Hi Richard,
From your email it is not clear if you are trying to use MPI in
different threads at the same time.
Currently, LAM does not support multi-threading. The only
multi-threaded support it provides is that it puts a lock on the MPI
library. So, if your code is expecting to run multiple threads in MPI
simultaneously, it won't work as you would want it to.
Whatever is your first call to MPI Library will be blocking and
MPI_Irecv wont be able to enter MPI library until the first call returns.
You could find more details about this in the User Manual at
http://www.lam-mpi.org/download/files/7.0-user.pdf in section 12.4.
Nihar
On Thu, 18 Sep 2003, Bailey, Richard T (US SSA) wrote:
- I developed a C++ app w/ a master/slave architecture for splitting an
- array in the master and having the slaves each process part of the
- array. The master sets up the slaves, including the communicator, when
- the master object is constructed. The Master->ProcessArray() member
- splits the array and, depending on input params either does or does not
- create a separate thread to send and receive the subarrays from the
- previously-established slaves. In either case, I use nonblocking
- MPI_Irecv() and MPI_Isend() calls for master/slave communication. When I
- do not use a separate thread, all is well. However, if I do use a
- separate thread (so the client code can do other work while the thread
- spawned by Master->ProcessArray() is running), then MPI_Irecv() blocks,
- with the effect that only 1 slave ever gets work and all processing is
- sequential. I put 1 second sleeps in the slaves and put fprintfs around
- the code to verify the it is the MPI_Irecv() that is causing the
- problem:
-
-
-
- fprintf(
-
- stderr,
-
- "V: Starting AsyncRecvSubarrayParamsOutFromSlave %d @T %8.3f\n",
-
- TileJob->SlaveStatus->Rank,
-
- GetSecs()
-
- );
-
-
-
- MPI_Irecv(
-
- & TileJob->SubarrayParamsOut,
-
- sizeof(SubarrayParamsOutType) / sizeof(int),
-
- MPI_INT,
-
- TileJob->SlaveStatus->Rank, // Source
-
- SubarrayParamsOutTag,
-
- AllComms,
-
- & TileJob->SlaveStatus->MPIRequest
-
- );
-
-
-
- fprintf(
-
- stderr,
-
- "V: Done w/ AsyncRecvSubarrayParamsOutFromSlave %d @T %8.3f\n",
-
- TileJob->SlaveStatus->Rank,
-
- GetSecs()
-
- );
-
-
-
- Here is the output:
-
- V: Starting AsyncRecvSubarrayParamsOutFromSlave 1 @T 1.755
-
- V: Done w/ AsyncRecvSubarrayParamsOutFromSlave 1 @T 2.763
-
-
-
- The same output from a non-threaded run shows that MPI_Irecv() is
- nonblocking.
-
-
-
- I am running LAM v. 7.0 compiled w/ gcc 2.95.3 on a Sun workstation OS
- 5.7. The thread is created with pthread_create(). I tried initializing
- MPI 3 different ways with the same result:
-
- MPI_Init(NULL, NULL);
-
- MPI_Init_thread(NULL, NULL, MPI_THREAD_SINGLE, &DontCare);
-
- MPI_Init_thread(NULL, NULL, MPI_THREAD_SERIALIZED, &DontCare);
-
-
-
- What do I need to do to get this to work in the multithreaded mode?
-
-
-
-
-
- R. T. Bailey
-
-
---------------------------------------
Nihar Sanghvi
LAM-MPI Team
Graduate Student (Indiana University)
http://www.lam-mpi.org
--------------------------------------
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