18.2.406. MPI_T_init_thread

MPI_T_init_thread — Initializes the MPI Tool information interface

18.2.406.1. SYNTAX

18.2.406.1.1. C Syntax

int MPI_T_init_thread(int required, int* provided)

18.2.406.2. INPUT PARAMETERS

  • required: Desired level of thread support (integer).

18.2.406.3. OUTPUT PARAMETERS

  • provided: Available level of thread support (integer).

18.2.406.4. DESCRIPTION

MPI_T_init_thread() initializes the MPI tool information interface. Calls to MPI tool functions are allowed at any point in execution (including before MPI_Init() and after MPI_Finalize()) as long as MPI_T_init_thread() has been called at least once and the number of calls to MPI_T_init_thread() is greater than the number of calls to MPI_T_finalize(). If at any point in execution the number of calls to MPI_T_finalize() equals the number of calls to MPI_T_init_thread() the MPI tool interface will no longer be available until another call to MPI_T_init_thread().

The required and provided thread support levels apply to the MPI tool information interface only; they are distinct from the thread support level of the World Model (reported by MPI_Query_thread) and from each session’s thread_level info key. The level granted in provided is fixed for as long as the interface remains initialized: additional calls to MPI_T_init_thread while the interface is initialized only increase the reference count and return the already-established level. If another MPI scope (the World Model or a session) is already active at a lower thread level, a request for MPI_THREAD_MULTIPLE may be granted MPI_THREAD_SERIALIZED instead, because the running process cannot be safely upgraded; MPI-5.0 explicitly permits one scope’s thread level to influence the level granted to a later initialization.

MPI_T_init_thread(), like MPI_Init_thread(), has a provision to request a certain level of thread support in required:

  • MPI_THREAD_SINGLE: Only one thread will execute.

  • MPI_THREAD_FUNNELED: If the process is multithreaded, only the thread that called MPI_Init_thread will make MPI calls.

  • MPI_THREAD_SERIALIZED: If the process is multithreaded, only one thread will make MPI library calls at one time.

  • MPI_THREAD_MULTIPLE: If the process is multithreaded, multiple threads may call MPI at once with no restrictions.

The level of thread support available to the program is set in provided. In Open MPI, the value is dependent on how the library was configured and built. Note that there is no guarantee that provided will be greater than or equal to required.

18.2.406.5. NOTES

It is the caller’s responsibility to check the value of provided, as it may be less than what was requested in required.

18.2.406.6. ERRORS

MPI_T_init_thread will fail if:

  • MPI_T_ERR_MEMORY: Out of memory

  • MPI_T_ERR_CANNOT_INIT: Interface not in the state to be initialized

See also