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

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