Perl-совместимые регулярные выражения (Perl-compatible regular expressions)
JIT FAST PATH API
Because the API described above falls back to interpreted
execution when JIT is not available, it is convenient for
programs that are written for general use in many environments.
However, calling JIT via pcre_exec() does have a performance
impact. Programs that are written for use where JIT is known to
be available, and which need the best possible performance, can
instead use a "fast path" API to call JIT execution directly
instead of calling pcre_exec() (obviously only for patterns that
have been successfully studied by JIT).
The fast path function is called pcre_jit_exec(), and it takes
exactly the same arguments as pcre_exec(), plus one additional
argument that must point to a JIT stack. The JIT stack
arrangements described above do not apply. The return values are
the same as for pcre_exec().
When you call pcre_exec(), as well as testing for invalid
options, a number of other sanity checks are performed on the
arguments. For example, if the subject pointer is NULL, or its
length is negative, an immediate error is given. Also, unless
PCRE_NO_UTF[8|16|32] is set, a UTF subject string is tested for
validity. In the interests of speed, these checks do not happen
on the JIT fast path, and if invalid data is passed, the result
is undefined.
Bypassing the sanity checks and the pcre_exec() wrapping can give
speedups of more than 10%.
Note that the pcre_jit_exec() function is not available in
versions of PCRE before 8.32 (released in November 2012). If you
need to support versions that old you must either use the slower
pcre_exec(), or switch between the two codepaths by checking the
values of PCRE_MAJOR and PCRE_MINOR.
Due to an unfortunate implementation oversight, even in versions
8.32 and later there will be no pcre_jit_exec() stub function
defined when PCRE is compiled with --disable-jit, which is the
default, and there's no way to detect whether PCRE was compiled
with --enable-jit via a macro.
If you need to support versions older than 8.32, or versions that
may not build with --enable-jit, you must either use the slower
pcre_exec(), or switch between the two codepaths by checking the
values of PCRE_MAJOR and PCRE_MINOR.
Switching between the two by checking the version assumes that
all the versions being targeted are built with --enable-jit. To
also support builds that may use --disable-jit either pcre_exec()
must be used, or a compile-time check for JIT via pcre_config()
(which assumes the runtime environment will be the same), or as
the Git project decided to do, simply assume that pcre_jit_exec()
is present in 8.32 or later unless a compile-time flag is
provided, see the "grep: un-break building with PCRE >= 8.32
without --enable-jit" commit in git.git for an example of that.
