Sorry for the delay in replying; I was out last week. MPI_SEND and MPI_RECV take pointers to the buffer to send and receive, respectively.
When you send a scalar variable, like an int, you get the address of the buffer via the & operator (e.g., MPI_Send(&i, ...)). When you send a new'ed/malloc'ed array, you only need to send the pointer value -- i.e., the address pointing to the buffer. Don't send the address of the pointer, because then you're telling MPI to overwrite the pointer itself. I.e.,: work = new char[...]; MPI_Send(work, ...) not work = new char[...]; MPI_Send(&work, ...); More below. On Apr 11, 2012, at 3:03 PM, Peter Sels wrote: > Probably a buffer overrun or so, but I cannot see where. The buffer overrun is where you specify &array in your MPI_SEND/MPI_RECV calls. > On linux I get: Segmentation fault (11) > > Increasing the length gives more problems... > > How can I get this code stable? > What am I doing wrong? > Is there a maximum length to MPI messages? No. > For sending a string, do I use MPI_CHARACTER or MPI_BYTE or ...? MPI_BYTE. MPI_CHARACTER is for Fortran CHARACTERs. > How come I cannot assert that my messages end in '\0' when received? > And how come that when I print them, I also get a segmentation fault? I think these two issues are symptoms of (work) vs. (&work), from above. > Can I send two subsequent messages using MPI_Send, or do I have to do Sure. > the first as MPI_Isend and then do a MPI_Wait before the next > MPI_Send?... You can do multiple Isend's and then a Waitall, if you want. > Why do I not find code online for receiving the length first and then > allocating a buffer of this size and then receiving the next message? I don't know. Perhaps you didn't google enough? :-) FWIW, the new MPI-3 functions MPI_MPROBE and MPI_IMPROBE will help with unknown-length messages, too. We have that implemented on the Open MPI SVN trunk, but they are not yet available in a stable release. They'll debut in OMPI v1.7. -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
