89 lines
3.3 KiB
Text
89 lines
3.3 KiB
Text
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= nng_aio_alloc(3)
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//
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// Copyright 2021 Staysail Systems, Inc. <info@staysail.tech>
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// Copyright 2018 Capitar IT Group BV <info@capitar.com>
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//
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// This document is supplied under the terms of the MIT License, a
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// copy of which should be located in the distribution where this
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// file was obtained (LICENSE.txt). A copy of the license may also be
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// found online at https://opensource.org/licenses/MIT.
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//
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== NAME
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nng_aio_alloc - allocate asynchronous I/O handle
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== SYNOPSIS
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[source, c]
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----
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#include <nng/nng.h>
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int nng_aio_alloc(nng_aio **aiop, void (*callb)(void *), void *arg);
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----
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== DESCRIPTION
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The `nng_aio_alloc()` function allocates a handle for ((asynchronous I/O))
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operations, and stores a pointer to it in __aiop__.
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The handle is initialized with a completion ((callback)) of _callb_,
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which will be executed when an associated asynchronous operation finishes.
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It will be called with the argument _arg_.
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NOTE: The callback _callb_ must not perform any blocking operations, and
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must complete its execution quickly. If _callb_ does block, this can
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lead ultimately to an apparent "hang" or deadlock in the application.
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This also means you should avoid operations such as allocating new objects,
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which also means opening or closing sockets, dialers, and so forth.
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TIP: If more complex or blocking work needs to be performed by _callb_, a separate
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thread can be used, along with a xref:nng_cv_alloc.3.adoc[condition variable]
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which can be signaled by the callback.
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Asynchronous I/O operations all take an xref:nng_aio.5.adoc[`nng_aio`]
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handle such as allocated by this function.
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Such operations are usually started by a function that returns immediately.
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The operation is then run asynchronously, and completes sometime later.
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When that operation is complete, the callback supplied here is called,
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and that callback is able to determine the result of the operation using
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xref:nng_aio_result.3.adoc[`nng_aio_result()`],
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xref:nng_aio_count.3.adoc[`nng_aio_count()`],
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and xref:nng_aio_get_output.3.adoc[`nng_aio_get_output()`].
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It is possible to wait synchronously for an otherwise asynchronous operation
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by using the function xref:nng_aio_wait.3.adoc[`nng_aio_wait()`].
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In that case, it is permissible for _callb_ and _arg_ to both be `NULL`.
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Note that if these are `NULL`, then it will not be possible to determine when the
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operation is complete except by calling the aforementioned
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xref:nng_aio_wait.3.adoc[`nng_aio_wait()`].
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== RETURN VALUES
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This function returns 0 on success, and non-zero otherwise.
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== ERRORS
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[horizontal]
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`NNG_ENOMEM`:: Insufficient free memory to perform the operation.
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== SEE ALSO
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[.text-left]
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xref:nng_aio_abort.3.adoc[nng_aio_abort(3)],
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xref:nng_aio_cancel.3.adoc[nng_aio_cancel(3)],
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xref:nng_aio_count.3.adoc[nng_aio_count(3)],
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xref:nng_aio_free.3.adoc[nng_aio_free(3)],
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xref:nng_aio_get_input.3.adoc[nng_aio_get_input(3)],
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xref:nng_aio_get_msg.3.adoc[nng_aio_get_msg(3)],
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xref:nng_aio_get_output.3.adoc[nng_aio_get_output(3)],
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xref:nng_aio_result.3.adoc[nng_aio_result(3)],
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xref:nng_aio_set_input.3.adoc[nng_aio_set_input(3)],
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xref:nng_aio_set_iov.3.adoc[nng_aio_set_iov(3)],
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xref:nng_aio_set_msg.3.adoc[nng_aio_set_msg(3)],
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xref:nng_aio_set_timeout.3.adoc[nng_aio_set_timeout(3)],
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xref:nng_aio_stop.3.adoc[nng_aio_stop(3)],
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xref:nng_aio_wait.3.adoc[nng_aio_wait(3)],
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xref:nng_strerror.3.adoc[nng_strerror(3)],
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xref:nng_aio.5.adoc[nng_aio(5)],
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xref:nng.7.adoc[nng(7)]
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