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diff --git a/plugins/Pcre16/docs/doc/pcrestack.3 b/plugins/Pcre16/docs/doc/pcrestack.3 deleted file mode 100644 index 798f0bca63..0000000000 --- a/plugins/Pcre16/docs/doc/pcrestack.3 +++ /dev/null @@ -1,215 +0,0 @@ -.TH PCRESTACK 3 "24 June 2012" "PCRE 8.30" -.SH NAME -PCRE - Perl-compatible regular expressions -.SH "PCRE DISCUSSION OF STACK USAGE" -.rs -.sp -When 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 -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 -\fBmatch()\fP function is also called in other circumstances, for example, -whenever a parenthesized sub-pattern is entered, and in certain cases of -repetition. -.P -Not all calls of \fBmatch()\fP 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 -The above comments apply when \fBpcre[16|32]_exec()\fP 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 \fBpcre[16|32]_exec()\fP were not incompatible, the matching -process uses the JIT-compiled code instead of the \fBmatch()\fP function. In -this case, the memory requirements are handled entirely differently. See the -.\" HREF -\fBpcrejit\fP -.\" -documentation for details. -.P -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 -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 -\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; -such patterns will cause \fBpcre[16|32]_dfa_exec()\fP to run out of stack. At -present, there is no protection against this. -.P -The comments that follow do NOT apply to \fBpcre[16|32]_dfa_exec()\fP; they are -relevant only for \fBpcre[16|32]_exec()\fP without the JIT optimization. -. -. -.SS "Reducing \fBpcre[16|32]_exec()\fP's stack usage" -.rs -.sp -Each time that \fBmatch()\fP 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: -.sp - ([^<]|<(?!inet))+ -.sp -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: -.sp - ([^<]++|<(?!inet))+ -.sp -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 -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. -. -. -.SS "Compiling PCRE to use heap instead of stack for \fBpcre[16|32]_exec()\fP" -.rs -.sp -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 -\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 -.\" HREF -\fBpcrebuild\fP -.\" -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 -\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 -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. -. -. -.SS "Limiting \fBpcre[16|32]_exec()\fP's stack usage" -.rs -.sp -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|32]_exec()\fP 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 -\fBpcre[16|32]_exec()\fP is called. For details of these interfaces, see the -.\" HREF -\fBpcrebuild\fP -.\" -documentation and the -.\" HTML <a href="pcreapi.html#extradata"> -.\" </a> -section on extra data for \fBpcre[16|32]_exec()\fP -.\" -in the -.\" HREF -\fBpcreapi\fP -.\" -documentation. -.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 -In Unix-like environments, the \fBpcretest\fP test program has a command line -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 -smallest limits that allow a particular pattern to match a given subject -string. This is done by calling \fBpcre[16|32]_exec()\fP repeatedly with different -limits. -. -. -.SS "Obtaining an estimate of stack usage" -.rs -.sp -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: -.sp - pcretest -m -C -.sp -The \fB-C\fP option causes \fBpcretest\fP to output information about the -options with which PCRE was compiled. When \fB-m\fP is also given (before -\fB-C\fP), information about stack use is given in a line like this: -.sp - Match recursion uses stack: approximate frame size = 640 bytes -.sp -The value is approximate because some recursions need a bit more (up to perhaps -16 more bytes). -.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. -. -. -.SS "Changing stack size in Unix-like systems" -.rs -.sp -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: -.sp - ulimit -s -.sp -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: -.sp - struct rlimit rlim; - getrlimit(RLIMIT_STACK, &rlim); - rlim.rlim_cur = 100*1024*1024; - setrlimit(RLIMIT_STACK, &rlim); -.sp -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 -do this before calling \fBpcre[16|32]_exec()\fP. -. -. -.SS "Changing stack size in Mac OS X" -.rs -.sp -Using \fBsetrlimit()\fP, 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: -.\" HTML <a href="http://developer.apple.com/qa/qa2005/qa1419.html"> -.\" </a> -http://developer.apple.com/qa/qa2005/qa1419.html. -.\" -. -. -.SH AUTHOR -.rs -.sp -.nf -Philip Hazel -University Computing Service -Cambridge CB2 3QH, England. -.fi -. -. -.SH REVISION -.rs -.sp -.nf -Last updated: 24 June 2012 -Copyright (c) 1997-2012 University of Cambridge. -.fi |