[Mpi-forum] Cancelling a send matched by a matching probe

[Marek Tomáštík]

2015-10-31 17:33 GMT+01:00 William Gropp <wgropp at illinois.edu>:
>Under the interpretation of using whether the target process has observed,
>rather than received the message, a consistent interpretation is that the
>MPI_Cancel fails at the source, as it would if the message had been
received.

But does that satisfy the requirement that "[i]f a communication is marked
for cancellation, then a MPI_WAIT call for that communication is guaranteed
to return, irrespective of the activities of other processes (i.e.,
MPI_WAIT behaves as a local function); similarly if MPI_TEST is repeatedly
called in a busy wait loop for a cancelled communication, then MPI_TEST
will eventually be successful"? As far as I can see, MPI_Wait for the
matched send cannot be local, since it can complete only once the receiver
actually receives the message.

I understand that cancelling of sends is in the process of being phased out
of the standard, but I would like to find out how/if it's possible to
implement this feature correctly given that it is, currently, a part of the
standard.

Marek Tomáštík
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