RS> I'm writing a program with two threads. There are two 
 RS> unnamed pipes, created with DosCreatePipe(), to 
 RS> communicate between the threads. 

 RS> One of the pipes is used to send commands from the 
 RS> main thread to the other thread, the other one to send 
 RS> status information from the other thread to the main 
 RS> thread.

This is a very odd use for a pipe.  Unnamed pipes were provided primarily
for separate _processes_ to send data to each other,  ala Unix stuff.

They are slow and cumbersome in the eyes of a Thread,  who has more
flexible/powerful/faster IPC mechanisms available.  In your case,  I would
have used queues (see DosCreateQueue()).

 RS> Since I also have to do other things in both threads, 
 RS> I don't want the DosRead()-call to block.

If you ever find yourself saying a thread has "other things to
do" it means you need another thread!   When nothing is happening, 
ALL threads should be blocked on a system call.

For the same reason,  DosReadQueue() should always be called with DCWW_WAIT
(wait for an element to be placed in the queue).  If you find yourself
wanting to call it with DCWW_NOWAIT,  you have made a design error
somewhere.

There is a DosPeekQueue() and DosQueryQueue() function,  but no one should
ever use them for the reasons just stated...

Pete's Thread Axiom:  A threads primary purpose is to do nothing very well.


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