Jeff Squyres wrote:
> On Sat, 26 Jun 2004 hye_at_[hidden] wrote:
>
[snip]
>>
>> My question is: is the First-sent-First-Received can be guaranteed?
>> For example, if one processor sends out message to other processor
>> using MPI_Isend or MPI_Send or both, in the sequence of TAG1, TAG2,
>> TAG1, TAG3, TAG2. Can it be guaranteed that, in the receiver side, the
>> sequence is still TAG1, TAG2, TAG1, TAG3, TAG2?
>
>
> No.
>
> MPI only guarantees that the order of messages sent with the same
> signature (i.e., sender and receiver, communicator, and tag) are
> ordered. Hence, it is possible (and legal) for MPI to allow messages
> with different tags to be delivered out of order (even with ANY_TAG).
The way I read the standard (page 29 of 1.0 standard and page 30 of the
1.1 standard) this is incorrect as order is guaranteed even with
different tags. Same sender, receiver, and communicator yes, but the
tags can differ. This is explicitely covered on page 53 of "MPI - The
Complete Reference Volume 1, The MPI Core" Second edition.
Dave.
>
>
[snip]
--
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
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