Thanks, 

This is the main part of me code, which may have deadlock. 

Master: 

for (iRank = 0; iRank < availableRank ; iRank++)

{

destRank = iRank+1;

for (taski = 1; taski <=  TaskNumPerRank ; taski++)

{

resultSourceRank = destRank;

recvReqs[taskCounterT2] = world.irecv(resultSourceRank, upStreamTaskTag, resultTaskPackageT2[iRank][taskCounterT3]);

reqs = world.isend(destRank, taskTag, myTaskPackage);

++taskCounterT2;

}

// taskTotalNum = availableRank * TaskNumPerRank 

// right now, availableRank =1, TaskNumPerRank =2

mpi::wait_all(recvReqs, recvReqs+(taskTotalNum));

-----------------------------------------------

worker: 

while (1)

{

world.recv(managerRank, downStreamTaskTag, resultTaskPackageW);

do its local work on received task;

destRank = masterRank;

reqs = world.isend(destRank, taskTag, myTaskPackage);

if (recv end signal)

  break;

}

Any help is appreciated.

Jack