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version 1.1.1.3, 2012/10/09 09:19:17 version 1.1.1.4, 2013/07/22 08:25:57
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.TH PCRESTACK 3 "21 January 2012" "PCRE 8.30".TH PCRESTACK 3 "24 June 2012" "PCRE 8.30"
 .SH NAME  .SH NAME
 PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
 .SH "PCRE DISCUSSION OF STACK USAGE"  .SH "PCRE DISCUSSION OF STACK USAGE"
 .rs  .rs
 .sp  .sp
When you call \fBpcre[16]_exec()\fP, it makes use of an internal functionWhen you call \fBpcre[16|32]_exec()\fP, it makes use of an internal function
 called \fBmatch()\fP. This calls itself recursively at branch points in the  called \fBmatch()\fP. This calls itself recursively at branch points in the
 pattern, in order to remember the state of the match so that it can back up and  pattern, in order to remember the state of the match so that it can back up and
 try a different alternative if the first one fails. As matching proceeds deeper  try a different alternative if the first one fails. As matching proceeds deeper
Line 19  different numbers of a's. Furthermore, in a number of  Line 19  different numbers of a's. Furthermore, in a number of 
 the recursive call would immediately be passed back as the result of the  the recursive call would immediately be passed back as the result of the
 current call (a "tail recursion"), the function is just restarted instead.  current call (a "tail recursion"), the function is just restarted instead.
 .P  .P
The above comments apply when \fBpcre[16]_exec()\fP is run in its normalThe above comments apply when \fBpcre[16|32]_exec()\fP is run in its normal
 interpretive manner. If the pattern was studied with the  interpretive manner. If the pattern was studied with the
 PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was successful, and  PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was successful, and
the options passed to \fBpcre[16]_exec()\fP were not incompatible, the matchingthe options passed to \fBpcre[16|32]_exec()\fP were not incompatible, the matching
 process uses the JIT-compiled code instead of the \fBmatch()\fP function. In  process uses the JIT-compiled code instead of the \fBmatch()\fP function. In
 this case, the memory requirements are handled entirely differently. See the  this case, the memory requirements are handled entirely differently. See the
 .\" HREF  .\" HREF
Line 30  this case, the memory requirements are handled entirel Line 30  this case, the memory requirements are handled entirel
 .\"  .\"
 documentation for details.  documentation for details.
 .P  .P
The \fBpcre[16]_dfa_exec()\fP function operates in an entirely different way,The \fBpcre[16|32]_dfa_exec()\fP function operates in an entirely different way,
 and uses recursion only when there is a regular expression recursion or  and uses recursion only when there is a regular expression recursion or
 subroutine call in the pattern. This includes the processing of assertion and  subroutine call in the pattern. This includes the processing of assertion and
 "once-only" subpatterns, which are handled like subroutine calls. Normally,  "once-only" subpatterns, which are handled like subroutine calls. Normally,
 these are never very deep, and the limit on the complexity of  these are never very deep, and the limit on the complexity of
\fBpcre[16]_dfa_exec()\fP is controlled by the amount of workspace it is given.\fBpcre[16|32]_dfa_exec()\fP is controlled by the amount of workspace it is given.
 However, it is possible to write patterns with runaway infinite recursions;  However, it is possible to write patterns with runaway infinite recursions;
such patterns will cause \fBpcre[16]_dfa_exec()\fP to run out of stack. Atsuch patterns will cause \fBpcre[16|32]_dfa_exec()\fP to run out of stack. At
 present, there is no protection against this.  present, there is no protection against this.
 .P  .P
The comments that follow do NOT apply to \fBpcre[16]_dfa_exec()\fP; they areThe comments that follow do NOT apply to \fBpcre[16|32]_dfa_exec()\fP; they are
relevant only for \fBpcre[16]_exec()\fP without the JIT optimization.relevant only for \fBpcre[16|32]_exec()\fP without the JIT optimization.
 .  .
 .  .
.SS "Reducing \fBpcre[16]_exec()\fP's stack usage".SS "Reducing \fBpcre[16|32]_exec()\fP's stack usage"
 .rs  .rs
 .sp  .sp
 Each time that \fBmatch()\fP is actually called recursively, it uses memory  Each time that \fBmatch()\fP is actually called recursively, it uses memory
Line 79  subject strings is to write repeated parenthesized sub Line 79  subject strings is to write repeated parenthesized sub
 than one character whenever possible.  than one character whenever possible.
 .  .
 .  .
.SS "Compiling PCRE to use heap instead of stack for \fBpcre[16]_exec()\fP".SS "Compiling PCRE to use heap instead of stack for \fBpcre[16|32]_exec()\fP"
 .rs  .rs
 .sp  .sp
 In environments where stack memory is constrained, you might want to compile  In environments where stack memory is constrained, you might want to compile
 PCRE to use heap memory instead of stack for remembering back-up points when  PCRE to use heap memory instead of stack for remembering back-up points when
\fBpcre[16]_exec()\fP is running. This makes it run a lot more slowly, however.\fBpcre[16|32]_exec()\fP is running. This makes it run a lot more slowly, however.
 Details of how to do this are given in the  Details of how to do this are given in the
 .\" HREF  .\" HREF
 \fBpcrebuild\fP  \fBpcrebuild\fP
 .\"  .\"
 documentation. When built in this way, instead of using the stack, PCRE obtains  documentation. When built in this way, instead of using the stack, PCRE obtains
 and frees memory by calling the functions that are pointed to by the  and frees memory by calling the functions that are pointed to by the
\fBpcre[16]_stack_malloc\fP and \fBpcre[16]_stack_free\fP variables. By\fBpcre[16|32]_stack_malloc\fP and \fBpcre[16|32]_stack_free\fP variables. By
 default, these point to \fBmalloc()\fP and \fBfree()\fP, but you can replace  default, these point to \fBmalloc()\fP and \fBfree()\fP, but you can replace
 the pointers to cause PCRE to use your own functions. Since the block sizes are  the pointers to cause PCRE to use your own functions. Since the block sizes are
 always the same, and are always freed in reverse order, it may be possible to  always the same, and are always freed in reverse order, it may be possible to
Line 99  implement customized memory handlers that are more eff Line 99  implement customized memory handlers that are more eff
 functions.  functions.
 .  .
 .  .
.SS "Limiting \fBpcre[16]_exec()\fP's stack usage".SS "Limiting \fBpcre[16|32]_exec()\fP's stack usage"
 .rs  .rs
 .sp  .sp
 You can set limits on the number of times that \fBmatch()\fP is called, both in  You can set limits on the number of times that \fBmatch()\fP is called, both in
total and recursively. If a limit is exceeded, \fBpcre[16]_exec()\fP returns antotal and recursively. If a limit is exceeded, \fBpcre[16|32]_exec()\fP returns an
 error code. Setting suitable limits should prevent it from running out of  error code. Setting suitable limits should prevent it from running out of
 stack. The default values of the limits are very large, and unlikely ever to  stack. The default values of the limits are very large, and unlikely ever to
 operate. They can be changed when PCRE is built, and they can also be set when  operate. They can be changed when PCRE is built, and they can also be set when
\fBpcre[16]_exec()\fP is called. For details of these interfaces, see the\fBpcre[16|32]_exec()\fP is called. For details of these interfaces, see the
 .\" HREF  .\" HREF
 \fBpcrebuild\fP  \fBpcrebuild\fP
 .\"  .\"
 documentation and the  documentation and the
 .\" HTML <a href="pcreapi.html#extradata">  .\" HTML <a href="pcreapi.html#extradata">
 .\" </a>  .\" </a>
section on extra data for \fBpcre[16]_exec()\fPsection on extra data for \fBpcre[16|32]_exec()\fP
 .\"  .\"
 in the  in the
 .\" HREF  .\" HREF
Line 131  In Unix-like environments, the \fBpcretest\fP test pro Line 131  In Unix-like environments, the \fBpcretest\fP test pro
 option (\fB-S\fP) that can be used to increase the size of its stack. As long  option (\fB-S\fP) that can be used to increase the size of its stack. As long
 as the stack is large enough, another option (\fB-M\fP) can be used to find the  as the stack is large enough, another option (\fB-M\fP) can be used to find the
 smallest limits that allow a particular pattern to match a given subject  smallest limits that allow a particular pattern to match a given subject
string. This is done by calling \fBpcre[16]_exec()\fP repeatedly with differentstring. This is done by calling \fBpcre[16|32]_exec()\fP repeatedly with different
 limits.  limits.
 .  .
 .  .
Line 181  limit on stack size by code such as this: Line 181  limit on stack size by code such as this:
 .sp  .sp
 This reads the current limits (soft and hard) using \fBgetrlimit()\fP, then  This reads the current limits (soft and hard) using \fBgetrlimit()\fP, then
 attempts to increase the soft limit to 100Mb using \fBsetrlimit()\fP. You must  attempts to increase the soft limit to 100Mb using \fBsetrlimit()\fP. You must
do this before calling \fBpcre[16]_exec()\fP.do this before calling \fBpcre[16|32]_exec()\fP.
 .  .
 .  .
 .SS "Changing stack size in Mac OS X"  .SS "Changing stack size in Mac OS X"
Line 210  Cambridge CB2 3QH, England. Line 210  Cambridge CB2 3QH, England.
 .rs  .rs
 .sp  .sp
 .nf  .nf
Last updated: 21 January 2012Last updated: 24 June 2012
 Copyright (c) 1997-2012 University of Cambridge.  Copyright (c) 1997-2012 University of Cambridge.
 .fi  .fi
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  Added in v.1.1.1.4

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