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 - implements the Perl Multicore Specification

=head1 SYNOPSIS

  #include "perlmulticore.h"

  // in your XS function:

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

  // optional, in BOOT section:

  perlmulticore_advertise ();

=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 ADVERTISING MULTICORE API SUPPORT

To help users find out whether a particular build of your module is, in
fact, multicore enabled, you can invoke the C<perlmulticore_advertise>
macro in your C<BOOT:> section, e.g.:


   MODULE = My::Mod    PACKAGE = My::Mod::Pkg

   BOOT:
      perlmulticore_advertise ();

What this does is set the C<$My::Mod::PERLMULTICORE_SUPPORT> variable to
the major API version * 1000 + minor version, for example, version C<1002>
introduced this feature.

For this to work, the C<cv> parameter passed to C<BOOT:> must still be
in scope. To ensure this, either invoke the macro early in your C<BOOT:>
section, or don't declare a local variable called C<cv>, either of which
should be easy to do.

Note that this is I<optional>, so you don't have to do that.


=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 2 /* bumped on every change */

#if PERL_MULTICORE_DISABLE

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

#else

START_EXTERN_C

/* 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);

static 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)
{
}

static const char perl_multicore_api_key[] = "perl_multicore_api";

/* 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_key,
                           sizeof (perl_multicore_api_key) - 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 */
      #ifdef NEWSV
      SV *api_sv = NEWSV (0, sizeof (*perl_multicore_api));
      #else
      SV *api_sv = newSV (   sizeof (*perl_multicore_api));
      #endif
      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 ();
}

#define perlmulticore_advertise() \
  sv_setiv (get_sv ( \
      form ("%s::PERLMULTICORE_SUPPORT", HvNAME (GvSTASH (CvGV (cv)))), \
      GV_ADD | GV_ADDMULTI), \
    PERL_MULTICORE_MAJOR * 1000 + PERL_MULTICORE_MINOR); \

END_EXTERN_C

#endif

#endif

Revision:	1.6
Committed:	Sun Mar 3 13:06:01 2019 UTC (5 years, 3 months ago) by root
Content type:	text/plain
Branch:	MAIN
Changes since 1.5:	+38 -3 lines
Log Message:	* empty log message *
#	Content
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 - implements the Perl Multicore Specification
19
20	=head1 SYNOPSIS
21
22	#include "perlmulticore.h"
23
24	// in your XS function:
25
26	perlinterp_release ();
27	do_the_C_thing ();
28	perlinterp_acquire ();
29
30	// optional, in BOOT section:
31
32	perlmulticore_advertise ();
33
34	=head1 DESCRIPTION
35
36	This documentation is the abridged version of the full documention at
37	L<http://perlmulticore.schmorp.de/>. It's recommended to go there instead
38	of reading this document.
39
40	This header file implements a very low overhead (both in code and runtime)
41	mechanism for XS modules to allow re-use of the perl interpreter for other
42	threads while doing some lengthy operation, such as cryptography, SQL
43	queries, disk I/O and so on.
44
45	The newest version of the header file itself, can be downloaded from
46	L<http://perlmulticore.schmorp.de/perlmulticore.h>.
47
48	=head1 HOW DO I USE THIS IN MY MODULES?
49
50	The usage is very simple - you include this header file in your XS module. Then, before you
51	do your lengthy operation, you release the perl interpreter:
52
53	perlinterp_release ();
54
55	And when you are done with your computation, you acquire it again:
56
57	perlinterp_acquire ();
58
59	And that's it. This doesn't load any modules and consists of only a few
60	machine instructions when no module to take advantage of it is loaded.
61
62	More documentation and examples can be found at the perl multicore site at
63	L<http://perlmulticore.schmorp.de>.
64
65	=head1 THE HARD AND FAST RULES
66
67	As with everything, there are a number of rules to follow.
68
69	=over 4
70
71	=item I<Never> touch any perl data structures after calling C<perlinterp_release>.
72
73	Anything perl is completely off-limits after C<perlinterp_release>, until
74	you call C<perlinterp_acquire>, after which you can access perl stuff
75	again.
76
77	That includes anything in the perl interpreter that you didn't prove to be
78	safe, and didn't prove to be safe in older and future versions of perl:
79	global variables, local perl scalars, even if you are sure nobody accesses
80	them and you only try to "read" their value.
81
82	=item I<Always> call C<perlinterp_release> and C<perlinterp_acquire> in pairs.
83
84	For each C<perlinterp_release> call there must be a C<perlinterp_acquire>
85	call. They don't have to be in the same function, and you can have
86	multiple calls to them, as long as every C<perlinterp_release> call is
87	followed by exactly one C<perlinterp_acquire> call at runtime.
88
89	=item I<Never> nest calls to C<perlinterp_release> and C<perlinterp_acquire>.
90
91	That simply means that after calling C<perlinterp_release>, you must
92	call C<perlinterp_acquire> before calling C<perlinterp_release>
93	again. Likewise, after C<perlinterp_acquire>, you can call
94	C<perlinterp_release> but not another C<perlinterp_acquire>.
95
96	=item I<Always> call C<perlinterp_release> first.
97
98	You I<must not> call C<perlinterp_acquire> without having called
99	C<perlinterp_release> before.
100
101	=item I<Never> underestimate threads.
102
103	While it's easy to add parallel execution ability to your XS module, it
104	doesn't mean it is safe. After you release the perl interpreter, it's
105	perfectly possible that it will call your XS function in another thread,
106	even while your original function still executes. In other words: your C
107	code must be thread safe, and if you use any library, that library must be
108	thread-safe, too.
109
110	Always assume that the code between C<perlinterp_release> and
111	C<perlinterp_acquire> is executed in parallel on multiple CPUs at the same
112	time.
113
114	=back
115
116
117	=head1 DISABLING PERL MULTICORE AT COMPILE TIME
118
119	You can disable the complete perl multicore API by defining the
120	symbol C<PERL_MULTICORE_DISABLE> to C<1> (e.g. by specifying
121	F<-DPERL_MULTICORE_DISABLE> as compiler argument).
122
123	This could be added to perl's C<CPPFLAGS> when configuring perl on
124	platforms that do not support threading at all for example.
125
126
127	=head1 ADVERTISING MULTICORE API SUPPORT
128
129	To help users find out whether a particular build of your module is, in
130	fact, multicore enabled, you can invoke the C<perlmulticore_advertise>
131	macro in your C<BOOT:> section, e.g.:
132
133
134	MODULE = My::Mod PACKAGE = My::Mod::Pkg
135
136	BOOT:
137	perlmulticore_advertise ();
138
139	What this does is set the C<$My::Mod::PERLMULTICORE_SUPPORT> variable to
140	the major API version * 1000 + minor version, for example, version C<1002>
141	introduced this feature.
142
143	For this to work, the C<cv> parameter passed to C<BOOT:> must still be
144	in scope. To ensure this, either invoke the macro early in your C<BOOT:>
145	section, or don't declare a local variable called C<cv>, either of which
146	should be easy to do.
147
148	Note that this is I<optional>, so you don't have to do that.
149
150
151	=head1 AUTHOR
152
153	Marc A. Lehmann <perlmulticore@schmorp.de>
154	http://perlmulticore.schmorp.de/
155
156	=head1 LICENSE
157
158	The F<perlmulticore.h> header file is put into the public
159	domain. Where this is legally not possible, or at your
160	option, it can be licensed under creativecommons CC0
161	license: L<https://creativecommons.org/publicdomain/zero/1.0/>.
162
163	=cut
164
165	*/
166
167	#define PERL_MULTICORE_MAJOR 1 /* bumped on incompatible changes */
168	#define PERL_MULTICORE_MINOR 2 /* bumped on every change */
169
170	#if PERL_MULTICORE_DISABLE
171
172	#define perlinterp_release() do { } while (0)
173	#define perlinterp_acquire() do { } while (0)
174	#define perlmulticore_advertise() do { } while (0)
175
176	#else
177
178	START_EXTERN_C
179
180	/* this struct is shared between all modules, and currently */
181	/* contain only the two function pointers for release/acquire */
182	struct perl_multicore_api
183	{
184	void (*pmapi_release)(void);
185	void (*pmapi_acquire)(void);
186	};
187
188	static void perl_multicore_init (void);
189
190	static const struct perl_multicore_api perl_multicore_api_init
191	= { perl_multicore_init, 0 };
192
193	static struct perl_multicore_api *perl_multicore_api
194	= (struct perl_multicore_api *)&perl_multicore_api_init;
195
196	#define perlinterp_release() perl_multicore_api->pmapi_release ()
197	#define perlinterp_acquire() perl_multicore_api->pmapi_acquire ()
198
199	/* this is the release/acquire implementation used as fallback */
200	static void
201	perl_multicore_nop (void)
202	{
203	}
204
205	static const char perl_multicore_api_key[] = "perl_multicore_api";
206
207	/* this is the initial implementation of "release" - it initialises */
208	/* the api and then calls the real release function */
209	static void
210	perl_multicore_init (void)
211	{
212	dTHX;
213
214	/* check for existing API struct in PL_modglobal */
215	SV **api_svp = hv_fetch (PL_modglobal, perl_multicore_api_key,
216	sizeof (perl_multicore_api_key) - 1, 1);
217
218	if (SvPOKp (*api_svp))
219	perl_multicore_api = (struct perl_multicore_api )SvPVX (api_svp); /* we have one, use the existing one */
220	else
221	{
222	/* create a new one with a dummy nop implementation */
223	#ifdef NEWSV
224	SV api_sv = NEWSV (0, sizeof (perl_multicore_api));
225	#else
226	SV api_sv = newSV ( sizeof (perl_multicore_api));
227	#endif
228	SvCUR_set (api_sv, sizeof (*perl_multicore_api));
229	SvPOK_only (api_sv);
230	perl_multicore_api = (struct perl_multicore_api *)SvPVX (api_sv);
231	perl_multicore_api->pmapi_release =
232	perl_multicore_api->pmapi_acquire = perl_multicore_nop;
233	*api_svp = api_sv;
234	}
235
236	/* call the real (or dummy) implementation now */
237	perlinterp_release ();
238	}
239
240	#define perlmulticore_advertise() \
241	sv_setiv (get_sv ( \
242	form ("%s::PERLMULTICORE_SUPPORT", HvNAME (GvSTASH (CvGV (cv)))), \
243	GV_ADD \| GV_ADDMULTI), \
244	PERL_MULTICORE_MAJOR * 1000 + PERL_MULTICORE_MINOR); \
245
246	END_EXTERN_C
247
248	#endif
249
250	#endif
251