Environment

Environment

Launching MPI programs

MPI.mpiexec — Function.
mpiexec(fn)

A wrapper function for the MPI launcher executable. Calls fn(cmd), where cmd is a Cmd object of the MPI launcher.

Environment Variables

The behaviour of mpiexec can be controlled by the following environment variables:

  • JULIA_MPIEXEC: the name or path of the launcher executable (set at compile time).
  • JULIA_MPIEXEC_ARGS: additional arguments that are passed to the launcher. These are space seperated, supporting the same quoting rules as Julia Cmd objects. These can be modified at run time.

Usage

julia> mpiexec(cmd -> run(`$cmd -n 3 echo hello world`));
hello world
hello world
hello world
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Enums

MPI.ThreadLevel — Type.
ThreadLevel

An Enum denoting the level of threading support in the current process:

  • MPI.THREAD_SINGLE: Only one thread will execute.

  • MPI.THREAD_FUNNELED: The process may be multi-threaded, but the application must ensure that only the main thread makes MPI calls. See Is_thread_main.

  • MPI.THREAD_SERIALIZED: The process may be multi-threaded, and multiple threads may make MPI calls, but only one at a time (i.e. all MPI calls are serialized).

  • MPI.THREAD_MULTIPLE: Multiple threads may call MPI, with no restrictions.

See also

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Functions

MPI.Abort — Function.
Abort(comm::Comm, errcode::Integer)

Make a “best attempt” to abort all tasks in the group of comm. This function does not require that the invoking environment take any action with the error code. However, a Unix or POSIX environment should handle this as a return errorcode from the main program.

External links

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MPI.Init — Function.
Init()

Initialize MPI in the current process.

All MPI programs must contain exactly one call to MPI.Init or MPI.Init_thread. In particular, note that it is not valid to call MPI.Init or MPI.Init_thread again after calling MPI.Finalize.

The only MPI functions that may be called before MPI.Init/MPI.Init_thread are MPI.Initialized and MPI.Finalized.

External links

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MPI.Init_thread — Function.
Init_thread(required::ThreadLevel)

Initialize MPI and the MPI thread environment in the current process. The argument specifies the required level of threading support, see ThreadLevel.

The function will return the provided ThreadLevel, and values may be compared via inequalities, i.e.

provided = Init_thread(required)
@assert provided >= required

All MPI programs must contain exactly one call to MPI.Init or MPI.Init_thread. In particular, note that it is not valid to call MPI.Init or MPI.Init_thread again after calling MPI.Finalize.

The only MPI functions that may be called before MPI.Init/MPI.Init_thread are MPI.Initialized and MPI.Finalized.

External links

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MPI.Query_thread — Function.
Query_thread()

Query the level of threading support in the current process. Returns a ThreadLevel value denoting

External links

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MPI.Is_thread_main — Function.
Is_thread_main()

Queries whether the current thread is the main thread according to MPI. This can be called by any thread, and is useful for the THREAD_FUNNELED ThreadLevel.

External links

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MPI.Initialized — Function.
Initialized()

Returns true if MPI.Init has been called, false otherwise.

It is unaffected by MPI.Finalize, and is one of the few functions that may be called before MPI.Init.

External links

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MPI.Finalize — Function.
Finalize()

Marks MPI state for cleanup. This should be called after Init, at most once, and no further MPI calls (other than Initialized or Finalized) should be made after it is called.

Note that this does not correspond exactly to MPI_FINALIZE in the MPI specification. In particular:

  • It may not finalize MPI immediately. Julia will wait until all MPI-related objects are garbage collected before finalizing MPI. As a result, Finalized() may return false after Finalize() has been called. See Finalizers for more details.

  • It is optional: Init will automatically insert a hook to finalize MPI when Julia exits.

External links

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MPI.Finalized — Function.
Finalized()

Returns true if MPI.Finalize has completed, false otherwise.

It is safe to call before MPI.Init and after MPI.Finalize.

External links

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MPI.universe_size — Function.
universe_size()

The total number of available slots, or nothing if it is not defined. This is determined by the MPI_UNIVERSE_SIZE attribute of COMM_WORLD.

This is typically dependent on the MPI implementation: for MPICH-based implementations, this is specified by the -usize argument. OpenMPI defines a default value based on the number of processes available.

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