I'll take a stab at this since I don't remember seeing any other
replies.
At least in the original code you sent out, you used Isend/sleep/Wait
to send messages. So, I'm guessing that part of the message is sent,
Iprobe detects that a matching message is in-coming, and then the
receiver goes into MPI_Recv. This call then can begin to receive the
message, but it's stuck waiting for the remainder of the message to
arrive. Off hand, I don't know if that is how MPI_Iprobe is supposed
to behave or not. I see
http://www.mpi-forum.org/docs/mpi-11-html/node50.html#Node50
MPI_IPROBE(source, tag, comm, flag, 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.
I suppose this language leaves open the possibility that the message is
not yet 100% available to be read, but only that the message header has
been received and that it sufficiently matches that specified matching
criteria.
David Zhang wrote:
I have modified the code so that all the terminal outputs
are done by one executable. I have attached the source files, after
compiling type "make go" and the code will execute.
The previous code output was from a supercomputer cluster where the two
processes resides on two different nodes. When running the same code
on a regular-multiprocessor machine (mac mini in this case), I got this
output:
F
F
T
1
F
T
2
F
T
3
F
T
4
If I'm sending a message every 2 seconds and I'm polling every 0.05
second, I would expect 39 F and 1 T between each number. At least when
I ran it on the supercomputer, this is true during the very beginning;
however I don't even see this when I'm running the code on my mac mini.
On Sat, Jun 5, 2010 at 2:44 PM, David Zhang <solarbik...@gmail.com>
wrote:
Dear all:
I'm using mpi_iprobe to serve as a way to send signals between
different mpi executables. I'm using the following test codes (fortran):
#1
program send
implicit none
include 'mpif.h'
real*8 :: vec(20000)=1.0
integer :: ierr,i=0,request(1)
call mpi_init(ierr)
do
call mpi_isend(vec,20000,mpi_real8,
0,1,mpi_comm_world,request(1),ierr)
i=i+1
print *,i
vec=-vec
call usleep_fortran(2.d0)
call mpi_wait(request(1),MPI_STATUS_IGNORE,ierr)
end do
end program send
--------------------------------------------------
#2
program send
implicit none
include 'mpif.h'
real*8 :: vec(20000)
integer :: ierr
call mpi_init(ierr)
do
if(key_present()) then
call
mpi_recv(vec,20000,mpi_real8,1,1,mpi_comm_world,MPI_STATUS_IGNORE,ierr)
end if
call usleep_fortran(0.05d0)
end do
contains
function key_present()
implicit none
logical :: key_present
key_present = .false.
call
mpi_iprobe(1,1,mpi_comm_world,key_present,MPI_STATUS_IGNORE,ierr)
print *, key_present
end function key_present
end program send
-----------------------------------
The usleep_fortran is a routine I've written to pause the program for
that amount of time (in seconds). As you can see, on the receiving end
I'm probing to see whether the message has being received every 0.05
seconds, where each probing would result a print of the probing result;
while the sending is once every 2 seconds.
Doing
mpirun -np 1 recv : -np 1 send
Naturally I expect the output to be something like:
1
(fourty or so F)
T
2
(another fourty or so F)
T
3
however this is the output I get:
1
(fourty or so F)
T
2
(about a two second delay)
T
3
It seems to me that after the first set of probes, once the message was
received, the non-blocking mpi probe becomes blocking for some strange
reason. I'm using mpi_iprobe for the first time, so I'm not sure if
I'm doing something blatantly wrong.
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