[ViewVC] Diff of: cvs/IO-AIO/AIO.pm

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.59 by root, Sun Oct 22 10:33:26 2006 UTC vs.
Revision 1.73 by root, Tue Oct 24 16:35:04 2006 UTC

  };
  # 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 ...;
 =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
+In this version, a number of threads are started that execute your
-and signal their completion. You don't need thread support in your libc or
+requests and signal their completion. You don't need thread support
-perl, and the threads created by this module will not be visible to the
+in perl, and the threads created by this module will not be visible
-pthreads library. In the future, this module might make use of the native
+to perl. In the future, this module might make use of the native aio
-aio functions available on many operating systems. However, they are often
+functions available on many operating systems. However, they are often
-not well-supported (Linux doesn't allow them on normal files currently,
+not well-supported or restricted (Linux doesn't allow them on normal
-for example), and they would only support aio_read and aio_write, so the
+files currently, for example), and they would only support aio_read and
-remaining functionality would have to be implemented using threads anyway.
+aio_write, so the remaining functionality would have to be implemented
+using threads anyway.
-Although the module will work with in the presence of other threads, it is
+Although the module will work with in the presence of other (Perl-)
-currently not reentrant, so use appropriate locking yourself, always call
+threads, it is currently not reentrant in any way, so use appropriate
-C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
+locking yourself, always call C<poll_cb> from within the same thread, or
-C<aio_> functions) recursively.
+never call C<poll_cb> (or other C<aio_> functions) recursively.
+=head1 REQUEST ANATOMY AND LIFETIME
+Every C<aio_*> function creates a request. which is a C data structure not
+directly visible to Perl.
+If called in non-void context, every request function returns a Perl
+object representing the request. In void context, nothing is returned,
+which saves a bit of memory.
+The perl object is a fairly standard ref-to-hash object. The hash contents
+are not used by IO::AIO so you are free to store anything you like in it.
+During their existance, aio requests travel through the following states,
+in order:
+=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<poll_cb>
+(or another function with the same effect).
+=item result
+The request results are processed synchronously by C<poll_cb>.
+The C<poll_cb> function will process all outstanding aio requests by
+calling their callbacks, freeing memory associated with them and managing
+any groups they are contained in.
+=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';
 BEGIN {
    our $VERSION = '2.0';
-   our @EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
+   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_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
-                    aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
+                     aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
-                    aio_group);
+                     aio_group aio_nop);
-   our @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
+   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);
    @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
    require XSLoader;
    XSLoader::load ("IO::AIO", $VERSION);
 environment, d) use Glib::filename_from_unicode on unicode filenames or e)
 use something else.
 =over 4
+=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<aio_>
+functions.
+Example: open a file with low priority, then read something from it with
+higher priority so the read request is serviced before other low priority
+open requests (potentially spamming the cache):
+   aioreq_pri -3;
+   aio_open ..., sub {
+      return unless $_[0];
+      aioreq_pri -2;
+      aio_read $_[0], ..., sub {
+         ...
+      };
+   };
+=item aioreq_nice $pri_adjust
+Similar to C<aioreq_pri>, 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.
       $_[0] > 0 or die "read error: $!";
       print "read $_[0] bytes: <$buffer>\n";
    };
 =item aio_move $srcpath, $dstpath, $callback->($status)
-[EXPERIMENTAL due to internal aio_group use]
 Try to move the I<file> (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.
 The callback a single argument which is either C<undef> or an array-ref
 with the filenames.
 =item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
-[EXPERIMENTAL due to internal aio_group use]
 Scans a directory (similar to C<aio_readdir>) but additionally tries to
 separate the entries of directory C<$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<aio_scandir> is a composite request that consists of many sub
+C<aio_scandir> is a composite request that creates of many sub requests_
-requests. C<$maxreq> specifies the maximum number of outstanding aio
+C<$maxreq> specifies the maximum number of outstanding aio requests that
-requests that this function generates. If it is C<< <= 0 >>, then a
+this function generates. If it is C<< <= 0 >>, then a suitable default
-suitable default will be chosen (currently 8).
+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:
 sub aio_scandir($$$) {
    my ($path, $maxreq, $cb) = @_;
    my $grp = aio_group $cb;
-   $maxreq = 8 if $maxreq <= 0;
+   $maxreq = 6 if $maxreq <= 0;
    # stat once
    add $grp aio_stat $path, sub {
       return $grp->result () if $_[0];
       my $now = time;
             my (@dirs, @nondirs);
             my ($statcb, $schedcb);
             my $nreq = 0;
+            my $statgrp = add $grp aio_group;
             $schedcb = sub {
                if (@$entries) {
                   if ($nreq < $maxreq) {
                      my $ent = pop @$entries;
                      $nreq++;
-                     add $grp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
+                     add $statgrp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
                   }
                } elsif (!$nreq) {
                   # finished
+                  $statgrp->cancel;
                   undef $statcb;
                   undef $schedcb;
-                  $grp->result (\@dirs, \@nondirs) if $cb;
+                  $grp->result (\@dirs, \@nondirs);
-                  undef $cb;
                }
             };
             $statcb = sub {
                my ($status, $entry) = @_;
 [EXPERIMENTAL]
 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.
+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<IO::AIO::GRP>. See its documentation below
 for more info.
 Example:
    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_sleep $fractional_seconds, $callback->()  *NOT EXPORTED*
+=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
+like sleep and file handle readable/writable, the overhead this creates is
-is immense, so do not use this function except to put your application
+immense (it blocks a thread for a long time) so do not use this function
-under artificial I/O pressure.
+except to put your application under artificial I/O pressure.
 =back
 =head2 IO::AIO::REQ CLASS
 All non-aggregate C<aio_*> functions return an object of this class when
 called in non-void context.
-A request always moves through the following five states in its lifetime,
-in order: B<ready> (request has been created, but has not been executed
-yet), B<execute> (request is currently being executed), B<pending>
-(request has been executed but callback has not been called yet),
-B<result> (results are being processed synchronously, includes calling the
-callback) and B<done> (request has reached the end of its lifetime and
-holds no resources anymore).
 =over 4
-=item $req->cancel
+=item cancel $req
 Cancels the request, if possible. Has the effect of skipping execution
 when entering the B<execute> state and skipping calling the callback when
 entering the the B<result> state, but will leave the request otherwise
 untouched. That means that requests that currently execute will not be
 stopped and resources held by the request will not be freed prematurely.
+=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<IO::AIO::REQ>, so all its methods apply to
    };
 This makes it very easy to create composite requests (see the source of
 C<aio_move> for an application) that work and feel like simple requests.
+=over 4
-The IO::AIO::GRP objects will be cleaned up during calls to
+=item * The IO::AIO::GRP objects will be cleaned up during calls to
 C<IO::AIO::poll_cb>, just like any other request.
-They can be canceled like any other request. Canceling will cancel not
+=item * They can be canceled like any other request. Canceling will cancel not
 only the request itself, but also all requests it contains.
-They can also can also be added to other IO::AIO::GRP objects.
+=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<max_outstanding>, so best do
+not combine C<aio_group> 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<done> state, they will also finish. Otherwise they will continue to
 exist.
 group. And only when all those requests have finished will the the group
 itself finish.
 =over 4
+=item add $grp ...
 =item $grp->add (...)
-=item add $grp ...
 Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
 be added, including other groups, as long as you do not create circular
 dependencies.
 =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)
+[VERY EXPERIMENTAL]
+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<aio_scandir> might generate hundreds of thousands C<aio_stat>
+requests, delaying any later requests for a long time.
+To avoid this, and allow incremental generation of requests, you can
+instead a group and set a feeder on it that generates those requests. The
+feed callback will be called whenever there are few enough (see C<limit>,
+below) requests active in the group itself and is expected to queue more
+requests.
+The feed callback can queue as many requests as it likes (i.e. C<add> does
+not impose any limits).
+If the feed does not queue more requests when called, it will be
+automatically removed from the group.
+If the feed limit is 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
    IO::AIO::poll_wait, IO::AIO::poll_cb
       if IO::AIO::nreqs;
 =item IO::AIO::min_parallel $nthreads
-Set the minimum number of AIO threads to C<$nthreads>. The current default
+Set the minimum number of AIO threads to C<$nthreads>. The current
-is C<4>, which means four asynchronous operations can be done at one time
+default is C<8>, which means eight asynchronous operations can execute
-(the number of outstanding operations, however, is unlimited).
+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 low, as some Linux
+It is recommended to keep the number of threads relatively low, as some
-kernel versions will scale negatively with the number of threads (higher
+Linux kernel versions will scale negatively with the number of threads
-parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
+(higher parallelity => MUCH higher latency). With current Linux 2.6
-threads should be fine.
+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
 Under normal circumstances you don't need to call this function.
 =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 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<aio_group>'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
       or return undef;
    *$sym
 }
-min_parallel 4;
+min_parallel 8;
 END {
    max_parallel 0;
 }
 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 clears the request/result
+request/result processing, while the child frees the request/result queue
-queue (so the requests started before the fork will only be handled in
+(so that the requests started before the fork will only be handled in the
-the parent). Threads will be started on demand until the limit ste 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<Coro>, L<Linux::AIO> (obsolete).
+L<Coro::AIO>.
 =head1 AUTHOR
  Marc Lehmann <schmorp@schmorp.de>
  http://home.schmorp.de/

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Comparing IO-AIO/AIO.pm (file contents): Revision 1.59 by root, Sun Oct 22 10:33:26 2006 UTC vs. Revision 1.73 by root, Tue Oct 24 16:35:04 2006 UTC

Diff Legend

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.59 by root, Sun Oct 22 10:33:26 2006 UTC vs.
Revision 1.73 by root, Tue Oct 24 16:35:04 2006 UTC