trunk/doc/pcrejit.3

.TH PCREJIT 3
.SH NAME
PCRE - Perl-compatible regular expressions
.SH "PCRE JUST-IN-TIME COMPILER SUPPORT"
.rs
.sp
Just-in-time compiling is a heavyweight optimization that can greatly speed up
pattern matching. However, it comes at the cost of extra processing before the
match is performed. Therefore, it is of most benefit when the same pattern is
going to be matched many times. This does not necessarily mean many calls of
\fPpcre_exec()\fP; if the pattern is not anchored, matching attempts may take
place many times at various positions in the subject, even for a single call to
\fBpcre_exec()\fP. If the subject string is very long, it may still pay to use
JIT for one-off matches.
.P
JIT support applies only to the traditional matching function,
\fBpcre_exec()\fP. It does not apply when \fBpcre_dfa_exec()\fP is being used.
The code for this support was written by Zoltan Herczeg.
.
.
.SH "AVAILABILITY OF JIT SUPPORT"
.rs
.sp
JIT support is an optional feature of PCRE. The "configure" option --enable-jit
(or equivalent CMake option) must be set when PCRE is built if you want to use
JIT. The support is limited to the following hardware platforms:
.sp
  ARM v5, v7, and Thumb2
  Intel x86 32-bit and 64-bit
  MIPS 32-bit
  Power PC 32-bit and 64-bit (experimental)
.sp
The Power PC support is designated as experimental because it has not been 
fully tested. If --enable-jit is set on an unsupported platform, compilation
fails.
.P
A program can tell if JIT support is available by calling \fBpcre_config()\fP
with the PCRE_CONFIG_JIT option. The result is 1 when JIT is available, and 0
otherwise. However, a simple program does not need to check this in order to
use JIT. The API is implemented in a way that falls back to the ordinary PCRE
code if JIT is not available.
.
.
.SH "SIMPLE USE OF JIT"
.rs
.sp
You have to do two things to make use of the JIT support in the simplest way:
.sp
  (1) Call \fBpcre_study()\fP with the PCRE_STUDY_JIT_COMPILE option for
      each compiled pattern, and pass the resulting \fBpcre_extra\fP block to
      \fBpcre_exec()\fP.
.sp
  (2) Use \fBpcre_free_study()\fP to free the \fBpcre_extra\fP block when it is
      no longer needed instead of just freeing it yourself. This
      ensures that any JIT data is also freed.
.sp
In some circumstances you may need to call additional functions. These are
described in the section entitled
.\" HTML <a href="#stackcontrol">
.\" </a>
"Controlling the JIT stack"
.\"
below.
.P
If JIT support is not available, PCRE_STUDY_JIT_COMPILE is ignored, and no JIT
data is set up. Otherwise, the compiled pattern is passed to the JIT compiler,
which turns it into machine code that executes much faster than the normal
interpretive code. When \fBpcre_exec()\fP is passed a \fBpcre_extra\fP block
containing a pointer to JIT code, it obeys that instead of the normal code. The
result is identical, but the code runs much faster.
.P
There are some \fBpcre_exec()\fP options that are not supported for JIT
execution. There are also some pattern items that JIT cannot handle. Details
are given below. In both cases, execution automatically falls back to the
interpretive code.
.P
If the JIT compiler finds an unsupported item, no JIT data is generated. You
can find out if JIT execution is available after studying a pattern by calling
\fBpcre_fullinfo()\fP with the PCRE_INFO_JIT option. A result of 1 means that
JIT compilation was successful. A result of 0 means that JIT support is not
available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE, or the
JIT compiler was not able to handle the pattern.
.P
Once a pattern has been studied, with or without JIT, it can be used as many
times as you like for matching different subject strings.
.
.
.SH "UNSUPPORTED OPTIONS AND PATTERN ITEMS"
.rs
.sp
The only \fBpcre_exec()\fP options that are supported for JIT execution are
PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and
PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not
supported.
.P
The unsupported pattern items are:
.sp
  \eC            match a single byte, even in UTF-8 mode
  (?Cn)          callouts
  (?(<name>)...  conditional test on setting of a named subpattern
  (?(R)...       conditional test on whole pattern recursion
  (?(Rn)...      conditional test on recursion, by number
  (?(R&name)...  conditional test on recursion, by name
  (*COMMIT)      )
  (*MARK)        )
  (*PRUNE)       ) the backtracking control verbs
  (*SKIP)        )
  (*THEN)        )
.sp
Support for some of these may be added in future.
.
.
.SH "RETURN VALUES FROM JIT EXECUTION"
.rs
.sp
When a pattern is matched using JIT execution, the return values are the same
as those given by the interpretive \fBpcre_exec()\fP code, with the addition of
one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means that the memory used
for the JIT stack was insufficient. See
.\" HTML <a href="#stackcontrol">
.\" </a>
"Controlling the JIT stack"
.\"
below for a discussion of JIT stack usage. For compatibility with the
interpretive \fBpcre_exec()\fP code, no more than two-thirds of the
\fIovector\fP argument is used for passing back captured substrings.
.P
The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if searching a
very large pattern tree goes on for too long, as it is in the same circumstance
when JIT is not used, but the details of exactly what is counted are not the
same. The PCRE_ERROR_RECURSIONLIMIT error code is never returned by JIT
execution.
.
.
.SH "SAVING AND RESTORING COMPILED PATTERNS"
.rs
.sp
The code that is generated by the JIT compiler is architecture-specific, and is
also position dependent. For those reasons it cannot be saved (in a file or
database) and restored later like the bytecode and other data of a compiled
pattern. Saving and restoring compiled patterns is not something many people
do. More detail about this facility is given in the
.\" HREF
\fBpcreprecompile\fP
.\"
documentation. It should be possible to run \fBpcre_study()\fP on a saved and
restored pattern, and thereby recreate the JIT data, but because JIT
compilation uses significant resources, it is probably not worth doing this;
you might as well recompile the original pattern.
.
.
.\" HTML <a name="stackcontrol"></a>
.SH "CONTROLLING THE JIT STACK"
.rs
.sp
When the compiled JIT code runs, it needs a block of memory to use as a stack.
By default, it uses 32K on the machine stack. However, some large or
complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT
is given when there is not enough stack. Three functions are provided for
managing blocks of memory for use as JIT stacks.
.P
The \fBpcre_jit_stack_alloc()\fP function creates a JIT stack. Its arguments
are a starting size and a maximum size, and it returns a pointer to an opaque
structure of type \fBpcre_jit_stack\fP, or NULL if there is an error. The
\fBpcre_jit_stack_free()\fP function can be used to free a stack that is no
longer needed. (For the technically minded: the address space is allocated by
mmap or VirtualAlloc.)
.P
JIT uses far less memory for recursion than the interpretive code,
and a maximum stack size of 512K to 1M should be more than enough for any
pattern.
.P
The \fBpcre_assign_jit_stack()\fP function specifies which stack JIT code
should use. Its arguments are as follows:
.sp
  pcre_extra         *extra
  pcre_jit_callback  callback
  void               *data
.sp
The \fIextra\fP argument must be the result of studying a pattern with
PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the other two
options:
.sp
  (1) If \fIcallback\fP is NULL and \fIdata\fP is NULL, an internal 32K block
      on the machine stack is used.
.sp
  (2) If \fIcallback\fP is NULL and \fIdata\fP is not NULL, \fIdata\fP must be
      a valid JIT stack, the result of calling \fBpcre_jit_stack_alloc()\fP.
.sp
  (3) If \fIcallback\fP not NULL, it must point to a function that is called
      with \fIdata\fP as an argument at the start of matching, in order to
      set up a JIT stack. If the result is NULL, the internal 32K stack
      is used; otherwise the return value must be a valid JIT stack,
      the result of calling \fBpcre_jit_stack_alloc()\fP.
.sp
You may safely assign the same JIT stack to more than one pattern, as long as
they are all matched sequentially in the same thread. In a multithread
application, each thread must use its own JIT stack.
.P
Strictly speaking, even more is allowed. You can assign the same stack to any
number of patterns as long as they are not used for matching by multiple
threads at the same time. For example, you can assign the same stack to all
compiled patterns, and use a global mutex in the callback to wait until the
stack is available for use. However, this is an inefficient solution, and
not recommended.
.P
This is a suggestion for how a typical multithreaded program might operate:
.sp
  During thread initalization
    thread_local_var = pcre_jit_stack_alloc(...)
.sp
  During thread exit
    pcre_jit_stack_free(thread_local_var)
.sp
  Use a one-line callback function
    return thread_local_var
.sp
All the functions described in this section do nothing if JIT is not available,
and \fBpcre_assign_jit_stack()\fP does nothing unless the \fBextra\fP argument
is non-NULL and points to a \fBpcre_extra\fP block that is the result of a
successful study with PCRE_STUDY_JIT_COMPILE.
.
.
.SH "EXAMPLE CODE"
.rs
.sp
This is a single-threaded example that specifies a JIT stack without using a
callback.
.sp
  int rc;
  int ovector[30];
  pcre *re;
  pcre_extra *extra;
  pcre_jit_stack *jit_stack;
.sp
  re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
  /* Check for errors */
  extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
  jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024);
  /* Check for error (NULL) */
  pcre_assign_jit_stack(extra, NULL, jit_stack);
  rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
  /* Check results */
  pcre_free(re);
  pcre_free_study(extra);
  pcre_jit_stack_free(jit_stack);
.sp
.
.
.SH "SEE ALSO"
.rs
.sp
\fBpcreapi\fP(3)
.
.
.SH AUTHOR
.rs
.sp
.nf
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
.fi
.
.
.SH REVISION
.rs
.sp
.nf
Last updated: 05 October 2011
Copyright (c) 1997-2011 University of Cambridge.
.fi
1	ph10	678	.TH PCREJIT 3
2			.SH NAME
3			PCRE - Perl-compatible regular expressions
4			.SH "PCRE JUST-IN-TIME COMPILER SUPPORT"
5			.rs
6			.sp
7			Just-in-time compiling is a heavyweight optimization that can greatly speed up
8	ph10	683	pattern matching. However, it comes at the cost of extra processing before the
9			match is performed. Therefore, it is of most benefit when the same pattern is
10			going to be matched many times. This does not necessarily mean many calls of
11	ph10	678	\fPpcre_exec()\fP; if the pattern is not anchored, matching attempts may take
12			place many times at various positions in the subject, even for a single call to
13	ph10	683	\fBpcre_exec()\fP. If the subject string is very long, it may still pay to use
14	ph10	678	JIT for one-off matches.
15			.P
16	ph10	683	JIT support applies only to the traditional matching function,
17	ph10	678	\fBpcre_exec()\fP. It does not apply when \fBpcre_dfa_exec()\fP is being used.
18			The code for this support was written by Zoltan Herczeg.
19			.
20			.
21			.SH "AVAILABILITY OF JIT SUPPORT"
22			.rs
23			.sp
24			JIT support is an optional feature of PCRE. The "configure" option --enable-jit
25			(or equivalent CMake option) must be set when PCRE is built if you want to use
26			JIT. The support is limited to the following hardware platforms:
27			.sp
28			ARM v5, v7, and Thumb2
29	ph10	683	Intel x86 32-bit and 64-bit
30	ph10	678	MIPS 32-bit
31	ph10	717	Power PC 32-bit and 64-bit (experimental)
32	ph10	683	.sp
33	ph10	717	The Power PC support is designated as experimental because it has not been
34			fully tested. If --enable-jit is set on an unsupported platform, compilation
35			fails.
36	ph10	678	.P
37	ph10	683	A program can tell if JIT support is available by calling \fBpcre_config()\fP
38			with the PCRE_CONFIG_JIT option. The result is 1 when JIT is available, and 0
39	ph10	678	otherwise. However, a simple program does not need to check this in order to
40			use JIT. The API is implemented in a way that falls back to the ordinary PCRE
41			code if JIT is not available.
42			.
43			.
44			.SH "SIMPLE USE OF JIT"
45			.rs
46			.sp
47			You have to do two things to make use of the JIT support in the simplest way:
48			.sp
49			(1) Call \fBpcre_study()\fP with the PCRE_STUDY_JIT_COMPILE option for
50			each compiled pattern, and pass the resulting \fBpcre_extra\fP block to
51			\fBpcre_exec()\fP.
52	ph10	691	.sp
53	ph10	678	(2) Use \fBpcre_free_study()\fP to free the \fBpcre_extra\fP block when it is
54	ph10	691	no longer needed instead of just freeing it yourself. This
55	ph10	683	ensures that any JIT data is also freed.
56	ph10	678	.sp
57	ph10	683	In some circumstances you may need to call additional functions. These are
58	ph10	678	described in the section entitled
59			.\" HTML <a href="#stackcontrol">
60			.\" </a>
61			"Controlling the JIT stack"
62			.\"
63			below.
64			.P
65	ph10	683	If JIT support is not available, PCRE_STUDY_JIT_COMPILE is ignored, and no JIT
66			data is set up. Otherwise, the compiled pattern is passed to the JIT compiler,
67			which turns it into machine code that executes much faster than the normal
68			interpretive code. When \fBpcre_exec()\fP is passed a \fBpcre_extra\fP block
69			containing a pointer to JIT code, it obeys that instead of the normal code. The
70			result is identical, but the code runs much faster.
71	ph10	678	.P
72			There are some \fBpcre_exec()\fP options that are not supported for JIT
73	ph10	683	execution. There are also some pattern items that JIT cannot handle. Details
74			are given below. In both cases, execution automatically falls back to the
75	ph10	678	interpretive code.
76			.P
77			If the JIT compiler finds an unsupported item, no JIT data is generated. You
78			can find out if JIT execution is available after studying a pattern by calling
79			\fBpcre_fullinfo()\fP with the PCRE_INFO_JIT option. A result of 1 means that
80	ph10	693	JIT compilation was successful. A result of 0 means that JIT support is not
81	ph10	678	available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE, or the
82			JIT compiler was not able to handle the pattern.
83	ph10	707	.P
84	ph10	708	Once a pattern has been studied, with or without JIT, it can be used as many
85	ph10	707	times as you like for matching different subject strings.
86	ph10	678	.
87			.
88			.SH "UNSUPPORTED OPTIONS AND PATTERN ITEMS"
89			.rs
90			.sp
91			The only \fBpcre_exec()\fP options that are supported for JIT execution are
92	ph10	683	PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and
93			PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not
94	ph10	678	supported.
95			.P
96			The unsupported pattern items are:
97			.sp
98			\eC match a single byte, even in UTF-8 mode
99			(?Cn) callouts
100			(?(<name>)... conditional test on setting of a named subpattern
101	ph10	683	(?(R)... conditional test on whole pattern recursion
102	ph10	678	(?(Rn)... conditional test on recursion, by number
103			(?(R&name)... conditional test on recursion, by name
104			(*COMMIT) )
105			(*MARK) )
106			(*PRUNE) ) the backtracking control verbs
107			(*SKIP) )
108			(*THEN) )
109	ph10	683	.sp
110	ph10	678	Support for some of these may be added in future.
111			.
112			.
113			.SH "RETURN VALUES FROM JIT EXECUTION"
114			.rs
115			.sp
116	ph10	683	When a pattern is matched using JIT execution, the return values are the same
117			as those given by the interpretive \fBpcre_exec()\fP code, with the addition of
118			one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means that the memory used
119	ph10	678	for the JIT stack was insufficient. See
120			.\" HTML <a href="#stackcontrol">
121			.\" </a>
122			"Controlling the JIT stack"
123			.\"
124	ph10	683	below for a discussion of JIT stack usage. For compatibility with the
125			interpretive \fBpcre_exec()\fP code, no more than two-thirds of the
126			\fIovector\fP argument is used for passing back captured substrings.
127	ph10	678	.P
128			The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if searching a
129			very large pattern tree goes on for too long, as it is in the same circumstance
130			when JIT is not used, but the details of exactly what is counted are not the
131			same. The PCRE_ERROR_RECURSIONLIMIT error code is never returned by JIT
132			execution.
133			.
134			.
135			.SH "SAVING AND RESTORING COMPILED PATTERNS"
136			.rs
137			.sp
138	ph10	683	The code that is generated by the JIT compiler is architecture-specific, and is
139	ph10	708	also position dependent. For those reasons it cannot be saved (in a file or
140	ph10	707	database) and restored later like the bytecode and other data of a compiled
141	ph10	708	pattern. Saving and restoring compiled patterns is not something many people
142	ph10	707	do. More detail about this facility is given in the
143			.\" HREF
144			\fBpcreprecompile\fP
145			.\"
146			documentation. It should be possible to run \fBpcre_study()\fP on a saved and
147			restored pattern, and thereby recreate the JIT data, but because JIT
148	ph10	708	compilation uses significant resources, it is probably not worth doing this;
149	ph10	707	you might as well recompile the original pattern.
150	ph10	678	.
151			.
152			.\" HTML <a name="stackcontrol"></a>
153			.SH "CONTROLLING THE JIT STACK"
154			.rs
155			.sp
156	ph10	683	When the compiled JIT code runs, it needs a block of memory to use as a stack.
157			By default, it uses 32K on the machine stack. However, some large or
158			complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT
159			is given when there is not enough stack. Three functions are provided for
160			managing blocks of memory for use as JIT stacks.
161	ph10	678	.P
162	ph10	683	The \fBpcre_jit_stack_alloc()\fP function creates a JIT stack. Its arguments
163	ph10	691	are a starting size and a maximum size, and it returns a pointer to an opaque
164	ph10	686	structure of type \fBpcre_jit_stack\fP, or NULL if there is an error. The
165			\fBpcre_jit_stack_free()\fP function can be used to free a stack that is no
166			longer needed. (For the technically minded: the address space is allocated by
167			mmap or VirtualAlloc.)
168	ph10	678	.P
169	ph10	691	JIT uses far less memory for recursion than the interpretive code,
170	ph10	683	and a maximum stack size of 512K to 1M should be more than enough for any
171			pattern.
172			.P
173			The \fBpcre_assign_jit_stack()\fP function specifies which stack JIT code
174	ph10	678	should use. Its arguments are as follows:
175			.sp
176			pcre_extra *extra
177			pcre_jit_callback callback
178			void *data
179	ph10	683	.sp
180			The \fIextra\fP argument must be the result of studying a pattern with
181			PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the other two
182	ph10	678	options:
183			.sp
184			(1) If \fIcallback\fP is NULL and \fIdata\fP is NULL, an internal 32K block
185			on the machine stack is used.
186			.sp
187			(2) If \fIcallback\fP is NULL and \fIdata\fP is not NULL, \fIdata\fP must be
188			a valid JIT stack, the result of calling \fBpcre_jit_stack_alloc()\fP.
189			.sp
190			(3) If \fIcallback\fP not NULL, it must point to a function that is called
191	ph10	683	with \fIdata\fP as an argument at the start of matching, in order to
192			set up a JIT stack. If the result is NULL, the internal 32K stack
193			is used; otherwise the return value must be a valid JIT stack,
194	ph10	678	the result of calling \fBpcre_jit_stack_alloc()\fP.
195			.sp
196			You may safely assign the same JIT stack to more than one pattern, as long as
197			they are all matched sequentially in the same thread. In a multithread
198			application, each thread must use its own JIT stack.
199			.P
200	ph10	683	Strictly speaking, even more is allowed. You can assign the same stack to any
201			number of patterns as long as they are not used for matching by multiple
202			threads at the same time. For example, you can assign the same stack to all
203			compiled patterns, and use a global mutex in the callback to wait until the
204			stack is available for use. However, this is an inefficient solution, and
205			not recommended.
206			.P
207			This is a suggestion for how a typical multithreaded program might operate:
208			.sp
209			During thread initalization
210			thread_local_var = pcre_jit_stack_alloc(...)
211	ph10	691	.sp
212	ph10	683	During thread exit
213			pcre_jit_stack_free(thread_local_var)
214	ph10	691	.sp
215	ph10	683	Use a one-line callback function
216			return thread_local_var
217			.sp
218	ph10	678	All the functions described in this section do nothing if JIT is not available,
219	ph10	683	and \fBpcre_assign_jit_stack()\fP does nothing unless the \fBextra\fP argument
220			is non-NULL and points to a \fBpcre_extra\fP block that is the result of a
221	ph10	678	successful study with PCRE_STUDY_JIT_COMPILE.
222			.
223			.
224			.SH "EXAMPLE CODE"
225			.rs
226			.sp
227	ph10	683	This is a single-threaded example that specifies a JIT stack without using a
228	ph10	691	callback.
229	ph10	678	.sp
230			int rc;
231	ph10	683	int ovector[30];
232	ph10	678	pcre *re;
233	ph10	683	pcre_extra *extra;
234			pcre_jit_stack *jit_stack;
235			.sp
236	ph10	678	re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
237			/* Check for errors */
238			extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
239	ph10	683	jit_stack = pcre_jit_stack_alloc(321024, 5121024);
240	ph10	678	/* Check for error (NULL) */
241			pcre_assign_jit_stack(extra, NULL, jit_stack);
242	ph10	683	rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
243	ph10	678	/* Check results */
244			pcre_free(re);
245	ph10	683	pcre_free_study(extra);
246	ph10	691	pcre_jit_stack_free(jit_stack);
247	ph10	678	.sp
248			.
249			.
250			.SH "SEE ALSO"
251			.rs
252			.sp
253			\fBpcreapi\fP(3)
254			.
255			.
256			.SH AUTHOR
257			.rs
258			.sp
259			.nf
260			Philip Hazel
261			University Computing Service
262			Cambridge CB2 3QH, England.
263			.fi
264			.
265			.
266			.SH REVISION
267			.rs
268			.sp
269			.nf
270	ph10	717	Last updated: 05 October 2011
271	ph10	678	Copyright (c) 1997-2011 University of Cambridge.
272			.fi