ompi/request: Fix a persistent request creation bug #2545
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According to the MPI-3.1 p.52 and p.53 (cited below), a request created by `MPI_*_INIT` but not yet started by `MPI_START` or `MPI_STARTALL` is inactive therefore `MPI_WAIT` or its friends must return immediately if such a request is passed. The current implementation hangs in `MPI_WAIT` and its friends in such case because a persistent request is initialized as `req_complete = REQUEST_PENDING`. This commit fixes the initialization. Also, this commit fixes internal requests used in `MPI_PROBE` and `MPI_IPROBE` which was marked wrongly as persistent. MPI-3.1 p.52: We shall use the following terminology: A null handle is a handle with value MPI_REQUEST_NULL. A persistent request and the handle to it are inactive if the request is not associated with any ongoing communication (see Section 3.9). A handle is active if it is neither null nor inactive. An empty status is a status which is set to return tag = MPI_ANY_TAG, source = MPI_ANY_SOURCE, error = MPI_SUCCESS, and is also internally configured so that calls to MPI_GET_COUNT, MPI_GET_ELEMENTS, and MPI_GET_ELEMENTS_X return count = 0 and MPI_TEST_CANCELLED returns false. We set a status variable to empty when the value returned by it is not significant. Status is set in this way so as to prevent errors due to accesses of stale information. MPI-3.1 p.53: One is allowed to call MPI_WAIT with a null or inactive request argument. In this case the operation returns immediately with empty status. Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>
bosilca
approved these changes
Dec 8, 2016
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@bosilca Could you review? It's a simple corner case bug.
I'll create PRs for v2.0.2 and v2.1.0.
According to the MPI-3.1 p.52 and p.53 (cited below), a request
created by
MPI_*_INITbut not yet started byMPI_STARTorMPI_STARTALLis inactive thereforeMPI_WAITor its friendsmust return immediately if such a request is passed.
The current implementation hangs in
MPI_WAITand its friendsin such case because a persistent request is initialized as
req_complete = REQUEST_PENDING. This commit fixes theinitialization.
Also, this commit fixes internal requests used in
MPI_PROBEand
MPI_IPROBEwhich was marked wrongly as persistent.MPI-3.1 p.52:
We shall use the following terminology: A null handle is a handle
with value MPI_REQUEST_NULL. A persistent request and the handle
to it are inactive if the request is not associated with any ongoing
communication (see Section 3.9). A handle is active if it is neither
null nor inactive. An empty status is a status which is set to return
tag = MPI_ANY_TAG, source = MPI_ANY_SOURCE, error = MPI_SUCCESS, and
is also internally configured so that calls to MPI_GET_COUNT,
MPI_GET_ELEMENTS, and MPI_GET_ELEMENTS_X return count = 0 and
MPI_TEST_CANCELLED returns false. We set a status variable to empty
when the value returned by it is not significant. Status is set in
this way so as to prevent errors due to accesses of stale information.
MPI-3.1 p.53:
One is allowed to call MPI_WAIT with a null or inactive request
argument. In this case the operation returns immediately with empty
status.
Signed-off-by: KAWASHIMA Takahiro t-kawashima@jp.fujitsu.com