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revision 678 by ph10, Sun Aug 28 15:23:03 2011 UTC revision 717 by ph10, Wed Oct 5 15:58:51 2011 UTC
# Line 5  PCRE - Perl-compatible regular expressio Line 5  PCRE - Perl-compatible regular expressio
5  .rs  .rs
6  .sp  .sp
7  Just-in-time compiling is a heavyweight optimization that can greatly speed up  Just-in-time compiling is a heavyweight optimization that can greatly speed up
8  pattern matching. However, it comes at the cost of extra processing before the  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  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  going to be matched many times. This does not necessarily mean many calls of
11  \fPpcre_exec()\fP; if the pattern is not anchored, matching attempts may take  \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  place many times at various positions in the subject, even for a single call to
13  \fBpcre_exec()\fP. If the subject string is very long, it may still pay to use  \fBpcre_exec()\fP. If the subject string is very long, it may still pay to use
14  JIT for one-off matches.  JIT for one-off matches.
15  .P  .P
16  JIT support applies only to the traditional matching function,  JIT support applies only to the traditional matching function,
17  \fBpcre_exec()\fP. It does not apply when \fBpcre_dfa_exec()\fP is being used.  \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.  The code for this support was written by Zoltan Herczeg.
19  .  .
# Line 26  JIT support is an optional feature of PC Line 26  JIT support is an optional feature of PC
26  JIT. The support is limited to the following hardware platforms:  JIT. The support is limited to the following hardware platforms:
27  .sp  .sp
28    ARM v5, v7, and Thumb2    ARM v5, v7, and Thumb2
   MIPS 32-bit  
   Power PC 32-bit and 64-bit  
29    Intel x86 32-bit and 64-bit    Intel x86 32-bit and 64-bit
30  .sp    MIPS 32-bit
31  If --enable-jit is set on an unsupported platform, compilation fails.    Power PC 32-bit and 64-bit (experimental)
32    .sp
33    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  .P  .P
37  A program can tell if JIT support is available by calling \fBpcre_config()\fP  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  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  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  use JIT. The API is implemented in a way that falls back to the ordinary PCRE
41  code if JIT is not available.  code if JIT is not available.
# Line 47  You have to do two things to make use of Line 49  You have to do two things to make use of
49    (1) Call \fBpcre_study()\fP with the PCRE_STUDY_JIT_COMPILE option for    (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        each compiled pattern, and pass the resulting \fBpcre_extra\fP block to
51        \fBpcre_exec()\fP.        \fBpcre_exec()\fP.
52    .sp
53    (2) Use \fBpcre_free_study()\fP to free the \fBpcre_extra\fP block when it is    (2) Use \fBpcre_free_study()\fP to free the \fBpcre_extra\fP block when it is
54        no longer needed instead of just freeing it yourself. This ensures that        no longer needed instead of just freeing it yourself. This
55        any JIT data is also freed.        ensures that any JIT data is also freed.
56  .sp  .sp
57  In some circumstances you may need to call additional functions. These are  In some circumstances you may need to call additional functions. These are
58  described in the section entitled  described in the section entitled
59  .\" HTML <a href="#stackcontrol">  .\" HTML <a href="#stackcontrol">
60  .\" </a>  .\" </a>
# Line 60  described in the section entitled Line 62  described in the section entitled
62  .\"  .\"
63  below.  below.
64  .P  .P
65  If JIT support is not available, PCRE_STUDY_JIT_COMPILE is ignored, and no JIT  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,  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  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  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  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.  result is identical, but the code runs much faster.
71  .P  .P
72  There are some \fBpcre_exec()\fP options that are not supported for JIT  There are some \fBpcre_exec()\fP options that are not supported for JIT
73  execution. There are also some pattern items that JIT cannot handle. Details  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  are given below. In both cases, execution automatically falls back to the
75  interpretive code.  interpretive code.
76  .P  .P
77  If the JIT compiler finds an unsupported item, no JIT data is generated. You  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  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  \fBpcre_fullinfo()\fP with the PCRE_INFO_JIT option. A result of 1 means that
80  JIT compilationw was successful. A result of 0 means that JIT support is not  JIT compilation was successful. A result of 0 means that JIT support is not
81  available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE, or the  available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE, or the
82  JIT compiler was not able to handle the pattern.  JIT compiler was not able to handle the pattern.
83    .P
84    Once a pattern has been studied, with or without JIT, it can be used as many
85    times as you like for matching different subject strings.
86  .  .
87  .  .
88  .SH "UNSUPPORTED OPTIONS AND PATTERN ITEMS"  .SH "UNSUPPORTED OPTIONS AND PATTERN ITEMS"
89  .rs  .rs
90  .sp  .sp
91  The only \fBpcre_exec()\fP options that are supported for JIT execution are  The only \fBpcre_exec()\fP options that are supported for JIT execution are
92  PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and  PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and
93  PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not  PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not
94  supported.  supported.
95  .P  .P
96  The unsupported pattern items are:  The unsupported pattern items are:
# Line 93  The unsupported pattern items are: Line 98  The unsupported pattern items are:
98    \eC            match a single byte, even in UTF-8 mode    \eC            match a single byte, even in UTF-8 mode
99    (?Cn)          callouts    (?Cn)          callouts
100    (?(<name>)...  conditional test on setting of a named subpattern    (?(<name>)...  conditional test on setting of a named subpattern
101    (?(R)...       conditional test on whole pattern recursion    (?(R)...       conditional test on whole pattern recursion
102    (?(Rn)...      conditional test on recursion, by number    (?(Rn)...      conditional test on recursion, by number
103    (?(R&name)...  conditional test on recursion, by name    (?(R&name)...  conditional test on recursion, by name
104    (*COMMIT)      )    (*COMMIT)      )
# Line 101  The unsupported pattern items are: Line 106  The unsupported pattern items are:
106    (*PRUNE)       ) the backtracking control verbs    (*PRUNE)       ) the backtracking control verbs
107    (*SKIP)        )    (*SKIP)        )
108    (*THEN)        )    (*THEN)        )
109  .sp  .sp
110  Support for some of these may be added in future.  Support for some of these may be added in future.
111  .  .
112  .  .
113  .SH "RETURN VALUES FROM JIT EXECUTION"  .SH "RETURN VALUES FROM JIT EXECUTION"
114  .rs  .rs
115  .sp  .sp
116  When a pattern is matched using JIT execution, the return values are the same  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  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  one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means that the memory used
119  for the JIT stack was insufficient. See  for the JIT stack was insufficient. See
120  .\" HTML <a href="#stackcontrol">  .\" HTML <a href="#stackcontrol">
121  .\" </a>  .\" </a>
122  "Controlling the JIT stack"  "Controlling the JIT stack"
123  .\"  .\"
124  below for a discussion of JIT stack usage.  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  .P  .P
128  The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if searching a  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  very large pattern tree goes on for too long, as it is in the same circumstance
# Line 128  execution. Line 135  execution.
135  .SH "SAVING AND RESTORING COMPILED PATTERNS"  .SH "SAVING AND RESTORING COMPILED PATTERNS"
136  .rs  .rs
137  .sp  .sp
138  The code that is generated by the JIT compiler is architecture-specific, and is  The code that is generated by the JIT compiler is architecture-specific, and is
139  also position dependent. For those reasons it cannot be saved and restored like  also position dependent. For those reasons it cannot be saved (in a file or
140  the bytecode and other data of a compiled pattern. You should be able run  database) and restored later like the bytecode and other data of a compiled
141  \fBpcre_study()\fP on a saved and restored pattern, and thereby recreate the  pattern. Saving and restoring compiled patterns is not something many people
142  JIT data, but because JIT compilation uses significant resources, it is  do. More detail about this facility is given in the
143  probably not worth doing.  .\" 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    compilation uses significant resources, it is probably not worth doing this;
149    you might as well recompile the original pattern.
150  .  .
151  .  .
152  .\" HTML <a name="stackcontrol"></a>  .\" HTML <a name="stackcontrol"></a>
153  .SH "CONTROLLING THE JIT STACK"  .SH "CONTROLLING THE JIT STACK"
154  .rs  .rs
155  .sp  .sp
156  When the compiled JIT code runs, it needs a block of memory to use as a stack.  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  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  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  is given when there is not enough stack. Three functions are provided for
160  setting up alternative blocks of memory for use as JIT stacks.  managing blocks of memory for use as JIT stacks.
161  .P  .P
162  The \fBpcre_jit_stack_alloc()\fP function creates a JIT stack. Its arguments  The \fBpcre_jit_stack_alloc()\fP function creates a JIT stack. Its arguments
163  are a starting size and a maximum size, and it returns an opaque value  are a starting size and a maximum size, and it returns a pointer to an opaque
164  of type \fBpcre_jit_stack\fP that represents a JIT stack, or NULL if there is  structure of type \fBpcre_jit_stack\fP, or NULL if there is an error. The
165  an error. The \fBpcre_jit_stack_free()\fP function can be used to free a stack  \fBpcre_jit_stack_free()\fP function can be used to free a stack that is no
166  that is no longer needed.  longer needed. (For the technically minded: the address space is allocated by
167    mmap or VirtualAlloc.)
168  .P  .P
169  The \fBpcre_assign_jit_stack()\fP function specifies which stack JIT code  JIT uses far less memory for recursion than the interpretive code,
170    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  should use. Its arguments are as follows:  should use. Its arguments are as follows:
175  .sp  .sp
176    pcre_extra         *extra    pcre_extra         *extra
177    pcre_jit_callback  callback    pcre_jit_callback  callback
178    void               *data    void               *data
179  .sp  .sp
180  The \fIextra\fP argument must be the result of studying a pattern with  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  PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the other two
182  options:  options:
183  .sp  .sp
184    (1) If \fIcallback\fP is NULL and \fIdata\fP is NULL, an internal 32K block    (1) If \fIcallback\fP is NULL and \fIdata\fP is NULL, an internal 32K block
# Line 170  options: Line 188  options:
188        a valid JIT stack, the result of calling \fBpcre_jit_stack_alloc()\fP.        a valid JIT stack, the result of calling \fBpcre_jit_stack_alloc()\fP.
189  .sp  .sp
190    (3) If \fIcallback\fP not NULL, it must point to a function that is called    (3) If \fIcallback\fP not NULL, it must point to a function that is called
191        with \fIdata\fP as an argument at the start of matching, in order to        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        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,        is used; otherwise the return value must be a valid JIT stack,
194        the result of calling \fBpcre_jit_stack_alloc()\fP.        the result of calling \fBpcre_jit_stack_alloc()\fP.
195  .sp  .sp
196  You may safely assign the same JIT stack to more than one pattern, as long as  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  they are all matched sequentially in the same thread. In a multithread
198  application, each thread must use its own JIT stack.  application, each thread must use its own JIT stack.
199  .P  .P
200    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    .sp
212      During thread exit
213        pcre_jit_stack_free(thread_local_var)
214    .sp
215      Use a one-line callback function
216        return thread_local_var
217    .sp
218  All the functions described in this section do nothing if JIT is not available,  All the functions described in this section do nothing if JIT is not available,
219  and \fBpcre_assign_jit_stack()\fP does nothing unless the \fBextra\fP argument  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  is non-NULL and points to a \fBpcre_extra\fP block that is the result of a
221  successful study with PCRE_STUDY_JIT_COMPILE.  successful study with PCRE_STUDY_JIT_COMPILE.
222  .  .
223  .  .
224  .SH "EXAMPLE CODE"  .SH "EXAMPLE CODE"
225  .rs  .rs
226  .sp  .sp
227  This is a single-threaded example that specifies a JIT stack without using a  This is a single-threaded example that specifies a JIT stack without using a
228  callback.  callback.
229  .sp  .sp
230    int rc;    int rc;
231      int ovector[30];
232    pcre *re;    pcre *re;
233    pcre_extra *extra;    pcre_extra *extra;
234    pcre_jit_stack *jit_stack;    pcre_jit_stack *jit_stack;
235  .sp  .sp
236    re = pcre_compile(pattern, 0, &error, &erroffset, NULL);    re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
237    /* Check for errors */    /* Check for errors */
238    extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);    extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
239    jit_stack = pcre_jit_stack_alloc(1, 512 * 1024);    jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024);
240    /* Check for error (NULL) */    /* Check for error (NULL) */
241    pcre_assign_jit_stack(extra, NULL, jit_stack);    pcre_assign_jit_stack(extra, NULL, jit_stack);
242    rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, ovecsize);    rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
243    /* Check results */    /* Check results */
244    pcre_free(re);    pcre_free(re);
245    pcre_free_study(extra);    pcre_free_study(extra);
246      pcre_jit_stack_free(jit_stack);
247  .sp  .sp
248  .  .
249  .  .
# Line 229  Cambridge CB2 3QH, England. Line 267  Cambridge CB2 3QH, England.
267  .rs  .rs
268  .sp  .sp
269  .nf  .nf
270  Last updated: 28 August 2011  Last updated: 05 October 2011
271  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
272  .fi  .fi

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