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| author | George Hazan <george.hazan@gmail.com> | 2015-06-16 11:04:10 +0000 |
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| committer | George Hazan <george.hazan@gmail.com> | 2015-06-16 11:04:10 +0000 |
| commit | 437835559168a5945a1196161660c439266eb59d (patch) | |
| tree | 60ee164dbe2d9fed20a7455b5e72f3d5b54e6839 /plugins/Pcre16/docs/doc/html/pcrestack.html | |
| parent | ef9e5821a695a9f875712c2d767360cce15c0f6b (diff) | |
unified project for pcre16 moved to libs
git-svn-id: http://svn.miranda-ng.org/main/trunk@14195 1316c22d-e87f-b044-9b9b-93d7a3e3ba9c
Diffstat (limited to 'plugins/Pcre16/docs/doc/html/pcrestack.html')
| -rw-r--r-- | plugins/Pcre16/docs/doc/html/pcrestack.html | 225 |
1 files changed, 0 insertions, 225 deletions
diff --git a/plugins/Pcre16/docs/doc/html/pcrestack.html b/plugins/Pcre16/docs/doc/html/pcrestack.html deleted file mode 100644 index af6406d070..0000000000 --- a/plugins/Pcre16/docs/doc/html/pcrestack.html +++ /dev/null @@ -1,225 +0,0 @@ -<html> -<head> -<title>pcrestack specification</title> -</head> -<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> -<h1>pcrestack man page</h1> -<p> -Return to the <a href="index.html">PCRE index page</a>. -</p> -<p> -This page is part of the PCRE HTML documentation. It was generated automatically -from the original man page. If there is any nonsense in it, please consult the -man page, in case the conversion went wrong. -<br> -<br><b> -PCRE DISCUSSION OF STACK USAGE -</b><br> -<P> -When you call <b>pcre[16|32]_exec()</b>, it makes use of an internal function -called <b>match()</b>. 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 -try a different alternative if the first one fails. As matching proceeds deeper -and deeper into the tree of possibilities, the recursion depth increases. The -<b>match()</b> function is also called in other circumstances, for example, -whenever a parenthesized sub-pattern is entered, and in certain cases of -repetition. -</P> -<P> -Not all calls of <b>match()</b> increase the recursion depth; for an item such -as a* it may be called several times at the same level, after matching -different numbers of a's. Furthermore, in a number of cases where the result of -the recursive call would immediately be passed back as the result of the -current call (a "tail recursion"), the function is just restarted instead. -</P> -<P> -The above comments apply when <b>pcre[16|32]_exec()</b> is run in its normal -interpretive manner. If the pattern was studied with the -PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was successful, and -the options passed to <b>pcre[16|32]_exec()</b> were not incompatible, the matching -process uses the JIT-compiled code instead of the <b>match()</b> function. In -this case, the memory requirements are handled entirely differently. See the -<a href="pcrejit.html"><b>pcrejit</b></a> -documentation for details. -</P> -<P> -The <b>pcre[16|32]_dfa_exec()</b> function operates in an entirely different way, -and uses recursion only when there is a regular expression recursion or -subroutine call in the pattern. This includes the processing of assertion and -"once-only" subpatterns, which are handled like subroutine calls. Normally, -these are never very deep, and the limit on the complexity of -<b>pcre[16|32]_dfa_exec()</b> is controlled by the amount of workspace it is given. -However, it is possible to write patterns with runaway infinite recursions; -such patterns will cause <b>pcre[16|32]_dfa_exec()</b> to run out of stack. At -present, there is no protection against this. -</P> -<P> -The comments that follow do NOT apply to <b>pcre[16|32]_dfa_exec()</b>; they are -relevant only for <b>pcre[16|32]_exec()</b> without the JIT optimization. -</P> -<br><b> -Reducing <b>pcre[16|32]_exec()</b>'s stack usage -</b><br> -<P> -Each time that <b>match()</b> is actually called recursively, it uses memory -from the process stack. For certain kinds of pattern and data, very large -amounts of stack may be needed, despite the recognition of "tail recursion". -You can often reduce the amount of recursion, and therefore the amount of stack -used, by modifying the pattern that is being matched. Consider, for example, -this pattern: -<pre> - ([^<]|<(?!inet))+ -</pre> -It matches from wherever it starts until it encounters "<inet" or the end of -the data, and is the kind of pattern that might be used when processing an XML -file. Each iteration of the outer parentheses matches either one character that -is not "<" or a "<" that is not followed by "inet". However, each time a -parenthesis is processed, a recursion occurs, so this formulation uses a stack -frame for each matched character. For a long string, a lot of stack is -required. Consider now this rewritten pattern, which matches exactly the same -strings: -<pre> - ([^<]++|<(?!inet))+ -</pre> -This uses very much less stack, because runs of characters that do not contain -"<" are "swallowed" in one item inside the parentheses. Recursion happens only -when a "<" character that is not followed by "inet" is encountered (and we -assume this is relatively rare). A possessive quantifier is used to stop any -backtracking into the runs of non-"<" characters, but that is not related to -stack usage. -</P> -<P> -This example shows that one way of avoiding stack problems when matching long -subject strings is to write repeated parenthesized subpatterns to match more -than one character whenever possible. -</P> -<br><b> -Compiling PCRE to use heap instead of stack for <b>pcre[16|32]_exec()</b> -</b><br> -<P> -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 -<b>pcre[16|32]_exec()</b> is running. This makes it run a lot more slowly, however. -Details of how to do this are given in the -<a href="pcrebuild.html"><b>pcrebuild</b></a> -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 -<b>pcre[16|32]_stack_malloc</b> and <b>pcre[16|32]_stack_free</b> variables. By -default, these point to <b>malloc()</b> and <b>free()</b>, but you can replace -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 -implement customized memory handlers that are more efficient than the standard -functions. -</P> -<br><b> -Limiting <b>pcre[16|32]_exec()</b>'s stack usage -</b><br> -<P> -You can set limits on the number of times that <b>match()</b> is called, both in -total and recursively. If a limit is exceeded, <b>pcre[16|32]_exec()</b> returns an -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 -operate. They can be changed when PCRE is built, and they can also be set when -<b>pcre[16|32]_exec()</b> is called. For details of these interfaces, see the -<a href="pcrebuild.html"><b>pcrebuild</b></a> -documentation and the -<a href="pcreapi.html#extradata">section on extra data for <b>pcre[16|32]_exec()</b></a> -in the -<a href="pcreapi.html"><b>pcreapi</b></a> -documentation. -</P> -<P> -As a very rough rule of thumb, you should reckon on about 500 bytes per -recursion. Thus, if you want to limit your stack usage to 8Mb, you should set -the limit at 16000 recursions. A 64Mb stack, on the other hand, can support -around 128000 recursions. -</P> -<P> -In Unix-like environments, the <b>pcretest</b> test program has a command line -option (<b>-S</b>) that can be used to increase the size of its stack. As long -as the stack is large enough, another option (<b>-M</b>) can be used to find the -smallest limits that allow a particular pattern to match a given subject -string. This is done by calling <b>pcre[16|32]_exec()</b> repeatedly with different -limits. -</P> -<br><b> -Obtaining an estimate of stack usage -</b><br> -<P> -The actual amount of stack used per recursion can vary quite a lot, depending -on the compiler that was used to build PCRE and the optimization or debugging -options that were set for it. The rule of thumb value of 500 bytes mentioned -above may be larger or smaller than what is actually needed. A better -approximation can be obtained by running this command: -<pre> - pcretest -m -C -</pre> -The <b>-C</b> option causes <b>pcretest</b> to output information about the -options with which PCRE was compiled. When <b>-m</b> is also given (before -<b>-C</b>), information about stack use is given in a line like this: -<pre> - Match recursion uses stack: approximate frame size = 640 bytes -</pre> -The value is approximate because some recursions need a bit more (up to perhaps -16 more bytes). -</P> -<P> -If the above command is given when PCRE is compiled to use the heap instead of -the stack for recursion, the value that is output is the size of each block -that is obtained from the heap. -</P> -<br><b> -Changing stack size in Unix-like systems -</b><br> -<P> -In Unix-like environments, there is not often a problem with the stack unless -very long strings are involved, though the default limit on stack size varies -from system to system. Values from 8Mb to 64Mb are common. You can find your -default limit by running the command: -<pre> - ulimit -s -</pre> -Unfortunately, the effect of running out of stack is often SIGSEGV, though -sometimes a more explicit error message is given. You can normally increase the -limit on stack size by code such as this: -<pre> - struct rlimit rlim; - getrlimit(RLIMIT_STACK, &rlim); - rlim.rlim_cur = 100*1024*1024; - setrlimit(RLIMIT_STACK, &rlim); -</pre> -This reads the current limits (soft and hard) using <b>getrlimit()</b>, then -attempts to increase the soft limit to 100Mb using <b>setrlimit()</b>. You must -do this before calling <b>pcre[16|32]_exec()</b>. -</P> -<br><b> -Changing stack size in Mac OS X -</b><br> -<P> -Using <b>setrlimit()</b>, as described above, should also work on Mac OS X. It -is also possible to set a stack size when linking a program. There is a -discussion about stack sizes in Mac OS X at this web site: -<a href="http://developer.apple.com/qa/qa2005/qa1419.html">http://developer.apple.com/qa/qa2005/qa1419.html.</a> -</P> -<br><b> -AUTHOR -</b><br> -<P> -Philip Hazel -<br> -University Computing Service -<br> -Cambridge CB2 3QH, England. -<br> -</P> -<br><b> -REVISION -</b><br> -<P> -Last updated: 24 June 2012 -<br> -Copyright © 1997-2012 University of Cambridge. -<br> -<p> -Return to the <a href="index.html">PCRE index page</a>. -</p> |