NAME
    IO::AIO - Asynchronous Input/Output

SYNOPSIS
     use IO::AIO;

     aio_open "/etc/passwd", O_RDONLY, 0, sub {
        my ($fh) = @_;
        ...
     };

     aio_unlink "/tmp/file", sub { };

     aio_read $fh, 30000, 1024, $buffer, 0, sub {
        $_[0] > 0 or die "read error: $!";
     };

     # Event
     Event->io (fd => IO::AIO::poll_fileno,
                poll => 'r',
                cb => \&IO::AIO::poll_cb);

     # Glib/Gtk2
     add_watch Glib::IO IO::AIO::poll_fileno,
               in => sub { IO::AIO::poll_cb; 1 };

     # Tk
     Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
                               readable => \&IO::AIO::poll_cb);

     # Danga::Socket
     Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
                                 \&IO::AIO::poll_cb);

DESCRIPTION
    This module implements asynchronous I/O using whatever means your
    operating system supports.

    Currently, a number of threads are started that execute your read/writes
    and signal their completion. You don't need thread support in your libc
    or perl, and the threads created by this module will not be visible to
    the pthreads library. In the future, this module might make use of the
    native aio functions available on many operating systems. However, they
    are often not well-supported (Linux doesn't allow them on normal files
    currently, for example), and they would only support aio_read and
    aio_write, so the remaining functionality would have to be implemented
    using threads anyway.

    Although the module will work with in the presence of other threads, it
    is currently not reentrant, so use appropriate locking yourself, always
    call "poll_cb" from within the same thread, or never call "poll_cb" (or
    other "aio_" functions) recursively.

FUNCTIONS
  AIO FUNCTIONS
    All the "aio_*" calls are more or less thin wrappers around the syscall
    with the same name (sans "aio_"). The arguments are similar or
    identical, and they all accept an additional (and optional) $callback
    argument which must be a code reference. This code reference will get
    called with the syscall return code (e.g. most syscalls return -1 on
    error, unlike perl, which usually delivers "false") as it's sole
    argument when the given syscall has been executed asynchronously.

    All functions expecting a filehandle keep a copy of the filehandle
    internally until the request has finished.

    The pathnames you pass to these routines *must* be absolute and encoded
    in byte form. The reason for the former is that at the time the request
    is being executed, the current working directory could have changed.
    Alternatively, you can make sure that you never change the current
    working directory.

    To encode pathnames to byte form, either make sure you either: a) always
    pass in filenames you got from outside (command line, readdir etc.), b)
    are ASCII or ISO 8859-1, c) use the Encode module and encode your
    pathnames to the locale (or other) encoding in effect in the user
    environment, d) use Glib::filename_from_unicode on unicode filenames or
    e) use something else.

    aio_open $pathname, $flags, $mode, $callback
        Asynchronously open or create a file and call the callback with a
        newly created filehandle for the file.

        The pathname passed to "aio_open" must be absolute. See API NOTES,
        above, for an explanation.

        The $flags argument is a bitmask. See the "Fcntl" module for a list.
        They are the same as used by "sysopen".

        Likewise, $mode specifies the mode of the newly created file, if it
        didn't exist and "O_CREAT" has been given, just like perl's
        "sysopen", except that it is mandatory (i.e. use 0 if you don't
        create new files, and 0666 or 0777 if you do).

        Example:

           aio_open "/etc/passwd", O_RDONLY, 0, sub {
              if ($_[0]) {
                 print "open successful, fh is $_[0]\n";
                 ...
              } else {
                 die "open failed: $!\n";
              }
           };

    aio_close $fh, $callback
        Asynchronously close a file and call the callback with the result
        code. *WARNING:* although accepted, you should not pass in a perl
        filehandle here, as perl will likely close the file descriptor
        another time when the filehandle is destroyed. Normally, you can
        safely call perls "close" or just let filehandles go out of scope.

        This is supposed to be a bug in the API, so that might change. It's
        therefore best to avoid this function.

    aio_read $fh,$offset,$length, $data,$dataoffset,$callback
    aio_write $fh,$offset,$length, $data,$dataoffset,$callback
        Reads or writes "length" bytes from the specified "fh" and "offset"
        into the scalar given by "data" and offset "dataoffset" and calls
        the callback without the actual number of bytes read (or -1 on
        error, just like the syscall).

        Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
        offset 0 within the scalar:

           aio_read $fh, 7, 15, $buffer, 0, sub {
              $_[0] > 0 or die "read error: $!";
              print "read $_[0] bytes: <$buffer>\n";
           };

    aio_readahead $fh,$offset,$length, $callback
        "aio_readahead" populates the page cache with data from a file so
        that subsequent reads from that file will not block on disk I/O. The
        $offset argument specifies the starting point from which data is to
        be read and $length specifies the number of bytes to be read. I/O is
        performed in whole pages, so that offset is effectively rounded down
        to a page boundary and bytes are read up to the next page boundary
        greater than or equal to (off-set+length). "aio_readahead" does not
        read beyond the end of the file. The current file offset of the file
        is left unchanged.

        If that syscall doesn't exist (likely if your OS isn't Linux) it
        will be emulated by simply reading the data, which would have a
        similar effect.

    aio_stat $fh_or_path, $callback
    aio_lstat $fh, $callback
        Works like perl's "stat" or "lstat" in void context. The callback
        will be called after the stat and the results will be available
        using "stat _" or "-s _" etc...

        The pathname passed to "aio_stat" must be absolute. See API NOTES,
        above, for an explanation.

        Currently, the stats are always 64-bit-stats, i.e. instead of
        returning an error when stat'ing a large file, the results will be
        silently truncated unless perl itself is compiled with large file
        support.

        Example: Print the length of /etc/passwd:

           aio_stat "/etc/passwd", sub {
              $_[0] and die "stat failed: $!";
              print "size is ", -s _, "\n";
           };

    aio_unlink $pathname, $callback
        Asynchronously unlink (delete) a file and call the callback with the
        result code.

    aio_rmdir $pathname, $callback
        Asynchronously rmdir (delete) a directory and call the callback with
        the result code.

    aio_fsync $fh, $callback
        Asynchronously call fsync on the given filehandle and call the
        callback with the fsync result code.

    aio_fdatasync $fh, $callback
        Asynchronously call fdatasync on the given filehandle and call the
        callback with the fdatasync result code.

        If this call isn't available because your OS lacks it or it couldn't
        be detected, it will be emulated by calling "fsync" instead.

  SUPPORT FUNCTIONS
    $fileno = IO::AIO::poll_fileno
        Return the *request result pipe file descriptor*. This filehandle
        must be polled for reading by some mechanism outside this module
        (e.g. Event or select, see below or the SYNOPSIS). If the pipe
        becomes readable you have to call "poll_cb" to check the results.

        See "poll_cb" for an example.

    IO::AIO::poll_cb
        Process all outstanding events on the result pipe. You have to call
        this regularly. Returns the number of events processed. Returns
        immediately when no events are outstanding.

        Example: Install an Event watcher that automatically calls
        IO::AIO::poll_cb with high priority:

           Event->io (fd => IO::AIO::poll_fileno,
                      poll => 'r', async => 1,
                      cb => \&IO::AIO::poll_cb);

    IO::AIO::poll_wait
        Wait till the result filehandle becomes ready for reading (simply
        does a "select" on the filehandle. This is useful if you want to
        synchronously wait for some requests to finish).

        See "nreqs" for an example.

    IO::AIO::nreqs
        Returns the number of requests currently outstanding (i.e. for which
        their callback has not been invoked yet).

        Example: wait till there are no outstanding requests anymore:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              while IO::AIO::nreqs;

    IO::AIO::flush
        Wait till all outstanding AIO requests have been handled.

        Strictly equivalent to:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              while IO::AIO::nreqs;

    IO::AIO::poll
        Waits until some requests have been handled.

        Strictly equivalent to:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              if IO::AIO::nreqs;

    IO::AIO::min_parallel $nthreads
        Set the minimum number of AIO threads to $nthreads. The default is
        1, which means a single asynchronous operation can be done at one
        time (the number of outstanding operations, however, is unlimited).

        It is recommended to keep the number of threads low, as some Linux
        kernel versions will scale negatively with the number of threads
        (higher parallelity => MUCH higher latency). With current Linux 2.6
        versions, 4-32 threads should be fine.

        Under normal circumstances you don't need to call this function, as
        this module automatically starts some threads (the exact number
        might change, and is currently 4).

    IO::AIO::max_parallel $nthreads
        Sets the maximum number of AIO threads to $nthreads. If more than
        the specified number of threads are currently running, kill them.
        This function blocks until the limit is reached.

        This module automatically runs "max_parallel 0" at program end, to
        ensure that all threads are killed and that there are no outstanding
        requests.

        Under normal circumstances you don't need to call this function.

    $oldnreqs = IO::AIO::max_outstanding $nreqs
        Sets the maximum number of outstanding requests to $nreqs. If you
        try to queue up more than this number of requests, the caller will
        block until some requests have been handled.

        The default is very large, so normally there is no practical limit.
        If you queue up many requests in a loop it it often improves speed
        if you set this to a relatively low number, such as 100.

        Under normal circumstances you don't need to call this function.

  FORK BEHAVIOUR
    IO::AIO handles all outstanding AIO requests before the fork, destroys
    all AIO threads, and recreates them in both the parent and the child
    after the fork.

SEE ALSO
    Coro, Linux::AIO.

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/

