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Revision 1.94 by root, Wed Nov 8 02:01:02 2006 UTC

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5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use IO::AIO; 7 use IO::AIO;
8 8
9 aio_open "/etc/passwd", O_RDONLY, 0, sub { 9 aio_open "/etc/passwd", O_RDONLY, 0, sub {
10 my ($fh) = @_; 10 my $fh = shift
11 or die "/etc/passwd: $!";
11 ... 12 ...
12 }; 13 };
13 14
14 aio_unlink "/tmp/file", sub { }; 15 aio_unlink "/tmp/file", sub { };
15 16
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61etc.), but can also be used to easily do operations in parallel that are 62etc.), but can also be used to easily do operations in parallel that are
62normally done sequentially, e.g. stat'ing many files, which is much faster 63normally done sequentially, e.g. stat'ing many files, which is much faster
63on a RAID volume or over NFS when you do a number of stat operations 64on a RAID volume or over NFS when you do a number of stat operations
64concurrently. 65concurrently.
65 66
66While this works on all types of file descriptors (for example sockets), 67While most of this works on all types of file descriptors (for example
67using these functions on file descriptors that support nonblocking 68sockets), using these functions on file descriptors that support
68operation (again, sockets, pipes etc.) is very inefficient. Use an event 69nonblocking operation (again, sockets, pipes etc.) is very inefficient or
70might not work (aio_read fails on sockets/pipes/fifos). Use an event loop
69loop for that (such as the L<Event|Event> module): IO::AIO will naturally 71for that (such as the L<Event|Event> module): IO::AIO will naturally fit
70fit into such an event loop itself. 72into such an event loop itself.
71 73
72In this version, a number of threads are started that execute your 74In this version, a number of threads are started that execute your
73requests and signal their completion. You don't need thread support 75requests and signal their completion. You don't need thread support
74in perl, and the threads created by this module will not be visible 76in perl, and the threads created by this module will not be visible
75to perl. In the future, this module might make use of the native aio 77to perl. In the future, this module might make use of the native aio
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82Although the module will work with in the presence of other (Perl-) 84Although the module will work with in the presence of other (Perl-)
83threads, it is currently not reentrant in any way, so use appropriate 85threads, it is currently not reentrant in any way, so use appropriate
84locking yourself, always call C<poll_cb> from within the same thread, or 86locking yourself, always call C<poll_cb> from within the same thread, or
85never call C<poll_cb> (or other C<aio_> functions) recursively. 87never call C<poll_cb> (or other C<aio_> functions) recursively.
86 88
89=head2 EXAMPLE
90
91This is a simple example that uses the Event module and loads
92F</etc/passwd> asynchronously:
93
94 use Fcntl;
95 use Event;
96 use IO::AIO;
97
98 # register the IO::AIO callback with Event
99 Event->io (fd => IO::AIO::poll_fileno,
100 poll => 'r',
101 cb => \&IO::AIO::poll_cb);
102
103 # queue the request to open /etc/passwd
104 aio_open "/etc/passwd", O_RDONLY, 0, sub {
105 my $fh = shift
106 or die "error while opening: $!";
107
108 # stat'ing filehandles is generally non-blocking
109 my $size = -s $fh;
110
111 # queue a request to read the file
112 my $contents;
113 aio_read $fh, 0, $size, $contents, 0, sub {
114 $_[0] == $size
115 or die "short read: $!";
116
117 close $fh;
118
119 # file contents now in $contents
120 print $contents;
121
122 # exit event loop and program
123 Event::unloop;
124 };
125 };
126
127 # possibly queue up other requests, or open GUI windows,
128 # check for sockets etc. etc.
129
130 # process events as long as there are some:
131 Event::loop;
132
87=head1 REQUEST ANATOMY AND LIFETIME 133=head1 REQUEST ANATOMY AND LIFETIME
88 134
89Every C<aio_*> function creates a request. which is a C data structure not 135Every C<aio_*> function creates a request. which is a C data structure not
90directly visible to Perl. 136directly visible to Perl.
91 137
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132Request has reached the end of its lifetime and holds no resources anymore 178Request has reached the end of its lifetime and holds no resources anymore
133(except possibly for the Perl object, but its connection to the actual 179(except possibly for the Perl object, but its connection to the actual
134aio request is severed and calling its methods will either do nothing or 180aio request is severed and calling its methods will either do nothing or
135result in a runtime error). 181result in a runtime error).
136 182
183=back
184
137=cut 185=cut
138 186
139package IO::AIO; 187package IO::AIO;
140 188
141no warnings; 189no warnings;
142use strict 'vars'; 190use strict 'vars';
143 191
144use base 'Exporter'; 192use base 'Exporter';
145 193
146BEGIN { 194BEGIN {
147 our $VERSION = '2.0'; 195 our $VERSION = '2.2';
148 196
149 our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat 197 our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
150 aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink 198 aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
151 aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move 199 aio_readlink aio_fsync aio_fdatasync aio_readahead aio_rename aio_link
152 aio_copy aio_group aio_nop aio_mknod); 200 aio_move aio_copy aio_group aio_nop aio_mknod);
153 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice)); 201 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
154 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush 202 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
155 min_parallel max_parallel nreqs nready npending); 203 min_parallel max_parallel max_idle
204 nreqs nready npending nthreads
205 max_poll_time max_poll_reqs);
156 206
157 @IO::AIO::GRP::ISA = 'IO::AIO::REQ'; 207 @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
158 208
159 require XSLoader; 209 require XSLoader;
160 XSLoader::load ("IO::AIO", $VERSION); 210 XSLoader::load ("IO::AIO", $VERSION);
161} 211}
162 212
163=head1 FUNCTIONS 213=head1 FUNCTIONS
164 214
165=head2 AIO FUNCTIONS 215=head2 AIO REQUEST FUNCTIONS
166 216
167All the C<aio_*> calls are more or less thin wrappers around the syscall 217All the C<aio_*> calls are more or less thin wrappers around the syscall
168with the same name (sans C<aio_>). The arguments are similar or identical, 218with the same name (sans C<aio_>). The arguments are similar or identical,
169and they all accept an additional (and optional) C<$callback> argument 219and they all accept an additional (and optional) C<$callback> argument
170which must be a code reference. This code reference will get called with 220which must be a code reference. This code reference will get called with
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173syscall has been executed asynchronously. 223syscall has been executed asynchronously.
174 224
175All functions expecting a filehandle keep a copy of the filehandle 225All functions expecting a filehandle keep a copy of the filehandle
176internally until the request has finished. 226internally until the request has finished.
177 227
178All requests return objects of type L<IO::AIO::REQ> that allow further 228All functions return request objects of type L<IO::AIO::REQ> that allow
179manipulation of those requests while they are in-flight. 229further manipulation of those requests while they are in-flight.
180 230
181The pathnames you pass to these routines I<must> be absolute and 231The pathnames you pass to these routines I<must> be absolute and
182encoded in byte form. The reason for the former is that at the time the 232encoded as octets. The reason for the former is that at the time the
183request is being executed, the current working directory could have 233request is being executed, the current working directory could have
184changed. Alternatively, you can make sure that you never change the 234changed. Alternatively, you can make sure that you never change the
185current working directory. 235current working directory anywhere in the program and then use relative
236paths.
186 237
187To encode pathnames to byte form, either make sure you either: a) 238To encode pathnames as octets, either make sure you either: a) always pass
188always pass in filenames you got from outside (command line, readdir 239in filenames you got from outside (command line, readdir etc.) without
189etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode 240tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
190your pathnames to the locale (or other) encoding in effect in the user 241your pathnames to the locale (or other) encoding in effect in the user
191environment, d) use Glib::filename_from_unicode on unicode filenames or e) 242environment, d) use Glib::filename_from_unicode on unicode filenames or e)
192use something else. 243use something else to ensure your scalar has the correct contents.
244
245This works, btw. independent of the internal UTF-8 bit, which IO::AIO
246handles correctly wether it is set or not.
193 247
194=over 4 248=over 4
195 249
196=item $prev_pri = aioreq_pri [$pri] 250=item $prev_pri = aioreq_pri [$pri]
197 251
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220 }; 274 };
221 275
222=item aioreq_nice $pri_adjust 276=item aioreq_nice $pri_adjust
223 277
224Similar to C<aioreq_pri>, but subtracts the given value from the current 278Similar to C<aioreq_pri>, but subtracts the given value from the current
225priority, so effects are cumulative. 279priority, so the effect is cumulative.
226 280
227=item aio_open $pathname, $flags, $mode, $callback->($fh) 281=item aio_open $pathname, $flags, $mode, $callback->($fh)
228 282
229Asynchronously open or create a file and call the callback with a newly 283Asynchronously open or create a file and call the callback with a newly
230created filehandle for the file. 284created filehandle for the file.
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347Asynchronously unlink (delete) a file and call the callback with the 401Asynchronously unlink (delete) a file and call the callback with the
348result code. 402result code.
349 403
350=item aio_mknod $path, $mode, $dev, $callback->($status) 404=item aio_mknod $path, $mode, $dev, $callback->($status)
351 405
406[EXPERIMENTAL]
407
352Asynchronously create a device node (or fifo). See mknod(2). 408Asynchronously create a device node (or fifo). See mknod(2).
353 409
354The only portable (POSIX) way of calling this function is: 410The only (POSIX-) portable way of calling this function is:
355 411
356 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ... 412 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
357 413
358=item aio_link $srcpath, $dstpath, $callback->($status) 414=item aio_link $srcpath, $dstpath, $callback->($status)
359 415
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362 418
363=item aio_symlink $srcpath, $dstpath, $callback->($status) 419=item aio_symlink $srcpath, $dstpath, $callback->($status)
364 420
365Asynchronously create a new symbolic link to the existing object at C<$srcpath> at 421Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
366the path C<$dstpath> and call the callback with the result code. 422the path C<$dstpath> and call the callback with the result code.
423
424=item aio_readlink $path, $callback->($link)
425
426Asynchronously read the symlink specified by C<$path> and pass it to
427the callback. If an error occurs, nothing or undef gets passed to the
428callback.
367 429
368=item aio_rename $srcpath, $dstpath, $callback->($status) 430=item aio_rename $srcpath, $dstpath, $callback->($status)
369 431
370Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as 432Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
371rename(2) and call the callback with the result code. 433rename(2) and call the callback with the result code.
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845 907
846=back 908=back
847 909
848=head2 SUPPORT FUNCTIONS 910=head2 SUPPORT FUNCTIONS
849 911
912=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
913
850=over 4 914=over 4
851 915
852=item $fileno = IO::AIO::poll_fileno 916=item $fileno = IO::AIO::poll_fileno
853 917
854Return the I<request result pipe file descriptor>. This filehandle must be 918Return the I<request result pipe file descriptor>. This filehandle must be
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858 922
859See C<poll_cb> for an example. 923See C<poll_cb> for an example.
860 924
861=item IO::AIO::poll_cb 925=item IO::AIO::poll_cb
862 926
863Process all outstanding events on the result pipe. You have to call this 927Process some outstanding events on the result pipe. You have to call this
864regularly. Returns the number of events processed. Returns immediately 928regularly. Returns the number of events processed. Returns immediately
865when no events are outstanding. 929when no events are outstanding. The amount of events processed depends on
930the settings of C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
866 931
867If not all requests were processed for whatever reason, the filehandle 932If not all requests were processed for whatever reason, the filehandle
868will still be ready when C<poll_cb> returns. 933will still be ready when C<poll_cb> returns.
869 934
870Example: Install an Event watcher that automatically calls 935Example: Install an Event watcher that automatically calls
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872 937
873 Event->io (fd => IO::AIO::poll_fileno, 938 Event->io (fd => IO::AIO::poll_fileno,
874 poll => 'r', async => 1, 939 poll => 'r', async => 1,
875 cb => \&IO::AIO::poll_cb); 940 cb => \&IO::AIO::poll_cb);
876 941
877=item IO::AIO::poll_some $max_requests 942=item IO::AIO::max_poll_reqs $nreqs
878 943
879Similar to C<poll_cb>, but only processes up to C<$max_requests> requests 944=item IO::AIO::max_poll_time $seconds
880at a time.
881 945
882Useful if you want to ensure some level of interactiveness when perl is 946These set the maximum number of requests (default C<0>, meaning infinity)
883not fast enough to process all requests in time. 947that are being processed by C<IO::AIO::poll_cb> in one call, respectively
948the maximum amount of time (default C<0>, meaning infinity) spent in
949C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
950of time C<poll_cb> is allowed to use).
951
952Setting C<max_poll_time> to a non-zero value creates an overhead of one
953syscall per request processed, which is not normally a problem unless your
954callbacks are really really fast or your OS is really really slow (I am
955not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
956
957Setting these is useful if you want to ensure some level of
958interactiveness when perl is not fast enough to process all requests in
959time.
960
961For interactive programs, values such as C<0.01> to C<0.1> should be fine.
884 962
885Example: Install an Event watcher that automatically calls 963Example: Install an Event watcher that automatically calls
886IO::AIO::poll_some with low priority, to ensure that other parts of the 964IO::AIO::poll_cb with low priority, to ensure that other parts of the
887program get the CPU sometimes even under high AIO load. 965program get the CPU sometimes even under high AIO load.
888 966
967 # try not to spend much more than 0.1s in poll_cb
968 IO::AIO::max_poll_time 0.1;
969
970 # use a low priority so other tasks have priority
889 Event->io (fd => IO::AIO::poll_fileno, 971 Event->io (fd => IO::AIO::poll_fileno,
890 poll => 'r', nice => 1, 972 poll => 'r', nice => 1,
891 cb => sub { IO::AIO::poll_some 256 }); 973 cb => &IO::AIO::poll_cb);
892 974
893=item IO::AIO::poll_wait 975=item IO::AIO::poll_wait
894 976
977If there are any outstanding requests and none of them in the result
895Wait till the result filehandle becomes ready for reading (simply does a 978phase, wait till the result filehandle becomes ready for reading (simply
896C<select> on the filehandle. This is useful if you want to synchronously wait 979does a C<select> on the filehandle. This is useful if you want to
897for some requests to finish). 980synchronously wait for some requests to finish).
898 981
899See C<nreqs> for an example. 982See C<nreqs> for an example.
900 983
984=item IO::AIO::poll
985
986Waits until some requests have been handled.
987
988Returns the number of requests processed, but is otherwise strictly
989equivalent to:
990
991 IO::AIO::poll_wait, IO::AIO::poll_cb
992
901=item IO::AIO::nreqs 993=item IO::AIO::flush
902 994
903Returns the number of requests currently in the ready, execute or pending 995Wait till all outstanding AIO requests have been handled.
904states (i.e. for which their callback has not been invoked yet).
905 996
906Example: wait till there are no outstanding requests anymore: 997Strictly equivalent to:
907 998
908 IO::AIO::poll_wait, IO::AIO::poll_cb 999 IO::AIO::poll_wait, IO::AIO::poll_cb
909 while IO::AIO::nreqs; 1000 while IO::AIO::nreqs;
910 1001
911=item IO::AIO::nready 1002=head3 CONTROLLING THE NUMBER OF THREADS
912
913Returns the number of requests currently in the ready state (not yet
914executed).
915
916=item IO::AIO::npending
917
918Returns the number of requests currently in the pending state (executed,
919but not yet processed by poll_cb).
920
921=item IO::AIO::flush
922
923Wait till all outstanding AIO requests have been handled.
924
925Strictly equivalent to:
926
927 IO::AIO::poll_wait, IO::AIO::poll_cb
928 while IO::AIO::nreqs;
929
930=item IO::AIO::poll
931
932Waits until some requests have been handled.
933
934Strictly equivalent to:
935
936 IO::AIO::poll_wait, IO::AIO::poll_cb
937 if IO::AIO::nreqs;
938 1003
939=item IO::AIO::min_parallel $nthreads 1004=item IO::AIO::min_parallel $nthreads
940 1005
941Set the minimum number of AIO threads to C<$nthreads>. The current 1006Set the minimum number of AIO threads to C<$nthreads>. The current
942default is C<8>, which means eight asynchronous operations can execute 1007default is C<8>, which means eight asynchronous operations can execute
943concurrently at any one time (the number of outstanding requests, 1008concurrently at any one time (the number of outstanding requests,
944however, is unlimited). 1009however, is unlimited).
945 1010
946IO::AIO starts threads only on demand, when an AIO request is queued and 1011IO::AIO starts threads only on demand, when an AIO request is queued and
947no free thread exists. 1012no free thread exists. Please note that queueing up a hundred requests can
1013create demand for a hundred threads, even if it turns out that everything
1014is in the cache and could have been processed faster by a single thread.
948 1015
949It is recommended to keep the number of threads relatively low, as some 1016It is recommended to keep the number of threads relatively low, as some
950Linux kernel versions will scale negatively with the number of threads 1017Linux kernel versions will scale negatively with the number of threads
951(higher parallelity => MUCH higher latency). With current Linux 2.6 1018(higher parallelity => MUCH higher latency). With current Linux 2.6
952versions, 4-32 threads should be fine. 1019versions, 4-32 threads should be fine.
… …
966This module automatically runs C<max_parallel 0> at program end, to ensure 1033This module automatically runs C<max_parallel 0> at program end, to ensure
967that all threads are killed and that there are no outstanding requests. 1034that all threads are killed and that there are no outstanding requests.
968 1035
969Under normal circumstances you don't need to call this function. 1036Under normal circumstances you don't need to call this function.
970 1037
1038=item IO::AIO::max_idle $nthreads
1039
1040Limit the number of threads (default: 4) that are allowed to idle (i.e.,
1041threads that did not get a request to process within 10 seconds). That
1042means if a thread becomes idle while C<$nthreads> other threads are also
1043idle, it will free its resources and exit.
1044
1045This is useful when you allow a large number of threads (e.g. 100 or 1000)
1046to allow for extremely high load situations, but want to free resources
1047under normal circumstances (1000 threads can easily consume 30MB of RAM).
1048
1049The default is probably ok in most situations, especially if thread
1050creation is fast. If thread creation is very slow on your system you might
1051want to use larger values.
1052
971=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs 1053=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
972 1054
973This is a very bad function to use in interactive programs because it 1055This is a very bad function to use in interactive programs because it
974blocks, and a bad way to reduce concurrency because it is inexact: Better 1056blocks, and a bad way to reduce concurrency because it is inexact: Better
975use an C<aio_group> together with a feed callback. 1057use an C<aio_group> together with a feed callback.
… …
983number of outstanding requests. 1065number of outstanding requests.
984 1066
985You can still queue as many requests as you want. Therefore, 1067You can still queue as many requests as you want. Therefore,
986C<max_oustsanding> is mainly useful in simple scripts (with low values) or 1068C<max_oustsanding> is mainly useful in simple scripts (with low values) or
987as a stop gap to shield against fatal memory overflow (with large values). 1069as a stop gap to shield against fatal memory overflow (with large values).
1070
1071=head3 STATISTICAL INFORMATION
1072
1073=item IO::AIO::nreqs
1074
1075Returns the number of requests currently in the ready, execute or pending
1076states (i.e. for which their callback has not been invoked yet).
1077
1078Example: wait till there are no outstanding requests anymore:
1079
1080 IO::AIO::poll_wait, IO::AIO::poll_cb
1081 while IO::AIO::nreqs;
1082
1083=item IO::AIO::nready
1084
1085Returns the number of requests currently in the ready state (not yet
1086executed).
1087
1088=item IO::AIO::npending
1089
1090Returns the number of requests currently in the pending state (executed,
1091but not yet processed by poll_cb).
988 1092
989=back 1093=back
990 1094
991=cut 1095=cut
992 1096

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