El 22/08/14 20:44, Saliya Ekanayake escribió:
Thank you Oscar for the detailed information, but I'm still wondering
how would the copying in 2 would be different than what's done here
with copying to a buffer.
If you have a buffer array like this:
double buffer[] = new double[m * n];
Copy the 2D matrix to the buffer:
for(int i = 0; i < m; i++)
System.arraycopy(matrix[i], 0, buffer, i * n, n);
Copy from the buffer to the 2D matrix:
for(int i = 0; i < m; i++)
System.arraycopy(buffer, i * n, matrix[i], 0, n);
On Fri, Aug 22, 2014 at 2:17 PM, Oscar Vega-Gisbert <ov...@dsic.upv.es
<mailto:ov...@dsic.upv.es>> wrote:
El 22/08/14 17:10, Saliya Ekanayake escribió:
Hi,
I've a quick question about the usage of Java binding.
Say there's a 2 dimensional double array (size m x n) that
needs to be sent to another rank. I see two options to get
this done,
1. Copy values to a direct buffer of size m*n and send it
2. Copy values to a 1D array of size m*n and send it
I guess 2 would internally do the copying to a buffer and use
it, so suggesting 1. is the best option. Is this the case or
is there a better way to do this?
The best option is 1 because 2 requires one extra copy to C heap.
Supposing the matrix is the following:
double matrix[][] = new double[m][n];
Then you can allocate a direct DoubleBuffer:
DoubleBuffer buffer = MPI.newDoubleBuffer(m * n);
In order to send/receive the matrix I suggest to use the bulk
put/get methods:
for(int i = 0; i < m; i++)
buffer.put(matrix[i]); // Copy to the buffer.
MPI.COMM_WORLD.send(buffer, m*n, MPI.DOUBLE, 1, 0);
The receive code:
MPI.COMM_WORLD.recv(buffer, m*n, MPI.DOUBLE, 0, 0);
for(int i = 0; i < m; i++)
buffer.get(matrix[i]); // Copy from the buffer.
Note that bulk get/put methods increment the buffer position in n.
So if you want reuse the buffer you must set the buffer position
to 0 before copy the matrix:
buffer.position(0);
Regards,
Oscar
Thank you,
Saliya
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