ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/cvsroot/Coro/Coro.pm
(Generate patch)

Comparing cvsroot/Coro/Coro.pm (file contents):
Revision 1.92 by root, Fri Dec 1 03:47:55 2006 UTC vs.
Revision 1.178 by root, Thu Apr 17 22:33:10 2008 UTC

6 6
7 use Coro; 7 use Coro;
8 8
9 async { 9 async {
10 # some asynchronous thread of execution 10 # some asynchronous thread of execution
11 print "2\n";
12 cede; # yield back to main
13 print "4\n";
11 }; 14 };
15 print "1\n";
16 cede; # yield to coroutine
17 print "3\n";
18 cede; # and again
12 19
13 # alternatively create an async coroutine like this: 20 # use locking
21 my $lock = new Coro::Semaphore;
22 my $locked;
14 23
15 sub some_func : Coro { 24 $lock->down;
16 # some more async code 25 $locked = 1;
17 } 26 $lock->up;
18
19 cede;
20 27
21=head1 DESCRIPTION 28=head1 DESCRIPTION
22 29
23This module collection manages coroutines. Coroutines are similar to 30This module collection manages coroutines. Coroutines are similar
24threads but don't run in parallel. 31to threads but don't run in parallel at the same time even on SMP
32machines. The specific flavor of coroutine used in this module also
33guarantees you that it will not switch between coroutines unless
34necessary, at easily-identified points in your program, so locking and
35parallel access are rarely an issue, making coroutine programming much
36safer than threads programming.
25 37
38(Perl, however, does not natively support real threads but instead does a
39very slow and memory-intensive emulation of processes using threads. This
40is a performance win on Windows machines, and a loss everywhere else).
41
26In this module, coroutines are defined as "callchain + lexical variables 42In this module, coroutines are defined as "callchain + lexical variables +
27+ @_ + $_ + $@ + $^W + C stack), that is, a coroutine has it's own 43@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
28callchain, it's own set of lexicals and it's own set of perl's most 44its own set of lexicals and its own set of perls most important global
29important global variables. 45variables (see L<Coro::State> for more configuration).
30 46
31=cut 47=cut
32 48
33package Coro; 49package Coro;
34 50
41 57
42our $idle; # idle handler 58our $idle; # idle handler
43our $main; # main coroutine 59our $main; # main coroutine
44our $current; # current coroutine 60our $current; # current coroutine
45 61
46our $VERSION = '3.0'; 62our $VERSION = '4.51';
47 63
48our @EXPORT = qw(async cede schedule terminate current unblock_sub); 64our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
49our %EXPORT_TAGS = ( 65our %EXPORT_TAGS = (
50 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)], 66 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
51); 67);
52our @EXPORT_OK = @{$EXPORT_TAGS{prio}}; 68our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
53 69
54{ 70{
55 my @async; 71 my @async;
56 my $init; 72 my $init;
57 73
58 # this way of handling attributes simply is NOT scalable ;() 74 # this way of handling attributes simply is NOT scalable ;()
59 sub import { 75 sub import {
60 no strict 'refs'; 76 no strict 'refs';
61 77
62 Coro->export_to_level(1, @_); 78 Coro->export_to_level (1, @_);
63 79
64 my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE}; 80 my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
65 *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub { 81 *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
66 my ($package, $ref) = (shift, shift); 82 my ($package, $ref) = (shift, shift);
67 my @attrs; 83 my @attrs;
99 115
100The current coroutine (the last coroutine switched to). The initial value 116The current coroutine (the last coroutine switched to). The initial value
101is C<$main> (of course). 117is C<$main> (of course).
102 118
103This variable is B<strictly> I<read-only>. It is provided for performance 119This variable is B<strictly> I<read-only>. It is provided for performance
104reasons. If performance is not essentiel you are encouraged to use the 120reasons. If performance is not essential you are encouraged to use the
105C<Coro::current> function instead. 121C<Coro::current> function instead.
106 122
107=cut 123=cut
108 124
125$main->{desc} = "[main::]";
126
109# maybe some other module used Coro::Specific before... 127# maybe some other module used Coro::Specific before...
110if ($current) {
111 $main->{specific} = $current->{specific}; 128$main->{_specific} = $current->{_specific}
112} 129 if $current;
113 130
114$current = $main; 131_set_current $main;
115 132
116sub current() { $current } 133sub current() { $current }
117 134
118=item $idle 135=item $idle
119 136
124This hook is overwritten by modules such as C<Coro::Timer> and 141This hook is overwritten by modules such as C<Coro::Timer> and
125C<Coro::Event> to wait on an external event that hopefully wake up a 142C<Coro::Event> to wait on an external event that hopefully wake up a
126coroutine so the scheduler can run it. 143coroutine so the scheduler can run it.
127 144
128Please note that if your callback recursively invokes perl (e.g. for event 145Please note that if your callback recursively invokes perl (e.g. for event
129handlers), then it must be prepared to be called recursively. 146handlers), then it must be prepared to be called recursively itself.
130 147
131=cut 148=cut
132 149
133$idle = sub { 150$idle = sub {
134 print STDERR "FATAL: deadlock detected\n"; 151 require Carp;
135 exit (51); 152 Carp::croak ("FATAL: deadlock detected");
136}; 153};
154
155sub _cancel {
156 my ($self) = @_;
157
158 # free coroutine data and mark as destructed
159 $self->_destroy
160 or return;
161
162 # call all destruction callbacks
163 $_->(@{$self->{_status}})
164 for @{(delete $self->{_on_destroy}) || []};
165}
137 166
138# this coroutine is necessary because a coroutine 167# this coroutine is necessary because a coroutine
139# cannot destroy itself. 168# cannot destroy itself.
140my @destroy; 169my @destroy;
170my $manager;
171
141my $manager; $manager = new Coro sub { 172$manager = new Coro sub {
142 while () { 173 while () {
143 # by overwriting the state object with the manager we destroy it 174 (shift @destroy)->_cancel
144 # while still being able to schedule this coroutine (in case it has
145 # been readied multiple times. this is harmless since the manager
146 # can be called as many times as neccessary and will always
147 # remove itself from the runqueue
148 while (@destroy) { 175 while @destroy;
149 my $coro = pop @destroy;
150 $coro->{status} ||= [];
151 $_->ready for @{delete $coro->{join} || []};
152 176
153 # the next line destroys the coro state, but keeps the
154 # coroutine itself intact (we basically make it a zombie
155 # coroutine that always runs the manager thread, so it's possible
156 # to transfer() to this coroutine).
157 $coro->_clone_state_from ($manager);
158 }
159 &schedule; 177 &schedule;
160 } 178 }
161}; 179};
162 180$manager->desc ("[coro manager]");
163# static methods. not really. 181$manager->prio (PRIO_MAX);
164 182
165=back 183=back
166 184
167=head2 STATIC METHODS 185=head2 STATIC METHODS
168 186
174 192
175Create a new asynchronous coroutine and return it's coroutine object 193Create a new asynchronous coroutine and return it's coroutine object
176(usually unused). When the sub returns the new coroutine is automatically 194(usually unused). When the sub returns the new coroutine is automatically
177terminated. 195terminated.
178 196
179Calling C<exit> in a coroutine will not work correctly, so do not do that. 197See the C<Coro::State::new> constructor for info about the coroutine
198environment in which coroutines run.
180 199
181When the coroutine dies, the program will exit, just as in the main 200Calling C<exit> in a coroutine will do the same as calling exit outside
182program. 201the coroutine. Likewise, when the coroutine dies, the program will exit,
202just as it would in the main program.
183 203
184 # create a new coroutine that just prints its arguments 204 # create a new coroutine that just prints its arguments
185 async { 205 async {
186 print "@_\n"; 206 print "@_\n";
187 } 1,2,3,4; 207 } 1,2,3,4;
188 208
189=cut 209=cut
190 210
191sub async(&@) { 211sub async(&@) {
192 my $pid = new Coro @_; 212 my $coro = new Coro @_;
193 $pid->ready; 213 $coro->ready;
194 $pid 214 $coro
215}
216
217=item async_pool { ... } [@args...]
218
219Similar to C<async>, but uses a coroutine pool, so you should not call
220terminate or join (although you are allowed to), and you get a coroutine
221that might have executed other code already (which can be good or bad :).
222
223Also, the block is executed in an C<eval> context and a warning will be
224issued in case of an exception instead of terminating the program, as
225C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
226will not work in the expected way, unless you call terminate or cancel,
227which somehow defeats the purpose of pooling.
228
229The priority will be reset to C<0> after each job, tracing will be
230disabled, the description will be reset and the default output filehandle
231gets restored, so you can change alkl these. Otherwise the coroutine will
232be re-used "as-is": most notably if you change other per-coroutine global
233stuff such as C<$/> you need to revert that change, which is most simply
234done by using local as in C< local $/ >.
235
236The pool size is limited to 8 idle coroutines (this can be adjusted by
237changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
238required.
239
240If you are concerned about pooled coroutines growing a lot because a
241single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
242{ terminate }> once per second or so to slowly replenish the pool. In
243addition to that, when the stacks used by a handler grows larger than 16kb
244(adjustable with $Coro::POOL_RSS) it will also exit.
245
246=cut
247
248our $POOL_SIZE = 8;
249our $POOL_RSS = 16 * 1024;
250our @async_pool;
251
252sub pool_handler {
253 my $cb;
254
255 while () {
256 eval {
257 while () {
258 _pool_1 $cb;
259 &$cb;
260 _pool_2 $cb;
261 &schedule;
262 }
263 };
264
265 last if $@ eq "\3async_pool terminate\2\n";
266 warn $@ if $@;
267 }
268}
269
270sub async_pool(&@) {
271 # this is also inlined into the unlock_scheduler
272 my $coro = (pop @async_pool) || new Coro \&pool_handler;
273
274 $coro->{_invoke} = [@_];
275 $coro->ready;
276
277 $coro
195} 278}
196 279
197=item schedule 280=item schedule
198 281
199Calls the scheduler. Please note that the current coroutine will not be put 282Calls the scheduler. Please note that the current coroutine will not be put
212 # wake up sleeping coroutine 295 # wake up sleeping coroutine
213 $current->ready; 296 $current->ready;
214 undef $current; 297 undef $current;
215 }; 298 };
216 299
217 # call schedule until event occured. 300 # call schedule until event occurred.
218 # in case we are woken up for other reasons 301 # in case we are woken up for other reasons
219 # (current still defined), loop. 302 # (current still defined), loop.
220 Coro::schedule while $current; 303 Coro::schedule while $current;
221 } 304 }
222 305
224 307
225"Cede" to other coroutines. This function puts the current coroutine into the 308"Cede" to other coroutines. This function puts the current coroutine into the
226ready queue and calls C<schedule>, which has the effect of giving up the 309ready queue and calls C<schedule>, which has the effect of giving up the
227current "timeslice" to other coroutines of the same or higher priority. 310current "timeslice" to other coroutines of the same or higher priority.
228 311
312=item Coro::cede_notself
313
314Works like cede, but is not exported by default and will cede to any
315coroutine, regardless of priority, once.
316
229=item terminate [arg...] 317=item terminate [arg...]
230 318
231Terminates the current coroutine with the given status values (see L<cancel>). 319Terminates the current coroutine with the given status values (see L<cancel>).
320
321=item killall
322
323Kills/terminates/cancels all coroutines except the currently running
324one. This is useful after a fork, either in the child or the parent, as
325usually only one of them should inherit the running coroutines.
232 326
233=cut 327=cut
234 328
235sub terminate { 329sub terminate {
236 $current->cancel (@_); 330 $current->cancel (@_);
237} 331}
238 332
333sub killall {
334 for (Coro::State::list) {
335 $_->cancel
336 if $_ != $current && UNIVERSAL::isa $_, "Coro";
337 }
338}
339
239=back 340=back
240
241# dynamic methods
242 341
243=head2 COROUTINE METHODS 342=head2 COROUTINE METHODS
244 343
245These are the methods you can call on coroutine objects. 344These are the methods you can call on coroutine objects.
246 345
251Create a new coroutine and return it. When the sub returns the coroutine 350Create a new coroutine and return it. When the sub returns the coroutine
252automatically terminates as if C<terminate> with the returned values were 351automatically terminates as if C<terminate> with the returned values were
253called. To make the coroutine run you must first put it into the ready queue 352called. To make the coroutine run you must first put it into the ready queue
254by calling the ready method. 353by calling the ready method.
255 354
256Calling C<exit> in a coroutine will not work correctly, so do not do that. 355See C<async> and C<Coro::State::new> for additional info about the
356coroutine environment.
257 357
258=cut 358=cut
259 359
260sub _new_coro { 360sub _run_coro {
261 terminate &{+shift}; 361 terminate &{+shift};
262} 362}
263 363
264sub new { 364sub new {
265 my $class = shift; 365 my $class = shift;
266 366
267 $class->SUPER::new (\&_new_coro, @_) 367 $class->SUPER::new (\&_run_coro, @_)
268} 368}
269 369
270=item $success = $coroutine->ready 370=item $success = $coroutine->ready
271 371
272Put the given coroutine into the ready queue (according to it's priority) 372Put the given coroutine into the ready queue (according to it's priority)
278Return wether the coroutine is currently the ready queue or not, 378Return wether the coroutine is currently the ready queue or not,
279 379
280=item $coroutine->cancel (arg...) 380=item $coroutine->cancel (arg...)
281 381
282Terminates the given coroutine and makes it return the given arguments as 382Terminates the given coroutine and makes it return the given arguments as
283status (default: the empty list). 383status (default: the empty list). Never returns if the coroutine is the
384current coroutine.
284 385
285=cut 386=cut
286 387
287sub cancel { 388sub cancel {
288 my $self = shift; 389 my $self = shift;
289 $self->{status} = [@_]; 390 $self->{_status} = [@_];
391
392 if ($current == $self) {
290 push @destroy, $self; 393 push @destroy, $self;
291 $manager->ready; 394 $manager->ready;
292 &schedule if $current == $self; 395 &schedule while 1;
396 } else {
397 $self->_cancel;
398 }
293} 399}
294 400
295=item $coroutine->join 401=item $coroutine->join
296 402
297Wait until the coroutine terminates and return any values given to the 403Wait until the coroutine terminates and return any values given to the
298C<terminate> or C<cancel> functions. C<join> can be called multiple times 404C<terminate> or C<cancel> functions. C<join> can be called concurrently
299from multiple coroutine. 405from multiple coroutines.
300 406
301=cut 407=cut
302 408
303sub join { 409sub join {
304 my $self = shift; 410 my $self = shift;
411
305 unless ($self->{status}) { 412 unless ($self->{_status}) {
306 push @{$self->{join}}, $current; 413 my $current = $current;
307 &schedule; 414
415 push @{$self->{_on_destroy}}, sub {
416 $current->ready;
417 undef $current;
418 };
419
420 &schedule while $current;
308 } 421 }
422
309 wantarray ? @{$self->{status}} : $self->{status}[0]; 423 wantarray ? @{$self->{_status}} : $self->{_status}[0];
424}
425
426=item $coroutine->on_destroy (\&cb)
427
428Registers a callback that is called when this coroutine gets destroyed,
429but before it is joined. The callback gets passed the terminate arguments,
430if any.
431
432=cut
433
434sub on_destroy {
435 my ($self, $cb) = @_;
436
437 push @{ $self->{_on_destroy} }, $cb;
310} 438}
311 439
312=item $oldprio = $coroutine->prio ($newprio) 440=item $oldprio = $coroutine->prio ($newprio)
313 441
314Sets (or gets, if the argument is missing) the priority of the 442Sets (or gets, if the argument is missing) the priority of the
339=item $olddesc = $coroutine->desc ($newdesc) 467=item $olddesc = $coroutine->desc ($newdesc)
340 468
341Sets (or gets in case the argument is missing) the description for this 469Sets (or gets in case the argument is missing) the description for this
342coroutine. This is just a free-form string you can associate with a coroutine. 470coroutine. This is just a free-form string you can associate with a coroutine.
343 471
472This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
473can modify this member directly if you wish.
474
475=item $coroutine->throw ([$scalar])
476
477If C<$throw> is specified and defined, it will be thrown as an exception
478inside the coroutine at the next convinient point in time (usually after
479it gains control at the next schedule/transfer/cede). Otherwise clears the
480exception object.
481
482The exception object will be thrown "as is" with the specified scalar in
483C<$@>, i.e. if it is a string, no line number or newline will be appended
484(unlike with C<die>).
485
486This can be used as a softer means than C<cancel> to ask a coroutine to
487end itself, although there is no guarentee that the exception will lead to
488termination, and if the exception isn't caught it might well end the whole
489program.
490
344=cut 491=cut
345 492
346sub desc { 493sub desc {
347 my $old = $_[0]{desc}; 494 my $old = $_[0]{desc};
348 $_[0]{desc} = $_[1] if @_ > 1; 495 $_[0]{desc} = $_[1] if @_ > 1;
349 $old; 496 $old;
350} 497}
351 498
352=back 499=back
353 500
354=head2 UTILITY FUNCTIONS 501=head2 GLOBAL FUNCTIONS
355 502
356=over 4 503=over 4
504
505=item Coro::nready
506
507Returns the number of coroutines that are currently in the ready state,
508i.e. that can be switched to. The value C<0> means that the only runnable
509coroutine is the currently running one, so C<cede> would have no effect,
510and C<schedule> would cause a deadlock unless there is an idle handler
511that wakes up some coroutines.
512
513=item my $guard = Coro::guard { ... }
514
515This creates and returns a guard object. Nothing happens until the object
516gets destroyed, in which case the codeblock given as argument will be
517executed. This is useful to free locks or other resources in case of a
518runtime error or when the coroutine gets canceled, as in both cases the
519guard block will be executed. The guard object supports only one method,
520C<< ->cancel >>, which will keep the codeblock from being executed.
521
522Example: set some flag and clear it again when the coroutine gets canceled
523or the function returns:
524
525 sub do_something {
526 my $guard = Coro::guard { $busy = 0 };
527 $busy = 1;
528
529 # do something that requires $busy to be true
530 }
531
532=cut
533
534sub guard(&) {
535 bless \(my $cb = $_[0]), "Coro::guard"
536}
537
538sub Coro::guard::cancel {
539 ${$_[0]} = sub { };
540}
541
542sub Coro::guard::DESTROY {
543 ${$_[0]}->();
544}
545
357 546
358=item unblock_sub { ... } 547=item unblock_sub { ... }
359 548
360This utility function takes a BLOCK or code reference and "unblocks" it, 549This utility function takes a BLOCK or code reference and "unblocks" it,
361returning the new coderef. This means that the new coderef will return 550returning the new coderef. This means that the new coderef will return
362immediately without blocking, returning nothing, while the original code 551immediately without blocking, returning nothing, while the original code
363ref will be called (with parameters) from within its own coroutine. 552ref will be called (with parameters) from within its own coroutine.
364 553
365The reason this fucntion exists is that many event libraries (such as the 554The reason this function exists is that many event libraries (such as the
366venerable L<Event|Event> module) are not coroutine-safe (a weaker form 555venerable L<Event|Event> module) are not coroutine-safe (a weaker form
367of thread-safety). This means you must not block within event callbacks, 556of thread-safety). This means you must not block within event callbacks,
368otherwise you might suffer from crashes or worse. 557otherwise you might suffer from crashes or worse.
369 558
370This function allows your callbacks to block by executing them in another 559This function allows your callbacks to block by executing them in another
375In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when 564In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
376creating event callbacks that want to block. 565creating event callbacks that want to block.
377 566
378=cut 567=cut
379 568
380our @unblock_pool;
381our @unblock_queue; 569our @unblock_queue;
382our $UNBLOCK_POOL_SIZE = 2;
383 570
384sub unblock_handler_ { 571# we create a special coro because we want to cede,
385 while () { 572# to reduce pressure on the coro pool (because most callbacks
386 my ($cb, @arg) = @{ delete $Coro::current->{arg} }; 573# return immediately and can be reused) and because we cannot cede
387 $cb->(@arg); 574# inside an event callback.
388
389 last if @unblock_pool >= $UNBLOCK_POOL_SIZE;
390 push @unblock_pool, $Coro::current;
391 schedule;
392 }
393}
394
395our $unblock_scheduler = async { 575our $unblock_scheduler = new Coro sub {
396 while () { 576 while () {
397 while (my $cb = pop @unblock_queue) { 577 while (my $cb = pop @unblock_queue) {
398 my $handler = (pop @unblock_pool or new Coro \&unblock_handler_); 578 # this is an inlined copy of async_pool
399 $handler->{arg} = $cb; 579 my $coro = (pop @async_pool) || new Coro \&pool_handler;
580
581 $coro->{_invoke} = $cb;
400 $handler->ready; 582 $coro->ready;
401 cede; 583 cede; # for short-lived callbacks, this reduces pressure on the coro pool
402 } 584 }
403 585 schedule; # sleep well
404 schedule;
405 } 586 }
406}; 587};
588$unblock_scheduler->desc ("[unblock_sub scheduler]");
407 589
408sub unblock_sub(&) { 590sub unblock_sub(&) {
409 my $cb = shift; 591 my $cb = shift;
410 592
411 sub { 593 sub {
412 push @unblock_queue, [$cb, @_]; 594 unshift @unblock_queue, [$cb, @_];
413 $unblock_scheduler->ready; 595 $unblock_scheduler->ready;
414 } 596 }
415} 597}
416 598
417=back 599=back
424 606
425 - you must make very sure that no coro is still active on global 607 - you must make very sure that no coro is still active on global
426 destruction. very bad things might happen otherwise (usually segfaults). 608 destruction. very bad things might happen otherwise (usually segfaults).
427 609
428 - this module is not thread-safe. You should only ever use this module 610 - this module is not thread-safe. You should only ever use this module
429 from the same thread (this requirement might be losened in the future 611 from the same thread (this requirement might be loosened in the future
430 to allow per-thread schedulers, but Coro::State does not yet allow 612 to allow per-thread schedulers, but Coro::State does not yet allow
431 this). 613 this).
432 614
433=head1 SEE ALSO 615=head1 SEE ALSO
434 616
617Lower level Configuration, Coroutine Environment: L<Coro::State>.
618
619Debugging: L<Coro::Debug>.
620
435Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>. 621Support/Utility: L<Coro::Specific>, L<Coro::Util>.
436 622
437Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>. 623Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
438 624
439Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>. 625Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>.
440 626
627Compatibility: L<Coro::LWP>, L<Coro::Storable>, L<Coro::Select>.
628
441Embedding: L<Coro:MakeMaker> 629Embedding: L<Coro::MakeMaker>.
442 630
443=head1 AUTHOR 631=head1 AUTHOR
444 632
445 Marc Lehmann <schmorp@schmorp.de> 633 Marc Lehmann <schmorp@schmorp.de>
446 http://home.schmorp.de/ 634 http://home.schmorp.de/

Diff Legend

Removed lines
+ Added lines
< Changed lines
> Changed lines