/[pcre]/code/trunk/doc/pcrejit.3
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revision 761 by ph10, Tue Nov 22 12:24:26 2011 UTC revision 836 by ph10, Wed Dec 28 17:16:11 2011 UTC
# Line 34  The Power PC support is designated as ex Line 34  The Power PC support is designated as ex
34  fully tested. If --enable-jit is set on an unsupported platform, compilation  fully tested. If --enable-jit is set on an unsupported platform, compilation
35  fails.  fails.
36  .P  .P
37  A program can tell if JIT support is available by calling \fBpcre_config()\fP  A program that is linked with PCRE 8.20 or later can tell if JIT support is
38  with the PCRE_CONFIG_JIT option. The result is 1 when JIT is available, and 0  available by calling \fBpcre_config()\fP with the PCRE_CONFIG_JIT option. The
39  otherwise. However, a simple program does not need to check this in order to  result is 1 when JIT is available, and 0 otherwise. However, a simple program
40  use JIT. The API is implemented in a way that falls back to the ordinary PCRE  does not need to check this in order to use JIT. The API is implemented in a
41  code if JIT is not available.  way that falls back to the ordinary PCRE code if JIT is not available.
42    .P
43    If your program may sometimes be linked with versions of PCRE that are older
44    than 8.20, but you want to use JIT when it is available, you can test
45    the values of PCRE_MAJOR and PCRE_MINOR, or the existence of a JIT macro such
46    as PCRE_CONFIG_JIT, for compile-time control of your code.
47  .  .
48  .  .
49  .SH "SIMPLE USE OF JIT"  .SH "SIMPLE USE OF JIT"
# Line 54  You have to do two things to make use of Line 59  You have to do two things to make use of
59        no longer needed instead of just freeing it yourself. This        no longer needed instead of just freeing it yourself. This
60        ensures that any JIT data is also freed.        ensures that any JIT data is also freed.
61  .sp  .sp
62    For a program that may be linked with pre-8.20 versions of PCRE, you can insert
63    .sp
64      #ifndef PCRE_STUDY_JIT_COMPILE
65      #define PCRE_STUDY_JIT_COMPILE 0
66      #endif
67    .sp
68    so that no option is passed to \fBpcre_study()\fP, and then use something like
69    this to free the study data:
70    .sp
71      #ifdef PCRE_CONFIG_JIT
72          pcre_free_study(study_ptr);
73      #else
74          pcre_free(study_ptr);
75      #endif
76    .sp
77  In some circumstances you may need to call additional functions. These are  In some circumstances you may need to call additional functions. These are
78  described in the section entitled  described in the section entitled
79  .\" HTML <a href="#stackcontrol">  .\" HTML <a href="#stackcontrol">
# Line 95  supported. Line 115  supported.
115  .P  .P
116  The unsupported pattern items are:  The unsupported pattern items are:
117  .sp  .sp
118    \eC            match a single byte; not supported in UTF-8 mode    \eC             match a single byte; not supported in UTF-8 mode
119    (?Cn)          callouts    (?Cn)          callouts
120    (*COMMIT)      )    (*COMMIT)      )
121    (*MARK)        )    (*MARK)        )
# Line 159  about the use of JIT stacks in the secti Line 179  about the use of JIT stacks in the secti
179  .\" </a>  .\" </a>
180  "JIT stack FAQ"  "JIT stack FAQ"
181  .\"  .\"
182  below.  below.
183  .P  .P
184  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
185  are a starting size and a maximum size, and it returns a pointer to an opaque  are a starting size and a maximum size, and it returns a pointer to an opaque
# Line 236  stack chain needs to be updated every ti Line 256  stack chain needs to be updated every ti
256  Although it is possible, its updating time overhead decreases performance. So  Although it is possible, its updating time overhead decreases performance. So
257  we do the recursion in memory.  we do the recursion in memory.
258  .P  .P
259  (2) Why don't we simply allocate blocks of memory with \fBmalloc()\fP?  (2) Why don't we simply allocate blocks of memory with \fBmalloc()\fP?
260  .sp  .sp
261  Modern operating systems have a nice feature: they can reserve an address space  Modern operating systems have a nice feature: they can reserve an address space
262  instead of allocating memory. We can safely allocate memory pages inside this  instead of allocating memory. We can safely allocate memory pages inside this
# Line 245  important because of pointers). Thus we Line 265  important because of pointers). Thus we
265  only a single memory page (usually 4K) if that is enough. However, we can still  only a single memory page (usually 4K) if that is enough. However, we can still
266  grow up to 1M anytime if needed.  grow up to 1M anytime if needed.
267  .P  .P
268  (3) Who "owns" a JIT stack?  (3) Who "owns" a JIT stack?
269  .sp  .sp
270  The owner of the stack is the user program, not the JIT studied pattern or  The owner of the stack is the user program, not the JIT studied pattern or
271  anything else. The user program must ensure that if a stack is used by  anything else. The user program must ensure that if a stack is used by
# Line 276  list of the currently JIT studied patter Line 296  list of the currently JIT studied patter
296  .P  .P
297  (6) OK, the stack is for long term memory allocation. But what happens if a  (6) OK, the stack is for long term memory allocation. But what happens if a
298  pattern causes stack overflow with a stack of 1M? Is that 1M kept until the  pattern causes stack overflow with a stack of 1M? Is that 1M kept until the
299  stack is freed?  stack is freed?
300  .sp  .sp
301  Especially on embedded sytems, it might be a good idea to release  Especially on embedded sytems, it might be a good idea to release
302  memory sometimes without freeing the stack. There is no API for this at the  memory sometimes without freeing the stack. There is no API for this at the
# Line 285  memory for any stack and another which a Line 305  memory for any stack and another which a
305  stack) would be a good idea if someone needs this.  stack) would be a good idea if someone needs this.
306  .P  .P
307  (7) This is too much of a headache. Isn't there any better solution for JIT  (7) This is too much of a headache. Isn't there any better solution for JIT
308  stack handling?  stack handling?
309  .sp  .sp
310  No, thanks to Windows. If POSIX threads were used everywhere, we could throw  No, thanks to Windows. If POSIX threads were used everywhere, we could throw
311  out this complicated API.  out this complicated API.
# Line 337  Cambridge CB2 3QH, England. Line 357  Cambridge CB2 3QH, England.
357  .rs  .rs
358  .sp  .sp
359  .nf  .nf
360  Last updated: 22 November 2011  Last updated: 26 November 2011
361  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
362  .fi  .fi

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