Newsgroups: comp.parallel.pvm
From: Sandor Bozoki <sbozoki@ccsmtp.tii.matav.hu>
Reply-To: sbozoki@ccsmtp.tii.matav.hu
Subject: Is pvm_send() always asynchronous?
Organization: MATAV-PKI
Date: Tue, 31 Mar 1998 16:50:21 +0200
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Message-ID: <352102AD.3546@ccsmtp.tii.matav.hu>

Dear PVM users!

The PVM documentation states that pvm_send() and pvm_psend() are
asynchronous operations, that is, pvm_recv() does not need to be called
when the transfer begins. This is certainly true if the message is
routed via the daemons.
However, I have experienced that pvm_send() halts until pvm_recv() is
executed if direct routing is used and the two processes (sender and
receiver) are on different hosts. If they are on the same host, this
problem does not appear.
In the 1st case, the communication becomes synchronous for some reasons.
Why?
This inhibits the overlapping of computation and communication, which
would be very important for me. Could somebody explain this to me?

Regards,
      Sandor