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50 50
51=head1 DESCRIPTION 51=head1 DESCRIPTION
52 52
53This module implements asynchronous I/O using whatever means your 53This module implements asynchronous I/O using whatever means your
54operating system supports. 54operating system supports.
55
56Asynchronous means that operations that can normally block your program
57(e.g. reading from disk) will be done asynchronously: the operation
58will still block, but you can do something else in the meantime. This
59is extremely useful for programs that need to stay interactive even
60when doing heavy I/O (GUI programs, high performance network servers
61etc.), 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
63on a RAID volume or over NFS when you do a number of stat operations
64concurrently.
65
66While most of this works on all types of file descriptors (for example
67sockets), using these functions on file descriptors that support
68nonblocking operation (again, sockets, pipes etc.) is very inefficient or
69might not work (aio_read fails on sockets/pipes/fifos). Use an event loop
70for that (such as the L<Event|Event> module): IO::AIO will naturally fit
71into such an event loop itself.
55 72
56In this version, a number of threads are started that execute your 73In this version, a number of threads are started that execute your
57requests and signal their completion. You don't need thread support 74requests and signal their completion. You don't need thread support
58in perl, and the threads created by this module will not be visible 75in 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 76to perl. In the future, this module might make use of the native aio
60functions available on many operating systems. However, they are often 77functions available on many operating systems. However, they are often
61not well-supported or restricted (Linux doesn't allow them on normal 78not well-supported or restricted (GNU/Linux doesn't allow them on normal
62files currently, for example), and they would only support aio_read and 79files currently, for example), and they would only support aio_read and
63aio_write, so the remaining functionality would have to be implemented 80aio_write, so the remaining functionality would have to be implemented
64using threads anyway. 81using threads anyway.
65 82
66Although the module will work with in the presence of other (Perl-) 83Although the module will work with in the presence of other (Perl-)
67threads, it is currently not reentrant in any way, so use appropriate 84threads, it is currently not reentrant in any way, so use appropriate
68locking yourself, always call C<poll_cb> from within the same thread, or 85locking yourself, always call C<poll_cb> from within the same thread, or
69never call C<poll_cb> (or other C<aio_> functions) recursively. 86never call C<poll_cb> (or other C<aio_> functions) recursively.
70 87
88=head2 EXAMPLE
89
90This is a simple example that uses the Event module and loads
91F</etc/passwd> asynchronously:
92
93 use Fcntl;
94 use Event;
95 use IO::AIO;
96
97 # register the IO::AIO callback with Event
98 Event->io (fd => IO::AIO::poll_fileno,
99 poll => 'r',
100 cb => \&IO::AIO::poll_cb);
101
102 # queue the request to open /etc/passwd
103 aio_open "/etc/passwd", O_RDONLY, 0, sub {
104 my $fh = $_[0]
105 or die "error while opening: $!";
106
107 # stat'ing filehandles is generally non-blocking
108 my $size = -s $fh;
109
110 # queue a request to read the file
111 my $contents;
112 aio_read $fh, 0, $size, $contents, 0, sub {
113 $_[0] == $size
114 or die "short read: $!";
115
116 close $fh;
117
118 # file contents now in $contents
119 print $contents;
120
121 # exit event loop and program
122 Event::unloop;
123 };
124 };
125
126 # possibly queue up other requests, or open GUI windows,
127 # check for sockets etc. etc.
128
129 # process events as long as there are some:
130 Event::loop;
131
71=head1 REQUEST ANATOMY AND LIFETIME 132=head1 REQUEST ANATOMY AND LIFETIME
72 133
73Every C<aio_*> function creates a request. which is a C data structure not 134Every C<aio_*> function creates a request. which is a C data structure not
74directly visible to Perl. 135directly visible to Perl.
75 136
… …
116Request has reached the end of its lifetime and holds no resources anymore 177Request 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 178(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 179aio request is severed and calling its methods will either do nothing or
119result in a runtime error). 180result in a runtime error).
120 181
182=back
183
121=cut 184=cut
122 185
123package IO::AIO; 186package IO::AIO;
124 187
125no warnings; 188no warnings;
126use strict 'vars'; 189use strict 'vars';
127 190
128use base 'Exporter'; 191use base 'Exporter';
129 192
130BEGIN { 193BEGIN {
131 our $VERSION = '2.0'; 194 our $VERSION = '2.2';
132 195
133 our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat 196 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 197 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 198 aio_readlink aio_fsync aio_fdatasync aio_readahead aio_rename aio_link
136 aio_copy aio_group aio_nop aio_mknod); 199 aio_move aio_copy aio_group aio_nop aio_mknod);
137 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice)); 200 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
138 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush 201 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
139 min_parallel max_parallel nreqs nready npending); 202 min_parallel max_parallel max_idle
203 nreqs nready npending nthreads
204 max_poll_time max_poll_reqs);
140 205
141 @IO::AIO::GRP::ISA = 'IO::AIO::REQ'; 206 @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
142 207
143 require XSLoader; 208 require XSLoader;
144 XSLoader::load ("IO::AIO", $VERSION); 209 XSLoader::load ("IO::AIO", $VERSION);
145} 210}
146 211
147=head1 FUNCTIONS 212=head1 FUNCTIONS
148 213
149=head2 AIO FUNCTIONS 214=head2 AIO REQUEST FUNCTIONS
150 215
151All the C<aio_*> calls are more or less thin wrappers around the syscall 216All the C<aio_*> calls are more or less thin wrappers around the syscall
152with the same name (sans C<aio_>). The arguments are similar or identical, 217with the same name (sans C<aio_>). The arguments are similar or identical,
153and they all accept an additional (and optional) C<$callback> argument 218and they all accept an additional (and optional) C<$callback> argument
154which must be a code reference. This code reference will get called with 219which must be a code reference. This code reference will get called with
… …
157syscall has been executed asynchronously. 222syscall has been executed asynchronously.
158 223
159All functions expecting a filehandle keep a copy of the filehandle 224All functions expecting a filehandle keep a copy of the filehandle
160internally until the request has finished. 225internally until the request has finished.
161 226
162All requests return objects of type L<IO::AIO::REQ> that allow further 227All functions return request objects of type L<IO::AIO::REQ> that allow
163manipulation of those requests while they are in-flight. 228further manipulation of those requests while they are in-flight.
164 229
165The pathnames you pass to these routines I<must> be absolute and 230The 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 231encoded as octets. The reason for the former is that at the time the
167request is being executed, the current working directory could have 232request is being executed, the current working directory could have
168changed. Alternatively, you can make sure that you never change the 233changed. Alternatively, you can make sure that you never change the
169current working directory. 234current working directory anywhere in the program and then use relative
235paths.
170 236
171To encode pathnames to byte form, either make sure you either: a) 237To encode pathnames as octets, either make sure you either: a) always pass
172always pass in filenames you got from outside (command line, readdir 238in 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 239tinkering, 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 240your pathnames to the locale (or other) encoding in effect in the user
175environment, d) use Glib::filename_from_unicode on unicode filenames or e) 241environment, d) use Glib::filename_from_unicode on unicode filenames or e)
176use something else. 242use something else to ensure your scalar has the correct contents.
243
244This works, btw. independent of the internal UTF-8 bit, which IO::AIO
245handles correctly wether it is set or not.
177 246
178=over 4 247=over 4
179 248
180=item $prev_pri = aioreq_pri [$pri] 249=item $prev_pri = aioreq_pri [$pri]
181 250
… …
204 }; 273 };
205 274
206=item aioreq_nice $pri_adjust 275=item aioreq_nice $pri_adjust
207 276
208Similar to C<aioreq_pri>, but subtracts the given value from the current 277Similar to C<aioreq_pri>, but subtracts the given value from the current
209priority, so effects are cumulative. 278priority, so the effect is cumulative.
210 279
211=item aio_open $pathname, $flags, $mode, $callback->($fh) 280=item aio_open $pathname, $flags, $mode, $callback->($fh)
212 281
213Asynchronously open or create a file and call the callback with a newly 282Asynchronously open or create a file and call the callback with a newly
214created filehandle for the file. 283created filehandle for the file.
… …
331Asynchronously unlink (delete) a file and call the callback with the 400Asynchronously unlink (delete) a file and call the callback with the
332result code. 401result code.
333 402
334=item aio_mknod $path, $mode, $dev, $callback->($status) 403=item aio_mknod $path, $mode, $dev, $callback->($status)
335 404
405[EXPERIMENTAL]
406
336Asynchronously create a device node (or fifo). See mknod(2). 407Asynchronously create a device node (or fifo). See mknod(2).
337 408
338The only portable (POSIX) way of calling this function is: 409The only (POSIX-) portable way of calling this function is:
339 410
340 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ... 411 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
341 412
342=item aio_link $srcpath, $dstpath, $callback->($status) 413=item aio_link $srcpath, $dstpath, $callback->($status)
343 414
… …
346 417
347=item aio_symlink $srcpath, $dstpath, $callback->($status) 418=item aio_symlink $srcpath, $dstpath, $callback->($status)
348 419
349Asynchronously create a new symbolic link to the existing object at C<$srcpath> at 420Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
350the path C<$dstpath> and call the callback with the result code. 421the path C<$dstpath> and call the callback with the result code.
422
423=item aio_readlink $path, $callback->($link)
424
425Asynchronously read the symlink specified by C<$path> and pass it to
426the callback. If an error occurs, nothing or undef gets passed to the
427callback.
351 428
352=item aio_rename $srcpath, $dstpath, $callback->($status) 429=item aio_rename $srcpath, $dstpath, $callback->($status)
353 430
354Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as 431Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
355rename(2) and call the callback with the result code. 432rename(2) and call the callback with the result code.
… …
829 906
830=back 907=back
831 908
832=head2 SUPPORT FUNCTIONS 909=head2 SUPPORT FUNCTIONS
833 910
911=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
912
834=over 4 913=over 4
835 914
836=item $fileno = IO::AIO::poll_fileno 915=item $fileno = IO::AIO::poll_fileno
837 916
838Return the I<request result pipe file descriptor>. This filehandle must be 917Return the I<request result pipe file descriptor>. This filehandle must be
… …
842 921
843See C<poll_cb> for an example. 922See C<poll_cb> for an example.
844 923
845=item IO::AIO::poll_cb 924=item IO::AIO::poll_cb
846 925
847Process all outstanding events on the result pipe. You have to call this 926Process some outstanding events on the result pipe. You have to call this
848regularly. Returns the number of events processed. Returns immediately 927regularly. Returns the number of events processed. Returns immediately
849when no events are outstanding. 928when no events are outstanding. The amount of events processed depends on
929the settings of C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
850 930
851If not all requests were processed for whatever reason, the filehandle 931If not all requests were processed for whatever reason, the filehandle
852will still be ready when C<poll_cb> returns. 932will still be ready when C<poll_cb> returns.
853 933
854Example: Install an Event watcher that automatically calls 934Example: Install an Event watcher that automatically calls
… …
856 936
857 Event->io (fd => IO::AIO::poll_fileno, 937 Event->io (fd => IO::AIO::poll_fileno,
858 poll => 'r', async => 1, 938 poll => 'r', async => 1,
859 cb => \&IO::AIO::poll_cb); 939 cb => \&IO::AIO::poll_cb);
860 940
861=item IO::AIO::poll_some $max_requests 941=item IO::AIO::max_poll_reqs $nreqs
862 942
863Similar to C<poll_cb>, but only processes up to C<$max_requests> requests 943=item IO::AIO::max_poll_time $seconds
864at a time.
865 944
866Useful if you want to ensure some level of interactiveness when perl is 945These set the maximum number of requests (default C<0>, meaning infinity)
867not fast enough to process all requests in time. 946that are being processed by C<IO::AIO::poll_cb> in one call, respectively
947the maximum amount of time (default C<0>, meaning infinity) spent in
948C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
949of time C<poll_cb> is allowed to use).
950
951Setting C<max_poll_time> to a non-zero value creates an overhead of one
952syscall per request processed, which is not normally a problem unless your
953callbacks are really really fast or your OS is really really slow (I am
954not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
955
956Setting these is useful if you want to ensure some level of
957interactiveness when perl is not fast enough to process all requests in
958time.
959
960For interactive programs, values such as C<0.01> to C<0.1> should be fine.
868 961
869Example: Install an Event watcher that automatically calls 962Example: Install an Event watcher that automatically calls
870IO::AIO::poll_some with low priority, to ensure that other parts of the 963IO::AIO::poll_cb with low priority, to ensure that other parts of the
871program get the CPU sometimes even under high AIO load. 964program get the CPU sometimes even under high AIO load.
872 965
966 # try not to spend much more than 0.1s in poll_cb
967 IO::AIO::max_poll_time 0.1;
968
969 # use a low priority so other tasks have priority
873 Event->io (fd => IO::AIO::poll_fileno, 970 Event->io (fd => IO::AIO::poll_fileno,
874 poll => 'r', nice => 1, 971 poll => 'r', nice => 1,
875 cb => sub { IO::AIO::poll_some 256 }); 972 cb => &IO::AIO::poll_cb);
876 973
877=item IO::AIO::poll_wait 974=item IO::AIO::poll_wait
878 975
976If there are any outstanding requests and none of them in the result
879Wait till the result filehandle becomes ready for reading (simply does a 977phase, wait till the result filehandle becomes ready for reading (simply
880C<select> on the filehandle. This is useful if you want to synchronously wait 978does a C<select> on the filehandle. This is useful if you want to
881for some requests to finish). 979synchronously wait for some requests to finish).
882 980
883See C<nreqs> for an example. 981See C<nreqs> for an example.
884 982
983=item IO::AIO::poll
984
985Waits until some requests have been handled.
986
987Returns the number of requests processed, but is otherwise strictly
988equivalent to:
989
990 IO::AIO::poll_wait, IO::AIO::poll_cb
991
885=item IO::AIO::nreqs 992=item IO::AIO::flush
886 993
887Returns the number of requests currently in the ready, execute or pending 994Wait till all outstanding AIO requests have been handled.
888states (i.e. for which their callback has not been invoked yet).
889 995
890Example: wait till there are no outstanding requests anymore: 996Strictly equivalent to:
891 997
892 IO::AIO::poll_wait, IO::AIO::poll_cb 998 IO::AIO::poll_wait, IO::AIO::poll_cb
893 while IO::AIO::nreqs; 999 while IO::AIO::nreqs;
894 1000
895=item IO::AIO::nready 1001=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 1002
923=item IO::AIO::min_parallel $nthreads 1003=item IO::AIO::min_parallel $nthreads
924 1004
925Set the minimum number of AIO threads to C<$nthreads>. The current 1005Set the minimum number of AIO threads to C<$nthreads>. The current
926default is C<8>, which means eight asynchronous operations can execute 1006default is C<8>, which means eight asynchronous operations can execute
927concurrently at any one time (the number of outstanding requests, 1007concurrently at any one time (the number of outstanding requests,
928however, is unlimited). 1008however, is unlimited).
929 1009
930IO::AIO starts threads only on demand, when an AIO request is queued and 1010IO::AIO starts threads only on demand, when an AIO request is queued and
931no free thread exists. 1011no free thread exists. Please note that queueing up a hundred requests can
1012create demand for a hundred threads, even if it turns out that everything
1013is in the cache and could have been processed faster by a single thread.
932 1014
933It is recommended to keep the number of threads relatively low, as some 1015It is recommended to keep the number of threads relatively low, as some
934Linux kernel versions will scale negatively with the number of threads 1016Linux kernel versions will scale negatively with the number of threads
935(higher parallelity => MUCH higher latency). With current Linux 2.6 1017(higher parallelity => MUCH higher latency). With current Linux 2.6
936versions, 4-32 threads should be fine. 1018versions, 4-32 threads should be fine.
… …
950This module automatically runs C<max_parallel 0> at program end, to ensure 1032This module automatically runs C<max_parallel 0> at program end, to ensure
951that all threads are killed and that there are no outstanding requests. 1033that all threads are killed and that there are no outstanding requests.
952 1034
953Under normal circumstances you don't need to call this function. 1035Under normal circumstances you don't need to call this function.
954 1036
1037=item IO::AIO::max_idle $nthreads
1038
1039Limit the number of threads (default: 4) that are allowed to idle (i.e.,
1040threads that did not get a request to process within 10 seconds). That
1041means if a thread becomes idle while C<$nthreads> other threads are also
1042idle, it will free its resources and exit.
1043
1044This is useful when you allow a large number of threads (e.g. 100 or 1000)
1045to allow for extremely high load situations, but want to free resources
1046under normal circumstances (1000 threads can easily consume 30MB of RAM).
1047
1048The default is probably ok in most situations, especially if thread
1049creation is fast. If thread creation is very slow on your system you might
1050want to use larger values.
1051
955=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs 1052=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
956 1053
957This is a very bad function to use in interactive programs because it 1054This 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 1055blocks, and a bad way to reduce concurrency because it is inexact: Better
959use an C<aio_group> together with a feed callback. 1056use an C<aio_group> together with a feed callback.
… …
967number of outstanding requests. 1064number of outstanding requests.
968 1065
969You can still queue as many requests as you want. Therefore, 1066You can still queue as many requests as you want. Therefore,
970C<max_oustsanding> is mainly useful in simple scripts (with low values) or 1067C<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). 1068as a stop gap to shield against fatal memory overflow (with large values).
1069
1070=head3 STATISTICAL INFORMATION
1071
1072=item IO::AIO::nreqs
1073
1074Returns the number of requests currently in the ready, execute or pending
1075states (i.e. for which their callback has not been invoked yet).
1076
1077Example: wait till there are no outstanding requests anymore:
1078
1079 IO::AIO::poll_wait, IO::AIO::poll_cb
1080 while IO::AIO::nreqs;
1081
1082=item IO::AIO::nready
1083
1084Returns the number of requests currently in the ready state (not yet
1085executed).
1086
1087=item IO::AIO::npending
1088
1089Returns the number of requests currently in the pending state (executed,
1090but not yet processed by poll_cb).
972 1091
973=back 1092=back
974 1093
975=cut 1094=cut
976 1095

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