=head1 NAME IO::AIO - Asynchronous Input/Output =head1 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); =head1 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 L 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 C from within the same thread, or never call C (or other C functions) recursively. =head2 EXAMPLE This is a simple example that uses the Event module and loads F 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; =head1 REQUEST ANATOMY AND LIFETIME Every C 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: =over 4 =item ready Immediately after a request is created it is put into the ready state, waiting for a thread to execute it. =item execute A thread has accepted the request for processing and is currently executing it (e.g. blocking in read). =item 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 C (or another function with the same effect). =item result The request results are processed synchronously by C. The C function will process all outstanding aio requests by calling their callbacks, freeing memory associated with them and managing any groups they are contained in. =item 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). =back =cut package IO::AIO; no warnings; use strict 'vars'; use base 'Exporter'; BEGIN { our $VERSION = '2.4'; our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink aio_readlink aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move aio_copy aio_group aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown aio_chmod aio_utime aio_truncate); our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice aio_block)); our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush min_parallel max_parallel max_idle nreqs nready npending nthreads max_poll_time max_poll_reqs); @IO::AIO::GRP::ISA = 'IO::AIO::REQ'; require XSLoader; XSLoader::load ("IO::AIO", $VERSION); } =head1 FUNCTIONS =head2 AIO REQUEST FUNCTIONS All the C calls are more or less thin wrappers around the syscall with the same name (sans C). The arguments are similar or identical, and they all accept an additional (and optional) C<$callback> argument which must be a code reference. This code reference will get called with the syscall return code (e.g. most syscalls return C<-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 L that allow further manipulation of those requests while they are in-flight. The pathnames you pass to these routines I 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. =over 4 =item $prev_pri = aioreq_pri [$pri] Returns the priority value that would be used for the next request and, if C<$pri> is given, sets the priority for the next aio request. The default priority is C<0>, the minimum and maximum priorities are C<-4> and C<4>, respectively. Requests with higher priority will be serviced first. The priority will be reset to C<0> after each call to one of the C 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 { ... }; }; =item aioreq_nice $pri_adjust Similar to C, but subtracts the given value from the current priority, so the effect is cumulative. =item 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 C must be absolute. See API NOTES, above, for an explanation. The C<$flags> argument is a bitmask. See the C module for a list. They are the same as used by C. Likewise, C<$mode> specifies the mode of the newly created file, if it didn't exist and C has been given, just like perl's C, except that it is mandatory (i.e. use C<0> if you don't create new files, and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified by the umask in effect then the request is being executed, so better never change the umask. Example: aio_open "/etc/passwd", O_RDONLY, 0, sub { if ($_[0]) { print "open successful, fh is $_[0]\n"; ... } else { die "open failed: $!\n"; } }; =item aio_close $fh, $callback->($status) Asynchronously close a file and call the callback with the result code. I 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 C 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. =item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval) =item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval) Reads or writes C<$length> bytes from the specified C<$fh> and C<$offset> into the scalar given by C<$data> and offset C<$dataoffset> and calls the callback without the actual number of bytes read (or -1 on error, just like the syscall). If C<$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 C<$length> is undefined in C, use the remaining length of C<$data>. If C<$dataoffset> is less than zero, it will be counted from the end of C<$data>. The C<$data> scalar I be modified in any way while the request is outstanding. Modifying it can result in segfaults or World War III (if the necessary/optional hardware is installed). Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at offset C<0> within the scalar: aio_read $fh, 7, 15, $buffer, 0, sub { $_[0] > 0 or die "read error: $!"; print "read $_[0] bytes: <$buffer>\n"; }; =item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval) Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts reading at byte offset C<$in_offset>, and starts writing at the current file offset of C<$out_fh>. Because of that, it is not safe to issue more than one C per C<$out_fh>, as they will interfere with each other. This call tries to make use of a native C syscall to provide zero-copy operation. For this to work, C<$out_fh> should refer to a socket, and C<$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 C on any type of filehandle regardless of the limitations of the operating system. Please note, however, that C can read more bytes from C<$in_fh> than are written, and there is no way to find out how many bytes have been read from C alone, as C only provides the number of bytes written to C<$out_fh>. Only if the result value equals C<$length> one can assume that C<$length> bytes have been read. =item aio_readahead $fh,$offset,$length, $callback->($retval) C populates the page cache with data from a file so that subsequent reads from that file will not block on disk I/O. The C<$offset> argument specifies the starting point from which data is to be read and C<$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). C 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. =item aio_stat $fh_or_path, $callback->($status) =item aio_lstat $fh, $callback->($status) Works like perl's C or C in void context. The callback will be called after the stat and the results will be available using C or C<-s _> etc... The pathname passed to C 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 F: aio_stat "/etc/passwd", sub { $_[0] and die "stat failed: $!"; print "size is ", -s _, "\n"; }; =item aio_utime $fh_or_path, $atime, $mtime, $callback->($status) Works like perl's C 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 =item aio_chown $fh_or_path, $uid, $gid, $callback->($status) Works like perl's C function, except that C 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; =item aio_truncate $fh_or_path, $offset, $callback->($status) Works like truncate(2) or ftruncate(2). =item aio_chmod $fh_or_path, $mode, $callback->($status) Works like perl's C function. =item aio_unlink $pathname, $callback->($status) Asynchronously unlink (delete) a file and call the callback with the result code. =item 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 { ... =item aio_link $srcpath, $dstpath, $callback->($status) Asynchronously create a new link to the existing object at C<$srcpath> at the path C<$dstpath> and call the callback with the result code. =item aio_symlink $srcpath, $dstpath, $callback->($status) Asynchronously create a new symbolic link to the existing object at C<$srcpath> at the path C<$dstpath> and call the callback with the result code. =item aio_readlink $path, $callback->($link) Asynchronously read the symlink specified by C<$path> and pass it to the callback. If an error occurs, nothing or undef gets passed to the callback. =item aio_rename $srcpath, $dstpath, $callback->($status) Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as rename(2) and call the callback with the result code. =item aio_mkdir $pathname, $mode, $callback->($status) Asynchronously mkdir (create) a directory and call the callback with the result code. C<$mode> will be modified by the umask at the time the request is executed, so do not change your umask. =item aio_rmdir $pathname, $callback->($status) Asynchronously rmdir (delete) a directory and call the callback with the result code. =item aio_readdir $pathname, $callback->($entries) Unlike the POSIX call of the same name, C reads an entire directory (i.e. opendir + readdir + closedir). The entries will not be sorted, and will B include the C<.> and C<..> entries. The callback a single argument which is either C or an array-ref with the filenames. =item 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. =cut sub aio_load($$;$) { aio_block { my ($path, undef, $cb) = @_; my $data = \$_[1]; my $pri = aioreq_pri; my $grp = aio_group $cb; aioreq_pri $pri; add $grp aio_open $path, O_RDONLY, 0, sub { my $fh = shift or return $grp->result (-1); aioreq_pri $pri; add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub { $grp->result ($_[0]); }; }; $grp } } =item aio_copy $srcpath, $dstpath, $callback->($status) Try to copy the I (directories not supported as either source or destination) from C<$srcpath> to C<$dstpath> and call the callback with the C<0> (error) or C<-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 C, 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. =cut sub aio_copy($$;$) { aio_block { my ($src, $dst, $cb) = @_; my $pri = aioreq_pri; my $grp = aio_group $cb; aioreq_pri $pri; add $grp aio_open $src, O_RDONLY, 0, sub { if (my $src_fh = $_[0]) { my @stat = stat $src_fh; aioreq_pri $pri; add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub { if (my $dst_fh = $_[0]) { aioreq_pri $pri; add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub { if ($_[0] == $stat[7]) { $grp->result (0); close $src_fh; # those should not normally block. should. should. utime $stat[8], $stat[9], $dst; chmod $stat[2] & 07777, $dst_fh; chown $stat[4], $stat[5], $dst_fh; close $dst_fh; } else { $grp->result (-1); close $src_fh; close $dst_fh; aioreq $pri; add $grp aio_unlink $dst; } }; } else { $grp->result (-1); } }, } else { $grp->result (-1); } }; $grp } } =item aio_move $srcpath, $dstpath, $callback->($status) Try to move the I (directories not supported as either source or destination) from C<$srcpath> to C<$dstpath> and call the callback with the C<0> (error) or C<-1> ok. This is a composite request that tries to rename(2) the file first. If rename files with C, it copies the file with C and, if that is successful, unlinking the C<$srcpath>. =cut sub aio_move($$;$) { aio_block { my ($src, $dst, $cb) = @_; my $pri = aioreq_pri; my $grp = aio_group $cb; aioreq_pri $pri; add $grp aio_rename $src, $dst, sub { if ($_[0] && $! == EXDEV) { aioreq_pri $pri; add $grp aio_copy $src, $dst, sub { $grp->result ($_[0]); if (!$_[0]) { aioreq_pri $pri; add $grp aio_unlink $src; } }; } else { $grp->result ($_[0]); } }; $grp } } =item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs) Scans a directory (similar to C) but additionally tries to efficiently separate the entries of directory C<$path> into two sets of names, directories you can recurse into (directories), and ones you cannot recurse into (everything else, including symlinks to directories). C is a composite request that creates of many sub requests_ C<$maxreq> specifies the maximum number of outstanding aio requests that this function generates. If it is C<< <= 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 C cannot be avoided, but C'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 C will be C'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. =cut sub aio_scandir($$;$) { aio_block { my ($path, $maxreq, $cb) = @_; my $pri = aioreq_pri; my $grp = aio_group $cb; $maxreq = 4 if $maxreq <= 0; # stat once aioreq_pri $pri; add $grp aio_stat $path, sub { return $grp->result () if $_[0]; my $now = time; my $hash1 = join ":", (stat _)[0,1,3,7,9]; # read the directory entries aioreq_pri $pri; add $grp aio_readdir $path, sub { my $entries = shift or return $grp->result (); # stat the dir another time aioreq_pri $pri; add $grp aio_stat $path, sub { my $hash2 = join ":", (stat _)[0,1,3,7,9]; my $ndirs; # take the slow route if anything looks fishy if ($hash1 ne $hash2 or (stat _)[9] == $now) { $ndirs = -1; } else { # if nlink == 2, we are finished # on non-posix-fs's, we rely on nlink < 2 $ndirs = (stat _)[3] - 2 or return $grp->result ([], $entries); } # sort into likely dirs and likely nondirs # dirs == files without ".", short entries first $entries = [map $_->[0], sort { $b->[1] cmp $a->[1] } map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length], @$entries]; my (@dirs, @nondirs); my $statgrp = add $grp aio_group sub { $grp->result (\@dirs, \@nondirs); }; limit $statgrp $maxreq; feed $statgrp sub { return unless @$entries; my $entry = pop @$entries; aioreq_pri $pri; add $statgrp aio_stat "$path/$entry/.", sub { if ($_[0] < 0) { push @nondirs, $entry; } else { # need to check for real directory aioreq_pri $pri; add $statgrp aio_lstat "$path/$entry", sub { if (-d _) { push @dirs, $entry; unless (--$ndirs) { push @nondirs, @$entries; feed $statgrp; } } else { push @nondirs, $entry; } } } }; }; }; }; }; $grp } } =item aio_rmtree $path, $callback->($status) Delete a directory tree starting (and including) C<$path>, return the status of the final C only. This is a composite request that uses C to recurse into and rmdir directories, and unlink everything else. =cut sub aio_rmtree; sub aio_rmtree($;$) { aio_block { my ($path, $cb) = @_; my $pri = aioreq_pri; my $grp = aio_group $cb; aioreq_pri $pri; add $grp aio_scandir $path, 0, sub { my ($dirs, $nondirs) = @_; my $dirgrp = aio_group sub { add $grp aio_rmdir $path, sub { $grp->result ($_[0]); }; }; (aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs; (aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs; add $grp $dirgrp; }; $grp } } =item aio_fsync $fh, $callback->($status) Asynchronously call fsync on the given filehandle and call the callback with the fsync result code. =item 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 C instead. =item 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 L. See its documentation below for more info. Example: my $grp = aio_group sub { print "all stats done\n"; }; add $grp (aio_stat ...), (aio_stat ...), ...; =item 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. =item 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. =back =head2 IO::AIO::REQ CLASS All non-aggregate C functions return an object of this class when called in non-void context. =over 4 =item cancel $req Cancels the request, if possible. Has the effect of skipping execution when entering the B state and skipping calling the callback when entering the the B 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. =item cb $req $callback->(...) Replace (or simply set) the callback registered to the request. =back =head2 IO::AIO::GRP CLASS This class is a subclass of L, 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 C constructing function with a callback that will be called when all contained requests have entered the C state: my $grp = aio_group sub { print "all requests are done\n"; }; You add requests by calling the C method with one or more C 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 C for an application) that work and feel like simple requests. =over 4 =item * The IO::AIO::GRP objects will be cleaned up during calls to C, just like any other request. =item * They can be canceled like any other request. Canceling will cancel not only the request itself, but also all requests it contains. =item * They can also can also be added to other IO::AIO::GRP objects. =item * You must not add requests to a group from within the group callback (or any later time). =back Their lifetime, simplified, looks like this: when they are empty, they will finish very quickly. If they contain only requests that are in the C 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. =over 4 =item add $grp ... =item $grp->add (...) Add one or more requests to the group. Any type of L can be added, including other groups, as long as you do not create circular dependencies. Returns all its arguments. =item $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. =item $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 C without an error number). By default, no argument will be passed and errno is zero. =item $grp->errno ([$errno]) Sets the group errno value to C<$errno>, or the current value of errno when the argument is missing. Every aio request has an associated errno value that is restored when the callback is invoked. This method lets you change this value from its default (0). Calling C will also set errno, so make sure you either set C<$!> before the call to C, or call c after it. =item 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, C might generate hundreds of thousands C 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 C, 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. C 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 C<0>, it will be set to C<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 { ... }; }; =item 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 C<0> will pause the feeding process. =back =head2 SUPPORT FUNCTIONS =head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION =over 4 =item $fileno = IO::AIO::poll_fileno Return the I. 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 C to check the results. See C for an example. =item 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 C and C. If not all requests were processed for whatever reason, the filehandle will still be ready when C 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); =item IO::AIO::max_poll_reqs $nreqs =item IO::AIO::max_poll_time $seconds These set the maximum number of requests (default C<0>, meaning infinity) that are being processed by C in one call, respectively the maximum amount of time (default C<0>, meaning infinity) spent in C to process requests (more correctly the mininum amount of time C is allowed to use). Setting C 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 C 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 C<0.01> to C<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); =item 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 C