perlmulticore/perlmulticore.h

/*
 * Author: Marc A. Lehmann <xsthreadpool@schmorp.de>
 * License: public domain, or where this is not possible/at your option,
 *          CC0 (https://creativecommons.org/publicdomain/zero/1.0/)
 *
 * Full documentation can be found at http://perlmulticore.schmorp.de/
 * The newest version of this header can be downloaded from
 * http://perlmulticore.schmorp.de/perlmulticore.h
 */

#ifndef PERL_MULTICORE_H
#define PERL_MULTICORE_H

/*

=head1 NAME

perlmulticore.h - the Perl Multicore Specification and Implementation

=head1 SYNOPSIS

  #include "perlmultiore.h"

  // in your XS function:

  perlinterp_release ();
  do_the_C_thing ();
  perlinterp_acquire ();

=head1 DESCRIPTION

This documentation is the abridged version of the full documention at
L<http://perlmulticore.schmorp.de/>. It's recommended to go there instead
of reading this document.

This header file implements a very low overhead (both in code and runtime)
mechanism for XS modules to allow re-use of the perl interpreter for other
threads while doing some lengthy operation, such as cryptography, SQL
queries, disk I/O and so on.

The newest version of the header file itself, can be downloaded from
L<http://perlmulticore.schmorp.de/perlmulticore.h>.

=head1 HOW DO I USE THIS IN MY MODULES?

The usage is very simple - you include this header file in your XS module. Then, before you
do your lengthy operation, you release the perl interpreter:

   perlinterp_release ();

And when you are done with your computation, you acquire it again:

   perlinterp_acquire ();

And that's it. This doesn't load any modules and consists of only a few
machine instructions when no module to take advantage of it is loaded.

More documentation and examples can be found at the perl multicore site at
L<http://perlmulticore.schmorp.de>.

=head1 THE HARD AND FAST RULES

As with everything, there are a number of rules to follow.

=over 4

=item I<Never> touch any perl data structures after calling C<perlinterp_release>.

Anything perl is completely off-limits after C<perlinterp_release>, until
you call C<perlinterp_acquire>, after which you can access perl stuff
again.

That includes anything in the perl interpreter that you didn't prove to be
safe, and didn't prove to be safe in older and future versions of perl:
global variables, local perl scalars, even if you are sure nobody accesses
them and you only try to "read" their value.

=item I<Always> call C<perlinterp_release> and C<perlinterp_acquire> in pairs.

For each C<perlinterp_release> call there must be a C<perlinterp_acquire>
call. They don't have to be in the same function, and you can have
multiple calls to them, as long as every C<perlinterp_release> call is
followed by exactly one C<perlinterp_acquire> call at runtime.

=item I<Never> nest calls to C<perlinterp_release> and C<perlinterp_acquire>.

That simply means that after calling C<perlinterp_release>, you must
call C<perlinterp_acquire> before calling C<perlinterp_release>
again. Likewise, after C<perlinterp_acquire>, you can call
C<perlinterp_release> but not another C<perlinterp_acquire>.

=item I<Always> call C<perlinterp_release> first.

You I<must not> call C<perlinterp_acquire> without having called
C<perlinterp_release> before.

=item I<Never> underestimate threads.

While it's easy to add parallel execution ability to your XS module, it
doesn't mean it is safe. After you release the perl interpreter, it's
perfectly possible that it will call your XS function in another thread,
even while your original function still executes. In other words: your C
code must be thread safe, and if you use any library, that library must be
thread-safe, too.

Always assume that the code between C<perlinterp_release> and
C<perlinterp_acquire> is executed in parallel on multiple CPUs at the same
time.

=back


=head1 DISABLING PERL MULTICORE AT COMPILE TIME

You can disable the complete perl multicore API by defining the
symbol C<PERL_MULTICORE_DISABLE> to C<1> (e.g. by specifying
F<-DPERL_MULTICORE_DISABLE> as compiler argument).

This could be added to perl's C<CPPFLAGS> when configuring perl on
platforms that do not support threading at all for example.


=head1 AUTHOR

   Marc A. Lehmann <perlmulticore@schmorp.de>
   http://perlmulticore.schmorp.de/

=head1 LICENSE

The F<perlmulticore.h> header file is put into the public
domain. Where this is legally not possible, or at your
option, it can be licensed under creativecommons CC0
license: L<https://creativecommons.org/publicdomain/zero/1.0/>.

=cut

*/

#define PERL_MULTICORE_MAJOR 1 /* bumped on incompatible changes */
#define PERL_MULTICORE_MINOR 0 /* bumped on every change */

#if PERL_MULTICORE_DISABLE

#define perlinterp_release() do { } while (0)
#define perlinterp_acquire() do { } while (0)

#else

/* this struct is shared between all modules, and currently */
/* contain only the two function pointers for release/acquire */
struct perl_multicore_api
{
  void (*pmapi_release)(void);
  void (*pmapi_acquire)(void);
};

static void perl_multicore_init (void);

const struct perl_multicore_api perl_multicore_api_init = { perl_multicore_init, 0 };

static struct perl_multicore_api *perl_multicore_api
   = (struct perl_multicore_api *)&perl_multicore_api_init;

#define perlinterp_release() perl_multicore_api->pmapi_release ()
#define perlinterp_acquire() perl_multicore_api->pmapi_acquire ()

/* this is the release/acquire implementation used as fallback */
static void
perl_multicore_nop (void)
{
}

/* this is the initial implementation of "release" - it initialises */
/* the api and then calls the real release function */
static void
perl_multicore_init (void)
{
  dTHX;

  /* check for existing API struct in PL_modglobal */
  SV **api_svp = hv_fetch (PL_modglobal, "perl_multicore_api", sizeof ("perl_multicore_api") - 1, 1);

  if (SvPOKp (*api_svp))
    perl_multicore_api = (struct perl_multicore_api *)SvPVX (*api_svp); /* we have one, use the existing one */
  else
    {
      /* create a new one with a dummy nop implementation */
      SV *api_sv = NEWSV (0, sizeof (*perl_multicore_api));
      SvCUR_set (api_sv, sizeof (*perl_multicore_api));
      SvPOK_only (api_sv);
      perl_multicore_api = (struct perl_multicore_api *)SvPVX (api_sv);
      perl_multicore_api->pmapi_release =
      perl_multicore_api->pmapi_acquire = perl_multicore_nop;
      *api_svp = api_sv;
    }

  /* call the real (or dummy) implementation now */
  perlinterp_release ();
}

#endif

#endif
Revision:	1.1
Committed:	Thu Jul 2 22:39:56 2015 UTC (9 years ago) by root
Content type:	text/plain
Branch:	MAIN
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	/*
2			* Author: Marc A. Lehmann <xsthreadpool@schmorp.de>
3			* License: public domain, or where this is not possible/at your option,
4			* CC0 (https://creativecommons.org/publicdomain/zero/1.0/)
5			*
6			* Full documentation can be found at http://perlmulticore.schmorp.de/
7			* The newest version of this header can be downloaded from
8			* http://perlmulticore.schmorp.de/perlmulticore.h
9			*/
10
11			#ifndef PERL_MULTICORE_H
12			#define PERL_MULTICORE_H
13
14			/*
15
16			=head1 NAME
17
18			perlmulticore.h - the Perl Multicore Specification and Implementation
19
20			=head1 SYNOPSIS
21
22			#include "perlmultiore.h"
23
24			// in your XS function:
25
26			perlinterp_release ();
27			do_the_C_thing ();
28			perlinterp_acquire ();
29
30			=head1 DESCRIPTION
31
32			This documentation is the abridged version of the full documention at
33			L<http://perlmulticore.schmorp.de/>. It's recommended to go there instead
34			of reading this document.
35
36			This header file implements a very low overhead (both in code and runtime)
37			mechanism for XS modules to allow re-use of the perl interpreter for other
38			threads while doing some lengthy operation, such as cryptography, SQL
39			queries, disk I/O and so on.
40
41			The newest version of the header file itself, can be downloaded from
42			L<http://perlmulticore.schmorp.de/perlmulticore.h>.
43
44			=head1 HOW DO I USE THIS IN MY MODULES?
45
46			The usage is very simple - you include this header file in your XS module. Then, before you
47			do your lengthy operation, you release the perl interpreter:
48
49			perlinterp_release ();
50
51			And when you are done with your computation, you acquire it again:
52
53			perlinterp_acquire ();
54
55			And that's it. This doesn't load any modules and consists of only a few
56			machine instructions when no module to take advantage of it is loaded.
57
58			More documentation and examples can be found at the perl multicore site at
59			L<http://perlmulticore.schmorp.de>.
60
61			=head1 THE HARD AND FAST RULES
62
63			As with everything, there are a number of rules to follow.
64
65			=over 4
66
67			=item I<Never> touch any perl data structures after calling C<perlinterp_release>.
68
69			Anything perl is completely off-limits after C<perlinterp_release>, until
70			you call C<perlinterp_acquire>, after which you can access perl stuff
71			again.
72
73			That includes anything in the perl interpreter that you didn't prove to be
74			safe, and didn't prove to be safe in older and future versions of perl:
75			global variables, local perl scalars, even if you are sure nobody accesses
76			them and you only try to "read" their value.
77
78			=item I<Always> call C<perlinterp_release> and C<perlinterp_acquire> in pairs.
79
80			For each C<perlinterp_release> call there must be a C<perlinterp_acquire>
81			call. They don't have to be in the same function, and you can have
82			multiple calls to them, as long as every C<perlinterp_release> call is
83			followed by exactly one C<perlinterp_acquire> call at runtime.
84
85			=item I<Never> nest calls to C<perlinterp_release> and C<perlinterp_acquire>.
86
87			That simply means that after calling C<perlinterp_release>, you must
88			call C<perlinterp_acquire> before calling C<perlinterp_release>
89			again. Likewise, after C<perlinterp_acquire>, you can call
90			C<perlinterp_release> but not another C<perlinterp_acquire>.
91
92			=item I<Always> call C<perlinterp_release> first.
93
94			You I<must not> call C<perlinterp_acquire> without having called
95			C<perlinterp_release> before.
96
97			=item I<Never> underestimate threads.
98
99			While it's easy to add parallel execution ability to your XS module, it
100			doesn't mean it is safe. After you release the perl interpreter, it's
101			perfectly possible that it will call your XS function in another thread,
102			even while your original function still executes. In other words: your C
103			code must be thread safe, and if you use any library, that library must be
104			thread-safe, too.
105
106			Always assume that the code between C<perlinterp_release> and
107			C<perlinterp_acquire> is executed in parallel on multiple CPUs at the same
108			time.
109
110			=back
111
112
113			=head1 DISABLING PERL MULTICORE AT COMPILE TIME
114
115			You can disable the complete perl multicore API by defining the
116			symbol C<PERL_MULTICORE_DISABLE> to C<1> (e.g. by specifying
117			F<-DPERL_MULTICORE_DISABLE> as compiler argument).
118
119			This could be added to perl's C<CPPFLAGS> when configuring perl on
120			platforms that do not support threading at all for example.
121
122
123			=head1 AUTHOR
124
125			Marc A. Lehmann <perlmulticore@schmorp.de>
126			http://perlmulticore.schmorp.de/
127
128			=head1 LICENSE
129
130			The F<perlmulticore.h> header file is put into the public
131			domain. Where this is legally not possible, or at your
132			option, it can be licensed under creativecommons CC0
133			license: L<https://creativecommons.org/publicdomain/zero/1.0/>.
134
135			=cut
136
137			*/
138
139			#define PERL_MULTICORE_MAJOR 1 /* bumped on incompatible changes */
140			#define PERL_MULTICORE_MINOR 0 /* bumped on every change */
141
142			#if PERL_MULTICORE_DISABLE
143
144			#define perlinterp_release() do { } while (0)
145			#define perlinterp_acquire() do { } while (0)
146
147			#else
148
149			/* this struct is shared between all modules, and currently */
150			/* contain only the two function pointers for release/acquire */
151			struct perl_multicore_api
152			{
153			void (*pmapi_release)(void);
154			void (*pmapi_acquire)(void);
155			};
156
157			static void perl_multicore_init (void);
158
159			const struct perl_multicore_api perl_multicore_api_init = { perl_multicore_init, 0 };
160
161			static struct perl_multicore_api *perl_multicore_api
162			= (struct perl_multicore_api *)&perl_multicore_api_init;
163
164			#define perlinterp_release() perl_multicore_api->pmapi_release ()
165			#define perlinterp_acquire() perl_multicore_api->pmapi_acquire ()
166
167			/* this is the release/acquire implementation used as fallback */
168			static void
169			perl_multicore_nop (void)
170			{
171			}
172
173			/* this is the initial implementation of "release" - it initialises */
174			/* the api and then calls the real release function */
175			static void
176			perl_multicore_init (void)
177			{
178			dTHX;
179
180			/* check for existing API struct in PL_modglobal */
181			SV **api_svp = hv_fetch (PL_modglobal, "perl_multicore_api", sizeof ("perl_multicore_api") - 1, 1);
182
183			if (SvPOKp (*api_svp))
184			perl_multicore_api = (struct perl_multicore_api )SvPVX (api_svp); /* we have one, use the existing one */
185			else
186			{
187			/* create a new one with a dummy nop implementation */
188			SV api_sv = NEWSV (0, sizeof (perl_multicore_api));
189			SvCUR_set (api_sv, sizeof (*perl_multicore_api));
190			SvPOK_only (api_sv);
191			perl_multicore_api = (struct perl_multicore_api *)SvPVX (api_sv);
192			perl_multicore_api->pmapi_release =
193			perl_multicore_api->pmapi_acquire = perl_multicore_nop;
194			*api_svp = api_sv;
195			}
196
197			/* call the real (or dummy) implementation now */
198			perlinterp_release ();
199			}
200
201			#endif
202
203			#endif