[bug #58006] Massive slow down due to slow get_env because libintl doesn't cache untranslated strings

[Jianxiang Wang]

URL:
  <https://savannah.gnu.org/bugs/?58006>

                 Summary: Massive slow down due to slow get_env because
libintl doesn't cache untranslated strings
                 Project: GNU gettext
            Submitted by: qrox
            Submitted on: Tue 17 Mar 2020 04:06:08 PM UTC
                Category: End-user / runtime
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

We're using `gettext/libintl` in a text-intensive project (Cataclysm:DDA, to
be precise). Since we use English as the source language, we do not compile a
.mo file for English. In some of the program's UIs, a large amount of text is
translated, processed, and displayed, where I noticed a significant slow down,
particularly on MinGW target. Profiling the program showed that `getenv()`,
called by `libintl`, took the majority of CPU time (~50%). So I profiled
`libintl` and found out it was caused by a caching issue when `libintl` does
not find a translation for a source string.

The following are tested on git commit
`284d55ec4c24479789b250bdcba9e3782cca2994` of `gettext`.

So, in `libintl_dcigettext`, when a translation is not found
(`dcigettext.c:765`), the code to cache translation (`dcigettext.c:816`) is
skipped, and the source string is returned without caching
(`dcigettext.c:850`). The next time `libintl_dcigettext` is called with the
same source string, the whole process of translation lookup happens again,
including a call to `getenv("GETTEXT_LOG_UNTRANSLATED")` in
`libintl_dcigettext()`, a call to `getenv("LANGUAGE")` in
`guess_category_value()`, and several `getenv()` calls in
`gl_locale_name_environ()`, which took up the majority of execution time of
these functions.

After switching the language of the program to a non-English one, I observed a
noticeable performance improvement, which confirmed my theory.

While I think there might be a performance issue with Windows' `getenv()`
itself, I think this is also a bug of `libintl` that needs to be fixed.




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