There are 2 issues you need to be aware of. First, unless you know a
message has been copied out of the send buffer you cannot touch the send
buffer. Touching the buffer before the data has been copied out (for
either reading or writing) is strictly prohibited by the standard.
There are only 2 ways to know the message has been copied out of the
send buffer. One is by completing the Isend (with a wait or test
operation). The other is for the receiver to report that the message
has been received.
The other issue is the request handle returned from the Isend routine.
There are a finit number of these handles available. If you do not free
these handles (by completing a wait, a test that returns true, or
explicitely with MPI_Request_free) you will eventually run out of
available handles and your app will die on the Isend. You may not run
into this for short runs, but the limit exists and you should free requests.
To answer your real question, there should be (as long as the
implementation is standard compliant) no worry about buffer overflow.
What may happen is, if the system runs out of system resources your send
data will remain in the send buffer until enough system resources have
been freed or the message is matched to a send. See point 1 above for
the conseequences of this.
I hope this helps.
Dave.
Guanhua Yan wrote:
> Hi all,
>
> Sorry if this is off topic. I used MPI_Isend (to the same destination) for
> many times without checking whether each sending operation has finished. Is
> it possible that this will run into buffer overflow problem at the receiver
> side? Should I do message control by myself or the MPI kernell handles all
> these? Or is it MPI implementation dependent?
>
> Thanks,
> Guanhua
> _______________________________________________
> This list is archived at http://www.lam-mpi.org/MailArchives/lam/
>
--
Dr. David Cronk, Ph.D. phone: (865) 974-3735
Research Leader fax: (865) 974-8296
Innovative Computing Lab http://www.cs.utk.edu/~cronk
University of Tennessee, Knoxville
|
