Thread Aware Regex

Directory Server used to use the regular expression pattern matching and replacing library which was not thread safe. Thus, the regular expression operation should have been protected by the mutex lock. Regular expressions could be used by the search filters (syntax plugin), acl, schema file load, and SASL Mapping. If one of them took a long time, the rest should have been blocked. Replacing the library with the thread aware library solves the problem and improves the throughput.

PCRE - Perl Compatible Regular Expressions library is installed on RHELs/Fedoras, by default. The pattern compiled by the library is thread safe:

The compiled form of a regular expression is not altered during matching,  so the same compiled pattern can safely be used by several threads at once.

We are taking advantage of it and replacing the old functions with PCRE.

PCRE is a rich library. We need just a subset of the APIs. We provide simplified slapi APIs wrapping the PCRE APIs.

NAME slapi_re_comp -- compiles a regular expression pattern. A thin wrapper of pcre_compile. SYNOPSIS Slapi_Regex *slapi_re_comp( char *pat, char **error ); PARAMS pat: Pattern to be compiled. error: The error string is set if the compile fails. RETURN VALUE a pointer to the regex handler which stores the compiled pattern. NULL if the compile fails. WARNING The regex handler should be released by slapi_re_free().

NAME slapi_re_exec -- matches a compiled regular expression pattern against a given string. A thin wrapper of pcre_exec. SYNOPSIS int slapi_re_exec( Slapi_Regex *re_handle, char *subject, time_t time_up ); PARAMS re_handle: The regex handler returned from slapi_re_comp. subject: A string to be checked against the compiled pattern. time_up: If the current time is larger than the value, this function returns immediately.  (-1) means no time limit. RETURN VALUE 0 if the string did not match. 1 if the string matched. other values if any error occurred.

NAME slapi_re_subs -- substitutes '&' or '\#' in the param src with the matched string. SYNOPSIS int slapi_re_subs( Slapi_Regex *re_handle, char *subject, char *src, char **dst, unsigned long dstlen ); PARAMS re_handle: The regex handler returned from slapi_re_comp. subject: A string checked against the compiled pattern. src: A given string which could contain the substitution symbols. dst: A pointer pointing to the memory which stores the output string. dstlen: Size of the memory dst. RETURN VALUE 1 if the substitution was successful. 0 if the substitution failed.

NAME slapi_re_free -- releases the regex handler which was returned from slapi_re_comp. SYNOPSIS void slapi_re_free(Slapi_Regex *re_handle); PARAMS re_handle: The regex handler to be released. RETURN VALUE none

Last modified on 11 August 2023