Poco::ThreadPool

Poco::ThreadPool提供線程池功能，減少線程的創建和銷毀所帶來的開銷，適合在服務器上應用。創建線程池時指定最少運行線程數和線程池的最大容量，若不指定則采用默認值，取2和16 。線程池的實現機制：有一部分線程始終處於運行狀態，但阻塞在Event的wait調用上，所以處於休眠狀態，開銷並不大。如果我們需要一個線程來運行一段代碼（在Poco中，用Runnable的子類表示一個target），則從線程池中去除一個線程，並將這段代碼賦給它，並觸發Event。然後線程就繼續運行了。

活動圖

demo
[cpp] 
void ThreadPoolTest::testThreadPool() 
{ 
    ThreadPool pool(2, 3, 3); 
 
    assert (pool.allocated() == 2); 
    assert (pool.used() == 0); 
    assert (pool.capacity() == 3); 
    assert (pool.available() == 3); 
    pool.addCapacity(1); 
    assert (pool.allocated() == 2); 
    assert (pool.used() == 0); 
    assert (pool.capacity() == 4); 
    assert (pool.available() == 4); 
 
    RunnableAdapter<ThreadPoolTest> ra(*this, &ThreadPoolTest::hello); 
    pool.start(ra); 
    assert (pool.allocated() == 2); 
    assert (pool.used() == 1); 
    assert (pool.capacity() == 4); 
    assert (pool.available() == 3); 
 
    pool.start(ra); 
    assert (pool.allocated() == 2); 
    assert (pool.used() == 2); 
    assert (pool.capacity() == 4); 
    assert (pool.available() == 2); 
 
    pool.start(ra); 
    assert (pool.allocated() == 3); 
    assert (pool.used() == 3); 
    assert (pool.capacity() == 4); 
    assert (pool.available() == 1); 
 
    pool.start(ra); 
    assert (pool.allocated() == 4); 
    assert (pool.used() == 4); 
    assert (pool.capacity() == 4); 
    assert (pool.available() == 0); 
}