--- IO-AIO/AIO.pm 2005/07/10 22:20:25 1.8 +++ IO-AIO/AIO.pm 2007/01/07 21:36:58 1.100 @@ -7,7 +7,8 @@ use IO::AIO; aio_open "/etc/passwd", O_RDONLY, 0, sub { - my ($fh) = @_; + my $fh = shift + or die "/etc/passwd: $!"; ... }; @@ -17,77 +18,267 @@ $_[0] > 0 or die "read error: $!"; }; - # Event + # 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 + # Glib/Gtk2 integration add_watch Glib::IO IO::AIO::poll_fileno, - \&IO::AIO::poll_cb; + in => sub { IO::AIO::poll_cb; 1 }; - # Tk + # 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. -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. +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 or +might not work (aio_read fails on sockets/pipes/fifos). 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 with 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 -Although the module will work with in the presence of other threads, it is -currently not reentrant, so use appropriate locking yourself. +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; -use base 'Exporter'; +no warnings; +use strict 'vars'; -use Fcntl (); +use base 'Exporter'; BEGIN { - $VERSION = 0.2; + our $VERSION = '2.32'; + + 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); + 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); - @EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink - aio_fsync aio_fdatasync aio_readahead); - @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs); + @IO::AIO::GRP::ISA = 'IO::AIO::REQ'; require XSLoader; - XSLoader::load IO::AIO, $VERSION; + XSLoader::load ("IO::AIO", $VERSION); } =head1 FUNCTIONS -=head2 AIO FUNCTIONS +=head2 AIO REQUEST FUNCTIONS All the C calls are more or less thin wrappers around the syscall with the same name (sans C). The arguments are similar or identical, -and they all accept an additional C<$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 that expect a filehandle will also accept a file descriptor. - -The filenames you pass to these routines I be absolute. The reason -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. +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 aio_open $pathname, $flags, $mode, $callback +=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. @@ -95,8 +286,13 @@ The pathname passed to C must be absolute. See API NOTES, above, for an explanation. -The C<$mode> argument is a bitmask. See the C module for a -list. They are the same as used in C. +The C<$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). Example: @@ -109,49 +305,78 @@ } }; -=item aio_close $fh, $callback +=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 itself when -the filehandle is destroyed. Normally, you can safely call perls C -or just let filehandles go out of scope. +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. -=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback +This is supposed to be a bug in the API, so that might change. It's +therefore best to avoid this function. -=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback +=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval) + +=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval) Reads or writes C bytes from the specified C and C into the scalar given by C and offset C 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 C<$buffer>, strating at +The C<$data> scalar I be modified in any way while the request +is outstanding. Modifying it can result in segfaults or WW3 (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: $!"; - print "read <$buffer>\n"; + $_[0] > 0 or die "read error: $!"; + print "read $_[0] bytes: <$buffer>\n"; }; -=item aio_readahead $fh,$offset,$length, $callback +=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval) -Asynchronously reads the specified byte range into the page cache, using -the C syscall. If that syscall doesn't exist the status will be -C<-1> and C<$!> is set to ENOSYS. +Tries to copy C<$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. -readahead() populates the page cache with data from a file so that +=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). aio_readahead() does not read beyond the end of the +(off-set+length). C does not read beyond the end of the file. The current file offset of the file is left unchanged. -=item aio_stat $fh_or_path, $callback +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 +=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 @@ -171,102 +396,772 @@ print "size is ", -s _, "\n"; }; -=item aio_unlink $pathname, $callback +=item aio_unlink $pathname, $callback->($status) Asynchronously unlink (delete) a file and call the callback with the result code. -=item aio_fsync $fh, $callback +=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_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($$;$) { + aio_block { + my ($path, undef, $cb) = @_; + my $data = \$_[1]; + + my $pri = aioreq_pri; + my $grp = aio_group $cb; + + aioreq_pri $pri; + add $grp aio_open $path, O_RDONLY, 0, sub { + my ($fh) = @_ + or return $grp->result (-1); + + aioreq_pri $pri; + add $grp aio_read $fh, 0, (-s $fh), $$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 +=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). If the pipe becomes readable you have to call -C to check the results. +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 all outstanding events on the result pipe. You have to call this +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. +when no events are outstanding. The amount of events processed depends on +the settings of C and C. -You can use Event to multiplex, e.g.: +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 -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). +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