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+# nng_aio
+
+## NAME
+
+nng_aio --- asynchronous I/O handle
+
+```c
+#include <nng/nng.h>
+
+typedef struct nng_aio nng_aio;
+```
+
+## DESCRIPTION
+
+An `nng_aio`{{hi:aio}} is an opaque structure used in conjunction with
+{{i:asynchronous I/O}} operations.
+Every asynchronous operation uses one of these structures, each of which
+can only be used with a single operation at a time.
+
+Asynchronous operations are performed without blocking calling application
+threads.
+Instead the application registers a callback function to be executed
+when the operation is complete (whether successfully or not).
+This callback will be executed exactly once.
+
+The asynchronous I/O framework also supports cancellation of
+operations that are already in progress
+(see [`nng_aio_cancel()`](nng_aio_cancel.md)), as well setting a maximum
+timeout for them to complete within
+(see [`nng_aio_set_timeout()`](nng_aio_set_timeout.md)).
+
+It is also possible to initiate an asynchronous operation, and wait for it to
+complete [`nng_aio_wait()`](nng_aio_wait.md).
+
+These structures are created using the [`nng_aio_alloc()`](nng_aio_alloc.md),
+and destroyed using [`nng_aio_free()`](nng_aio_free.md).
+
+> [!IMPORTANT]
+> A given `nng_aio` can only have a single operation in progress
+> at any given time. Attempts to reuse an `nng_aio` while another
+> operation is in progress will generally cause a crash.
+
+## SEE ALSO
+
+[nng_aio_abort()](nng_aio_abort.md),
+[nng_aio_alloc()](nng_aio_alloc.md),
+[nng_aio_cancel()](nng_aio_cancel.md),
+[nng_aio_count()](nng_aio_count.md),
+[nng_aio_free()](nng_aio_free.md),
+[nng_aio_get_input()](nng_aio_get_input.md),
+[nng_aio_get_msg()](nng_aio_get_msg.md),
+[nng_aio_get_output()](nng_aio_get_output.md),
+[nng_aio_result()](nng_aio_result.md),
+[nng_aio_set_input()](nng_aio_set_input.md),
+[nng_aio_set_iov()](nng_aio_set_iov.md),
+[nng_aio_set_msg()](nng_aio_set_msg.md),
+[nng_aio_set_timeout()](nng_aio_set_timeout.md),
+[nng_aio_stop()](nng_aio_stop.md),
+[nng_aio_wait()](nng_aio_wait.md),