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+# Interfaces for Aysnchronous I/O
+
+_NNG_ provides rich support for {{i:asynchronous I/O}}.
+This allows applications to achieve high levels of concurrency with a
+minimum of fuss, optimized for the platform.
+
+Asynchronous I/O is performed without blocking calling application
+threads, so they may continue to perform other work.
+
+## AIO Handles
+
+Applications create an `nng_aio` object with a function to call when
+the operation is done (along with a pointer to application private data),
+then submit the operation.
+
+These `nng_aio` objects are created using the [`nng_aio_alloc()`](nng_aio_alloc.md),
+and destroyed using [`nng_aio_free()`](nng_aio_free.md).
+
+The `nng_aio` object itself is declared like this:
+
+```c
+#include <nng/nng.h>
+
+typedef struct nng_aio nng_aio;
+```
+
+Every asynchronous operation uses its own instance an `nng_aio`, and each
+`nng_aio` can only be used with a single operation at a time.
+
+> [!IMPORTANT]
+> Attempting to submit an operation using an `nng_aio` that is already
+> in use for another operation will crash the application.
+> However, it is possible to submit another operation on the `nng_aio` from
+> the callback associated with the same `nng_aio`.
+
+When the operation is complete, whether successfully
+or otherwise, the callback function is executed.
+The callback will be executed exactly once.
+
+## Cancellation
+
+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)).
+
+## Waiting for Completion
+
+It is also possible to initiate an asynchronous operation, and wait for it to
+complete [`nng_aio_wait()`](nng_aio_wait.md).
+
+> [!IMPORTANT]
+> Applications must never call [`nng_aio_wait()`](nng_aio_wait.md) or
+> [`nng_aio_stop()`](nng_aio_stop.md) from a callback registered to
+> an `nng_aio` object. Doing so can lead to a deadlock.
+
+## 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)