[Beowulf] mutex (remote memory access) question for MPI-2

[William Gropp]

At 12:49 PM 7/31/2005, Plinius Frobenius wrote:
>Hi,
>I've red through the chapter in "Using MPI-2" about mutexes.
>Suppose that you know in advance that only one cumputer (say node y) can 
>access the memory-window on node x (except node x itself).
>How should your mutex-code look like (you still need a mutex, since both x 
>and y can access the memory)? (since you won't need the entire 
>"tree-mutex-code" provided by Rajeev Thakur, I guess, since there are only 
>two processes able to acces the memory...). I haven't enough experience 
>yet to find this one by myself, and really need it for the program I'm 
>working on.

You don't need mutexes for this.  Simply use MPI_Win_lock with a mode of 
MPI_LOCK_EXCLUSIVE, followed by either MPI_Put, MPI_Get, or MPI_Accumulate 
(from node y) or simple language access on node x (e.g., *a = 1; where a 
points into node x's memory window)., followed by MPI_Win_unlock.

Bill


>Thanks for any ideas/hints/help...
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William Gropp
http://www.mcs.anl.gov/~gropp