(LOCALTIME_CACHE): Define if tzset exists and

if localtime caches TZ.  Check for tzset.

1 files changed, 31 insertions, 1 deletions

diff --git a/configure.in b/configure.in
index ea656331423..98243750ca6 100644
--- a/configure.in
+++ b/configure.in
@@ -1259,7 +1259,37 @@ AC_FUNC_ALLOCA
 AC_CHECK_LIB(m, sqrt(0.0) + t)
 AC_CHECK_FUNCS(gettimeofday gethostname dup2 rename closedir mkdir rmdir \
 random lrand48 bcopy bcmp logb frexp fmod drem ftime res_init setsid \
-strerror fpathconf select mktime eaccess getpagesize)
+strerror fpathconf select mktime eaccess getpagesize tzset)
+
+AC_MSG_CHECKING(whether localtime caches TZ)
+AC_CACHE_VAL(emacs_cv_localtime_cache,
+[if test $ac_cv_func_tzset = yes; then
+AC_TRY_RUN([#include <time.h>
+#if STDC_HEADERS
+# include <stdlib.h>
+#endif
+main()
+{
+  time_t now = time ((time_t *) 0);
+  int hour;
+  if (putenv ("TZ=GMT0") != 0)
+    exit (1);
+  hour = localtime (&now)->tm_hour;
+  if (putenv ("TZ=PST8") != 0)
+    exit (1);
+  exit (localtime (&now)->tm_hour == hour);
+}], emacs_cv_localtime_cache=no, emacs_cv_localtime_cache=yes,
+[# If we have tzset, assume the worst when cross-compiling.
+emacs_cv_localtime_cache=yes])
+else
+	# If we lack tzset, report that localtime does not cache TZ,
+	# since we can't invalidate the cache if we don't have tzset.
+	emacs_cv_localtime_cache=no
+fi])dnl
+AC_MSG_RESULT($emacs_cv_localtime_cache)
+if test $emacs_cv_localtime_cache = yes; then
+  AC_DEFINE(LOCALTIME_CACHE)
+fi
 
 if test $HAVE_TIMEVAL = yes; then
 AC_MSG_CHECKING(whether gettimeofday can't accept two arguments)