Turns out the AV only occurs with MSVC 7.1. With VC 8.0 Express I was able to diagnose the true error: PostQueuedCompletionStatus is failing with ERROR_NO_SYSTEM_RESOURCES, however I was not checking the return value. My bad :*) Here is a diff to fix this (against CVS version of asio). With this change the test runs successfully to completion. Cheers, Chris ---------------------- Index: win_iocp_demuxer_service.hpp =================================================================== RCS file: /cvsroot/asio/asio/include/asio/detail/win_iocp_demuxer_service.hpp,v retrieving revision 1.21 diff -u -r1.21 win_iocp_demuxer_service.hpp --- win_iocp_demuxer_service.hpp 2 Dec 2005 01:44:56 -0000 1.21 +++ win_iocp_demuxer_service.hpp 16 Dec 2005 10:02:57 -0000 @@ -102,7 +102,12 @@ if (::InterlockedExchangeAdd(&interrupted_, 0) != 0) { // Wake up next thread that is blocked on GetQueuedCompletionStatus. - ::PostQueuedCompletionStatus(iocp_.handle, 0, 0, 0); + if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, 0)) + { + DWORD last_error = ::GetLastError(); + system_exception e("pqcs", last_error); + boost::throw_exception(e); + } break; } } @@ -113,7 +118,14 @@ void interrupt() { if (::InterlockedExchange(&interrupted_, 1) == 0) - ::PostQueuedCompletionStatus(iocp_.handle, 0, 0, 0); + { + if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, 0)) + { + DWORD last_error = ::GetLastError(); + system_exception e("pqcs", last_error); + boost::throw_exception(e); + } + } } // Reset the demuxer in preparation for a subsequent run invocation. @@ -183,8 +195,15 @@ template <typename Handler> void post(Handler handler) { - win_iocp_operation* op = new handler_operation<Handler>(*this, handler); - ::PostQueuedCompletionStatus(iocp_.handle, 0, 0, op); + handler_operation<Handler>* op = + new handler_operation<Handler>(*this, handler); + if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, op)) + { + DWORD last_error = ::GetLastError(); + delete op; + system_exception e("pqcs", last_error); + boost::throw_exception(e); + } } private: