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 common::sense;

use Carp;

our $DIEHOOK;
our $WARNHOOK;

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

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

use XSLoader;

BEGIN {
   our $VERSION = 5.372;

   # 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 must
not return from your die hook - call C<Coro::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.

Yet another way that works onyl for variables is C<< ->swap_sv >>.

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

=item $state->is_new

=item $state->is_zombie

See the corresponding method for L<Coro> objects. 

=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
effectively dead, destructors have been freed, it cannot be transfered to
anymore, it's pushing up the daisies.

=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->swap_sv (\$sv, \$swap_sv)

This (very advanced) function can be used to make I<any> variable local to
a thread.

It works by swapping the contents of C<$sv> and C<$swap_sv> each time the
thread is entered and left again, i.e. it is similar to:

   $tmp = $sv; $sv = $swap_sv; $swap_sv = $tmp;

Except that it doesn't make an copies and works on hashes and even more
exotic values (code references!).

Needless to say, this function can be very very dangerous: you can easily
swap a hash with a reference (i.e. C<%hash> I<becomes> a reference), and perl
will not like this at all.

It will also swap "magicalness" - so when swapping a builtin perl variable
(such as C<$.>), it will lose it's magicalness, which, again, perl will
not like, so don't do it.

Lastly, the C<$swap_sv> itself will be used, not a copy, so make sure you
give each thread it's own C<$swap_sv> instance.

It is, however, quite safe to swap some normal variable with
another. For example, L<PApp::SQL> stores the default database handle in
C<$PApp::SQL::DBH>. To make this a per-thread variable, use this:

   my $private_dbh = ...;
   $coro->swap_sv (\$PApp::SQL::DBH, \$private_dbh);

This results in C<$PApp::SQL::DBH> having the value of C<$private_dbh>
while it executes, and whatever other value it had when it doesn't
execute.

You can also swap hashes and other values:

   my %private_hash;
   $coro->swap_sv (\%some_hash, \%private_hash);

=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 thread contexts allocated. If this number is
very high (more than a dozen) it might be beneficial to identify points of
C-level recursion (perl calls C/XS, which calls perl again which switches
coros - this forces an allocation of a C-level thread context) in your
code and moving this into a separate coro.

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

Returns the number of allocated but idle (currently unused and free for
reuse) C level thread contexts.

=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 $old = Coro::State::cctx_stacksize [$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 @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::new Coro::;

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

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

   _set_current $main;
}

# we also make sure we have Coro::AnyEvent when AnyEvent is used,
# without loading or initialising AnyEvent
if (defined $AnyEvent::MODEL) {
   require Coro::AnyEvent;
} else {
   push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
}

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:	1.166
Committed:	Thu May 12 23:55:39 2011 UTC (13 years ago) by root
Branch:	MAIN
Changes since 1.165:	+7 -16 lines
Log Message:	* empty log message *
#	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	1.153	use common::sense;
76	root	1.47
77	root	1.84	use Carp;
78	root	1.87
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	root	1.84
90	root	1.47	use XSLoader;
91	root	1.18
92	root	1.1	BEGIN {
93	root	1.165	our $VERSION = 5.372;
94	root	1.1
95	root	1.67	# 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	root	1.101	{
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	root	1.1	}
111
112	root	1.51	use Exporter;
113	root	1.47	use base Exporter::;
114	root	1.5
115	root	1.84	=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	root	1.140	hook for newly created Coro::States. This is useful if you want some generic
123			logging function that works for all threads that don't set their own
124	root	1.84	hook.
125
126			When Coro::State is first loaded it will install these handlers for the
127	root	1.101	main program, too, unless they have been overwritten already.
128	root	1.84
129	root	1.100	The default handlers provided will behave like the built-in ones (as if
130	root	1.84	they weren't there).
131
132	root	1.150	If you don't want to exit your program on uncaught exceptions, you must
133			not return from your die hook - call C<Coro::terminate> instead.
134	root	1.125
135	root	1.94	Note 1: You I<must> store a valid code reference in these variables,
136			C<undef> will I<not> do.
137	root	1.84
138	root	1.140	Note 2: The value of this variable will be shared among all threads, so
139			changing its value will change it in all threads that don't have their
140	root	1.100	own die handler.
141	root	1.84
142			=item $Coro::State::WARNHOOK
143
144			Similar to above die hook, but augments C<$SIG{__WARN__}>.
145
146			=back
147
148			=head2 FUNCTIONS
149
150			=over 4
151
152	root	1.65	=item $coro = new Coro::State [$coderef[, @args...]]
153	root	1.1
154	root	1.140	Create a new Coro::State thread object and return it. The first
155			C<transfer> call to this thread will start execution at the given
156			coderef, with the given arguments.
157	root	1.125
158			Note that the arguments will not be copied. Instead, as with normal
159	root	1.140	function calls, the thread receives passed arguments by reference, so
160	root	1.125	make sure you don't change them in unexpected ways.
161
162	root	1.140	Returning from such a thread is I<NOT> supported. Neither is calling
163	root	1.125	C<exit> or throwing an uncaught exception. The following paragraphs
164			describe what happens in current versions of Coro.
165	root	1.94
166			If the subroutine returns the program will be terminated as if execution
167			of the main program ended.
168
169			If it throws an exception the program will terminate unless the exception
170			is caught, exactly like in the main program.
171	root	1.74
172	root	1.140	Calling C<exit> in a thread does the same as calling it in the main
173	root	1.133	program, but due to libc bugs on many BSDs, this doesn't work reliable
174			everywhere.
175	root	1.1
176			If the coderef is omitted this function will create a new "empty"
177	root	1.140	thread, i.e. a thread that cannot be transfered to but can be used
178			to save the current thread state in (note that this is dangerous, as no
179			reference is taken to ensure that the "current thread state" survives,
180	root	1.104	the caller is responsible to ensure that the cloned state does not go
181			away).
182	root	1.1
183	root	1.55	The returned object is an empty hash which can be used for any purpose
184			whatsoever, for example when subclassing Coro::State.
185
186	root	1.140	Certain variables are "localised" to each thread, that is, certain
187			"global" variables are actually per thread. Not everything that would
188	root	1.79	sensibly be localised currently is, and not everything that is localised
189			makes sense for every application, and the future might bring changes.
190	root	1.1
191	root	1.140	The following global variables can have different values per thread,
192	root	1.84	and have the stated initial values:
193	root	1.5
194	root	1.83	Variable Initial Value
195			@_ whatever arguments were passed to the Coro
196			$_ undef
197			$@ undef
198			$/ "\n"
199	root	1.88	$SIG{__DIE__} aliased to $Coro::State::DIEHOOK(*)
200			$SIG{__WARN__} aliased to $Coro::State::WARNHOOK(*)
201	root	1.83	(default fh) *STDOUT
202	root	1.133	$^H, %^H zero/empty.
203	root	1.84	$1, $2... all regex results are initially undefined
204	root	1.2
205	root	1.88	(*) reading the value from %SIG is not supported, but local'ising is.
206
207	root	1.70	If you feel that something important is missing then tell me. Also
208	root	1.2	remember that every function call that might call C<transfer> (such
209			as C<Coro::Channel::put>) might clobber any global and/or special
210			variables. Yes, this is by design ;) You can always create your own
211			process abstraction model that saves these variables.
212	root	1.1
213	root	1.9	The easiest way to do this is to create your own scheduling primitive like
214	root	1.140	in the code below, and use it in your threads:
215	root	1.1
216	root	1.84	sub my_cede {
217	root	1.80	local ($;, ...);
218	root	1.84	Coro::cede;
219	root	1.1	}
220
221	root	1.140	Another way is to use dynamic winders, see C<Coro::on_enter> and
222			C<Coro::on_leave> for this.
223
224	root	1.160	Yet another way that works onyl for variables is C<< ->swap_sv >>.
225
226	root	1.140	=item $prev->transfer ($next)
227
228			Save the state of the current subroutine in C<$prev> and switch to the
229			thread saved in C<$next>.
230
231			The "state" of a subroutine includes the scope, i.e. lexical variables and
232			the current execution state (subroutine, stack).
233
234	root	1.166	=item $state->throw ([$scalar])
235
236	root	1.140	=item $state->is_new
237
238	root	1.166	=item $state->is_zombie
239
240			See the corresponding method for L<Coro> objects.
241	root	1.140
242			=item $state->cancel
243
244			Forcefully destructs the given Coro::State. While you can keep the
245			reference, and some memory is still allocated, the Coro::State object is
246	root	1.166	effectively dead, destructors have been freed, it cannot be transfered to
247			anymore, it's pushing up the daisies.
248	root	1.119
249	root	1.76	=item $state->call ($coderef)
250
251	root	1.94	Try to call the given C<$coderef> in the context of the given state. This
252	root	1.76	works even when the state is currently within an XS function, and can
253			be very dangerous. You can use it to acquire stack traces etc. (see the
254			Coro::Debug module for more details). The coderef MUST NOT EVER transfer
255			to another state.
256
257			=item $state->eval ($string)
258
259	root	1.94	Like C<call>, but eval's the string. Dangerous.
260	root	1.76
261	root	1.90	=item $state->swap_defsv
262
263			=item $state->swap_defav
264
265			Swap the current C<$_> (swap_defsv) or C<@_> (swap_defav) with the
266			equivalent in the saved state of C<$state>. This can be used to give the
267	root	1.140	coro a defined content for C<@_> and C<$_> before transfer'ing to it.
268	root	1.90
269	root	1.154	=item $state->swap_sv (\$sv, \$swap_sv)
270
271			This (very advanced) function can be used to make I<any> variable local to
272			a thread.
273
274			It works by swapping the contents of C<$sv> and C<$swap_sv> each time the
275	root	1.160	thread is entered and left again, i.e. it is similar to:
276	root	1.154
277			$tmp = $sv; $sv = $swap_sv; $swap_sv = $tmp;
278
279			Except that it doesn't make an copies and works on hashes and even more
280			exotic values (code references!).
281
282			Needless to say, this function can be very very dangerous: you can easily
283			swap a hash with a reference (i.e. C<%hash> I<becomes> a reference), and perl
284			will not like this at all.
285
286			It will also swap "magicalness" - so when swapping a builtin perl variable
287			(such as C<$.>), it will lose it's magicalness, which, again, perl will
288			not like, so don't do it.
289
290			Lastly, the C<$swap_sv> itself will be used, not a copy, so make sure you
291			give each thread it's own C<$swap_sv> instance.
292
293			It is, however, quite safe to swap some normal variable with
294			another. For example, L<PApp::SQL> stores the default database handle in
295			C<$PApp::SQL::DBH>. To make this a per-thread variable, use this:
296
297			my $private_dbh = ...;
298			$coro->swap_sv (\$PApp::SQL::DBH, \$private_dbh);
299
300			This results in C<$PApp::SQL::DBH> having the value of C<$private_dbh>
301			while it executes, and whatever other value it had when it doesn't
302			execute.
303
304			You can also swap hashes and other values:
305
306			my %private_hash;
307			$coro->swap_sv (\%some_hash, \%private_hash);
308
309	root	1.77	=item $state->trace ($flags)
310
311			Internal function to control tracing. I just mention this so you can stay
312	root	1.90	away from abusing it.
313	root	1.77
314	root	1.117	=item $bytes = $state->rss
315
316	root	1.140	Returns the memory allocated by the coro (which includes static
317	root	1.117	structures, various perl stacks but NOT local variables, arguments or any
318			C context data). This is a rough indication of how much memory it might
319			use.
320
321	root	1.94	=item $state->has_cctx
322
323	root	1.117	Returns whether the state currently uses a cctx/C context. An active
324	root	1.94	state always has a cctx, as well as the main program. Other states only
325			use a cctxts when needed.
326
327	root	1.117	=item Coro::State::force_cctx
328	root	1.94
329	root	1.140	Forces the allocation of a C context for the currently running coro
330	root	1.117	(if not already done). Apart from benchmarking there is little point
331			in doing so, however.
332	root	1.94
333	root	1.117	=item $ncctx = Coro::State::cctx_count
334	root	1.64
335	root	1.161	Returns the number of C-level thread contexts allocated. If this number is
336			very high (more than a dozen) it might be beneficial to identify points of
337			C-level recursion (perl calls C/XS, which calls perl again which switches
338			coros - this forces an allocation of a C-level thread context) in your
339			code and moving this into a separate coro.
340	root	1.64
341	root	1.117	=item $nidle = Coro::State::cctx_idle
342	root	1.64
343	root	1.161	Returns the number of allocated but idle (currently unused and free for
344			reuse) C level thread contexts.
345
346			=item $old = Coro::State::cctx_max_idle [$new_count]
347
348			Coro caches C contexts that are not in use currently, as creating them
349			from scratch has some overhead.
350
351			This function returns the current maximum number of idle C contexts and
352			optionally sets the new amount. The count must be at least C<1>, with the
353			default being C<4>.
354	root	1.64
355	root	1.117	=item $old = Coro::State::cctx_stacksize [$new_stacksize]
356	root	1.72
357			Returns the current C stack size and optionally sets the new I<minimum>
358			stack size to C<$new_stacksize> I<long>s. Existing stacks will not
359			be changed, but Coro will try to replace smaller stacks as soon as
360	root	1.91	possible. Any Coro::State that starts to use a stack after this call is
361	root	1.94	guaranteed this minimum stack size.
362
363	root	1.140	Please note that coros will only need to use a C-level stack if the
364	root	1.94	interpreter recurses or calls a function in a module that calls back into
365			the interpreter, so use of this feature is usually never needed.
366	root	1.72
367	root	1.76	=item @states = Coro::State::list
368
369			Returns a list of all states currently allocated.
370
371	root	1.144	=item $was_enabled = Coro::State::enable_times [$enable]
372
373			Enables/disables/queries the current state of per-thread real and
374			cpu-time gathering.
375
376			When enabled, the real time and the cpu time (user + system time)
377			spent in each thread is accumulated. If disabled, then the accumulated
378			times will stay as they are (they start at 0).
379
380			Currently, cpu time is only measured on GNU/Linux systems, all other
381			systems only gather real time.
382
383			Enabling time profiling slows down thread switching by a factor of 2 to
384			10, depending on platform on hardware.
385
386			The times will be displayed when running C<Coro::Debug::command "ps">, and
387			cna be queried by calling C<< $state->times >>.
388
389			=item ($real, $cpu) = $state->times
390
391			Returns the real time and cpu times spent in the given C<$state>. See
392			C<Coro::State::enable_times> for more info.
393
394	root	1.127	=item $clone = $state->clone
395
396	root	1.136	This exciting method takes a Coro::State object and clones it, i.e., it
397			creates a copy. This makes it possible to restore a state more than once,
398			and even return to states that have returned or have been terminated.
399	root	1.127
400	root	1.136	Since its only known purpose is for intellectual self-gratification, and
401	root	1.127	because it is a difficult piece of code, it is not enabled by default, and
402			not supported.
403
404	root	1.140	Here are a few little-known facts: First, coros are full/true/real
405	root	1.136	continuations. Secondly Coro::State objects (without clone) are first
406			class continuations. Thirdly, nobody has ever found a use for the full
407			power of call/cc that isn't better (faster, easier, more efficiently)
408			implemented differently, and nobody has yet found a useful control
409			construct that can't be implemented without it already, just much faster
410	root	1.138	and with fewer resources. And lastly, Scheme's call/cc doesn't support
411			using call/cc to implement threads.
412	root	1.136
413			Among the games you can play with this is implementing a scheme-like
414			call-with-current-continuation, as the following code does (well, with
415			small differences).
416
417			# perl disassociates from local lexicals on frame exit,
418			# so use a global variable for return values.
419			my @ret;
420	root	1.127
421	root	1.136	sub callcc($@) {
422	root	1.129	my ($func, @arg) = @_;
423	root	1.127
424	root	1.136	my $continuation = new Coro::State;
425			$continuation->transfer (new Coro::State sub {
426	root	1.129	my $escape = sub {
427	root	1.136	@ret = @_;
428			Coro::State->new->transfer ($continuation->clone);
429	root	1.129	};
430			$escape->($func->($escape, @arg));
431	root	1.136	});
432	root	1.127
433	root	1.136	my @ret_ = @ret; @ret = ();
434			wantarray ? @ret_ : pop @ret_
435	root	1.127	}
436
437	root	1.136	Which could be used to implement a loop like this:
438
439			async {
440			my $n;
441			my $l = callcc sub { $_[0] };
442
443			$n++;
444			print "iteration $n\n";
445
446			$l->($l) unless $n == 10;
447			};
448
449			If you find this confusing, then you already understand the coolness of
450			call/cc: It can turn anything into spaghetti code real fast.
451	root	1.127
452			Besides, call/cc is much less useful in a Perl-like dynamic language (with
453			references, and its scoping rules) then in, say, scheme.
454
455	root	1.130	Now, the known limitations of C<clone>:
456	root	1.127
457	root	1.140	It probably only works on perl 5.10; it cannot clone a coro inside
458	root	1.129	the substition operator (but windows perl can't fork from there either)
459			and some other contexts, and C<abort ()> is the preferred mechanism to
460			signal errors. It cannot clone a state that has a c context attached
461	root	1.131	(implementing clone on the C level is too hard for me to even try),
462	root	1.140	which rules out calling call/cc from the main coro. It cannot
463	root	1.131	clone a context that hasn't even been started yet. It doesn't work with
464	root	1.130	C<-DDEBUGGING> (but what does). It probably also leaks, and sometimes
465			triggers a few assertions inside Coro. Most of these limitations are
466			fixable with some effort, but that's pointless just to make a point that
467			it could be done.
468	root	1.127
469	root	1.136	The current implementation could without doubt be optimised to be a
470			constant-time operation by doing lazy stack copying, if somebody were
471			insane enough to invest the time.
472
473	root	1.1	=cut
474
475	root	1.115	# used by Coro::Debug only atm.
476	root	1.75	sub debug_desc {
477			$_[0]{desc}
478			}
479
480	root	1.122	# for very deep reasons, we must initialise $Coro::main here.
481
482			{
483			package Coro;
484
485	root	1.140	our $main; # main coro
486			our $current; # current coro
487	root	1.122
488	root	1.151	$main = Coro::new Coro::;
489	root	1.122
490			$main->{desc} = "[main::]";
491
492			# maybe some other module used Coro::Specific before...
493			$main->{_specific} = $current->{_specific}
494			if $current;
495
496			_set_current $main;
497			}
498
499	root	1.155	# we also make sure we have Coro::AnyEvent when AnyEvent is used,
500			# without loading or initialising AnyEvent
501			if (defined $AnyEvent::MODEL) {
502			require Coro::AnyEvent;
503			} else {
504			push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
505			}
506
507	root	1.1	1;
508
509			=back
510
511			=head1 BUGS
512
513	root	1.5	This module is not thread-safe. You must only ever use this module from
514	root	1.94	the same thread (this requirement might be removed in the future).
515	root	1.1
516			=head1 SEE ALSO
517
518			L<Coro>.
519
520			=head1 AUTHOR
521
522	root	1.41	Marc Lehmann <schmorp@schmorp.de>
523	root	1.39	http://home.schmorp.de/
524	root	1.1
525			=cut
526