NAME

       nng_aio_alloc - allocate asynchronous I/O handle

SYNOPSIS

           #include <nng/nng.h>

           int nng_aio_alloc(nng_aio **aiop, void (*callb)(void *), void *arg);

DESCRIPTION

       The nng_aio_alloc() function allocates a handle for asynchronous I/O operations, and stores a pointer to
       it in aiop. The handle is initialized with a completion callback of callb, which will be executed when an
       associated asynchronous operation finishes. It will be called with the argument arg.

           Note

           The callback callb must not perform any blocking operations, and must complete its execution quickly.
           If callb does block, this can lead ultimately to an apparent "hang" or deadlock in the application.
           This also means you should avoid operations such as allocating new objects, which also means opening
           or closing sockets, dialers, and so forth.

           Tip

           If more complex or blocking work needs to be performed by callb, a separate thread can be used, along
           with a condition variable which can be signaled by the callback.

       Asynchronous I/O operations all take an nng_aio handle such as allocated by this function. Such
       operations are usually started by a function that returns immediately. The operation is then run
       asynchronously, and completes sometime later. When that operation is complete, the callback supplied here
       is called, and that callback is able to determine the result of the operation using nng_aio_result(),
       nng_aio_count(), and nng_aio_get_output().

       It is possible to wait synchronously for an otherwise asynchronous operation by using the function
       nng_aio_wait(). In that case, it is permissible for callb and arg to both be NULL. Note that if these are
       NULL, then it will not be possible to determine when the operation is complete except by calling the
       aforementioned nng_aio_wait().

RETURN VALUES

       This function returns 0 on success, and non-zero otherwise.

ERRORS

       NNG_ENOMEM
           Insufficient free memory to perform the operation.

SEE ALSO

       nng_aio_abort(3), nng_aio_cancel(3), nng_aio_count(3), nng_aio_free(3), nng_aio_get_input(3),
       nng_aio_get_msg(3), nng_aio_get_output(3), nng_aio_result(3), nng_aio_set_input(3), nng_aio_set_iov(3),
       nng_aio_set_msg(3), nng_aio_set_timeout(3), nng_aio_stop(3), nng_aio_wait(3), nng_strerror(3),
       nng_aio(5), nng(7)

                                                   2025-08-18                                   NNG_AIO_ALLOC(3)