Newsgroups: comp.parallel.pvm
From: jtdougl@hubcap.clemson.edu (John T. Douglass)
Subject: UDP and TCP
Organization: Clemson University
Date: 23 Mar 1995 14:02:11 GMT
Message-ID: <3krv13$ig6@hubcap.clemson.edu>

Since my posting yesterday I have discovered a little more information.  I
had my local admin recompile pvm with the debugging option so that I could
trace through the library calls.  I am using pvm 3.7.  The behaviour that
I observed in the debugger when my program hangs is as follows:  at the 
first sync. point task 1 and task 2 exchange messages.  When these tasks
hang I get the following dumps:

	task 1				   task 2

	connect()			   select()

	pvmmcntl()			   mxfer()
	   -lpvm.c line 1142		      - lpvm.c line 1499
   
	mxfer()	  			   mroute()
	   -lpvm.c line 1532  		      - lpvm.c line 742

	mroute() 			   pvm_send()
	   -lpvm.c line 742		      - lpvmgen.c 1305

	pvm_send() 
	   -lpvmgen.c line 1305
 
The appearance is that when both tasks are trying to establish the 
tcp connection at the same time that there is a sequence of events 
which is time dependent (arrival of TC_CONREQ) that causes pvm
to hang (the timeout value to select was nil).  Any further suggestions??

-- jd

John T. Douglass (douglass@cs.clemson.edu)
Clemson University



