Coro/Coro/State.pm

=head1 NAME

Coro::State - first class continuations

=head1 SYNOPSIS

 use Coro::State;

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

 $main = new Coro::State;

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

=head1 DESCRIPTION

This module implements coro. Coros, similar to threads and continuations,
allow you to run more than one "thread of execution" in parallel. Unlike
so-called "kernel" threads, there is no parallelism and only voluntary
switching is used so locking problems are greatly reduced. The latter is
called "cooperative" threading as opposed to "preemptive" threading.

This can be used to implement non-local jumps, exception handling,
continuation objects and more.

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

=head2 MODEL

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

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

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

=head2 MEMORY CONSUMPTION

A newly created Coro::State 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/thread
(cctx) for threads 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) Coro::State.

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;

use Time::HiRes (); # currently only used for PerlIO::cede

our $DIEHOOK;
our $WARNHOOK;

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

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

use XSLoader;

BEGIN {
   our $VERSION = 5.151;

   # 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 Coro::States. This is useful if you want some generic
logging function that works for all threads 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).

If you don't want to exit your program on uncaught exceptions, you can
must not return from your die hook - terminate instead.

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 threads, so
changing its value will change it in all threads 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 Coro::State thread object and return it. The first
C<transfer> call to this thread will start execution at the given
coderef, with the given arguments.

Note that the arguments will not be copied. Instead, as with normal
function calls, the thread receives passed arguments by reference, so
make sure you don't change them in unexpected ways.

Returning from such a thread is I<NOT> supported. Neither is calling
C<exit> or throwing an uncaught exception. The following paragraphs
describe what happens in current versions of Coro.

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 thread does the same as calling it in the main
program, but due to libc bugs on many BSDs, this doesn't work reliable
everywhere.

If the coderef is omitted this function will create a new "empty"
thread, i.e. a thread that cannot be transfered to but can be used
to save the current thread state in (note that this is dangerous, as no
reference is taken to ensure that the "current thread state" survives,
the caller is responsible to ensure that the cloned state does not go
away).

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 thread, that is, certain
"global" variables are actually per thread. 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 thread,
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
   $^H, %^H       zero/empty.
   $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 threads:

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

Another way is to use dynamic winders, see C<Coro::on_enter> and
C<Coro::on_leave> for this.

=item $prev->transfer ($next)

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

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

=item $state->is_new

Returns true iff this Coro::State object is "new", i.e. has never been run
yet. Those states basically consist of only the code reference to call and
the arguments, but consumes very little other resources. New states will
automatically get assigned a perl interpreter when they are transfered to.

=item $state->is_destroyed

Returns true iff the Coro::State object has been destroyed (by
C<cancel>), i.e. it's resources freed because they were C<cancel>'d (or
C<terminate>'d).

=item $state->cancel

Forcefully destructs the given Coro::State. While you can keep the
reference, and some memory is still allocated, the Coro::State object is
effecticely dead, destructors have been freed, it cannot be transfered to
anymore.

=item $state->throw ([$scalar])

See L<< Coro->throw >>.

=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->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
coro 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 $bytes = $state->rss

Returns the memory allocated by the coro (which includes static
structures, various perl stacks but NOT local variables, arguments or any
C context data). This is a rough indication of how much memory it might
use.

=item $state->has_cctx

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

=item Coro::State::force_cctx

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

=item $ncctx = Coro::State::cctx_count

Returns the number of C-level coro 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 coro.

=item $nidle = Coro::State::cctx_idle

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

=item $old = Coro::State::cctx_stacksize [$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 coros 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 $old = Coro::State::cctx_max_idle [$new_count]

Coro caches C contexts that are not in use currently, as creating them
from scratch has some overhead.

This function returns the current maximum number of idle C contexts and
optionally sets the new amount. The count must be at least C<1>, with the
default being C<4>.

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

Returns a list of all states currently allocated.

=item $was_enabled = Coro::State::enable_times [$enable]

Enables/disables/queries the current state of per-thread real and
cpu-time gathering.

When enabled, the real time and the cpu time (user + system time)
spent in each thread is accumulated. If disabled, then the accumulated
times will stay as they are (they start at 0).

Currently, cpu time is only measured on GNU/Linux systems, all other
systems only gather real time.

Enabling time profiling slows down thread switching by a factor of 2 to
10, depending on platform on hardware.

The times will be displayed when running C<Coro::Debug::command "ps">, and
cna be queried by calling C<< $state->times >>.

=item ($real, $cpu) = $state->times

Returns the real time and cpu times spent in the given C<$state>. See
C<Coro::State::enable_times> for more info.

=item $clone = $state->clone

This exciting method takes a Coro::State object and clones it, i.e., it
creates a copy. This makes it possible to restore a state more than once,
and even return to states that have returned or have been terminated.

Since its only known purpose is for intellectual self-gratification, and
because it is a difficult piece of code, it is not enabled by default, and
not supported.

Here are a few little-known facts: First, coros *are* full/true/real
continuations. Secondly Coro::State objects (without clone) *are* first
class continuations. Thirdly, nobody has ever found a use for the full
power of call/cc that isn't better (faster, easier, more efficiently)
implemented differently, and nobody has yet found a useful control
construct that can't be implemented without it already, just much faster
and with fewer resources. And lastly, Scheme's call/cc doesn't support
using call/cc to implement threads.

Among the games you can play with this is implementing a scheme-like
call-with-current-continuation, as the following code does (well, with
small differences).

   # perl disassociates from local lexicals on frame exit,
   # so use a global variable for return values.
   my @ret;

   sub callcc($@) {
      my ($func, @arg) = @_;

      my $continuation = new Coro::State;
      $continuation->transfer (new Coro::State sub {
         my $escape = sub {
            @ret = @_;
            Coro::State->new->transfer ($continuation->clone);
         };
         $escape->($func->($escape, @arg));
      });

      my @ret_ = @ret; @ret = ();
      wantarray ? @ret_ : pop @ret_
   }

Which could be used to implement a loop like this:

   async {
      my $n; 
      my $l = callcc sub { $_[0] };
     
      $n++; 
      print "iteration $n\n";

      $l->($l) unless $n == 10;
   };  

If you find this confusing, then you already understand the coolness of
call/cc: It can turn anything into spaghetti code real fast.

Besides, call/cc is much less useful in a Perl-like dynamic language (with
references, and its scoping rules) then in, say, scheme.

Now, the known limitations of C<clone>:

It probably only works on perl 5.10; it cannot clone a coro inside
the substition operator (but windows perl can't fork from there either)
and some other contexts, and C<abort ()> is the preferred mechanism to
signal errors. It cannot clone a state that has a c context attached
(implementing clone on the C level is too hard for me to even try),
which rules out calling call/cc from the main coro. It cannot
clone a context that hasn't even been started yet. It doesn't work with
C<-DDEBUGGING> (but what does). It probably also leaks, and sometimes
triggers a few assertions inside Coro. Most of these limitations *are*
fixable with some effort, but that's pointless just to make a point that
it could be done.

The current implementation could without doubt be optimised to be a
constant-time operation by doing lazy stack copying, if somebody were
insane enough to invest the time.

=cut

# used by Coro::Debug only atm.
sub debug_desc {
   $_[0]{desc}
}

# for very deep reasons, we must initialise $Coro::main here.

{
   package Coro;

   our $main;    # main coro
   our $current; # current coro

   $main = Coro::State::new Coro::;

   $main->{desc} = "[main::]";

   # maybe some other module used Coro::Specific before...
   $main->{_specific} = $current->{_specific}
      if $current;

   _set_current $main;
}

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:	1.146
Committed:	Mon Jul 6 03:42:29 2009 UTC (14 years, 11 months ago) by root
Branch:	MAIN
CVS Tags:	rel-5_151
Changes since 1.145:	+1 -1 lines
Log Message:	5.151
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3	root	1.132	Coro::State - first class continuations
4	root	1.1
5			=head1 SYNOPSIS
6
7			use Coro::State;
8
9			$new = new Coro::State sub {
10	root	1.140	print "in coro (called with @_), switching back\n";
11	root	1.43	$new->transfer ($main);
12	root	1.140	print "in coro again, switching back\n";
13	root	1.43	$new->transfer ($main);
14	root	1.3	}, 5;
15	root	1.1
16			$main = new Coro::State;
17
18	root	1.140	print "in main, switching to coro\n";
19	root	1.43	$main->transfer ($new);
20	root	1.140	print "back in main, switch to coro again\n";
21	root	1.43	$main->transfer ($new);
22	root	1.1	print "back in main\n";
23
24			=head1 DESCRIPTION
25
26	root	1.140	This module implements coro. Coros, similar to threads and continuations,
27	root	1.1	allow you to run more than one "thread of execution" in parallel. Unlike
28	root	1.140	so-called "kernel" threads, there is no parallelism and only voluntary
29			switching is used so locking problems are greatly reduced. The latter is
30			called "cooperative" threading as opposed to "preemptive" threading.
31	root	1.42
32			This can be used to implement non-local jumps, exception handling,
33	root	1.140	continuation objects and more.
34	root	1.1
35			This module provides only low-level functionality. See L<Coro> and related
36	root	1.140	modules for a higher level threads abstraction including a scheduler.
37	root	1.1
38	root	1.86	=head2 MODEL
39
40	root	1.140	Coro::State implements two different thread models: Perl and C. The C
41			threads (called cctx's) are basically simplified perl interpreters
42			running/interpreting the Perl threads. A single interpreter can run any
43			number of Perl threads, so usually there are very few C threads.
44
45			When Perl code calls a C function (e.g. in an extension module) and that C
46			function then calls back into Perl or transfers control to another thread,
47			the C thread can no longer execute other Perl threads, so it stays tied to
48			the specific thread until it returns to the original Perl caller, after
49			which it is again available to run other Perl threads.
50	root	1.86
51	root	1.140	The main program always has its own "C thread" (which really is
52	root	1.86	the Perl interpreter running the whole program), so there will always
53	root	1.140	be at least one additional C thread. You can use the debugger (see
54			L<Coro::Debug>) to find out which threads are tied to their cctx and
55	root	1.86	which aren't.
56
57	root	1.9	=head2 MEMORY CONSUMPTION
58
59	root	1.140	A newly created Coro::State that has not been used only allocates a
60	root	1.84	relatively small (a hundred bytes) structure. Only on the first
61	root	1.94	C<transfer> will perl allocate stacks (a few kb, 64 bit architetcures
62	root	1.140	use twice as much, i.e. a few kb :) and optionally a C stack/thread
63			(cctx) for threads that recurse through C functions. All this is very
64	root	1.94	system-dependent. On my x86-pc-linux-gnu system this amounts to about 2k
65	root	1.140	per (non-trivial but simple) Coro::State.
66	root	1.94
67			You can view the actual memory consumption using Coro::Debug. Keep in mind
68			that a for loop or other block constructs can easily consume 100-200 bytes
69			per nesting level.
70	root	1.1
71			=cut
72
73			package Coro::State;
74
75	root	1.47	use strict;
76			no warnings "uninitialized";
77
78	root	1.84	use Carp;
79	root	1.87
80	root	1.109	use Time::HiRes (); # currently only used for PerlIO::cede
81
82	root	1.87	our $DIEHOOK;
83			our $WARNHOOK;
84
85			BEGIN {
86			$DIEHOOK = sub { };
87			$WARNHOOK = sub { warn $_[0] };
88			}
89
90			sub diehook { &$DIEHOOK }
91			sub warnhook { &$WARNHOOK }
92	root	1.84
93	root	1.47	use XSLoader;
94	root	1.18
95	root	1.1	BEGIN {
96	root	1.146	our $VERSION = 5.151;
97	root	1.1
98	root	1.67	# must be done here because the xs part expects it to exist
99			# it might exist already because Coro::Specific created it.
100			$Coro::current \|\|= { };
101
102	root	1.101	{
103			# save/restore the handlers before/after overwriting %SIG magic
104			local $SIG{__DIE__};
105			local $SIG{__WARN__};
106
107			XSLoader::load __PACKAGE__, $VERSION;
108			}
109
110			# need to do it after overwriting the %SIG magic
111			$SIG{__DIE__} \|\|= \&diehook;
112			$SIG{__WARN__} \|\|= \&warnhook;
113	root	1.1	}
114
115	root	1.51	use Exporter;
116	root	1.47	use base Exporter::;
117	root	1.5
118	root	1.84	=head2 GLOBAL VARIABLES
119
120			=over 4
121
122			=item $Coro::State::DIEHOOK
123
124			This works similarly to C<$SIG{__DIE__}> and is used as the default die
125	root	1.140	hook for newly created Coro::States. This is useful if you want some generic
126			logging function that works for all threads that don't set their own
127	root	1.84	hook.
128
129			When Coro::State is first loaded it will install these handlers for the
130	root	1.101	main program, too, unless they have been overwritten already.
131	root	1.84
132	root	1.100	The default handlers provided will behave like the built-in ones (as if
133	root	1.84	they weren't there).
134
135	root	1.125	If you don't want to exit your program on uncaught exceptions, you can
136			must not return from your die hook - terminate instead.
137
138	root	1.94	Note 1: You I<must> store a valid code reference in these variables,
139			C<undef> will I<not> do.
140	root	1.84
141	root	1.140	Note 2: The value of this variable will be shared among all threads, so
142			changing its value will change it in all threads that don't have their
143	root	1.100	own die handler.
144	root	1.84
145			=item $Coro::State::WARNHOOK
146
147			Similar to above die hook, but augments C<$SIG{__WARN__}>.
148
149			=back
150
151			=head2 FUNCTIONS
152
153			=over 4
154
155	root	1.65	=item $coro = new Coro::State [$coderef[, @args...]]
156	root	1.1
157	root	1.140	Create a new Coro::State thread object and return it. The first
158			C<transfer> call to this thread will start execution at the given
159			coderef, with the given arguments.
160	root	1.125
161			Note that the arguments will not be copied. Instead, as with normal
162	root	1.140	function calls, the thread receives passed arguments by reference, so
163	root	1.125	make sure you don't change them in unexpected ways.
164
165	root	1.140	Returning from such a thread is I<NOT> supported. Neither is calling
166	root	1.125	C<exit> or throwing an uncaught exception. The following paragraphs
167			describe what happens in current versions of Coro.
168	root	1.94
169			If the subroutine returns the program will be terminated as if execution
170			of the main program ended.
171
172			If it throws an exception the program will terminate unless the exception
173			is caught, exactly like in the main program.
174	root	1.74
175	root	1.140	Calling C<exit> in a thread does the same as calling it in the main
176	root	1.133	program, but due to libc bugs on many BSDs, this doesn't work reliable
177			everywhere.
178	root	1.1
179			If the coderef is omitted this function will create a new "empty"
180	root	1.140	thread, i.e. a thread that cannot be transfered to but can be used
181			to save the current thread state in (note that this is dangerous, as no
182			reference is taken to ensure that the "current thread state" survives,
183	root	1.104	the caller is responsible to ensure that the cloned state does not go
184			away).
185	root	1.1
186	root	1.55	The returned object is an empty hash which can be used for any purpose
187			whatsoever, for example when subclassing Coro::State.
188
189	root	1.140	Certain variables are "localised" to each thread, that is, certain
190			"global" variables are actually per thread. Not everything that would
191	root	1.79	sensibly be localised currently is, and not everything that is localised
192			makes sense for every application, and the future might bring changes.
193	root	1.1
194	root	1.140	The following global variables can have different values per thread,
195	root	1.84	and have the stated initial values:
196	root	1.5
197	root	1.83	Variable Initial Value
198			@_ whatever arguments were passed to the Coro
199			$_ undef
200			$@ undef
201			$/ "\n"
202	root	1.88	$SIG{__DIE__} aliased to $Coro::State::DIEHOOK(*)
203			$SIG{__WARN__} aliased to $Coro::State::WARNHOOK(*)
204	root	1.83	(default fh) *STDOUT
205	root	1.133	$^H, %^H zero/empty.
206	root	1.84	$1, $2... all regex results are initially undefined
207	root	1.2
208	root	1.88	(*) reading the value from %SIG is not supported, but local'ising is.
209
210	root	1.70	If you feel that something important is missing then tell me. Also
211	root	1.2	remember that every function call that might call C<transfer> (such
212			as C<Coro::Channel::put>) might clobber any global and/or special
213			variables. Yes, this is by design ;) You can always create your own
214			process abstraction model that saves these variables.
215	root	1.1
216	root	1.9	The easiest way to do this is to create your own scheduling primitive like
217	root	1.140	in the code below, and use it in your threads:
218	root	1.1
219	root	1.84	sub my_cede {
220	root	1.80	local ($;, ...);
221	root	1.84	Coro::cede;
222	root	1.1	}
223
224	root	1.140	Another way is to use dynamic winders, see C<Coro::on_enter> and
225			C<Coro::on_leave> for this.
226
227			=item $prev->transfer ($next)
228
229			Save the state of the current subroutine in C<$prev> and switch to the
230			thread saved in C<$next>.
231
232			The "state" of a subroutine includes the scope, i.e. lexical variables and
233			the current execution state (subroutine, stack).
234
235			=item $state->is_new
236
237			Returns true iff this Coro::State object is "new", i.e. has never been run
238			yet. Those states basically consist of only the code reference to call and
239			the arguments, but consumes very little other resources. New states will
240			automatically get assigned a perl interpreter when they are transfered to.
241
242			=item $state->is_destroyed
243
244			Returns true iff the Coro::State object has been destroyed (by
245			C<cancel>), i.e. it's resources freed because they were C<cancel>'d (or
246			C<terminate>'d).
247
248			=item $state->cancel
249
250			Forcefully destructs the given Coro::State. While you can keep the
251			reference, and some memory is still allocated, the Coro::State object is
252			effecticely dead, destructors have been freed, it cannot be transfered to
253			anymore.
254	root	1.79
255	root	1.119	=item $state->throw ([$scalar])
256
257			See L<< Coro->throw >>.
258
259	root	1.76	=item $state->call ($coderef)
260
261	root	1.94	Try to call the given C<$coderef> in the context of the given state. This
262	root	1.76	works even when the state is currently within an XS function, and can
263			be very dangerous. You can use it to acquire stack traces etc. (see the
264			Coro::Debug module for more details). The coderef MUST NOT EVER transfer
265			to another state.
266
267			=item $state->eval ($string)
268
269	root	1.94	Like C<call>, but eval's the string. Dangerous.
270	root	1.76
271	root	1.90	=item $state->swap_defsv
272
273			=item $state->swap_defav
274
275			Swap the current C<$_> (swap_defsv) or C<@_> (swap_defav) with the
276			equivalent in the saved state of C<$state>. This can be used to give the
277	root	1.140	coro a defined content for C<@_> and C<$_> before transfer'ing to it.
278	root	1.90
279	root	1.77	=item $state->trace ($flags)
280
281			Internal function to control tracing. I just mention this so you can stay
282	root	1.90	away from abusing it.
283	root	1.77
284	root	1.117	=item $bytes = $state->rss
285
286	root	1.140	Returns the memory allocated by the coro (which includes static
287	root	1.117	structures, various perl stacks but NOT local variables, arguments or any
288			C context data). This is a rough indication of how much memory it might
289			use.
290
291	root	1.94	=item $state->has_cctx
292
293	root	1.117	Returns whether the state currently uses a cctx/C context. An active
294	root	1.94	state always has a cctx, as well as the main program. Other states only
295			use a cctxts when needed.
296
297	root	1.117	=item Coro::State::force_cctx
298	root	1.94
299	root	1.140	Forces the allocation of a C context for the currently running coro
300	root	1.117	(if not already done). Apart from benchmarking there is little point
301			in doing so, however.
302	root	1.94
303	root	1.117	=item $ncctx = Coro::State::cctx_count
304	root	1.64
305	root	1.140	Returns the number of C-level coro allocated. If this number is
306	root	1.64	very high (more than a dozen) it might help to identify points of C-level
307	root	1.140	recursion in your code and moving this into a separate coro.
308	root	1.64
309	root	1.117	=item $nidle = Coro::State::cctx_idle
310	root	1.64
311			Returns the number of allocated but idle (free for reuse) C level
312	root	1.140	coro. Currently, Coro will limit the number of idle/unused cctxs to
313	root	1.76	8.
314	root	1.64
315	root	1.117	=item $old = Coro::State::cctx_stacksize [$new_stacksize]
316	root	1.72
317			Returns the current C stack size and optionally sets the new I<minimum>
318			stack size to C<$new_stacksize> I<long>s. Existing stacks will not
319			be changed, but Coro will try to replace smaller stacks as soon as
320	root	1.91	possible. Any Coro::State that starts to use a stack after this call is
321	root	1.94	guaranteed this minimum stack size.
322
323	root	1.140	Please note that coros will only need to use a C-level stack if the
324	root	1.94	interpreter recurses or calls a function in a module that calls back into
325			the interpreter, so use of this feature is usually never needed.
326	root	1.72
327	root	1.117	=item $old = Coro::State::cctx_max_idle [$new_count]
328
329			Coro caches C contexts that are not in use currently, as creating them
330			from scratch has some overhead.
331	root	1.92
332	root	1.117	This function returns the current maximum number of idle C contexts and
333			optionally sets the new amount. The count must be at least C<1>, with the
334			default being C<4>.
335	root	1.92
336	root	1.76	=item @states = Coro::State::list
337
338			Returns a list of all states currently allocated.
339
340	root	1.144	=item $was_enabled = Coro::State::enable_times [$enable]
341
342			Enables/disables/queries the current state of per-thread real and
343			cpu-time gathering.
344
345			When enabled, the real time and the cpu time (user + system time)
346			spent in each thread is accumulated. If disabled, then the accumulated
347			times will stay as they are (they start at 0).
348
349			Currently, cpu time is only measured on GNU/Linux systems, all other
350			systems only gather real time.
351
352			Enabling time profiling slows down thread switching by a factor of 2 to
353			10, depending on platform on hardware.
354
355			The times will be displayed when running C<Coro::Debug::command "ps">, and
356			cna be queried by calling C<< $state->times >>.
357
358			=item ($real, $cpu) = $state->times
359
360			Returns the real time and cpu times spent in the given C<$state>. See
361			C<Coro::State::enable_times> for more info.
362
363	root	1.127	=item $clone = $state->clone
364
365	root	1.136	This exciting method takes a Coro::State object and clones it, i.e., it
366			creates a copy. This makes it possible to restore a state more than once,
367			and even return to states that have returned or have been terminated.
368	root	1.127
369	root	1.136	Since its only known purpose is for intellectual self-gratification, and
370	root	1.127	because it is a difficult piece of code, it is not enabled by default, and
371			not supported.
372
373	root	1.140	Here are a few little-known facts: First, coros are full/true/real
374	root	1.136	continuations. Secondly Coro::State objects (without clone) are first
375			class continuations. Thirdly, nobody has ever found a use for the full
376			power of call/cc that isn't better (faster, easier, more efficiently)
377			implemented differently, and nobody has yet found a useful control
378			construct that can't be implemented without it already, just much faster
379	root	1.138	and with fewer resources. And lastly, Scheme's call/cc doesn't support
380			using call/cc to implement threads.
381	root	1.136
382			Among the games you can play with this is implementing a scheme-like
383			call-with-current-continuation, as the following code does (well, with
384			small differences).
385
386			# perl disassociates from local lexicals on frame exit,
387			# so use a global variable for return values.
388			my @ret;
389	root	1.127
390	root	1.136	sub callcc($@) {
391	root	1.129	my ($func, @arg) = @_;
392	root	1.127
393	root	1.136	my $continuation = new Coro::State;
394			$continuation->transfer (new Coro::State sub {
395	root	1.129	my $escape = sub {
396	root	1.136	@ret = @_;
397			Coro::State->new->transfer ($continuation->clone);
398	root	1.129	};
399			$escape->($func->($escape, @arg));
400	root	1.136	});
401	root	1.127
402	root	1.136	my @ret_ = @ret; @ret = ();
403			wantarray ? @ret_ : pop @ret_
404	root	1.127	}
405
406	root	1.136	Which could be used to implement a loop like this:
407
408			async {
409			my $n;
410			my $l = callcc sub { $_[0] };
411
412			$n++;
413			print "iteration $n\n";
414
415			$l->($l) unless $n == 10;
416			};
417
418			If you find this confusing, then you already understand the coolness of
419			call/cc: It can turn anything into spaghetti code real fast.
420	root	1.127
421			Besides, call/cc is much less useful in a Perl-like dynamic language (with
422			references, and its scoping rules) then in, say, scheme.
423
424	root	1.130	Now, the known limitations of C<clone>:
425	root	1.127
426	root	1.140	It probably only works on perl 5.10; it cannot clone a coro inside
427	root	1.129	the substition operator (but windows perl can't fork from there either)
428			and some other contexts, and C<abort ()> is the preferred mechanism to
429			signal errors. It cannot clone a state that has a c context attached
430	root	1.131	(implementing clone on the C level is too hard for me to even try),
431	root	1.140	which rules out calling call/cc from the main coro. It cannot
432	root	1.131	clone a context that hasn't even been started yet. It doesn't work with
433	root	1.130	C<-DDEBUGGING> (but what does). It probably also leaks, and sometimes
434			triggers a few assertions inside Coro. Most of these limitations are
435			fixable with some effort, but that's pointless just to make a point that
436			it could be done.
437	root	1.127
438	root	1.136	The current implementation could without doubt be optimised to be a
439			constant-time operation by doing lazy stack copying, if somebody were
440			insane enough to invest the time.
441
442	root	1.1	=cut
443
444	root	1.115	# used by Coro::Debug only atm.
445	root	1.75	sub debug_desc {
446			$_[0]{desc}
447			}
448
449	root	1.122	# for very deep reasons, we must initialise $Coro::main here.
450
451			{
452			package Coro;
453
454	root	1.140	our $main; # main coro
455			our $current; # current coro
456	root	1.122
457			$main = Coro::State::new Coro::;
458
459			$main->{desc} = "[main::]";
460
461			# maybe some other module used Coro::Specific before...
462			$main->{_specific} = $current->{_specific}
463			if $current;
464
465			_set_current $main;
466			}
467
468	root	1.1	1;
469
470			=back
471
472			=head1 BUGS
473
474	root	1.5	This module is not thread-safe. You must only ever use this module from
475	root	1.94	the same thread (this requirement might be removed in the future).
476	root	1.1
477			=head1 SEE ALSO
478
479			L<Coro>.
480
481			=head1 AUTHOR
482
483	root	1.41	Marc Lehmann <schmorp@schmorp.de>
484	root	1.39	http://home.schmorp.de/
485	root	1.1
486			=cut
487