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Coro::AIO - truly asynchronous file and directory I/O


   use Coro::AIO;

   # can now use any of the aio requests your IO::AIO module supports.

   # read 1MB of /etc/passwd, without blocking other coroutines
   my $fh = aio_open "/etc/passwd", O_RDONLY, 0
      or die "/etc/passwd: $!";
   aio_read $fh, 0, 1_000_000, my $buf, 0
      or die "aio_read: $!";
   aio_close $fh;


This module is an AnyEvent user, you need to make sure that you use and run a supported event loop.

This module implements a thin wrapper around IO::AIO. All of the functions that expect a callback are being wrapped by this module.

The API is exactly the same as that of the corresponding IO::AIO routines, except that you have to specify all arguments, even the ones optional in IO::AIO, except the callback argument. Instead of calling a callback, the routines return the values normally passed to the callback. Everything else, including $! and perls stat cache, are set as expected after these functions return.

You can mix calls to IO::AIO functions with calls to this module. You must not, however, call these routines from within IO::AIO callbacks, as this causes a deadlock. Start a coro inside the callback instead.

This module also loads AnyEvent::AIO to integrate into the event loop in use, so please refer to its (and AnyEvent's) documentation on how it selects an appropriate event module.

All other functions exported by default by IO::AIO (e.g. aioreq_pri) will be exported by default by Coro::AIO, too.

Functions that can be optionally imported from IO::AIO can be imported from Coro::AIO or can be called directly, e.g. Coro::AIO::nreqs.

You cannot specify priorities with aioreq_pri if your coroutine has a non-zero priority, as this module overwrites the request priority with the current coroutine priority in that case.

For your convenience, here are the changed function signatures for most of the requests, for documentation of these functions please have a look at IO::AIO. Note that requests added by newer versions of IO::AIO will be automatically wrapped as well.

@results = aio_wait $req

This is not originally an IO::AIO request: what it does is to wait for $req to finish and return the results. This is most useful with aio_group requests.

Is currently implemented by replacing the $req callback (and is very much like a wrapper around $req->cb ()).

$fh = aio_open $pathname, $flags, $mode
$status = aio_close $fh
$retval = aio_read $fh,$offset,$length, $data,$dataoffset
$retval = aio_write $fh,$offset,$length, $data,$dataoffset
$retval = aio_sendfile $out_fh, $in_fh, $in_offset, $length
$retval = aio_readahead $fh,$offset,$length
$status = aio_stat $fh_or_path
$status = aio_lstat $fh
$status = aio_rmdir $pathname
$entries = aio_readdir $pathname
($dirs, $nondirs) = aio_scandir $path, $maxreq
$status = aio_fsync $fh
$status = aio_fdatasync $fh
... = aio_xxx ...

Any additional aio requests follow the same scheme: same parameters except you must not specify a callback but instead get the callback arguments as return values.


Coro::Socket and Coro::Handle for non-blocking socket operation.


   Marc A. Lehmann <>