poco/Foundation/include/Poco/ThreadPool.h

//
// ThreadPool.h
//
// Library: Foundation
// Package: Threading
// Module:  ThreadPool
//
// Definition of the ThreadPool class.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_ThreadPool_INCLUDED
#define Foundation_ThreadPool_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/Thread.h"
#include "Poco/Mutex.h"
#include <vector>


namespace Poco {


class Runnable;
class PooledThread;


class Foundation_API ThreadPool
	/// A thread pool always keeps a number of threads running, ready
	/// to accept work.
	/// Creating and starting a threads can impose a significant runtime
	/// overhead to an application. A thread pool helps to improve
	/// the performance of an application by reducing the number
	/// of threads that have to be created (and destroyed again).
	/// Threads in a thread pool are re-used once they become
	/// available again.
	/// The thread pool always keeps a minimum number of threads
	/// running. If the demand for threads increases, additional
	/// threads are created. Once the demand for threads sinks
	/// again, no-longer used threads are stopped and removed
	/// from the pool.
{
public:
	ThreadPool(int minCapacity = 2,
		int maxCapacity = 16,
		int idleTime = 60,
		int stackSize = POCO_THREAD_STACK_SIZE);
		/// Creates a thread pool with minCapacity threads.
		/// If required, up to maxCapacity threads are created
		/// a NoThreadAvailableException exception is thrown.
		/// If a thread is running idle for more than idleTime seconds,
		/// and more than minCapacity threads are running, the thread
		/// is killed. Threads are created with given stack size.

	ThreadPool(const std::string& name,
		int minCapacity = 2,
		int maxCapacity = 16,
		int idleTime = 60,
		int stackSize = POCO_THREAD_STACK_SIZE);
		/// Creates a thread pool with the given name and minCapacity threads.
		/// If required, up to maxCapacity threads are created
		/// a NoThreadAvailableException exception is thrown.
		/// If a thread is running idle for more than idleTime seconds,
		/// and more than minCapacity threads are running, the thread
		/// is killed. Threads are created with given stack size.

	~ThreadPool();
		/// Currently running threads will remain active
		/// until they complete.

	void addCapacity(int n);
		/// Increases (or decreases, if n is negative)
		/// the maximum number of threads.

	int capacity() const;
		/// Returns the maximum capacity of threads.

	void setStackSize(int stackSize);
		/// Sets the stack size for threads.
		/// New stack size applies only for newly created threads.

	int getStackSize() const;
		/// Returns the stack size used to create new threads.

	int used() const;
		/// Returns the number of currently used threads.

	int allocated() const;
		/// Returns the number of currently allocated threads.

	int available() const;
		/// Returns the number available threads.

	void start(Runnable& target);
		/// Obtains a thread and starts the target.
		/// Throws a NoThreadAvailableException if no more
		/// threads are available.

	void start(Runnable& target, const std::string& name);
		/// Obtains a thread and starts the target.
		/// Assigns the given name to the thread.
		/// Throws a NoThreadAvailableException if no more
		/// threads are available.

	void startWithPriority(Thread::Priority priority, Runnable& target);
		/// Obtains a thread, adjusts the thread's priority, and starts the target.
		/// Throws a NoThreadAvailableException if no more
		/// threads are available.

	void startWithPriority(Thread::Priority priority, Runnable& target, const std::string& name);
		/// Obtains a thread, adjusts the thread's priority, and starts the target.
		/// Assigns the given name to the thread.
		/// Throws a NoThreadAvailableException if no more
		/// threads are available.

	void stopAll();
		/// Stops all running threads and waits for their completion.
		///
		/// Will also delete all thread objects.
		/// If used, this method should be the last action before
		/// the thread pool is deleted.
		///
		/// Note: If a thread fails to stop within 10 seconds
		/// (due to a programming error, for example), the
		/// underlying thread object will not be deleted and
		/// this method will return anyway. This allows for a
		/// more or less graceful shutdown in case of a misbehaving
		/// thread.

	void joinAll();
		/// Waits for all threads to complete.
		///
		/// Note that this will not actually join() the underlying
		/// thread, but rather wait for the thread's runnables
		/// to finish.

	void collect();
		/// Stops and removes no longer used threads from the
		/// thread pool. Can be called at various times in an
		/// application's life time to help the thread pool
		/// manage its threads. Calling this method is optional,
		/// as the thread pool is also implicitly managed in
		/// calls to start(), addCapacity() and joinAll().

	const std::string& name() const;
		/// Returns the name of the thread pool,
		/// or an empty string if no name has been
		/// specified in the constructor.

	static ThreadPool& defaultPool();
		/// Returns a reference to the default
		/// thread pool.

protected:
	PooledThread* getThread();
	PooledThread* createThread();

	void housekeep();

private:
	ThreadPool(const ThreadPool& pool);
	ThreadPool& operator = (const ThreadPool& pool);

	typedef std::vector<PooledThread*> ThreadVec;

	std::string _name;
	int _minCapacity;
	int _maxCapacity;
	int _idleTime;
	int _serial;
	int _age;
	int _stackSize;
	ThreadVec _threads;
	mutable FastMutex _mutex;
};


//
// inlines
//
inline void ThreadPool::setStackSize(int stackSize)
{
	_stackSize = stackSize;
}


inline int ThreadPool::getStackSize() const
{
	return _stackSize;
}


inline const std::string& ThreadPool::name() const
{
	return _name;
}


} // namespace Poco


#endif // Foundation_ThreadPool_INCLUDED