Hi - I'm using asio::io_service as a dispatcher for a thread pool. I'm wondering how I can synchronize the threads after I post the tasks to the io_service. I tried using a barrier but it doesn't always work correctly. The barrier waits indefinitely; although I verified the post() function gets called, the io_service doesn't seem to dispatch anything. I've also thread using the boost::threadpool library but the overall speed is slower. I'd appreciate any insight on what I'm doing wrong with the barrier or any other high performance thread pooling alternatives. Thanks, Daren <code> void handler ( int i, int nSize, double *pArray, double *pTemp, boost::barrier *pBarrier ) {     // compute on pArrray --> write result to pTemp[i] ....     pBarrier->wait(); } double doCalc ( int nSize, double *pArray, double *pTemp ) {     unsigned  int nNumThreads = 8;     int nSubSize = nSize / nNumThreads;     boost::barrier barrier( nNumThreads + 1 );     for( int i=0;i<nNumThreads;i++ )     { if( i == nNumThreads-1 ) { m_io_service.post( boost::bind( &handler, i, nSize-(i*nSubSize), pArray+(i*nSubSize), pTemp, &barrier )); } else { m_io_service.post( boost::bind( &handler, i, nSubSize, pArray+(i*nSubSize), pTemp, &barrier )); }     } barrier.wait(); // sum results double fSum = 0; for( int i=0;i<nNumThreads;i++ ) { fSum += pTemp[i]; } return fSum; }  I initialize the io_service with work elsewhere as: boost::asio::io_service::work m_work( m_io_service ); boost::thread_group m_threads; for (std::size_t i = 0; i < m_nNumThreads; ++i) m_threads.create_thread(boost::bind(&boost::asio::io_service::run, &m_io_service)); </code>