = 0;
    };
 
    explicit Workers (Callback& callback,
                      perf::PerfLog* perfLog,
                      std::string const& threadNames = "Worker",
                      int numberOfThreads =
                         static_cast<int>(std::thread::hardware_concurrency()));
 
    ~Workers ();
 
    int getNumberOfThreads () const noexcept;
 
    void setNumberOfThreads (int numberOfThreads);
 
    void pauseAllThreadsAndWait ();
 
    void addTask ();
 
    int numberOfCurrentlyRunningTasks () const noexcept;
 
    //--------------------------------------------------------------------------
 
private:
    struct PausedTag
    {
        explicit PausedTag() = default;
    };
 
    /*  A Worker executes tasks on its provided thread.
 
        These are the states:
 
        Active: Running the task processing loop.
        Idle:   Active, but blocked on waiting for a task.
        Paused: Blocked waiting to exit or become active.
    */
    class Worker
        : public beast::LockFreeStack <Worker>::Node
        , public beast::LockFreeStack <Worker, PausedTag>::Node
    {
    public:
        Worker (Workers& workers,
            std::string const& threadName,
            int const instance);
 
        ~Worker ();
 
        void notify ();
 
    private:
        void run ();
 
    private:
        Workers& m_workers;
        std::string const threadName_;
        int const instance_;
 
        std::thread thread_;
        std::mutex mutex_;
        std::condition_variable wakeup_;
        int wakeCount_;               // how many times to un-pause
        bool shouldExit_;
    };
 
private:
    static void deleteWorkers (beast::LockFreeStack <Worker>& stack);
 
private:
    Callback& m_callback;
    perf::PerfLog* perfLog_;
    std::string m_threadNames;                   // The name to give each thread
    std::condition_variable m_cv;                // signaled when all threads paused
    std::mutex              m_mut;
    bool                    m_allPaused;
    semaphore m_semaphore;                       // each pending task is 1 resource
    int m_numberOfThreads;                       // how many we want active now
    std::atomic <int> m_activeCount;             // to know when all are paused
    std::atomic <int> m_pauseCount;              // how many threads need to pause now
    std::atomic <int> m_runningTaskCount;        // how many calls to processTask() active
    beast::LockFreeStack <Worker> m_everyone;           // holds all created workers
    beast::LockFreeStack <Worker, PausedTag> m_paused;  // holds just paused workers
};
 
} // beast
 
#endif