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(libc.info)Configuration of AIO

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How to optimize the AIO implementation
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   The POSIX standard does not specify how the AIO functions are
implemented.  They could be system calls, but it is also possible to
emulate them at userlevel.

   At the point of this writing, the available implementation is a
userlevel implementation which uses threads for handling the enqueued
requests.  While this implementation requires making some decisions
about limitations, hard limitations are something which is best avoided
in the GNU C library.  Therefore, the GNU C library provides a means
for tuning the AIO implementation according to the individual use.

 - Data Type: struct aioinit
     This data type is used to pass the configuration or tunable
     parameters to the implementation.  The program has to initialize
     the members of this struct and pass it to the implementation using
     the `aio_init' function.

    `int aio_threads'
          This member specifies the maximal number of threads which may
          be used at any one time.

    `int aio_num'
          This number provides an estimate on the maximal number of
          simultaneously enqueued requests.

    `int aio_locks'
          Unused.

    `int aio_usedba'
          Unused.

    `int aio_debug'
          Unused.

    `int aio_numusers'
          Unused.

    `int aio_reserved[2]'
          Unused.

 - Function: void aio_init (const struct aioinit *INIT)
     This function must be called before any other AIO function.
     Calling it is completely voluntary, as it is only meant to help
     the AIO implementation perform better.

     Before calling the `aio_init', function the members of a variable
     of type `struct aioinit' must be initialized.  Then a reference to
     this variable is passed as the parameter to `aio_init' which itself
     may or may not pay attention to the hints.

     The function has no return value and no error cases are defined.
     It is a extension which follows a proposal from the SGI
     implementation in Irix 6.  It is not covered by POSIX.1b or Unix98.