Coro/Coro/State.pm

=head1 NAME

Coro::State - create and manage simple coroutines

=head1 SYNOPSIS

 use Coro::State;

 $new = new Coro::State sub {
    print "in coroutine (called with @_), switching back\n";
    $new->transfer ($main);
    print "in coroutine again, switching back\n";
    $new->transfer ($main);
 }, 5;

 $main = new Coro::State;

 print "in main, switching to coroutine\n";
 $main->transfer ($new);
 print "back in main, switch to coroutine again\n";
 $main->transfer ($new);
 print "back in main\n";

=head1 DESCRIPTION

This module implements coroutines. Coroutines, similar to continuations,
allow you to run more than one "thread of execution" in parallel. Unlike
threads, there is no parallelism and only voluntary switching is used so
locking problems are greatly reduced.

This can be used to implement non-local jumps, exception handling,
(non-clonable) continuations and more.

This module provides only low-level functionality. See L<Coro> and related
modules for a higher level process abstraction including scheduling.

=head2 MODEL

Coro::State implements two different coroutine models: Perl and C. The
C coroutines (called cctx's) are basically simplified perl interpreters
running/interpreting the Perl coroutines. A single interpreter can run any
number of Perl coroutines, so usually there are very few C coroutines.

When Perl code calls a C function (e.g. in an extension module) and that
C function then calls back into Perl or does a coroutine switch the C
coroutine can no longer execute other Perl coroutines, so it stays tied to
the specific coroutine until it returns to the original Perl caller, after
which it is again avaikable to run other Perl coroutines.

The main program always has its own "C coroutine" (which really is
*the* Perl interpreter running the whole program), so there will always
be at least one additional C coroutine. You can use the debugger (see
L<Coro::Debug>) to find out which coroutines are tied to their cctx and
which aren't.

=head2 MEMORY CONSUMPTION

A newly created coroutine that has not been used only allocates a
relatively small (a hundred bytes) structure. Only on the first
C<transfer> will perl allocate stacks (a few kb, 64 bit architetcures
use twice as much, i.e. a few kb :) and optionally a C stack/coroutine
(cctx) for coroutines that recurse through C functions. All this is very
system-dependent. On my x86-pc-linux-gnu system this amounts to about 2k
per (non-trivial but simple) coroutine.

You can view the actual memory consumption using Coro::Debug. Keep in mind
that a for loop or other block constructs can easily consume 100-200 bytes
per nesting level.

=cut

package Coro::State;

use strict;
no warnings "uninitialized";

use Carp;

our $DIEHOOK;
our $WARNHOOK;

BEGIN {
   $DIEHOOK  = sub { };
   $WARNHOOK = sub { warn $_[0] };
}

sub diehook  { &$DIEHOOK  }
sub warnhook { &$WARNHOOK }

use XSLoader;

BEGIN {
   our $VERSION = 4.745;

   # must be done here because the xs part expects it to exist
   # it might exist already because Coro::Specific created it.
   $Coro::current ||= { };

   {
      # save/restore the handlers before/after overwriting %SIG magic
      local $SIG{__DIE__};
      local $SIG{__WARN__};

      XSLoader::load __PACKAGE__, $VERSION;
   }

   # need to do it after overwriting the %SIG magic
   $SIG{__DIE__}  ||= \&diehook;
   $SIG{__WARN__} ||= \&warnhook;
}

use Exporter;
use base Exporter::;

=head2 GLOBAL VARIABLES

=over 4

=item $Coro::State::DIEHOOK

This works similarly to C<$SIG{__DIE__}> and is used as the default die
hook for newly created coroutines. This is useful if you want some generic
logging function that works for all coroutines that don't set their own
hook.

When Coro::State is first loaded it will install these handlers for the
main program, too, unless they have been overwritten already.

The default handlers provided will behave like the built-in ones (as if
they weren't there).

Note 1: You I<must> store a valid code reference in these variables,
C<undef> will I<not> do.

Note 2: The value of this variable will be shared among all coroutines, so
changing its value will change it in all coroutines that don't have their
own die handler.

=item $Coro::State::WARNHOOK

Similar to above die hook, but augments C<$SIG{__WARN__}>.

=back

=head2 FUNCTIONS

=over 4

=item $coro = new Coro::State [$coderef[, @args...]]

Create a new coroutine and return it. The first C<transfer> call to this
coroutine will start execution at the given coderef.

If the subroutine returns the program will be terminated as if execution
of the main program ended.

If it throws an exception the program will terminate unless the exception
is caught, exactly like in the main program.

Calling C<exit> in a coroutine does the same as calling it in the main
program.

If the coderef is omitted this function will create a new "empty"
coroutine, i.e. a coroutine that cannot be transfered to but can be used
to save the current coroutine in.

The returned object is an empty hash which can be used for any purpose
whatsoever, for example when subclassing Coro::State.

Certain variables are "localised" to each coroutine, that is, certain
"global" variables are actually per coroutine. Not everything that would
sensibly be localised currently is, and not everything that is localised
makes sense for every application, and the future might bring changes.

The following global variables can have different values per coroutine,
and have the stated initial values:

   Variable       Initial Value
   @_             whatever arguments were passed to the Coro
   $_             undef
   $@             undef
   $/             "\n"
   $SIG{__DIE__}  aliased to $Coro::State::DIEHOOK(*)
   $SIG{__WARN__} aliased to $Coro::State::WARNHOOK(*)
   (default fh)   *STDOUT
   $1, $2...      all regex results are initially undefined

   (*) reading the value from %SIG is not supported, but local'ising is.

If you feel that something important is missing then tell me. Also
remember that every function call that might call C<transfer> (such
as C<Coro::Channel::put>) might clobber any global and/or special
variables. Yes, this is by design ;) You can always create your own
process abstraction model that saves these variables.

The easiest way to do this is to create your own scheduling primitive like
in the code below, and use it in your coroutines:

  sub my_cede {
     local ($;, ...);
     Coro::cede;
  }

=cut

# this is called for each newly created C coroutine,
# and is being artificially injected into the opcode flow.
# its sole purpose is to call transfer() once so it knows
# the stop level stack frame for stack sharing.
sub _cctx_init {
   _set_stacklevel $_[0];
}

=item $state->call ($coderef)

Try to call the given C<$coderef> in the context of the given state. This
works even when the state is currently within an XS function, and can
be very dangerous. You can use it to acquire stack traces etc. (see the
Coro::Debug module for more details). The coderef MUST NOT EVER transfer
to another state.

=item $state->eval ($string)

Like C<call>, but eval's the string. Dangerous.

=item $state->throw ($exception)

Makes the coroutine throw the given exception as soon as it regains
control.

=item $state->swap_defsv

=item $state->swap_defav

Swap the current C<$_> (swap_defsv) or C<@_> (swap_defav) with the
equivalent in the saved state of C<$state>. This can be used to give the
coroutine a defined content for C<@_> and C<$_> before transfer'ing to it.

=item $state->trace ($flags)

Internal function to control tracing. I just mention this so you can stay
away from abusing it.

=item $prev->transfer ($next)

Save the state of the current subroutine in C<$prev> and switch to the
coroutine saved in C<$next>.

The "state" of a subroutine includes the scope, i.e. lexical variables and
the current execution state (subroutine, stack).

=item $state->has_cctx

Returns wether the state currently uses a cctx/C coroutine. An active
state always has a cctx, as well as the main program. Other states only
use a cctxts when needed.

=item $bytes = $state->rss

Returns the memory allocated by the coroutine (which includes
static structures, various perl stacks but NOT local variables,
arguments or any C stack).

=item Coro::State::cctx_count

Returns the number of C-level coroutines allocated. If this number is
very high (more than a dozen) it might help to identify points of C-level
recursion in your code and moving this into a separate coroutine.

=item Coro::State::cctx_idle

Returns the number of allocated but idle (free for reuse) C level
coroutines. Currently, Coro will limit the number of idle/unused cctxs to
8.

=item Coro::State::cctx_stacksize [$new_stacksize]

Returns the current C stack size and optionally sets the new I<minimum>
stack size to C<$new_stacksize> I<long>s. Existing stacks will not
be changed, but Coro will try to replace smaller stacks as soon as
possible. Any Coro::State that starts to use a stack after this call is
guaranteed this minimum stack size.

Please note that Coroutines will only need to use a C-level stack if the
interpreter recurses or calls a function in a module that calls back into
the interpreter, so use of this feature is usually never needed.

=item Coro::State::force_cctx

Forces the allocation of a C context for the currently running coroutine
(if not already done). Apart from benchmarking there is little point
in doing so, however.

=item @states = Coro::State::list

Returns a list of all states currently allocated.

=cut

sub debug_desc {
   $_[0]{desc}
}

1;

=back

=head1 BUGS

This module is not thread-safe. You must only ever use this module from
the same thread (this requirement might be removed in the future).

=head1 SEE ALSO

L<Coro>.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.103
Committed:	Wed Jul 23 22:15:25 2008 UTC (15 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-4_745
Changes since 1.102:	+1 -1 lines
Log Message:	4.745
#	Content
1	=head1 NAME
2
3	Coro::State - create and manage simple coroutines
4
5	=head1 SYNOPSIS
6
7	use Coro::State;
8
9	$new = new Coro::State sub {
10	print "in coroutine (called with @_), switching back\n";
11	$new->transfer ($main);
12	print "in coroutine again, switching back\n";
13	$new->transfer ($main);
14	}, 5;
15
16	$main = new Coro::State;
17
18	print "in main, switching to coroutine\n";
19	$main->transfer ($new);
20	print "back in main, switch to coroutine again\n";
21	$main->transfer ($new);
22	print "back in main\n";
23
24	=head1 DESCRIPTION
25
26	This module implements coroutines. Coroutines, similar to continuations,
27	allow you to run more than one "thread of execution" in parallel. Unlike
28	threads, there is no parallelism and only voluntary switching is used so
29	locking problems are greatly reduced.
30
31	This can be used to implement non-local jumps, exception handling,
32	(non-clonable) continuations and more.
33
34	This module provides only low-level functionality. See L<Coro> and related
35	modules for a higher level process abstraction including scheduling.
36
37	=head2 MODEL
38
39	Coro::State implements two different coroutine models: Perl and C. The
40	C coroutines (called cctx's) are basically simplified perl interpreters
41	running/interpreting the Perl coroutines. A single interpreter can run any
42	number of Perl coroutines, so usually there are very few C coroutines.
43
44	When Perl code calls a C function (e.g. in an extension module) and that
45	C function then calls back into Perl or does a coroutine switch the C
46	coroutine can no longer execute other Perl coroutines, so it stays tied to
47	the specific coroutine until it returns to the original Perl caller, after
48	which it is again avaikable to run other Perl coroutines.
49
50	The main program always has its own "C coroutine" (which really is
51	the Perl interpreter running the whole program), so there will always
52	be at least one additional C coroutine. You can use the debugger (see
53	L<Coro::Debug>) to find out which coroutines are tied to their cctx and
54	which aren't.
55
56	=head2 MEMORY CONSUMPTION
57
58	A newly created coroutine that has not been used only allocates a
59	relatively small (a hundred bytes) structure. Only on the first
60	C<transfer> will perl allocate stacks (a few kb, 64 bit architetcures
61	use twice as much, i.e. a few kb :) and optionally a C stack/coroutine
62	(cctx) for coroutines that recurse through C functions. All this is very
63	system-dependent. On my x86-pc-linux-gnu system this amounts to about 2k
64	per (non-trivial but simple) coroutine.
65
66	You can view the actual memory consumption using Coro::Debug. Keep in mind
67	that a for loop or other block constructs can easily consume 100-200 bytes
68	per nesting level.
69
70	=cut
71
72	package Coro::State;
73
74	use strict;
75	no warnings "uninitialized";
76
77	use Carp;
78
79	our $DIEHOOK;
80	our $WARNHOOK;
81
82	BEGIN {
83	$DIEHOOK = sub { };
84	$WARNHOOK = sub { warn $_[0] };
85	}
86
87	sub diehook { &$DIEHOOK }
88	sub warnhook { &$WARNHOOK }
89
90	use XSLoader;
91
92	BEGIN {
93	our $VERSION = 4.745;
94
95	# must be done here because the xs part expects it to exist
96	# it might exist already because Coro::Specific created it.
97	$Coro::current \|\|= { };
98
99	{
100	# save/restore the handlers before/after overwriting %SIG magic
101	local $SIG{__DIE__};
102	local $SIG{__WARN__};
103
104	XSLoader::load __PACKAGE__, $VERSION;
105	}
106
107	# need to do it after overwriting the %SIG magic
108	$SIG{__DIE__} \|\|= \&diehook;
109	$SIG{__WARN__} \|\|= \&warnhook;
110	}
111
112	use Exporter;
113	use base Exporter::;
114
115	=head2 GLOBAL VARIABLES
116
117	=over 4
118
119	=item $Coro::State::DIEHOOK
120
121	This works similarly to C<$SIG{__DIE__}> and is used as the default die
122	hook for newly created coroutines. This is useful if you want some generic
123	logging function that works for all coroutines that don't set their own
124	hook.
125
126	When Coro::State is first loaded it will install these handlers for the
127	main program, too, unless they have been overwritten already.
128
129	The default handlers provided will behave like the built-in ones (as if
130	they weren't there).
131
132	Note 1: You I<must> store a valid code reference in these variables,
133	C<undef> will I<not> do.
134
135	Note 2: The value of this variable will be shared among all coroutines, so
136	changing its value will change it in all coroutines that don't have their
137	own die handler.
138
139	=item $Coro::State::WARNHOOK
140
141	Similar to above die hook, but augments C<$SIG{__WARN__}>.
142
143	=back
144
145	=head2 FUNCTIONS
146
147	=over 4
148
149	=item $coro = new Coro::State [$coderef[, @args...]]
150
151	Create a new coroutine and return it. The first C<transfer> call to this
152	coroutine will start execution at the given coderef.
153
154	If the subroutine returns the program will be terminated as if execution
155	of the main program ended.
156
157	If it throws an exception the program will terminate unless the exception
158	is caught, exactly like in the main program.
159
160	Calling C<exit> in a coroutine does the same as calling it in the main
161	program.
162
163	If the coderef is omitted this function will create a new "empty"
164	coroutine, i.e. a coroutine that cannot be transfered to but can be used
165	to save the current coroutine in.
166
167	The returned object is an empty hash which can be used for any purpose
168	whatsoever, for example when subclassing Coro::State.
169
170	Certain variables are "localised" to each coroutine, that is, certain
171	"global" variables are actually per coroutine. Not everything that would
172	sensibly be localised currently is, and not everything that is localised
173	makes sense for every application, and the future might bring changes.
174
175	The following global variables can have different values per coroutine,
176	and have the stated initial values:
177
178	Variable Initial Value
179	@_ whatever arguments were passed to the Coro
180	$_ undef
181	$@ undef
182	$/ "\n"
183	$SIG{__DIE__} aliased to $Coro::State::DIEHOOK(*)
184	$SIG{__WARN__} aliased to $Coro::State::WARNHOOK(*)
185	(default fh) *STDOUT
186	$1, $2... all regex results are initially undefined
187
188	(*) reading the value from %SIG is not supported, but local'ising is.
189
190	If you feel that something important is missing then tell me. Also
191	remember that every function call that might call C<transfer> (such
192	as C<Coro::Channel::put>) might clobber any global and/or special
193	variables. Yes, this is by design ;) You can always create your own
194	process abstraction model that saves these variables.
195
196	The easiest way to do this is to create your own scheduling primitive like
197	in the code below, and use it in your coroutines:
198
199	sub my_cede {
200	local ($;, ...);
201	Coro::cede;
202	}
203
204	=cut
205
206	# this is called for each newly created C coroutine,
207	# and is being artificially injected into the opcode flow.
208	# its sole purpose is to call transfer() once so it knows
209	# the stop level stack frame for stack sharing.
210	sub _cctx_init {
211	_set_stacklevel $_[0];
212	}
213
214	=item $state->call ($coderef)
215
216	Try to call the given C<$coderef> in the context of the given state. This
217	works even when the state is currently within an XS function, and can
218	be very dangerous. You can use it to acquire stack traces etc. (see the
219	Coro::Debug module for more details). The coderef MUST NOT EVER transfer
220	to another state.
221
222	=item $state->eval ($string)
223
224	Like C<call>, but eval's the string. Dangerous.
225
226	=item $state->throw ($exception)
227
228	Makes the coroutine throw the given exception as soon as it regains
229	control.
230
231	=item $state->swap_defsv
232
233	=item $state->swap_defav
234
235	Swap the current C<$_> (swap_defsv) or C<@_> (swap_defav) with the
236	equivalent in the saved state of C<$state>. This can be used to give the
237	coroutine a defined content for C<@_> and C<$_> before transfer'ing to it.
238
239	=item $state->trace ($flags)
240
241	Internal function to control tracing. I just mention this so you can stay
242	away from abusing it.
243
244	=item $prev->transfer ($next)
245
246	Save the state of the current subroutine in C<$prev> and switch to the
247	coroutine saved in C<$next>.
248
249	The "state" of a subroutine includes the scope, i.e. lexical variables and
250	the current execution state (subroutine, stack).
251
252	=item $state->has_cctx
253
254	Returns wether the state currently uses a cctx/C coroutine. An active
255	state always has a cctx, as well as the main program. Other states only
256	use a cctxts when needed.
257
258	=item $bytes = $state->rss
259
260	Returns the memory allocated by the coroutine (which includes
261	static structures, various perl stacks but NOT local variables,
262	arguments or any C stack).
263
264	=item Coro::State::cctx_count
265
266	Returns the number of C-level coroutines allocated. If this number is
267	very high (more than a dozen) it might help to identify points of C-level
268	recursion in your code and moving this into a separate coroutine.
269
270	=item Coro::State::cctx_idle
271
272	Returns the number of allocated but idle (free for reuse) C level
273	coroutines. Currently, Coro will limit the number of idle/unused cctxs to
274	8.
275
276	=item Coro::State::cctx_stacksize [$new_stacksize]
277
278	Returns the current C stack size and optionally sets the new I<minimum>
279	stack size to C<$new_stacksize> I<long>s. Existing stacks will not
280	be changed, but Coro will try to replace smaller stacks as soon as
281	possible. Any Coro::State that starts to use a stack after this call is
282	guaranteed this minimum stack size.
283
284	Please note that Coroutines will only need to use a C-level stack if the
285	interpreter recurses or calls a function in a module that calls back into
286	the interpreter, so use of this feature is usually never needed.
287
288	=item Coro::State::force_cctx
289
290	Forces the allocation of a C context for the currently running coroutine
291	(if not already done). Apart from benchmarking there is little point
292	in doing so, however.
293
294	=item @states = Coro::State::list
295
296	Returns a list of all states currently allocated.
297
298	=cut
299
300	sub debug_desc {
301	$_[0]{desc}
302	}
303
304	1;
305
306	=back
307
308	=head1 BUGS
309
310	This module is not thread-safe. You must only ever use this module from
311	the same thread (this requirement might be removed in the future).
312
313	=head1 SEE ALSO
314
315	L<Coro>.
316
317	=head1 AUTHOR
318
319	Marc Lehmann <schmorp@schmorp.de>
320	http://home.schmorp.de/
321
322	=cut
323