Geoff Jacobs wrote:
Michel Dierks wrote:
Hello,
I'm developing an application to calculate the Mandelbrot fractal.
Hmm... I never did this when I was learning the ropes. There is a pretty
example included with the mpich source code to do Mandelbrot fractals if
you need something to crib from.
My problem is:
from the master I will send to each free node for computation a message
containing the values of one screen line.
I would think you can get away with transmitting just the boundaries of
the section of complex plane which you will be plotting, as well as the
iterative limit, color interpretation, etc. Slaves can determine what
portion they must calculate from their ranks.
After a time the nodes will send back the results.
I have see that I can use MPI_Isend and MPI_Irecv for non-blocking
communication. This give me no problem if we are talking about of one
send and one receive. But how can I handle the sending from each node to
the master without data corruption.
Must I implement a send and a receive buffer for each node (16 nodes
means 16 buffer in and 16 out) ?
The software I've implemented has tended to be rather dynamic, so it
seemed easier to use discrete sends and receives. In your case, you will
be calculating a vector of fixed size on each slave (one row for your
resultant image per). It would be logical to use a collective
communicator like MPI_Gather to automatically populate the array
representing your raster image.
http://csit1cwe.fsu.edu/extra_link/pe/d3a64mst07.html#HDRIGATH
Can someone help me? Please
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Hello,
it is now 2 days that I'm facing with the following problem.
The master send messages to nodes (about 200 separate messages for each node).
I cannot group them, I must send messages after messages to each nodes and to response to Geoff Jacobs I cannot use MPI_Gather because I must determined on which node I will send the next message ( based on list of free nodes).
My send is running correctly and my receive too for the first message
but not for the second. I can see that the master send the second
message and that MPI_Iprobe on the node see that a message is arrived.
But after this MPI_Iprobe , MPI_IRecv doesn't work this time. Why ?? I
have made some research on the mpi forum and on some other places but I
cannot found a correct explanation. All example given are more talking about
one send and one receive but not on multiple send and receive on more than one
node. I have found the routine MPI_Request_free and test it but this one give
error telling me that I have an invalid handler. After some research again, I
have found this at
http://www.pdc.kth.se/training/Talks/MPI/Persistent/more.html Point 2 on the
page:
"When a program calls a non-blocking message-passing routine such as
|MPI_Isend|, a request object is created, and then the
communication is started. These steps are equivalent to two other MPI
calls, |MPI_Send_init| and |MPI_Start|. When
the program calls |MPI_Wait|, it waits until all necessary
local operations have completed, and then frees the memory used to
store the request object. This second step equals a call to
|MPI_Request_free|."
So I don't understand anymore what to do.
Can someone of you tell me clearly what I'm doing wrong?
Here below the part of my code who run on the nodes:
/*****************************
* Parts running on node *
*****************************/
/* Memory Allocation to buffer_sendi and buffer_recvd */
if ((buffer_sendi=(int *)malloc(MAX_INT * sizeof(int)))==NULL)
{
exit(1);
}
if ((buffer_recvd=(double *)malloc(MAX_DOUBLE * sizeof(double)))==NULL)
{
exit(1);
}
/* Until receive tag with value -99 loop */
do
{
MPI_Iprobe(0,MPI_ANY_TAG,MPI_COMM_WORLD,&flag,&status_recvd);
if (flag==1)
{
/* Reception from master */
MPI_IRecv(buffer_recvd,MAX_DOUBLE,MPI_DOUBLE,0,tag,MPI_COMM_WORLD,&status_recvd); MPI_Wait(&request_recvd,&status);
/*
some calculation
*/
/* send buffer_sendi to master */
MPI_ISend(buffer_sendi,MAX_INT,MPI_INT,0,tag,MPI_COMM_WORLD);
MPI_Wait(&request_recvd,&status);
}
}while(buffer_recvd[0]!=-99.00);
Thanks for your help.
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