lib/cpp/src/concurrency/ThreadManager.cc

#include "ThreadManager.h"
#include "Exception.h"
#include "Monitor.h"

#include <assert.h>
#include <queue>
#include <set>

namespace facebook { namespace thrift { namespace concurrency { 


/** ThreadManager class
    
    This class manages a pool of threads.  It uses a ThreadFactory to create threads.  It never actually creates or destroys worker threads, rather
    it maintains statistics on number of idle threads, number of active threads, task backlog, and average wait and service times.

    @author marc
    @version $Id:$ */

class ThreadManager::Impl : public ThreadManager  {

 public:

  Impl() : _state(ThreadManager::UNINITIALIZED) {}

  ~Impl() {stop();}

  void start();

  void stop();

  const ThreadManager::STATE state() const {
    return _state;
  };

  const ThreadFactory* threadFactory() const {

    Synchronized s(_monitor); 

    return _threadFactory;
  }
      
  void threadFactory(const ThreadFactory*  value) {
    
    Synchronized s(_monitor); 
    
    _threadFactory = value;
  }

  void addWorker(size_t value);
  
  void removeWorker(size_t value);
  
  size_t idleWorkerCount() const {return _idleCount;}

  size_t workerCount() const {

    Synchronized s(_monitor); 

    return _workerCount;
  }
  
  size_t pendingTaskCount() const {

    Synchronized s(_monitor); 

    return _tasks.size();
  }

  size_t totalTaskCount() const {

    Synchronized s(_monitor); 
    
    return _tasks.size() + _workerCount - _idleCount;
  }
  
  void add(Runnable* value);

  void remove(Runnable* task);

private:

  size_t _workerCount;

  size_t _workerMaxCount;

  size_t _idleCount;

  ThreadManager::STATE _state;

  const ThreadFactory* _threadFactory;

  friend class ThreadManager::Task;

  std::queue<Task*> _tasks;

  Monitor _monitor;

  Monitor _workerMonitor;

  friend class ThreadManager::Worker;

  std::set<Thread*> _workers;
  
  std::set<Thread*> _deadWorkers;
};

class ThreadManager::Task : public Runnable {

public:
  enum STATE {
    WAITING,
    EXECUTING,
    CANCELLED,
    COMPLETE
  };

  Task(Runnable* runnable) :
    _runnable(runnable),
    _state(WAITING) 
    {}

  ~Task() {};

  void run() {
    if(_state == EXECUTING) {
      _runnable->run();
      _state = COMPLETE;
    }
  }

 private:

  Runnable* _runnable;
  
  friend class ThreadManager::Worker;

  STATE _state;
};

class ThreadManager::Worker: public Runnable {

  enum STATE {
    UNINITIALIZED,
    STARTING,
    STARTED,
    STOPPING,
    STOPPED
  };

 public:

  Worker(ThreadManager::Impl* manager) : 
    _manager(manager),
    _state(UNINITIALIZED),
    _idle(false)
  {}

  ~Worker() {}

  bool isActive() const { return _manager->_workerCount <= _manager->_workerMaxCount;}

  /** Worker entry point

      As long as worker thread is running, pull tasks off the task queue and execute. */

  void run() {

    bool active = false;
    
    bool notifyManager = false;

    /** Increment worker semaphore and notify manager if worker count reached desired max
	
	Note
	We have to release the monitor and acquire the workerMonitor since that is what the manager
	blocks on for worker add/remove */

    {Synchronized s(_manager->_monitor);

      active = _manager->_workerCount < _manager->_workerMaxCount;

      if(active) {

	_manager->_workerCount++;

	notifyManager = _manager->_workerCount == _manager->_workerMaxCount;
      }
    }

    if(notifyManager) {

      Synchronized s(_manager->_workerMonitor);

      _manager->_workerMonitor.notify();

      notifyManager = false;
    }

    while(active) {

      ThreadManager::Task* task = NULL;

      /* While holding manager monitor block for non-empty task queue (Also check that the thread hasn't been requested to stop).

	 Once the queue is non-empty, dequeue a task, release monitor, and execute. If the worker max count has been decremented
	 such that we exceed it, mark ourself inactive, decrement the worker count and notify the manager (technically we're notifying
	 the next blocked thread but eventually the manager will see it. */

      {Synchronized s(_manager->_monitor);

	active = isActive();

	while(active && _manager->_tasks.empty()) {
	  
	  _manager->_idleCount++;

	  _idle = true;
	  
	  _manager->_monitor.wait();
	  
	  active = isActive();

	  _idle = false;
	  
	  _manager->_idleCount--;
	}

	if(active) {

	  if(!_manager->_tasks.empty()) {
	  
	    task = _manager->_tasks.front();

	    _manager->_tasks.pop();
	    
	    if(task->_state == ThreadManager::Task::WAITING) {
	    
	      task->_state = ThreadManager::Task::EXECUTING;
	    }
	  }
	} else {

	  _idle = true;
	  
	  _manager->_workerCount--;
	  
	  notifyManager = _manager->_workerCount == _manager->_workerMaxCount;
	}
      }

      if(task != NULL) {

	if(task->_state == ThreadManager::Task::EXECUTING) {
	  try {
	    
	    task->run();
	    
	  } catch(...) {
	    
	    // XXX need to log this
	  }
	  
	  delete task;
	  
	  task = NULL;
	}
      }
    }

    {Synchronized s(_manager->_workerMonitor);    

      _manager->_deadWorkers.insert(this->thread());
      
      if(notifyManager) {

	_manager->_workerMonitor.notify();
      }
    }

    return;
  }

 private:

  ThreadManager::Impl* _manager;

  friend class ThreadManager::Impl;

  STATE _state;

  bool _idle;
};

void ThreadManager::Impl::addWorker(size_t value) {
    
  std::set<Thread*> newThreads;
  
  for(size_t ix = 0; ix < value; ix++) {

    class ThreadManager::Worker;
      
    ThreadManager::Worker* worker = new ThreadManager::Worker(this);

    newThreads.insert(_threadFactory->newThread(worker));
  }

  {Synchronized s(_monitor);

    _workerMaxCount+= value;

    _workers.insert(newThreads.begin(), newThreads.end());
  }
  
  for(std::set<Thread*>::iterator ix = newThreads.begin(); ix != newThreads.end(); ix++) {

    ThreadManager::Worker* worker = (ThreadManager::Worker*)(*ix)->runnable();

    worker->_state = ThreadManager::Worker::STARTING;

    (*ix)->start();
  }

  {Synchronized s(_workerMonitor); 
      
    while(_workerCount != _workerMaxCount) {
      _workerMonitor.wait();
    }
  }
}

void ThreadManager::Impl::start() {

  if(_state == ThreadManager::STOPPED) {
    return;
  }

  {Synchronized s(_monitor); 

    if(_state == ThreadManager::UNINITIALIZED) {

      if(_threadFactory == NULL) {throw InvalidArgumentException();}

      _state = ThreadManager::STARTED;

      _monitor.notifyAll();
    }

    while(_state == STARTING) {

      _monitor.wait();
    }
  }
}

void ThreadManager::Impl::stop() {

  bool doStop = false;

  if(_state == ThreadManager::STOPPED) {
    return;
  }

  {Synchronized s(_monitor); 

    if(!_state != ThreadManager::STOPPING && _state != ThreadManager::STOPPED) {

      doStop = true;

      _state = ThreadManager::STOPPING;
    }
  }

  if(doStop) {

    removeWorker(_workerCount);

    _state = ThreadManager::STOPPING;
  }

  // Don't block for stopping->stopped transition here, since if stop is being performed in context of a delete, the monitor may be invalid
     
}
  
void ThreadManager::Impl::removeWorker(size_t value) {

  std::set<Thread*> removedThreads;

  {Synchronized s(_monitor); 

    if(value > _workerMaxCount) {

      throw InvalidArgumentException();
    }

    _workerMaxCount-= value;

    if(_idleCount < value) {
      
      for(size_t ix = 0; ix < _idleCount; ix++) {

	_monitor.notify();
      }
    } else {

      _monitor.notifyAll();
    }
  }

  {Synchronized s(_workerMonitor); 

    while(_workerCount != _workerMaxCount) {
      _workerMonitor.wait();
    }

    for(std::set<Thread*>::iterator ix = _deadWorkers.begin(); ix != _deadWorkers.end(); ix++) {

	_workers.erase(*ix);
	
	delete (*ix)->runnable();

	delete (*ix);
    }

    _deadWorkers.clear();
  }
}
  
void ThreadManager::Impl::add(Runnable* value) {

    Synchronized s(_monitor); 

    if(_state != ThreadManager::STARTED) {

      throw IllegalStateException();
    }

    _tasks.push(new ThreadManager::Task(value));

    /* If idle thread is available notify it, otherwise all worker threads are running and will get around to this
       task in time. */

    if(_idleCount > 0) {

      _monitor.notify();
    }
  }

void ThreadManager::Impl::remove(Runnable* task) {

    Synchronized s(_monitor); 

    if(_state != ThreadManager::STARTED) {

      throw IllegalStateException();
    }
}

class SimpleThreadManager : public ThreadManager::Impl {

public:

  SimpleThreadManager(size_t workerCount=4) : 
    _workerCount(workerCount),
    _firstTime(true) {
  }

  void start() {
    ThreadManager::Impl::start();

    addWorker(_workerCount);
  }

private:

  const size_t _workerCount;
  bool _firstTime;
  Monitor _monitor;
};


ThreadManager* ThreadManager::newThreadManager() {
   return new ThreadManager::Impl();
}

ThreadManager* ThreadManager::newSimpleThreadManager(size_t count) {
   return new SimpleThreadManager(count);
}

}}} // facebook::thrift::concurrency