/[pcre]/code/trunk/doc/pcrejit.3
ViewVC logotype

Diff of /code/trunk/doc/pcrejit.3

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 678 by ph10, Sun Aug 28 15:23:03 2011 UTC revision 748 by ph10, Tue Nov 15 17:44:38 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:
97  .sp  .sp
98    \eC            match a single byte, even in UTF-8 mode    \eC            match a single byte; not supported in UTF-8 mode
99    (?Cn)          callouts    (?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  
100    (*COMMIT)      )    (*COMMIT)      )
101    (*MARK)        )    (*MARK)        )
102    (*PRUNE)       ) the backtracking control verbs    (*PRUNE)       ) the backtracking control verbs
103    (*SKIP)        )    (*SKIP)        )
104    (*THEN)        )    (*THEN)        )
105  .sp  .sp
106  Support for some of these may be added in future.  Support for some of these may be added in future.
107  .  .
108  .  .
109  .SH "RETURN VALUES FROM JIT EXECUTION"  .SH "RETURN VALUES FROM JIT EXECUTION"
110  .rs  .rs
111  .sp  .sp
112  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
113  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
114  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
115  for the JIT stack was insufficient. See  for the JIT stack was insufficient. See
116  .\" HTML <a href="#stackcontrol">  .\" HTML <a href="#stackcontrol">
117  .\" </a>  .\" </a>
118  "Controlling the JIT stack"  "Controlling the JIT stack"
119  .\"  .\"
120  below for a discussion of JIT stack usage.  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  .P  .P
124  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
125  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 131  execution.
131  .SH "SAVING AND RESTORING COMPILED PATTERNS"  .SH "SAVING AND RESTORING COMPILED PATTERNS"
132  .rs  .rs
133  .sp  .sp
134  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
135  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
136  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
137  \fBpcre_study()\fP on a saved and restored pattern, and thereby recreate the  pattern. Saving and restoring compiled patterns is not something many people
138  JIT data, but because JIT compilation uses significant resources, it is  do. More detail about this facility is given in the
139  probably not worth doing.  .\" 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    compilation uses significant resources, it is probably not worth doing this;
145    you might as well recompile the original pattern.
146  .  .
147  .  .
148  .\" HTML <a name="stackcontrol"></a>  .\" HTML <a name="stackcontrol"></a>
149  .SH "CONTROLLING THE JIT STACK"  .SH "CONTROLLING THE JIT STACK"
150  .rs  .rs
151  .sp  .sp
152  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.
153  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
154  complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT  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  is given when there is not enough stack. Three functions are provided for
156  setting up alternative blocks of memory for use as JIT stacks.  managing blocks of memory for use as JIT stacks.
157  .P  .P
158  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
159  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
160  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
161  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
162  that is no longer needed.  longer needed. (For the technically minded: the address space is allocated by
163    mmap or VirtualAlloc.)
164  .P  .P
165  The \fBpcre_assign_jit_stack()\fP function specifies which stack JIT code  JIT uses far less memory for recursion than the interpretive code,
166    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  should use. Its arguments are as follows:  should use. Its arguments are as follows:
171  .sp  .sp
172    pcre_extra         *extra    pcre_extra         *extra
173    pcre_jit_callback  callback    pcre_jit_callback  callback
174    void               *data    void               *data
175  .sp  .sp
176  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
177  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
178  options:  options:
179  .sp  .sp
180    (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 184  options:
184        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.
185  .sp  .sp
186    (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
187        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
188        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
189        is used; otherwise the return value must be a valid JIT stack,        is used; otherwise the return value must be a valid JIT stack,
190        the result of calling \fBpcre_jit_stack_alloc()\fP.        the result of calling \fBpcre_jit_stack_alloc()\fP.
191  .sp  .sp
192  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
193  they are all matched sequentially in the same thread. In a multithread  they are all matched sequentially in the same thread. In a multithread
194  application, each thread must use its own JIT stack.  application, each thread must use its own JIT stack.
195  .P  .P
196    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    .sp
208      During thread exit
209        pcre_jit_stack_free(thread_local_var)
210    .sp
211      Use a one-line callback function
212        return thread_local_var
213    .sp
214  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,
215  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
216  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
217  successful study with PCRE_STUDY_JIT_COMPILE.  successful study with PCRE_STUDY_JIT_COMPILE.
218  .  .
219  .  .
220  .SH "EXAMPLE CODE"  .SH "EXAMPLE CODE"
221  .rs  .rs
222  .sp  .sp
223  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
224  callback.  callback.
225  .sp  .sp
226    int rc;    int rc;
227      int ovector[30];
228    pcre *re;    pcre *re;
229    pcre_extra *extra;    pcre_extra *extra;
230    pcre_jit_stack *jit_stack;    pcre_jit_stack *jit_stack;
231  .sp  .sp
232    re = pcre_compile(pattern, 0, &error, &erroffset, NULL);    re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
233    /* Check for errors */    /* Check for errors */
234    extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);    extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
235    jit_stack = pcre_jit_stack_alloc(1, 512 * 1024);    jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024);
236    /* Check for error (NULL) */    /* Check for error (NULL) */
237    pcre_assign_jit_stack(extra, NULL, jit_stack);    pcre_assign_jit_stack(extra, NULL, jit_stack);
238    rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, ovecsize);    rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
239    /* Check results */    /* Check results */
240    pcre_free(re);    pcre_free(re);
241    pcre_free_study(extra);    pcre_free_study(extra);
242      pcre_jit_stack_free(jit_stack);
243  .sp  .sp
244  .  .
245  .  .
# Line 229  Cambridge CB2 3QH, England. Line 263  Cambridge CB2 3QH, England.
263  .rs  .rs
264  .sp  .sp
265  .nf  .nf
266  Last updated: 28 August 2011  Last updated: 15 November 2011
267  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
268  .fi  .fi

Legend:
Removed from v.678  
changed lines
  Added in v.748

  ViewVC Help
Powered by ViewVC 1.1.5