* configure.in: check whether localtime caches TZ. copied from

Emacs 20.5.
	* acconfig.h: add LOCALTIME_CACHE.

	* These changes should make it unnecessary to call tzset from
	Scheme after modifying the TZ environment variable, even if the
	system date facilities cache the value.
	* stime.c (setzone, scm_localtime): added comments.
	(tzset): don't define a noop tzset macro if HAVE_TZSET not defined.
	(setzone): don't call tzset.
	(restorezone): call tzset only if HAVE_TZSET is defined.
	(scm_tzset): don't define if HAVE_TZSET not defined.  Change the
	doc string to indicate that this procedure isn't likely to do
	anything useful.
	(scm_localtime, scm_strftime, scm_mktime): call tzset if
	LOCALTIME_CACHE is defined.

ChangeLog

@@ -1,3 +1,9 @@
+2000-01-09  Gary Houston  <ghouston@arglist.com>
+
+	* configure.in: check whether localtime caches TZ.  copied from
+	Emacs 20.5.
+	* acconfig.h: add LOCALTIME_CACHE.
+
 Tue Dec 14 09:12:22 1999  Greg J. Badros  <gjb@cs.washington.edu>
 
 	* configure.in: Make it be guile-snarf.awk, since we'll be

NEWS

@@ -142,6 +142,10 @@ need minor modification: an error will be thrown with key
 now possible to use `defined?' to check whether the facility is
 available.
 
+** Procedures which depend on the timezone should now give the correct
+result on systems which cache the TZ environment variable, even if TZ 
+is changed without calling tzset.
+
 * Changes to the networking interfaces:
 
 ** New functions: htons, ntohs, htonl, ntohl: for converting short and

acconfig.h

@@ -110,6 +110,9 @@
 /* Define if dlsym automatically supplies a leading underscore. */
 #undef DLSYM_ADDS_USCORE
 
+/* Define if localtime caches the TZ setting.  */
+#undef LOCALTIME_CACHE
+
 /* Define if the operating system can restart system calls.  */
 #undef HAVE_RESTARTS
 

configure.in

@@ -248,6 +248,53 @@ AC_CHECK_FUNCS(sethostent   gethostent   endhostent   dnl
 
 dnl </GNU-WIN32 hacks>
 
+AC_MSG_CHECKING(whether localtime caches TZ)
+AC_CACHE_VAL(guile_cv_localtime_cache,
+[if test x$ac_cv_func_tzset = xyes; then
+AC_TRY_RUN([#include <time.h>
+#if STDC_HEADERS
+# include <stdlib.h>
+#endif
+extern char **environ;
+unset_TZ ()
+{
+  char **from, **to;
+  for (to = from = environ; (*to = *from); from++)
+    if (! (to[0][0] == 'T' && to[0][1] == 'Z' && to[0][2] == '='))
+      to++;
+}
+char TZ_GMT0[] = "TZ=GMT0";
+char TZ_PST8[] = "TZ=PST8";
+main()
+{
+  time_t now = time ((time_t *) 0);
+  int hour_GMT0, hour_unset;
+  if (putenv (TZ_GMT0) != 0)
+    exit (1);
+  hour_GMT0 = localtime (&now)->tm_hour;
+  unset_TZ ();
+  hour_unset = localtime (&now)->tm_hour;
+  if (putenv (TZ_PST8) != 0)
+    exit (1);
+  if (localtime (&now)->tm_hour == hour_GMT0)
+    exit (1);
+  unset_TZ ();
+  if (localtime (&now)->tm_hour != hour_unset)
+    exit (1);
+  exit (0);
+}], guile_cv_localtime_cache=no, guile_cv_localtime_cache=yes,
+[# If we have tzset, assume the worst when cross-compiling.
+guile_cv_localtime_cache=yes])
+else
+        # If we lack tzset, report that localtime does not cache TZ,
+        # since we can't invalidate the cache if we don't have tzset.
+        guile_cv_localtime_cache=no
+fi])dnl
+AC_MSG_RESULT($guile_cv_localtime_cache)
+if test $guile_cv_localtime_cache = yes; then
+  AC_DEFINE(LOCALTIME_CACHE)
+fi
+
 dnl Test whether system calls are restartable by default on the
 dnl current system.  If they are not, we put a loop around every system
 dnl call to check for EINTR (see SCM_SYSCALL) and do not attempt to

libguile/ChangeLog

@@ -1,3 +1,18 @@
+2000-01-09  Gary Houston  <ghouston@arglist.com>
+
+	* These changes should make it unnecessary to call tzset from
+	Scheme after modifying the TZ environment variable, even if the
+	system date facilities cache the value.
+	* stime.c (setzone, scm_localtime): added comments.
+	(tzset): don't define a noop tzset macro if HAVE_TZSET not defined.
+	(setzone): don't call tzset.
+	(restorezone): call tzset only if HAVE_TZSET is defined.
+	(scm_tzset): don't define if HAVE_TZSET not defined.  Change the
+	doc string to indicate that this procedure isn't likely to do
+	anything useful.
+	(scm_localtime, scm_strftime, scm_mktime): call tzset if
+	LOCALTIME_CACHE is defined.
+
 2000-01-09  Mikael Djurfeldt  <mdj@thalamus.nada.kth.se>
 
 	* posix.c (scm_sync): Return SCM_UNSPECIFIED.

libguile/stime.c

@@ -205,12 +205,6 @@ terminated child processes.
 #undef FUNC_NAME
 #endif /* HAVE_TIMES */
 
-#ifndef HAVE_TZSET
-/* GNU-WIN32's cygwin.dll doesn't have this. */
-#define tzset()
-#endif
-
-
 static long scm_my_base = 0;
 
 SCM_DEFINE (scm_get_internal_run_time, "get-internal-run-time", 0, 0, 0, 
@@ -298,6 +292,10 @@ filltime (struct tm *bd_time, int zoff, char *zname)
 static char tzvar[3] = "TZ";
 extern char ** environ;
 
+/* if zone is set, create a temporary environment with only a TZ
+   string.  other threads or interrupt handlers shouldn't be allowed
+   to run until the corresponding restorezone is called.  hence the use
+   of a static variable for tmpenv is no big deal.  */
 static char **
 setzone (SCM zone, int pos, const char *subr)
 {
@@ -308,7 +306,6 @@ setzone (SCM zone, int pos, const char *subr)
       static char *tmpenv[2];
       char *buf;
 
-      /* if zone was supplied, set the environment temporarily.  */
       SCM_ASSERT (SCM_ROSTRINGP (zone), zone, pos, subr);
       SCM_COERCE_SUBSTR (zone);
       buf = scm_must_malloc (SCM_LENGTH (zone) + sizeof (tzvar) + 1,
@@ -318,7 +315,6 @@ setzone (SCM zone, int pos, const char *subr)
       tmpenv[0] = buf;
       tmpenv[1] = 0;
       environ = tmpenv;
-      tzset();
     }
   return oldenv;
 }
@@ -330,7 +326,10 @@ restorezone (SCM zone, char **oldenv, const char *subr)
     {
       scm_must_free (environ[0]);
       environ = oldenv;
+#ifdef HAVE_TZSET
+      /* for the possible benefit of user code linked with libguile.  */
       tzset();
+#endif
     }
 }
 
@@ -353,8 +352,14 @@ used.")
   int err;
 
   itime = SCM_NUM2LONG (1,time);
+
+  /* deferring interupts is essential since a) setzone may install a temporary
+     environment b) localtime uses a static buffer.  */
   SCM_DEFER_INTS;
   oldenv = setzone (zone, SCM_ARG2, FUNC_NAME);
+#ifdef LOCALTIME_CACHE
+  tzset ();
+#endif
   ltptr = localtime (&itime);
   err = errno;
   if (ltptr)
@@ -487,6 +492,9 @@ as @var{bd-time} but with normalized values.")
 
   SCM_DEFER_INTS;
   oldenv = setzone (zone, SCM_ARG2, FUNC_NAME);
+#ifdef LOCALTIME_CACHE
+  tzset ();
+#endif
   itime = mktime (&lt);
   err = errno;
 
@@ -539,18 +547,20 @@ as @var{bd-time} but with normalized values.")
 }
 #undef FUNC_NAME
 
+#ifdef HAVE_TZSET
 SCM_DEFINE (scm_tzset, "tzset", 0, 0, 0, 
             (void),
-"Initialize the timezone from the TZ environment variable or the system
-default.  Usually this is done automatically by other procedures which
-use the time zone, but this procedure may need to be used if TZ
-is changed.")
+"Initialize the timezone from the TZ environment variable
+or the system default.  It's not usually necessary to call this procedure
+since it's done automatically by other procedures that depend on the
+timezone.")
 #define FUNC_NAME s_scm_tzset
 {
   tzset();
   return SCM_UNSPECIFIED;
 }
 #undef FUNC_NAME
+#endif /* HAVE_TZSET */
 
 SCM_DEFINE (scm_strftime, "strftime", 2, 0, 0,
             (SCM format, SCM stime),
@@ -579,6 +589,9 @@ is the formatted string.
   len = SCM_ROLENGTH (format);
 
   tbuf = SCM_MUST_MALLOC (size);
+#ifdef LOCALTIME_CACHE
+  tzset ();
+#endif
   while ((len = strftime (tbuf, size, fmt, &t)) == size)
     {
       scm_must_free (tbuf);