Microsoft KB Archive/59951

= DosWaitNmPipe Behavior =

Article ID: 59951

Article Last Modified on 10/31/2006



This article was previously published under Q59951



SUMMARY
The QuickHelp entry for DosWaitNmPipe says that the longest waiting client will receive the first go-ahead. Gordon Letwin's &quot;Inside OS/2&quot; says that the highest priority process will receive the first go-ahead.

The following information discusses how WaitNmPipe works when the clients are on separate workstations on a network.



MORE INFORMATION
Suppose a server program has only one instance of a pipe available and it is currently used by one client. Suppose there are other N clients waiting at DosWaitNmPipe. As soon as the pipe instance becomes available, the (client) process with highest priority will return first from DosWaitNmPipe. If all waiting (client) processes have the same priority, all such (client) processes will return from DosWaitNmPipe together in the (chronological) order they called DosWaitNmPipe.

Once a pipe instance becomes available, ALL (client) processes/threads waiting on DosWaitNmPipe will return; each such process/thread will return from DosWaitNmPipe in the order of its priority and the time of blocking on DosWaitNmPipe. Thus, when all processes have the same priority, the process waiting the longest will return from DosWaitNmPipe first.

Once a (client) process has returned successfully from DosWaitNmPipe, it still does not have the pipe instance until it does a DosOpen again.

For example, suppose all N clients have the same priority. All of the clients will then return from DosWaitNmPipe one by one. Then, the first (client) process to call a DosOpen will get the instance of the pipe; the rest will get an ERROR_PIPE_BUSY. The rest (N-1) of the clients must then wait again for the next available instance of the pipe.

Usually, in cases such as this, the first (client) process scheduled to run by the OS/2 scheduler (which is completely independent of the pipe contention scenario above) will get the pipe also.

For remote clients, the behavior is similar. The first DosOpen request to reach the server over the net will get the newly available pipe instance; the rest will get an ERROR_PIPE_BUSY response.

Additional query words: 2.00 2.10 2.10a 2.20 DosWaitNmPipe namedpipe

Keywords: KB59951

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