The function MPI_PROBE checks for incoming messages without receiving them. Since the list of incoming messages is global among the threads of each MPI process, it can be hard to use this functionality in threaded environments [29,26].
Like MPI_PROBE and MPI_IPROBE, the MPI_MPROBE and MPI_IMPROBE operations allow incoming messages to be queried without actually receiving them, except that MPI_MPROBE and MPI_IMPROBE provide a mechanism to receive the specific message that was matched regardless of other intervening probe or receive operations. This gives the application an opportunity to decide how to receive the message, based on the information returned by the probe. In particular, the user may allocate memory for the receive buffer, according to the length of the probed message.
| MPI_IMPROBE(source, tag, comm, flag, message, status) | |
| IN source | rank of source or MPI_ANY_SOURCE (integer) |
| IN tag | message tag or MPI_ANY_TAG (integer) |
| IN comm | communicator (handle) |
| OUT flag | flag (logical) |
| OUT message | returned message (handle) |
| OUT status | status object (Status) |
int MPI_Improbe(int source, int tag, MPI_Comm comm, int *flag, MPI_Message *message, MPI_Status *status)
MPI_Improbe(source, tag, comm, flag, message, status, ierror)
INTEGER, INTENT(IN) :: source, tag
TYPE(MPI_Comm), INTENT(IN) :: comm
LOGICAL, INTENT(OUT) :: flag
TYPE(MPI_Message), INTENT(OUT) :: message
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_IMPROBE(SOURCE, TAG, COMM, FLAG, MESSAGE, STATUS, IERROR)
INTEGER SOURCE, TAG, COMM, MESSAGE, STATUS(MPI_STATUS_SIZE), IERROR
LOGICAL FLAG
MPI_IMPROBE(source, tag, comm, flag, message, status) returns flag = true if there is a message that can be received and that matches the pattern specified by the arguments source, tag, and comm. The call matches the same message that would have been received by a call to MPI_RECV(..., source, tag, comm, status) executed at the same point in the program and returns in status the same value that would have been returned by MPI_RECV. In addition, it returns in message a handle to the matched message. Otherwise, the call returns flag = false, and leaves status and message undefined.
A matched receive ( MPI_MRECV or MPI_IMRECV) executed with the message handle will receive the message that was matched by the probe. Unlike MPI_IPROBE, no other probe or receive operation may match the message returned by MPI_IMPROBE. Each message returned by MPI_IMPROBE must be received with either MPI_MRECV or MPI_IMRECV.
The source argument of MPI_IMPROBE can be MPI_ANY_SOURCE, and the tag argument can be MPI_ANY_TAG, so that one can probe for messages from an arbitrary source and/or with an arbitrary tag. However, a specific communication context must be provided with the comm argument.
A synchronous send operation that is matched with MPI_IMPROBE or MPI_MPROBE will complete successfully only if both a matching receive is posted with MPI_MRECV or MPI_IMRECV, and the receive operation has started to receive the message sent by the synchronous send.
There is a special predefined message: MPI_MESSAGE_NO_PROC, which is a message which has MPI_PROC_NULL as its source process. The predefined constant MPI_MESSAGE_NULL is the value used for invalid message handles.
A matching probe with MPI_PROC_NULL as source returns flag = true, message = MPI_MESSAGE_NO_PROC, and the status object returns source = MPI_PROC_NULL, tag = MPI_ANY_TAG, and count = 0; see Section Null Processes . It is not necessary to call MPI_MRECV or MPI_IMRECV with MPI_MESSAGE_NO_PROC, but it is not erroneous to do so.
Rationale.
MPI_MESSAGE_NO_PROC was chosen instead of
MPI_MESSAGE_PROC_NULL to avoid possible confusion as another
null handle constant.
( End of rationale.)
| MPI_MPROBE(source, tag, comm, message, status) | |
| IN source | rank of source or MPI_ANY_SOURCE (integer) |
| IN tag | message tag or MPI_ANY_TAG (integer) |
| IN comm | communicator (handle) |
| OUT message | returned message (handle) |
| OUT status | status object (Status) |
int MPI_Mprobe(int source, int tag, MPI_Comm comm, MPI_Message *message, MPI_Status *status)
MPI_Mprobe(source, tag, comm, message, status, ierror)
INTEGER, INTENT(IN) :: source, tag
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Message), INTENT(OUT) :: message
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_MPROBE(SOURCE, TAG, COMM, MESSAGE, STATUS, IERROR)
INTEGER SOURCE, TAG, COMM, MESSAGE, STATUS(MPI_STATUS_SIZE), IERROR
MPI_MPROBE behaves like MPI_IMPROBE except that it is a blocking call that returns only after a matching message has been found.
The implementation of MPI_MPROBE and MPI_IMPROBE needs to guarantee progress in the same way as in the case of MPI_PROBE and MPI_IPROBE.