# NAME

MPI_T_init_thread - Initializes the MPI Tool information interface

# SYNTAX

## C Syntax

```c
#include <mpi.h>
int MPI_T_init_thread(int required, int *provided)
```

# INPUT PARAMETERS

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

# OUTPUT PARAMETERS

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

# 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()`.

`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`.

# NOTES

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

# 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

[`MPI_T`(5)](MPI_T.html),
[`MPI_Init_thread`(3)](MPI_Init_thread.html),
[`MPI_T_finalize`(3)](MPI_T_finalize.html)