AIO(3pm)

NAME

IO::AIO - Asynchronous Input/Output

SYNOPSIS

use IO::AIO;

aio_open "/etc/passwd", O_RDONLY, 0, sub {
   my $fh = shift
      or die "/etc/passwd: $!";
   ...
};

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

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

# version 2+ has request and group objects
use IO::AIO 2;

aioreq_pri 4; # give next request a very high priority
my $req = aio_unlink "/tmp/file", sub { };
$req->cancel; # cancel request if still in queue

my $grp = aio_group sub { print "all stats done\n" };
add $grp aio_stat "..." for ...;

# AnyEvent integration
open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });

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

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

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

# Danga::Socket integration
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.

Asynchronous means that operations that can normally block your program (e.g. reading from disk) will be done asynchronously: the operation
will still block, but you can do something else in the meantime. This
is extremely useful for programs that need to stay interactive even
when doing heavy I/O (GUI programs, high performance network servers
etc.), but can also be used to easily do operations in parallel that
are normally done sequentially, e.g. stat'ing many files, which is much faster on a RAID volume or over NFS when you do a number of stat
operations concurrently.

While most of this works on all types of file descriptors (for example sockets), using these functions on file descriptors that support
nonblocking operation (again, sockets, pipes etc.) is very inefficient. Use an event loop for that (such as the Event module): IO::AIO will
naturally fit into such an event loop itself.

In this version, a number of threads are started that execute your
requests and signal their completion. You don't need thread support in perl, and the threads created by this module will not be visible to
perl. 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 or restricted (GNU/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 in the presence of other (Perl-) threads, it is currently not reentrant in any way, so use appropriate locking
yourself, always call "poll_cb" from within the same thread, or never
call "poll_cb" (or other "aio_" functions) recursively.

EXAMPLE

This is a simple example that uses the Event module and loads /etc/passwd asynchronously:: use Fcntl;
use Event;
use IO::AIO;; # register the IO::AIO callback with Event
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r',
cb => \&IO::AIO::poll_cb);
# queue the request to open /etc/passwd aio_open "/etc/passwd", O_RDONLY, 0, sub {: my $fh = shift
or die "error while opening: $!";; # stat'ing filehandles is generally non-blocking
my $size = -s $fh;; # queue a request to read the file
my $contents;
aio_read $fh, 0, $size, $contents, 0, sub {
$_[0] == $size
or die "short read: $!";

close $fh;

# file contents now in $contents
print $contents;

# exit event loop and program
Event::unloop;; };
};
# possibly queue up other requests, or open GUI windows, # check for sockets etc. etc.
# process events as long as there are some: Event::loop;

REQUEST ANATOMY AND LIFETIME

Every "aio_*" function creates a request. which is a C data structure
not directly visible to Perl.

If called in non-void context, every request function returns a Perl
object representing the request. In void context, nothing is returned, which saves a bit of memory.

The perl object is a fairly standard ref-to-hash object. The hash
contents are not used by IO::AIO so you are free to store anything you like in it.

During their existance, aio requests travel through the following
states, in order:

ready: Immediately after a request is created it is put into the ready
state, waiting for a thread to execute it.
execute: A thread has accepted the request for processing and is currently
executing it (e.g. blocking in read).
pending: The request has been executed and is waiting for result processing.; While request submission and execution is fully asynchronous,
result processing is not and relies on the perl interpreter calling "poll_cb" (or another function with the same effect).
result: The request results are processed synchronously by "poll_cb".; The "poll_cb" function will process all outstanding aio requests by calling their callbacks, freeing memory associated with them and
managing any groups they are contained in.
done: Request has reached the end of its lifetime and holds no resources anymore (except possibly for the Perl object, but its connection to the actual aio request is severed and calling its methods will
either do nothing or result in a runtime error).

FUNCTIONS

AIO REQUEST 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.

All functions return request objects of type IO::AIO::REQ that allow
further manipulation of those requests while they are in-flight.

The pathnames you pass to these routines must be absolute and encoded as octets. 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 anywhere in the program and then use relative paths.

To encode pathnames as octets, either make sure you either: a) always
pass in filenames you got from outside (command line, readdir etc.)
without tinkering, 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 to ensure your scalar has the
correct contents.

This works, btw. independent of the internal UTF-8 bit, which IO::AIO
handles correctly wether it is set or not.

$prev_pri = aioreq_pri [$pri]: Returns the priority value that would be used for the next request and, if $pri is given, sets the priority for the next aio request.; The default priority is 0, the minimum and maximum priorities are
"-4" and 4, respectively. Requests with higher priority will be
serviced first.; The priority will be reset to 0 after each call to one of the
"aio_*" functions.; Example: open a file with low priority, then read something from it with higher priority so the read request is serviced before other
low priority open requests (potentially spamming the cache):

aioreq_pri -3;
aio_open ..., sub {
return unless $_[0];

aioreq_pri -2;
aio_read $_[0], ..., sub {
...

};

};; aioreq_nice $pri_adjust
Similar to "aioreq_pri", but subtracts the given value from the
current priority, so the effect is cumulative.; aio_open $pathname, $flags, $mode, $callback->($fh)
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). Note that the $mode will be modified by the umask in effect then the request is being
executed, so better never change the umask.

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, $callback->($status)

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, $callback->($retval) aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)

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).

If $offset is undefined, then the current file offset will be used (and updated), otherwise the file offset will not be changed by
these calls.

If $length is undefined in "aio_write", use the remaining length
of $data.

If $dataoffset is less than zero, it will be counted from the end
of $data.

The $data scalar MUST NOT be modified in any way while the request is outstanding. Modifying it can result in segfaults or World War
III (if the necessary/optional hardware is installed).

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_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)

Tries to copy $length bytes from $in_fh to $out_fh. It starts
reading at byte offset $in_offset, and starts writing at the
current file offset of $out_fh. Because of that, it is not safe to issue more than one "aio_sendfile" per $out_fh, as they will
interfere with each other.

This call tries to make use of a native "sendfile" syscall to
provide zero-copy operation. For this to work, $out_fh should refer to a socket, and $in_fh should refer to mmap'able file.

If the native sendfile call fails or is not implemented, it will be emulated, so you can call "aio_sendfile" on any type of filehandle regardless of the limitations of the operating system.

Please note, however, that "aio_sendfile" can read more bytes from $in_fh than are written, and there is no way to find out how many
bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
only provides the number of bytes written to $out_fh. Only if the
result value equals $length one can assume that $length bytes have been read.

aio_readahead $fh,$offset,$length, $callback->($retval)

"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, $callback->($status)
aio_lstat $fh, $callback->($status)

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_utime $fh_or_path, $atime, $mtime, $callback->($status)

Works like perl's "utime" function (including the special case of
$atime and $mtime being undef). Fractional times are supported if
the underlying syscalls support them.

When called with a pathname, uses utimes(2) if available, otherwise utime(2). If called on a file descriptor, uses futimes(2) if available, otherwise returns ENOSYS, so this is not portable.

Examples:

# set atime and mtime to current time (basically touch(1)):
aio_utime "path", undef, undef;
# set atime to current time and mtime to beginning of the epoch: aio_utime "path", time, undef; # undef==0

aio_chown $fh_or_path, $uid, $gid, $callback->($status)

Works like perl's "chown" function, except that "undef" for either $uid or $gid is being interpreted as "do not change" (but -1 can
also be used).

Examples:

# same as "chown root path" in the shell:
aio_chown "path", 0, -1;
# same as above:
aio_chown "path", 0, undef;

aio_truncate $fh_or_path, $offset, $callback->($status)

Works like truncate(2) or ftruncate(2).

aio_chmod $fh_or_path, $mode, $callback->($status)

Works like perl's "chmod" function.

aio_unlink $pathname, $callback->($status)

Asynchronously unlink (delete) a file and call the callback with
the result code.

aio_mknod $path, $mode, $dev, $callback->($status)

[EXPERIMENTAL]

Asynchronously create a device node (or fifo). See mknod(2).

The only (POSIX-) portable way of calling this function is:

aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...

aio_link $srcpath, $dstpath, $callback->($status)

Asynchronously create a new link to the existing object at $srcpath at the path $dstpath and call the callback with the result code.

aio_symlink $srcpath, $dstpath, $callback->($status)

Asynchronously create a new symbolic link to the existing object at $srcpath at the path $dstpath and call the callback with the result code.

aio_readlink $path, $callback->($link)

Asynchronously read the symlink specified by $path and pass it to
the callback. If an error occurs, nothing or undef gets passed to
the callback.

aio_rename $srcpath, $dstpath, $callback->($status)

Asynchronously rename the object at $srcpath to $dstpath, just as
rename(2) and call the callback with the result code.

aio_mkdir $pathname, $mode, $callback->($status)

Asynchronously mkdir (create) a directory and call the callback
with the result code. $mode will be modified by the umask at the
time the request is executed, so do not change your umask.

aio_rmdir $pathname, $callback->($status)

Asynchronously rmdir (delete) a directory and call the callback
with the result code.

aio_readdir $pathname, $callback->($entries)

Unlike the POSIX call of the same name, "aio_readdir" reads an
entire directory (i.e. opendir + readdir + closedir). The entries
will not be sorted, and will NOT include the "." and ".." entries.

The callback a single argument which is either "undef" or an arrayref with the filenames.

aio_load $path, $data, $callback->($status)

This is a composite request that tries to fully load the given file into memory. Status is the same as with aio_read.

aio_copy $srcpath, $dstpath, $callback->($status)

Try to copy the file (directories not supported as either source or destination) from $srcpath to $dstpath and call the callback with
the 0 (error) or "-1" ok.

This is a composite request that it creates the destination file
with mode 0200 and copies the contents of the source file into it
using "aio_sendfile", followed by restoring atime, mtime, access
mode and uid/gid, in that order.

If an error occurs, the partial destination file will be unlinked, if possible, except when setting atime, mtime, access mode and
uid/gid, where errors are being ignored.

aio_move $srcpath, $dstpath, $callback->($status)

Try to move the file (directories not supported as either source or destination) from $srcpath to $dstpath and call the callback with
the 0 (error) or "-1" ok.

This is a composite request that tries to rename(2) the file first. If rename files with "EXDEV", it copies the file with "aio_copy"
and, if that is successful, unlinking the $srcpath.

aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)

Scans a directory (similar to "aio_readdir") but additionally tries to efficiently separate the entries of directory $path into two
sets of names, directories you can recurse into (directories), and ones you cannot recurse into (everything else, including symlinks
to directories).

"aio_scandir" is a composite request that creates of many sub
requests_ $maxreq specifies the maximum number of outstanding aio
requests that this function generates. If it is "<= 0", then a
suitable default will be chosen (currently 4).

On error, the callback is called without arguments, otherwise it
receives two array-refs with path-relative entry names.

Example:

aio_scandir $dir, 0, sub {
my ($dirs, $nondirs) = @_;
print "real directories: @$dirs\n";
print "everything else: @$nondirs\n";

};

Implementation notes.

The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
can.

After reading the directory, the modification time, size etc. of
the directory before and after the readdir is checked, and if they match (and isn't the current time), the link count will be used to decide how many entries are directories (if >= 2). Otherwise, no
knowledge of the number of subdirectories will be assumed.

Then entries will be sorted into likely directories (everything
without a non-initial dot currently) and likely non-directories
(everything else). Then every entry plus an appended "/." will be
"stat"'ed, likely directories first. If that succeeds, it assumes
that the entry is a directory or a symlink to directory (which will be checked seperately). This is often faster than stat'ing the
entry itself because filesystems might detect the type of the entry without reading the inode data (e.g. ext2fs filetype feature).

If the known number of directories (link count - 2) has been
reached, the rest of the entries is assumed to be non-directories.

This only works with certainty on POSIX (= UNIX) filesystems, which fortunately are the vast majority of filesystems around.

It will also likely work on non-POSIX filesystems with reduced
efficiency as those tend to return 0 or 1 as link counts, which
disables the directory counting heuristic.

aio_rmtree $path, $callback->($status)

Delete a directory tree starting (and including) $path, return the status of the final "rmdir" only. This is a composite request that uses "aio_scandir" to recurse into and rmdir directories, and
unlink everything else.

aio_fsync $fh, $callback->($status)

Asynchronously call fsync on the given filehandle and call the
callback with the fsync result code.

aio_fdatasync $fh, $callback->($status)

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.

aio_group $callback->(...)

This is a very special aio request: Instead of doing something, it is a container for other aio requests, which is useful if you want to bundle many requests into a single, composite, request with a
definite callback and the ability to cancel the whole request with its subrequests.

Returns an object of class IO::AIO::GRP. See its documentation
below for more info.

Example:

my $grp = aio_group sub {

print "all stats done\n";

};

add $grp

(aio_stat ...),
(aio_stat ...),
...;
aio_nop $callback->(): This is a special request - it does nothing in itself and is only
used for side effects, such as when you want to add a dummy request to a group so that finishing the requests in the group depends on
executing the given code.; While this request does nothing, it still goes through the
execution phase and still requires a worker thread. Thus, the
callback will not be executed immediately but only after other
requests in the queue have entered their execution phase. This can be used to measure request latency.
IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*: Mainly used for debugging and benchmarking, this aio request puts
one of the request workers to sleep for the given time.; While it is theoretically handy to have simple I/O scheduling
requests like sleep and file handle readable/writable, the overhead this creates is immense (it blocks a thread for a long time) so do not use this function except to put your application under
artificial I/O pressure.
IO::AIO::REQ CLASS
All non-aggregate "aio_*" functions return an object of this class when called in non-void context.
cancel $req: Cancels the request, if possible. Has the effect of skipping
execution when entering the execute state and skipping calling the callback when entering the the result state, but will leave the request otherwise untouched. That means that requests that
currently execute will not be stopped and resources held by the
request will not be freed prematurely.
cb $req $callback->(...): Replace (or simply set) the callback registered to the request.
IO::AIO::GRP CLASS
This class is a subclass of IO::AIO::REQ, so all its methods apply to objects of this class, too.
A IO::AIO::GRP object is a special request that can contain multiple other aio requests.
You create one by calling the "aio_group" constructing function with a callback that will be called when all contained requests have entered the "done" state:: my $grp = aio_group sub {
print "all requests are done\n";; };
You add requests by calling the "add" method with one or more "IO::AIO::REQ" objects:: $grp->add (aio_unlink "...");; add $grp aio_stat "...", sub {
$_[0] or return $grp->result ("error");

# add another request dynamically, if first succeeded
add $grp aio_open "...", sub {
$grp->result ("ok");

};; };
This makes it very easy to create composite requests (see the source of "aio_move" for an application) that work and feel like simple requests.
o The IO::AIO::GRP objects will be cleaned up during calls to: "IO::AIO::poll_cb", just like any other request.
o They can be canceled like any other request. Canceling will cancel: not only the request itself, but also all requests it contains.
o They can also can also be added to other IO::AIO::GRP objects.
o You must not add requests to a group from within the group callback: (or any later time).
Their lifetime, simplified, looks like this: when they are empty, they will finish very quickly. If they contain only requests that are in the "done" state, they will also finish. Otherwise they will continue to exist.
That means after creating a group you have some time to add requests. And in the callbacks of those requests, you can add further requests to the group. And only when all those requests have finished will the the group itself finish.
add $grp ... $grp->add (...): Add one or more requests to the group. Any type of IO::AIO::REQ can be added, including other groups, as long as you do not create
circular dependencies.; Returns all its arguments.
$grp->cancel_subs: Cancel all subrequests and clears any feeder, but not the group
request itself. Useful when you queued a lot of events but got a
result early.
$grp->result (...): Set the result value(s) that will be passed to the group callback
when all subrequests have finished and set thre groups errno to the current value of errno (just like calling "errno" without an error number). By default, no argument will be passed and errno is zero.
$grp->errno ([$errno]): Sets the group errno value to $errno, or the current value of errno when the argument is missing.; Every aio request has an associated errno value that is restored
when the callback is invoked. This method lets you change this
value from its default (0).; Calling "result" will also set errno, so make sure you either set
$! before the call to "result", or call c<errno> after it.
feed $grp $callback->($grp): Sets a feeder/generator on this group: every group can have an
attached generator that generates requests if idle. The idea behind this is that, although you could just queue as many requests as you want in a group, this might starve other requests for a potentially long time. For example, "aio_scandir" might generate hundreds of
thousands "aio_stat" requests, delaying any later requests for a
long time.; To avoid this, and allow incremental generation of requests, you
can instead a group and set a feeder on it that generates those
requests. The feed callback will be called whenever there are few
enough (see "limit", below) requests active in the group itself and is expected to queue more requests.; The feed callback can queue as many requests as it likes (i.e.
"add" does not impose any limits).; If the feed does not queue more requests when called, it will be
automatically removed from the group.; If the feed limit is 0, it will be set to 2 automatically.; Example:

# stat all files in @files, but only ever use four aio requests concurrently:

my $grp = aio_group sub { print "finished\n" };
limit $grp 4;
feed $grp sub {
my $file = pop @files
or return;

add $grp aio_stat $file, sub { ... };

};; limit $grp $num
Sets the feeder limit for the group: The feeder will be called
whenever the group contains less than this many requests.

Setting the limit to 0 will pause the feeding process.; SUPPORT FUNCTIONS; EVENT PROCESSING AND EVENT LOOP INTEGRATION; $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 some 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. The amount of
events processed depends on the settings of "IO::AIO::max_poll_req" and "IO::AIO::max_poll_time".

If not all requests were processed for whatever reason, the
filehandle will still be ready when "poll_cb" returns.

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::max_poll_reqs $nreqs IO::AIO::max_poll_time $seconds: These set the maximum number of requests (default 0, meaning
infinity) that are being processed by "IO::AIO::poll_cb" in one
call, respectively the maximum amount of time (default 0, meaning
infinity) spent in "IO::AIO::poll_cb" to process requests (more
correctly the mininum amount of time "poll_cb" is allowed to use).; Setting "max_poll_time" to a non-zero value creates an overhead of one syscall per request processed, which is not normally a problem unless your callbacks are really really fast or your OS is really
really slow (I am not mentioning Solaris here). Using
"max_poll_reqs" incurs no overhead.; Setting these is useful if you want to ensure some level of
interactiveness when perl is not fast enough to process all
requests in time.; For interactive programs, values such as 0.01 to 0.1 should be
fine.; Example: Install an Event watcher that automatically calls
IO::AIO::poll_cb with low priority, to ensure that other parts of
the program get the CPU sometimes even under high AIO load.

# try not to spend much more than 0.1s in poll_cb
IO::AIO::max_poll_time 0.1;

# use a low priority so other tasks have priority
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r', nice => 1,
cb => &IO::AIO::poll_cb);
IO::AIO::poll_wait: If there are any outstanding requests and none of them in the
result phase, 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::poll: Waits until some requests have been handled.; Returns the number of requests processed, but is otherwise strictly equivalent to:

IO::AIO::poll_wait, IO::AIO::poll_cb; 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;
CONTROLLING THE NUMBER OF THREADS
IO::AIO::min_parallel $nthreads: Set the minimum number of AIO threads to $nthreads. The current
default is 8, which means eight asynchronous operations can execute concurrently at any one time (the number of outstanding requests,
however, is unlimited).; IO::AIO starts threads only on demand, when an AIO request is
queued and no free thread exists. Please note that queueing up a
hundred requests can create demand for a hundred threads, even if
it turns out that everything is in the cache and could have been
processed faster by a single thread.; It is recommended to keep the number of threads relatively 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 most circumstances you don't need to call this function, as
the module selects a default that is suitable for low to moderate
load.
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, this
function kills them. This function blocks until the limit is
reached.; While $nthreads are zero, aio requests get queued but not executed until the number of threads has been increased again.; 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.
IO::AIO::max_idle $nthreads: Limit the number of threads (default: 4) that are allowed to idle
(i.e., threads that did not get a request to process within 10
seconds). That means if a thread becomes idle while $nthreads other threads are also idle, it will free its resources and exit.; This is useful when you allow a large number of threads (e.g. 100
or 1000) to allow for extremely high load situations, but want to
free resources under normal circumstances (1000 threads can easily consume 30MB of RAM).; The default is probably ok in most situations, especially if thread creation is fast. If thread creation is very slow on your system
you might want to use larger values.
$oldmaxreqs = IO::AIO::max_outstanding $maxreqs: This is a very bad function to use in interactive programs because it blocks, and a bad way to reduce concurrency because it is
inexact: Better use an "aio_group" together with a feed callback.; Sets the maximum number of outstanding requests to $nreqs. If you
to queue up more than this number of requests, the next call to the "poll_cb" (and "poll_some" and other functions calling "poll_cb")
function will block until the limit is no longer exceeded.; The default value is very large, so there is no practical limit on the number of outstanding requests.; You can still queue as many requests as you want. Therefore,
"max_oustsanding" is mainly useful in simple scripts (with low
values) or as a stop gap to shield against fatal memory overflow
(with large values).
STATISTICAL INFORMATION
IO::AIO::nreqs: Returns the number of requests currently in the ready, execute or
pending states (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::nready: Returns the number of requests currently in the ready state (not
yet executed).
IO::AIO::npending: Returns the number of requests currently in the pending state
(executed, but not yet processed by poll_cb).
FORK BEHAVIOUR
This module should do "the right thing" when the process using it forks:
Before the fork, IO::AIO enters a quiescent state where no requests can be added in other threads and no results will be processed. After the fork the parent simply leaves the quiescent state and continues request/result processing, while the child frees the request/result queue (so that the requests started before the fork will only be handled in the parent). Threads will be started on demand until the limit set in the parent process has been reached again.
In short: the parent will, after a short pause, continue as if fork had not been called, while the child will act as if IO::AIO has not been used yet.
MEMORY USAGE
Per-request usage:
Each aio request uses - depending on your architecture - around 100-200 bytes of memory. In addition, stat requests need a stat buffer (possibly a few hundred bytes), readdir requires a result buffer and so on. Perl scalars and other data passed into aio requests will also be locked and will consume memory till the request has entered the done state.
This is now awfully much, so queuing lots of requests is not usually a problem.
Per-thread usage:
In the execution phase, some aio requests require more memory for temporary buffers, and each thread requires a stack and other data structures (usually around 16k-128k, depending on the OS).

KNOWN BUGS

Known bugs will be fixed in the next release.

AUTHOR

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

docs.sk

comprehensive documentation repository

See also