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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 ph10 717 Power PC 32-bit and 64-bit (experimental)
32 ph10 683 .sp
33 ph10 733 The Power PC support is designated as experimental because it has not been
34 ph10 717 fully tested. If --enable-jit is set on an unsupported platform, compilation
35     fails.
36 ph10 678 .P
37 ph10 835 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     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 ph10 678 .
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 ph10 835 \eC match a single byte; not supported in UTF-8 mode
99 ph10 678 (?Cn) callouts
100     (*COMMIT) )
101     (*MARK) )
102     (*PRUNE) ) the backtracking control verbs
103     (*SKIP) )
104     (*THEN) )
105 ph10 683 .sp
106 ph10 678 Support for some of these may be added in future.
107     .
108     .
109     .SH "RETURN VALUES FROM JIT EXECUTION"
110     .rs
111     .sp
112 ph10 683 When a pattern is matched using JIT execution, the return values are the same
113     as those given by the interpretive \fBpcre_exec()\fP code, with the addition of
114     one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means that the memory used
115 ph10 678 for the JIT stack was insufficient. See
116     .\" HTML <a href="#stackcontrol">
117     .\" </a>
118     "Controlling the JIT stack"
119     .\"
120 ph10 683 below for a discussion of JIT stack usage. For compatibility with the
121     interpretive \fBpcre_exec()\fP code, no more than two-thirds of the
122     \fIovector\fP argument is used for passing back captured substrings.
123 ph10 678 .P
124     The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if searching a
125     very large pattern tree goes on for too long, as it is in the same circumstance
126     when JIT is not used, but the details of exactly what is counted are not the
127     same. The PCRE_ERROR_RECURSIONLIMIT error code is never returned by JIT
128     execution.
129     .
130     .
131     .SH "SAVING AND RESTORING COMPILED PATTERNS"
132     .rs
133     .sp
134 ph10 683 The code that is generated by the JIT compiler is architecture-specific, and is
135 ph10 708 also position dependent. For those reasons it cannot be saved (in a file or
136 ph10 707 database) and restored later like the bytecode and other data of a compiled
137 ph10 708 pattern. Saving and restoring compiled patterns is not something many people
138 ph10 707 do. More detail about this facility is given in the
139     .\" HREF
140     \fBpcreprecompile\fP
141     .\"
142     documentation. It should be possible to run \fBpcre_study()\fP on a saved and
143     restored pattern, and thereby recreate the JIT data, but because JIT
144 ph10 708 compilation uses significant resources, it is probably not worth doing this;
145 ph10 707 you might as well recompile the original pattern.
146 ph10 678 .
147     .
148     .\" HTML <a name="stackcontrol"></a>
149     .SH "CONTROLLING THE JIT STACK"
150     .rs
151     .sp
152 ph10 683 When the compiled JIT code runs, it needs a block of memory to use as a stack.
153     By default, it uses 32K on the machine stack. However, some large or
154     complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT
155     is given when there is not enough stack. Three functions are provided for
156 ph10 835 managing blocks of memory for use as JIT stacks.
157 ph10 678 .P
158 ph10 683 The \fBpcre_jit_stack_alloc()\fP function creates a JIT stack. Its arguments
159 ph10 691 are a starting size and a maximum size, and it returns a pointer to an opaque
160 ph10 686 structure of type \fBpcre_jit_stack\fP, or NULL if there is an error. The
161     \fBpcre_jit_stack_free()\fP function can be used to free a stack that is no
162     longer needed. (For the technically minded: the address space is allocated by
163     mmap or VirtualAlloc.)
164 ph10 678 .P
165 ph10 691 JIT uses far less memory for recursion than the interpretive code,
166 ph10 683 and a maximum stack size of 512K to 1M should be more than enough for any
167     pattern.
168     .P
169     The \fBpcre_assign_jit_stack()\fP function specifies which stack JIT code
170 ph10 678 should use. Its arguments are as follows:
171     .sp
172     pcre_extra *extra
173     pcre_jit_callback callback
174     void *data
175 ph10 683 .sp
176     The \fIextra\fP argument must be the result of studying a pattern with
177     PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the other two
178 ph10 678 options:
179     .sp
180     (1) If \fIcallback\fP is NULL and \fIdata\fP is NULL, an internal 32K block
181     on the machine stack is used.
182     .sp
183     (2) If \fIcallback\fP is NULL and \fIdata\fP is not NULL, \fIdata\fP must be
184     a valid JIT stack, the result of calling \fBpcre_jit_stack_alloc()\fP.
185     .sp
186     (3) If \fIcallback\fP not NULL, it must point to a function that is called
187 ph10 683 with \fIdata\fP as an argument at the start of matching, in order to
188     set up a JIT stack. If the result is NULL, the internal 32K stack
189     is used; otherwise the return value must be a valid JIT stack,
190 ph10 678 the result of calling \fBpcre_jit_stack_alloc()\fP.
191     .sp
192     You may safely assign the same JIT stack to more than one pattern, as long as
193     they are all matched sequentially in the same thread. In a multithread
194     application, each thread must use its own JIT stack.
195     .P
196 ph10 683 Strictly speaking, even more is allowed. You can assign the same stack to any
197     number of patterns as long as they are not used for matching by multiple
198     threads at the same time. For example, you can assign the same stack to all
199     compiled patterns, and use a global mutex in the callback to wait until the
200     stack is available for use. However, this is an inefficient solution, and
201     not recommended.
202     .P
203     This is a suggestion for how a typical multithreaded program might operate:
204     .sp
205     During thread initalization
206     thread_local_var = pcre_jit_stack_alloc(...)
207 ph10 691 .sp
208 ph10 683 During thread exit
209     pcre_jit_stack_free(thread_local_var)
210 ph10 691 .sp
211 ph10 683 Use a one-line callback function
212     return thread_local_var
213     .sp
214 ph10 678 All the functions described in this section do nothing if JIT is not available,
215 ph10 683 and \fBpcre_assign_jit_stack()\fP does nothing unless the \fBextra\fP argument
216     is non-NULL and points to a \fBpcre_extra\fP block that is the result of a
217 ph10 678 successful study with PCRE_STUDY_JIT_COMPILE.
218     .
219     .
220     .SH "EXAMPLE CODE"
221     .rs
222     .sp
223 ph10 683 This is a single-threaded example that specifies a JIT stack without using a
224 ph10 691 callback.
225 ph10 678 .sp
226     int rc;
227 ph10 683 int ovector[30];
228 ph10 678 pcre *re;
229 ph10 683 pcre_extra *extra;
230     pcre_jit_stack *jit_stack;
231     .sp
232 ph10 678 re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
233     /* Check for errors */
234     extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
235 ph10 683 jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024);
236 ph10 678 /* Check for error (NULL) */
237     pcre_assign_jit_stack(extra, NULL, jit_stack);
238 ph10 683 rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
239 ph10 678 /* Check results */
240     pcre_free(re);
241 ph10 683 pcre_free_study(extra);
242 ph10 691 pcre_jit_stack_free(jit_stack);
243 ph10 678 .sp
244     .
245     .
246     .SH "SEE ALSO"
247     .rs
248     .sp
249     \fBpcreapi\fP(3)
250     .
251     .
252     .SH AUTHOR
253     .rs
254     .sp
255     .nf
256 ph10 835 Philip Hazel
257 ph10 678 University Computing Service
258     Cambridge CB2 3QH, England.
259     .fi
260     .
261     .
262     .SH REVISION
263     .rs
264     .sp
265     .nf
266 ph10 835 Last updated: 15 November 2011
267 ph10 678 Copyright (c) 1997-2011 University of Cambridge.
268     .fi

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