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I encountered some problems when using MPI_CANCEL. I call
Request::Cancel followed by Request::Wait to ensure that the request has
been cancelled. However Request::Wait does not return when I send bigger
messages. The following code should reproduce this behaviour:
using namespace std;
const int rank = MPI::COMM_WORLD.Get_rank();
const int numProcesses = MPI::COMM_WORLD.Get_size();
const int masterRank = 0;
if (rank == masterRank)
cout << "master" << endl;
const int numSlaves = numProcesses - 1;
for(int i = 0; i < numSlaves; ++i)
const int slaveRank = i + 1;
MPI::COMM_WORLD.Recv(&buffer, 1, MPI::INT, slaveRank,
cout << "slave " << rank << endl;
//const int size = 1;
const int size = 10000;
MPI::Request request = MPI::COMM_WORLD.Isend(buffer, size,
cout << "slave ("<< rank<<"): sent data" << endl;
cout << "slave ("<< rank<<"): cancel issued" << endl;
cout << "slave ("<< rank<<"): finished" << endl;
If I set size to 1, everything works as expected, the slave process
finishes execution. However if I use a bigger buffer (in this case
10000) the wait blocks forever. That's the output of the program when
run with two processes:
slave (1): sent data
slave (1): cancel issued
Have I misinterpreted the standard? Or does Request::Wait block until
the message is delievered?