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

… …
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
… …
50 51
51=head1 DESCRIPTION 52=head1 DESCRIPTION
52 53
53This module implements asynchronous I/O using whatever means your 54This module implements asynchronous I/O using whatever means your
54operating system supports. 55operating system supports.
56
57Asynchronous means that operations that can normally block your program
58(e.g. reading from disk) will be done asynchronously: the operation
59will still block, but you can do something else in the meantime. This
60is extremely useful for programs that need to stay interactive even
61when doing heavy I/O (GUI programs, high performance network servers
62etc.), but can also be used to easily do operations in parallel that are
63normally done sequentially, e.g. stat'ing many files, which is much faster
64on a RAID volume or over NFS when you do a number of stat operations
65concurrently.
66
67While most of this works on all types of file descriptors (for example
68sockets), using these functions on file descriptors that support
69nonblocking operation (again, sockets, pipes etc.) is very inefficient or
70might not work (aio_read fails on sockets/pipes/fifos). Use an event loop
71for that (such as the L<Event|Event> module): IO::AIO will naturally fit
72into such an event loop itself.
55 73
56In this version, a number of threads are started that execute your 74In this version, a number of threads are started that execute your
57requests and signal their completion. You don't need thread support 75requests and signal their completion. You don't need thread support
58in 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
59to 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
60functions available on many operating systems. However, they are often 78functions available on many operating systems. However, they are often
61not well-supported or restricted (Linux doesn't allow them on normal 79not well-supported or restricted (GNU/Linux doesn't allow them on normal
62files currently, for example), and they would only support aio_read and 80files currently, for example), and they would only support aio_read and
63aio_write, so the remaining functionality would have to be implemented 81aio_write, so the remaining functionality would have to be implemented
64using threads anyway. 82using threads anyway.
65 83
66Although the module will work with in the presence of other (Perl-) 84Although the module will work with in the presence of other (Perl-)
67threads, it is currently not reentrant in any way, so use appropriate 85threads, it is currently not reentrant in any way, so use appropriate
68locking 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
69never call C<poll_cb> (or other C<aio_> functions) recursively. 87never call C<poll_cb> (or other C<aio_> functions) recursively.
70 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
71=head1 REQUEST ANATOMY AND LIFETIME 133=head1 REQUEST ANATOMY AND LIFETIME
72 134
73Every 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
74directly visible to Perl. 136directly visible to Perl.
75 137
… …
116Request 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
117(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
118aio 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
119result in a runtime error). 181result in a runtime error).
120 182
183=back
184
121=cut 185=cut
122 186
123package IO::AIO; 187package IO::AIO;
124 188
125no warnings; 189no warnings;
126use strict 'vars'; 190use strict 'vars';
127 191
128use base 'Exporter'; 192use base 'Exporter';
129 193
130BEGIN { 194BEGIN {
131 our $VERSION = '2.0'; 195 our $VERSION = '2.2';
132 196
133 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
134 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
135 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
136 aio_copy aio_group aio_nop aio_mknod); 200 aio_move aio_copy aio_group aio_nop aio_mknod);
137 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice)); 201 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
138 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush 202 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
139 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);
140 206
141 @IO::AIO::GRP::ISA = 'IO::AIO::REQ'; 207 @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
142 208
143 require XSLoader; 209 require XSLoader;
144 XSLoader::load ("IO::AIO", $VERSION); 210 XSLoader::load ("IO::AIO", $VERSION);
145} 211}
146 212
147=head1 FUNCTIONS 213=head1 FUNCTIONS
148 214
149=head2 AIO FUNCTIONS 215=head2 AIO REQUEST FUNCTIONS
150 216
151All the C<aio_*> calls are more or less thin wrappers around the syscall 217All the C<aio_*> calls are more or less thin wrappers around the syscall
152with the same name (sans C<aio_>). The arguments are similar or identical, 218with the same name (sans C<aio_>). The arguments are similar or identical,
153and they all accept an additional (and optional) C<$callback> argument 219and they all accept an additional (and optional) C<$callback> argument
154which 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
… …
157syscall has been executed asynchronously. 223syscall has been executed asynchronously.
158 224
159All functions expecting a filehandle keep a copy of the filehandle 225All functions expecting a filehandle keep a copy of the filehandle
160internally until the request has finished. 226internally until the request has finished.
161 227
162All 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
163manipulation of those requests while they are in-flight. 229further manipulation of those requests while they are in-flight.
164 230
165The pathnames you pass to these routines I<must> be absolute and 231The pathnames you pass to these routines I<must> be absolute and
166encoded 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
167request is being executed, the current working directory could have 233request is being executed, the current working directory could have
168changed. Alternatively, you can make sure that you never change the 234changed. Alternatively, you can make sure that you never change the
169current working directory. 235current working directory anywhere in the program and then use relative
236paths.
170 237
171To encode pathnames to byte form, either make sure you either: a) 238To encode pathnames as octets, either make sure you either: a) always pass
172always pass in filenames you got from outside (command line, readdir 239in filenames you got from outside (command line, readdir etc.) without
173etc.), 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
174your 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
175environment, d) use Glib::filename_from_unicode on unicode filenames or e) 242environment, d) use Glib::filename_from_unicode on unicode filenames or e)
176use 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.
177 247
178=over 4 248=over 4
179 249
180=item $prev_pri = aioreq_pri [$pri] 250=item $prev_pri = aioreq_pri [$pri]
181 251
… …
204 }; 274 };
205 275
206=item aioreq_nice $pri_adjust 276=item aioreq_nice $pri_adjust
207 277
208Similar 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
209priority, so effects are cumulative. 279priority, so the effect is cumulative.
210 280
211=item aio_open $pathname, $flags, $mode, $callback->($fh) 281=item aio_open $pathname, $flags, $mode, $callback->($fh)
212 282
213Asynchronously 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
214created filehandle for the file. 284created filehandle for the file.
… …
331Asynchronously unlink (delete) a file and call the callback with the 401Asynchronously unlink (delete) a file and call the callback with the
332result code. 402result code.
333 403
334=item aio_mknod $path, $mode, $dev, $callback->($status) 404=item aio_mknod $path, $mode, $dev, $callback->($status)
335 405
406[EXPERIMENTAL]
407
336Asynchronously create a device node (or fifo). See mknod(2). 408Asynchronously create a device node (or fifo). See mknod(2).
337 409
338The only portable (POSIX) way of calling this function is: 410The only (POSIX-) portable way of calling this function is:
339 411
340 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ... 412 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
341 413
342=item aio_link $srcpath, $dstpath, $callback->($status) 414=item aio_link $srcpath, $dstpath, $callback->($status)
343 415
… …
346 418
347=item aio_symlink $srcpath, $dstpath, $callback->($status) 419=item aio_symlink $srcpath, $dstpath, $callback->($status)
348 420
349Asynchronously 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
350the 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.
351 429
352=item aio_rename $srcpath, $dstpath, $callback->($status) 430=item aio_rename $srcpath, $dstpath, $callback->($status)
353 431
354Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as 432Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
355rename(2) and call the callback with the result code. 433rename(2) and call the callback with the result code.
… …
829 907
830=back 908=back
831 909
832=head2 SUPPORT FUNCTIONS 910=head2 SUPPORT FUNCTIONS
833 911
912=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
913
834=over 4 914=over 4
835 915
836=item $fileno = IO::AIO::poll_fileno 916=item $fileno = IO::AIO::poll_fileno
837 917
838Return the I<request result pipe file descriptor>. This filehandle must be 918Return the I<request result pipe file descriptor>. This filehandle must be
… …
842 922
843See C<poll_cb> for an example. 923See C<poll_cb> for an example.
844 924
845=item IO::AIO::poll_cb 925=item IO::AIO::poll_cb
846 926
847Process 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
848regularly. Returns the number of events processed. Returns immediately 928regularly. Returns the number of events processed. Returns immediately
849when 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>.
850 931
851If not all requests were processed for whatever reason, the filehandle 932If not all requests were processed for whatever reason, the filehandle
852will still be ready when C<poll_cb> returns. 933will still be ready when C<poll_cb> returns.
853 934
854Example: Install an Event watcher that automatically calls 935Example: Install an Event watcher that automatically calls
… …
856 937
857 Event->io (fd => IO::AIO::poll_fileno, 938 Event->io (fd => IO::AIO::poll_fileno,
858 poll => 'r', async => 1, 939 poll => 'r', async => 1,
859 cb => \&IO::AIO::poll_cb); 940 cb => \&IO::AIO::poll_cb);
860 941
861=item IO::AIO::poll_some $max_requests 942=item IO::AIO::max_poll_reqs $nreqs
862 943
863Similar to C<poll_cb>, but only processes up to C<$max_requests> requests 944=item IO::AIO::max_poll_time $seconds
864at a time.
865 945
866Useful if you want to ensure some level of interactiveness when perl is 946These set the maximum number of requests (default C<0>, meaning infinity)
867not 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.
868 962
869Example: Install an Event watcher that automatically calls 963Example: Install an Event watcher that automatically calls
870IO::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
871program get the CPU sometimes even under high AIO load. 965program get the CPU sometimes even under high AIO load.
872 966
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
873 Event->io (fd => IO::AIO::poll_fileno, 971 Event->io (fd => IO::AIO::poll_fileno,
874 poll => 'r', nice => 1, 972 poll => 'r', nice => 1,
875 cb => sub { IO::AIO::poll_some 256 }); 973 cb => &IO::AIO::poll_cb);
876 974
877=item IO::AIO::poll_wait 975=item IO::AIO::poll_wait
878 976
977If there are any outstanding requests and none of them in the result
879Wait till the result filehandle becomes ready for reading (simply does a 978phase, wait till the result filehandle becomes ready for reading (simply
880C<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
881for some requests to finish). 980synchronously wait for some requests to finish).
882 981
883See C<nreqs> for an example. 982See C<nreqs> for an example.
884 983
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
885=item IO::AIO::nreqs 993=item IO::AIO::flush
886 994
887Returns the number of requests currently in the ready, execute or pending 995Wait till all outstanding AIO requests have been handled.
888states (i.e. for which their callback has not been invoked yet).
889 996
890Example: wait till there are no outstanding requests anymore: 997Strictly equivalent to:
891 998
892 IO::AIO::poll_wait, IO::AIO::poll_cb 999 IO::AIO::poll_wait, IO::AIO::poll_cb
893 while IO::AIO::nreqs; 1000 while IO::AIO::nreqs;
894 1001
895=item IO::AIO::nready 1002=head3 CONTROLLING THE NUMBER OF THREADS
896
897Returns the number of requests currently in the ready state (not yet
898executed).
899
900=item IO::AIO::npending
901
902Returns the number of requests currently in the pending state (executed,
903but not yet processed by poll_cb).
904
905=item IO::AIO::flush
906
907Wait till all outstanding AIO requests have been handled.
908
909Strictly equivalent to:
910
911 IO::AIO::poll_wait, IO::AIO::poll_cb
912 while IO::AIO::nreqs;
913
914=item IO::AIO::poll
915
916Waits until some requests have been handled.
917
918Strictly equivalent to:
919
920 IO::AIO::poll_wait, IO::AIO::poll_cb
921 if IO::AIO::nreqs;
922 1003
923=item IO::AIO::min_parallel $nthreads 1004=item IO::AIO::min_parallel $nthreads
924 1005
925Set the minimum number of AIO threads to C<$nthreads>. The current 1006Set the minimum number of AIO threads to C<$nthreads>. The current
926default is C<8>, which means eight asynchronous operations can execute 1007default is C<8>, which means eight asynchronous operations can execute
927concurrently at any one time (the number of outstanding requests, 1008concurrently at any one time (the number of outstanding requests,
928however, is unlimited). 1009however, is unlimited).
929 1010
930IO::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
931no 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.
932 1015
933It 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
934Linux kernel versions will scale negatively with the number of threads 1017Linux kernel versions will scale negatively with the number of threads
935(higher parallelity => MUCH higher latency). With current Linux 2.6 1018(higher parallelity => MUCH higher latency). With current Linux 2.6
936versions, 4-32 threads should be fine. 1019versions, 4-32 threads should be fine.
… …
950This 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
951that all threads are killed and that there are no outstanding requests. 1034that all threads are killed and that there are no outstanding requests.
952 1035
953Under normal circumstances you don't need to call this function. 1036Under normal circumstances you don't need to call this function.
954 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
955=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs 1053=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
956 1054
957This 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
958blocks, 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
959use an C<aio_group> together with a feed callback. 1057use an C<aio_group> together with a feed callback.
… …
968 1066
969You can still queue as many requests as you want. Therefore, 1067You can still queue as many requests as you want. Therefore,
970C<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
971as 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).
972 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).
1092
973=back 1093=back
974 1094
975=cut 1095=cut
976 1096
977# support function to convert a fd into a perl filehandle 1097# support function to convert a fd into a perl filehandle
… …
991} 1111}
992 1112
993min_parallel 8; 1113min_parallel 8;
994 1114
995END { 1115END {
1116 min_parallel 1;
996 flush; 1117 flush;
997}; 1118};
998 1119
9991; 11201;
1000 1121

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