--- IO-AIO/AIO.pm 2005/07/12 11:29:40 1.20 +++ IO-AIO/AIO.pm 2006/10/24 20:10:26 1.75 @@ -17,58 +17,131 @@ $_[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, - in => sub { IO::AIO::poll_cb, 1 }; + 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 + # 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. +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 (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. + +=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. -Although the module will work with in the presence of other threads, it is -currently not reentrant, so use appropriate locking yourself. +=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). =cut package IO::AIO; -use base 'Exporter'; +no warnings; +use strict 'vars'; -use Fcntl (); +use base 'Exporter'; BEGIN { - $VERSION = 0.5; + our $VERSION = '2.0'; + + 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_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move + aio_group aio_nop); + our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice)); + our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush + min_parallel max_parallel max_outstanding nreqs); - @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 @@ -83,16 +156,56 @@ 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. +All functions expecting a filehandle keep a copy of the filehandle +internally until the request has finished. + +All requests return objects of type L that allow further +manipulation of those requests while they are in-flight. -The filenames you pass to these routines I be absolute. The reason -for this 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. +The pathnames you pass to these routines I be absolute and +encoded in byte form. The reason for the former is that at the time the +request is being executed, the current working directory could have +changed. Alternatively, you can make sure that you never change the +current working directory. + +To encode pathnames to byte form, either make sure you either: a) +always pass in filenames you got from outside (command line, readdir +etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode +your pathnames to the locale (or other) encoding in effect in the user +environment, d) use Glib::filename_from_unicode on unicode filenames or e) +use something else. =over 4 -=item aio_open $pathname, $flags, $mode, $callback +=item aioreq_pri $pri + +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 effects are 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. @@ -119,7 +232,7 @@ } }; -=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 @@ -130,15 +243,19 @@ 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 +=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval) -=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback +=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). +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: @@ -147,11 +264,98 @@ print "read $_[0] bytes: <$buffer>\n"; }; -=item aio_readahead $fh,$offset,$length, $callback +=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 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, and unlinking the C<$srcpath>. + +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_move($$$) { + my ($src, $dst, $cb) = @_; -Asynchronously reads the specified byte range into the page cache, using -the C syscall. If that syscall doesn't exist (likely if your OS -isn't Linux) the status will be C<-1> and C<$!> is set to C. + my $grp = aio_group $cb; + + add $grp aio_rename $src, $dst, sub { + if ($_[0] && $! == EXDEV) { + add $grp aio_open $src, O_RDONLY, 0, sub { + if (my $src_fh = $_[0]) { + my @stat = stat $src_fh; + + add $grp aio_open $dst, O_WRONLY, 0200, sub { + if (my $dst_fh = $_[0]) { + add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub { + close $src_fh; + + if ($_[0] == $stat[7]) { + utime $stat[8], $stat[9], $dst; + chmod $stat[2] & 07777, $dst_fh; + chown $stat[4], $stat[5], $dst_fh; + close $dst_fh; + + add $grp aio_unlink $src, sub { + $grp->result ($_[0]); + }; + } else { + my $errno = $!; + add $grp aio_unlink $dst, sub { + $! = $errno; + $grp->result (-1); + }; + } + }; + } else { + $grp->result (-1); + } + }, + + } else { + $grp->result (-1); + } + }; + } else { + $grp->result ($_[0]); + } + }; + + $grp +} + +=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> @@ -162,9 +366,12 @@ (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_lstat $fh, $callback +=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 @@ -184,21 +391,379 @@ 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_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_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_scandir $path, $maxreq, $callback->($dirs, $nondirs) + +Scans a directory (similar to C) but additionally tries to +separate the entries of directory C<$path> into two sets of names, ones +you can recurse into (directories or links to them), and ones you cannot +recurse into (everything else). + +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 6). + +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($$$) { + my ($path, $maxreq, $cb) = @_; + + my $grp = aio_group $cb; + + $maxreq = 6 if $maxreq <= 0; + + # stat once + 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 + add $grp aio_readdir $path, sub { + my $entries = shift + or return $grp->result (); + + # stat the dir another time + 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; + + add $statgrp aio_stat "$path/$entry/.", sub { + if ($_[0] < 0) { + push @nondirs, $entry; + } else { + # need to check for real directory + 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_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. Might set C<$!> to C if -C is not available. +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). + +=item * This does not harmonise well with C, so best do +not combine C with it. Groups and feeders are recommended for +this kind of concurrency-limiting. + +=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. By default, no argument will be passed. + +=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 @@ -266,24 +831,30 @@ =item IO::AIO::min_parallel $nthreads -Set the minimum number of AIO threads to C<$nthreads>. The default is -C<1>, which means a single asynchronous operation can be done at one time -(the number of outstanding operations, however, is unlimited). - -It is recommended to keep the number of threads low, as some Linux -kernel versions will scale negatively with the number of threads (higher -parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32 -threads should be fine. - -Under normal circumstances you don't need to call this function, as this -module automatically starts some threads (the exact number might change, -and is currently 4). +Set the minimum number of AIO threads to C<$nthreads>. The current +default is C<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. + +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. =item IO::AIO::max_parallel $nthreads -Sets the maximum number of AIO threads to C<$nthreads>. If more than -the specified number of threads are currently running, kill them. This -function blocks until the limit is reached. +Sets the maximum number of AIO threads to C<$nthreads>. If more than the +specified number of threads are currently running, this function kills +them. This function blocks until the limit is reached. + +While C<$nthreads> are zero, aio requests get queued but not executed +until the number of threads has been increased again. This module automatically runs C at program end, to ensure that all threads are killed and that there are no outstanding requests. @@ -292,14 +863,20 @@ =item $oldnreqs = IO::AIO::max_outstanding $nreqs +[DEPRECATED] + Sets the maximum number of outstanding requests to C<$nreqs>. If you try to queue up more than this number of requests, the caller will block until some requests have been handled. The default is very large, so normally there is no practical limit. If you -queue up many requests in a loop it it often improves speed if you set +queue up many requests in a loop it often improves speed if you set this to a relatively low number, such as C<100>. +This function does not work well together with C's, and their +feeder interface is better suited to limiting concurrency, so do not use +this function. + Under normal circumstances you don't need to call this function. =back @@ -310,15 +887,19 @@ sub _fd2fh { return undef if $_[0] < 0; - # try to be perl5.6-compatible - local *AIO_FH; - open AIO_FH, "+<&=$_[0]" + # try to generate nice filehandles + my $sym = "IO::AIO::fd#$_[0]"; + local *$sym; + + open *$sym, "+<&=$_[0]" # usually works under any unix + or open *$sym, "<&=$_[0]" # cygwin needs this + or open *$sym, ">&=$_[0]" # or this or return undef; - *AIO_FH + *$sym } -min_parallel 4; +min_parallel 8; END { max_parallel 0; @@ -326,9 +907,48 @@ 1; +=head2 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. + +=head2 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). + +=head1 KNOWN BUGS + +Known bugs will be fixed in the next release. + =head1 SEE ALSO -L, L. +L. =head1 AUTHOR