/[pcre]/code/trunk/doc/pcre.txt
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revision 345 by ph10, Mon Apr 28 15:10:02 2008 UTC revision 358 by ph10, Wed Jul 9 11:03:07 2008 UTC
# Line 6536  PCRE DISCUSSION OF STACK USAGE Line 6536  PCRE DISCUSSION OF STACK USAGE
6536         ing long subject strings is to write repeated parenthesized subpatterns         ing long subject strings is to write repeated parenthesized subpatterns
6537         to match more than one character whenever possible.         to match more than one character whenever possible.
6538    
6539       Compiling PCRE to use heap instead of stack
6540    
6541         In environments where stack memory is constrained, you  might  want  to         In environments where stack memory is constrained, you  might  want  to
6542         compile  PCRE to use heap memory instead of stack for remembering back-         compile  PCRE to use heap memory instead of stack for remembering back-
6543         up points. This makes it run a lot more slowly, however. Details of how         up points. This makes it run a lot more slowly, however. Details of how
# Line 6548  PCRE DISCUSSION OF STACK USAGE Line 6550  PCRE DISCUSSION OF STACK USAGE
6550         freed in reverse order, it may be possible to implement customized mem-         freed in reverse order, it may be possible to implement customized mem-
6551         ory handlers that are more efficient than the standard functions.         ory handlers that are more efficient than the standard functions.
6552    
6553       Limiting PCRE's stack usage
6554    
6555           PCRE has an internal counter that can be used to  limit  the  depth  of
6556           recursion,  and  thus cause pcre_exec() to give an error code before it
6557           runs out of stack. By default, the limit is very  large,  and  unlikely
6558           ever  to operate. It can be changed when PCRE is built, and it can also
6559           be set when pcre_exec() is called. For details of these interfaces, see
6560           the pcrebuild and pcreapi documentation.
6561    
6562           As a very rough rule of thumb, you should reckon on about 500 bytes per
6563           recursion. Thus, if you want to limit your  stack  usage  to  8Mb,  you
6564           should  set  the  limit at 16000 recursions. A 64Mb stack, on the other
6565           hand, can support around 128000 recursions. The pcretest  test  program
6566           has a command line option (-S) that can be used to increase the size of
6567           its stack.
6568    
6569       Changing stack size in Unix-like systems
6570    
6571         In Unix-like environments, there is not often a problem with the  stack         In Unix-like environments, there is not often a problem with the  stack
6572         unless  very  long  strings  are  involved, though the default limit on         unless  very  long  strings  are  involved, though the default limit on
6573         stack size varies from system to system. Values from 8Mb  to  64Mb  are         stack size varies from system to system. Values from 8Mb  to  64Mb  are
# Line 6568  PCRE DISCUSSION OF STACK USAGE Line 6588  PCRE DISCUSSION OF STACK USAGE
6588         attempts to increase the soft limit to  100Mb  using  setrlimit().  You         attempts to increase the soft limit to  100Mb  using  setrlimit().  You
6589         must do this before calling pcre_exec().         must do this before calling pcre_exec().
6590    
6591         PCRE  has  an  internal  counter that can be used to limit the depth of     Changing stack size in Mac OS X
        recursion, and thus cause pcre_exec() to give an error code  before  it  
        runs  out  of  stack. By default, the limit is very large, and unlikely  
        ever to operate. It can be changed when PCRE is built, and it can  also  
        be set when pcre_exec() is called. For details of these interfaces, see  
        the pcrebuild and pcreapi documentation.  
6592    
6593         As a very rough rule of thumb, you should reckon on about 500 bytes per         Using setrlimit(), as described above, should also work on Mac OS X. It
6594         recursion.  Thus,  if  you  want  to limit your stack usage to 8Mb, you         is also possible to set a stack size when linking a program. There is a
6595         should set the limit at 16000 recursions. A 64Mb stack,  on  the  other         discussion   about   stack  sizes  in  Mac  OS  X  at  this  web  site:
6596         hand,  can  support around 128000 recursions. The pcretest test program         http://developer.apple.com/qa/qa2005/qa1419.html.
        has a command line option (-S) that can be used to increase the size of  
        its stack.  
6597    
6598    
6599  AUTHOR  AUTHOR
# Line 6592  AUTHOR Line 6605  AUTHOR
6605    
6606  REVISION  REVISION
6607    
6608         Last updated: 05 June 2007         Last updated: 09 July 2008
6609         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
6610  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
6611    
6612    
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