B.12.3 Blocking System Services

All blocking system services are thread synchronous in OpenVMS Alpha Version 7.0. That is, they block only the calling thread. When the thread is to be blocked by the system service, the OpenVMS scheduler makes an upcall to allow DECthreads to schedule another user thread to execute. Therefore, only the calling thread is blocked. All other threads are unaffected, and the process continues running. When the service completes, the thread is awakened by means of another upcall, and DECthreads schedules it to run again at the thread's next opportunity.

This applies to all "W" forms of system services. For example, $QIOW, $END_TRANSW, and $GETJPIW. Additionally, this applies to the following event flag services: $WAITFR, $WFLAND, and $WFLOR.