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revision 682 by ph10, Sun Aug 28 15:23:03 2011 UTC revision 683 by ph10, Tue Sep 6 10:37:15 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
29      Intel x86 32-bit and 64-bit
30    MIPS 32-bit    MIPS 32-bit
31    Power PC 32-bit and 64-bit    Power PC 32-bit and 64-bit
32    Intel x86 32-bit and 64-bit  .sp
 .sp  
33  If --enable-jit is set on an unsupported platform, compilation fails.  If --enable-jit is set on an unsupported platform, compilation fails.
34  .P  .P
35  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
36  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
37  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
38  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
39  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 47  You have to do two things to make use of
47    (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
48        each compiled pattern, and pass the resulting \fBpcre_extra\fP block to        each compiled pattern, and pass the resulting \fBpcre_extra\fP block to
49        \fBpcre_exec()\fP.        \fBpcre_exec()\fP.
50    
51    (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
52        no longer needed instead of just freeing it yourself. This ensures that        no longer needed instead of just freeing it yourself. This
53        any JIT data is also freed.        ensures that any JIT data is also freed.
54  .sp  .sp
55  In some circumstances you may need to call additional functions. These are  In some circumstances you may need to call additional functions. These are
56  described in the section entitled  described in the section entitled
57  .\" HTML <a href="#stackcontrol">  .\" HTML <a href="#stackcontrol">
58  .\" </a>  .\" </a>
# Line 60  described in the section entitled Line 60  described in the section entitled
60  .\"  .\"
61  below.  below.
62  .P  .P
63  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
64  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,
65  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
66  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
67  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
68  result is identical, but the code runs much faster.  result is identical, but the code runs much faster.
69  .P  .P
70  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
71  execution. There are also some pattern items that JIT cannot handle. Details  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  are given below. In both cases, execution automatically falls back to the
73  interpretive code.  interpretive code.
74  .P  .P
75  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
# Line 84  JIT compiler was not able to handle the Line 84  JIT compiler was not able to handle the
84  .rs  .rs
85  .sp  .sp
86  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
87  PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and  PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and
88  PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not  PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not
89  supported.  supported.
90  .P  .P
91  The unsupported pattern items are:  The unsupported pattern items are:
# Line 93  The unsupported pattern items are: Line 93  The unsupported pattern items are:
93    \eC            match a single byte, even in UTF-8 mode    \eC            match a single byte, even in UTF-8 mode
94    (?Cn)          callouts    (?Cn)          callouts
95    (?(<name>)...  conditional test on setting of a named subpattern    (?(<name>)...  conditional test on setting of a named subpattern
96    (?(R)...       conditional test on whole pattern recursion    (?(R)...       conditional test on whole pattern recursion
97    (?(Rn)...      conditional test on recursion, by number    (?(Rn)...      conditional test on recursion, by number
98    (?(R&name)...  conditional test on recursion, by name    (?(R&name)...  conditional test on recursion, by name
99    (*COMMIT)      )    (*COMMIT)      )
# Line 101  The unsupported pattern items are: Line 101  The unsupported pattern items are:
101    (*PRUNE)       ) the backtracking control verbs    (*PRUNE)       ) the backtracking control verbs
102    (*SKIP)        )    (*SKIP)        )
103    (*THEN)        )    (*THEN)        )
104  .sp  .sp
105  Support for some of these may be added in future.  Support for some of these may be added in future.
106  .  .
107  .  .
108  .SH "RETURN VALUES FROM JIT EXECUTION"  .SH "RETURN VALUES FROM JIT EXECUTION"
109  .rs  .rs
110  .sp  .sp
111  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
112  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
113  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
114  for the JIT stack was insufficient. See  for the JIT stack was insufficient. See
115  .\" HTML <a href="#stackcontrol">  .\" HTML <a href="#stackcontrol">
116  .\" </a>  .\" </a>
117  "Controlling the JIT stack"  "Controlling the JIT stack"
118  .\"  .\"
119  below for a discussion of JIT stack usage.  below for a discussion of JIT stack usage. For compatibility with the
120    interpretive \fBpcre_exec()\fP code, no more than two-thirds of the
121    \fIovector\fP argument is used for passing back captured substrings.
122  .P  .P
123  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
124  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 130  execution.
130  .SH "SAVING AND RESTORING COMPILED PATTERNS"  .SH "SAVING AND RESTORING COMPILED PATTERNS"
131  .rs  .rs
132  .sp  .sp
133  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
134  also position dependent. For those reasons it cannot be saved and restored like  also position dependent. For those reasons it cannot be saved and restored like
135  the bytecode and other data of a compiled pattern. You should be able run  the bytecode and other data of a compiled pattern. You should be able run
136  \fBpcre_study()\fP on a saved and restored pattern, and thereby recreate the  \fBpcre_study()\fP on a saved and restored pattern, and thereby recreate the
137  JIT data, but because JIT compilation uses significant resources, it is  JIT data, but because JIT compilation uses significant resources, it is
138  probably not worth doing.  probably not worth doing this.
139  .  .
140  .  .
141  .\" HTML <a name="stackcontrol"></a>  .\" HTML <a name="stackcontrol"></a>
142  .SH "CONTROLLING THE JIT STACK"  .SH "CONTROLLING THE JIT STACK"
143  .rs  .rs
144  .sp  .sp
145  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.
146  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
147  complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT  complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT
148  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
149  setting up alternative blocks of memory for use as JIT stacks.  managing blocks of memory for use as JIT stacks.
150  .P  .P
151  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
152  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 an opaque value
153  of type \fBpcre_jit_stack\fP that represents a JIT stack, or NULL if there is  of type \fBpcre_jit_stack\fP that represents a JIT stack, or NULL if there is
154  an error. The \fBpcre_jit_stack_free()\fP function can be used to free a stack  an error. The \fBpcre_jit_stack_free()\fP function can be used to free a stack
155  that is no longer needed.  that is no longer needed. (For the technically minded: the address space is
156    allocated by mmap or VirtualAlloc.)
157    .P
158    JIT uses far less memory for recursion than the interpretive code,
159    and a maximum stack size of 512K to 1M should be more than enough for any
160    pattern.
161  .P  .P
162  The \fBpcre_assign_jit_stack()\fP function specifies which stack JIT code  The \fBpcre_assign_jit_stack()\fP function specifies which stack JIT code
163  should use. Its arguments are as follows:  should use. Its arguments are as follows:
164  .sp  .sp
165    pcre_extra         *extra    pcre_extra         *extra
166    pcre_jit_callback  callback    pcre_jit_callback  callback
167    void               *data    void               *data
168  .sp  .sp
169  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
170  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
171  options:  options:
172  .sp  .sp
173    (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 177  options:
177        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.
178  .sp  .sp
179    (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
180        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
181        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
182        is used; otherwise the return value must be a valid JIT stack,        is used; otherwise the return value must be a valid JIT stack,
183        the result of calling \fBpcre_jit_stack_alloc()\fP.        the result of calling \fBpcre_jit_stack_alloc()\fP.
184  .sp  .sp
185  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
186  they are all matched sequentially in the same thread. In a multithread  they are all matched sequentially in the same thread. In a multithread
187  application, each thread must use its own JIT stack.  application, each thread must use its own JIT stack.
188  .P  .P
189    Strictly speaking, even more is allowed. You can assign the same stack to any
190    number of patterns as long as they are not used for matching by multiple
191    threads at the same time. For example, you can assign the same stack to all
192    compiled patterns, and use a global mutex in the callback to wait until the
193    stack is available for use. However, this is an inefficient solution, and
194    not recommended.
195    .P
196    This is a suggestion for how a typical multithreaded program might operate:
197    .sp
198      During thread initalization
199        thread_local_var = pcre_jit_stack_alloc(...)
200    
201      During thread exit
202        pcre_jit_stack_free(thread_local_var)
203    
204      Use a one-line callback function
205        return thread_local_var
206    .sp
207  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,
208  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
209  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
210  successful study with PCRE_STUDY_JIT_COMPILE.  successful study with PCRE_STUDY_JIT_COMPILE.
211  .  .
212  .  .
213  .SH "EXAMPLE CODE"  .SH "EXAMPLE CODE"
214  .rs  .rs
215  .sp  .sp
216  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
217  callback.  callback.
218  .sp  .sp
219    int rc;    int rc;
220      int ovector[30];
221    pcre *re;    pcre *re;
222    pcre_extra *extra;    pcre_extra *extra;
223    pcre_jit_stack *jit_stack;    pcre_jit_stack *jit_stack;
224  .sp  .sp
225    re = pcre_compile(pattern, 0, &error, &erroffset, NULL);    re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
226    /* Check for errors */    /* Check for errors */
227    extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);    extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
228    jit_stack = pcre_jit_stack_alloc(1, 512 * 1024);    jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024);
229    /* Check for error (NULL) */    /* Check for error (NULL) */
230    pcre_assign_jit_stack(extra, NULL, jit_stack);    pcre_assign_jit_stack(extra, NULL, jit_stack);
231    rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, ovecsize);    rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
232    /* Check results */    /* Check results */
233    pcre_free(re);    pcre_free(re);
234    pcre_free_study(extra);    pcre_free_study(extra);
235  .sp  .sp
236  .  .
237  .  .
# Line 229  Cambridge CB2 3QH, England. Line 255  Cambridge CB2 3QH, England.
255  .rs  .rs
256  .sp  .sp
257  .nf  .nf
258  Last updated: 28 August 2011  Last updated: 06 September 2011
259  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
260  .fi  .fi

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