Operations in MPI run

[WeikangXian]

Hi HOOMD community,

I have a general question regarding operations (like logging) in MPI run. From the tutorials with MPI, it writes:

All ranks must load the same input file, define the same operations with the same parameters and triggers~~~into smaller domains, one assigned to each rank, and executes the same operations on each domain.

I wonder if all operations (like logging) will be executed separately in each rank. If so, will different ranks write repeatedly to the same logging file, which may cause problem.

For example, I tried two MPI (with 2 ranks) simulations with setting (1) and (2). The first runs fine but the second, as expected, runs into deadlocks.

(1)
sim.operations.writers.append(gsd_writer)
sim.operations.writers.append(table_file)
sim.operations.writers.append(hdf5_writer)

(2)
if device.communicator.rank == 0:
sim.operations.writers.append(gsd_writer)
sim.operations.writers.append(table_file)
sim.operations.writers.append(hdf5_writer)

But in the first case, will different ranks write the same data to the logging file such that everything will be written twice?

Thank you.
Best,
Weikang

[joaander]

But in the first case, will different ranks write the same data to the logging file such that everything will be written twice?

No. The ranks cooperate to write a single file.

[WeikangXian]

Thank you!