How to stop and resume all processes by one process in MPI? - c++

Question

In MPI what is the correct way that at a specific moment, one process (I call it process A) stops all processes doing the application tasks and then that process A resumes all? For example:
#include <stdio.h>
#include <mpi.h>
#include <unistd.h>
int main(int argc, char **argv)
{
int num_procs, my_rank, my_id;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
MPI_Comm_size(MPI_COMM_WORLD, &num_procs);
my_id = getpid();
printf("Hello! I'm process with rank %i out of %i processes and my id is %i\n",
my_rank, num_procs, my_id);
// here I want process A stops all processes
// ....
usleep(3000000); // sleep for 3 seconds
// here I want that process A resumes all processes
printf("Bye! I'm process %i out of %i processes and my id is %i\n",
my_rank, num_procs, my_id);
MPI_Finalize();
return 0;
}
I tried using kill(pid, SIGSTOP); and kill(pid, SIGCONT); but the problem is that the id of each process obtained through getpid() is required so that that process A can use those ids to stop and resume the processes. I tried to see if I can obtain the processes ids and then one process can access them. So, I modified the above code as follows.
#include <stdio.h>
#include <mpi.h>
#include <unistd.h>
#include <vector>
std::vector<int> ids {};
int main(int argc, char **argv)
{
int num_procs, my_rank;
ids.push_back(getpid());
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
MPI_Comm_size(MPI_COMM_WORLD, &num_procs);
if (my_rank == 0){
for (const int& i : ids) {
std::cout << i << "\n";
}
}
MPI_Finalize();
return 0;
}
But due to the parallelism of processes, it didn't work and for loop only prints out the id of the process with rank 0.
To rephrase my question, is there any way in MPI to stop and resumes processes?
UPDATE
Since I was asked in the comments why I need to do so, I add more explanations here. I intend to implement a coordinated checkpointing approach. It works as follows. One process as a coordinator at a specific time stops other processes from executing the main program tasks. Then each process takes its checkpoint and subsequently informs the coordinator process that checkpointing is done. When all processes finish taking their checkpoints, the coordinator resumes the other processes to carry on executing the main program tasks. The coordinator process can be one of the processes that execute the main program, and at checkpointing time, it also takes its checkpoint.