time: New module

time: New module

[Bruno Haible]

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This set of patches introduces a new module 'time', that works around the
inconsistency of time(NULL) with gettimeofday().tv_sec and timespec_get().tv_sec
on glibc systems.

The replacement is a bit slower than the native glibc time(NULL) implementation
— 31 nanoseconds instead of 17 nanoseconds, according to Florian Weimer's
measurements
<https://sourceware.org/pipermail/libc-alpha/2023-March/146133.html>.

The new module is for those GNU programs that prefer to avoid trouble
due to clocks apparently going backwards.

As a bonus, it allows us to fix the test failures of the gettimeofday and
timespec_get tests that occurred with a probability between 0.1% and 0.3%
on glibc/Linux.


2023-03-08  Bruno Haible  <bruno@clisp.org>

	gettimeofday, timespec_get tests: Avoid test failure on glibc/Linux.
	* modules/gettimeofday-tests (Depends-on): Add 'time'.
	* modules/timespec_get-tests (Depends-on): Likewise.
	* tests/test-gettimeofday.c (test_consistency): Update comment.
	* tests/test-timespec_get.c (main): Likewise.

	time: Add tests.
	* tests/test-time.c: New file.
	* modules/time-tests: New file.

	time: New module.
	* lib/time.in.h (time): New declaration.
	* lib/time.c: New file.
	* m4/time_h.m4 (gl_TIME_H_REQUIRE_DEFAULTS): Initialize GNULIB_TIME.
	(gl_TIME_H_DEFAULTS): Initialize REPLACE_TIME.
	* m4/time.m4: New file.
	* modules/time-h (Makefile.am): Substitute GNULIB_TIME, REPLACE_TIME.
	* modules/time: New file.
	* tests/test-time-h-c++.cc: Check the signature of
	GNULIB_NAMESPACE::time.
	* doc/posix-functions/time.texi: Mention the glibc problem and the
	'time' module.


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From cbc0c1cda32bbcfab3ed0391cb9cfde444323571 Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Wed, 8 Mar 2023 17:00:48 +0100
Subject: [PATCH 1/3] time: New module.

* lib/time.in.h (time): New declaration.
* lib/time.c: New file.
* m4/time_h.m4 (gl_TIME_H_REQUIRE_DEFAULTS): Initialize GNULIB_TIME.
(gl_TIME_H_DEFAULTS): Initialize REPLACE_TIME.
* m4/time.m4: New file.
* modules/time-h (Makefile.am): Substitute GNULIB_TIME, REPLACE_TIME.
* modules/time: New file.
* tests/test-time-h-c++.cc: Check the signature of
GNULIB_NAMESPACE::time.
* doc/posix-functions/time.texi: Mention the glibc problem and the
'time' module.
---
 ChangeLog                     | 15 ++++++++++++
 doc/posix-functions/time.texi | 10 +++++++-
 lib/time.c                    | 41 +++++++++++++++++++++++++++++++++
 lib/time.in.h                 | 14 ++++++++++++
 m4/time.m4                    | 43 +++++++++++++++++++++++++++++++++++
 m4/time_h.m4                  |  4 +++-
 modules/time                  | 31 +++++++++++++++++++++++++
 modules/time-h                |  2 ++
 tests/test-time-h-c++.cc      |  4 ++++
 9 files changed, 162 insertions(+), 2 deletions(-)
 create mode 100644 lib/time.c
 create mode 100644 m4/time.m4
 create mode 100644 modules/time

diff --git a/ChangeLog b/ChangeLog
index aac31c31a5..d65b3393c4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+2023-03-08  Bruno Haible  <bruno@clisp.org>
+
+	time: New module.
+	* lib/time.in.h (time): New declaration.
+	* lib/time.c: New file.
+	* m4/time_h.m4 (gl_TIME_H_REQUIRE_DEFAULTS): Initialize GNULIB_TIME.
+	(gl_TIME_H_DEFAULTS): Initialize REPLACE_TIME.
+	* m4/time.m4: New file.
+	* modules/time-h (Makefile.am): Substitute GNULIB_TIME, REPLACE_TIME.
+	* modules/time: New file.
+	* tests/test-time-h-c++.cc: Check the signature of
+	GNULIB_NAMESPACE::time.
+	* doc/posix-functions/time.texi: Mention the glibc problem and the
+	'time' module.
+
 2023-03-08  Bruno Haible  <bruno@clisp.org>
 
 	time-h: Renamed from time.
diff --git a/doc/posix-functions/time.texi b/doc/posix-functions/time.texi
index 765de7aa2a..a8e9abcddf 100644
--- a/doc/posix-functions/time.texi
+++ b/doc/posix-functions/time.texi
@@ -4,10 +4,18 @@
 
 POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/time.html}
 
-Gnulib module: ---
+Gnulib module: time
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+This function is not consistent with @code{gettimeofday} and @code{timespec_get}
+on some platforms:
+@c https://sourceware.org/bugzilla/show_bug.cgi?id=30200
+glibc 2.31 or newer on Linux.
+Namely, in the first 1 to 2.5 milliseconds of every second, @code{time}
+returns a value that is one less than the @code{tv_sec} part of the return
+value of @code{gettimeofday} or @code{timespec_get}.
 @end itemize
 
 Portability problems not fixed by Gnulib:
diff --git a/lib/time.c b/lib/time.c
new file mode 100644
index 0000000000..4e2ee31b48
--- /dev/null
+++ b/lib/time.c
@@ -0,0 +1,41 @@
+/* Provide time() for systems for which it's broken.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   This file is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <time.h>
+
+#include <stdlib.h>
+#include <sys/time.h>
+
+time_t
+time (time_t *tp)
+{
+  struct timeval tv;
+  time_t tt;
+
+  if (gettimeofday (&tv, NULL) < 0)
+    abort ();
+  tt = tv.tv_sec;
+
+  if (tp)
+    *tp = tt;
+
+  return tt;
+}
diff --git a/lib/time.in.h b/lib/time.in.h
index 87cda21413..3f9af920e3 100644
--- a/lib/time.in.h
+++ b/lib/time.in.h
@@ -143,6 +143,20 @@ _GL_CXXALIAS_SYS (timespec_getres, int, (struct timespec *ts, int base));
 _GL_CXXALIASWARN (timespec_getres);
 # endif
 
+/* Return the number of seconds that have elapsed since the Epoch.  */
+# if @GNULIB_TIME@
+#  if @REPLACE_TIME@
+#   if !(defined __cplusplus && defined GNULIB_NAMESPACE)
+#    define time rpl_time
+#   endif
+_GL_FUNCDECL_RPL (time, time_t, (time_t *__tp));
+_GL_CXXALIAS_RPL (time, time_t, (time_t *__tp));
+#  else
+_GL_CXXALIAS_SYS (time, time_t, (time_t *__tp));
+#  endif
+_GL_CXXALIASWARN (time);
+# endif
+
 /* Sleep for at least RQTP seconds unless interrupted,  If interrupted,
    return -1 and store the remaining time into RMTP.  See
    <https://pubs.opengroup.org/onlinepubs/9699919799/functions/nanosleep.html>.  */
diff --git a/m4/time.m4 b/m4/time.m4
new file mode 100644
index 0000000000..0dbb6011ed
--- /dev/null
+++ b/m4/time.m4
@@ -0,0 +1,43 @@
+# time.m4 serial 1
+dnl Copyright (C) 2023 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl From Bruno Haible.
+
+AC_DEFUN([gl_FUNC_TIME],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  dnl glibc has the bug https://sourceware.org/bugzilla/show_bug.cgi?id=30200 .
+  AC_CACHE_CHECK([whether time() works],
+    [gl_cv_func_time_works],
+    [dnl Guess that it works except on glibc >= 2.31 with Linux.
+     dnl And binaries produced on glibc < 2.31 need to run fine on newer
+     dnl glibc versions as well; therefore ignore __GLIBC_MINOR__.
+     case "$host_os" in
+       linux*-gnu*)
+         AC_EGREP_CPP([Unlucky], [
+           #include <features.h>
+           #ifdef __GNU_LIBRARY__
+            #if __GLIBC__ == 2
+             Unlucky GNU user
+            #endif
+           #endif
+           ],
+           [gl_cv_func_time_works="guessing no"],
+           [gl_cv_func_time_works="guessing yes"])
+         ;;
+       *) gl_cv_func_time_works="guessing yes";;
+     esac
+    ])
+  case "$gl_cv_func_time_works" in
+    *no) REPLACE_TIME=1 ;;
+  esac
+])
+
+# Prerequisites of lib/time.c.
+AC_DEFUN([gl_PREREQ_TIME],
+[
+  :
+])
diff --git a/m4/time_h.m4 b/m4/time_h.m4
index b74870c3d0..51d553a2f1 100644
--- a/m4/time_h.m4
+++ b/m4/time_h.m4
@@ -2,7 +2,7 @@
 
 # Copyright (C) 2000-2001, 2003-2007, 2009-2023 Free Software Foundation, Inc.
 
-# serial 21
+# serial 22
 
 # This file is free software; the Free Software Foundation
 # gives unlimited permission to copy and/or distribute it,
@@ -137,6 +137,7 @@ AC_DEFUN([gl_TIME_H_REQUIRE_DEFAULTS]
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_NANOSLEEP])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_STRFTIME])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_STRPTIME])
+    gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_TIME])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_TIMEGM])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_TIMESPEC_GET])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_TIMESPEC_GETRES])
@@ -169,6 +170,7 @@ AC_DEFUN([gl_TIME_H_DEFAULTS]
   REPLACE_MKTIME=GNULIB_PORTCHECK;       AC_SUBST([REPLACE_MKTIME])
   REPLACE_NANOSLEEP=GNULIB_PORTCHECK;    AC_SUBST([REPLACE_NANOSLEEP])
   REPLACE_STRFTIME=GNULIB_PORTCHECK;     AC_SUBST([REPLACE_STRFTIME])
+  REPLACE_TIME=0;                        AC_SUBST([REPLACE_TIME])
   REPLACE_TIMEGM=GNULIB_PORTCHECK;       AC_SUBST([REPLACE_TIMEGM])
   REPLACE_TIMESPEC_GET=GNULIB_PORTCHECK; AC_SUBST([REPLACE_TIMESPEC_GET])
   REPLACE_TZSET=GNULIB_PORTCHECK;        AC_SUBST([REPLACE_TZSET])
diff --git a/modules/time b/modules/time
new file mode 100644
index 0000000000..45f5ffd35f
--- /dev/null
+++ b/modules/time
@@ -0,0 +1,31 @@
+Description:
+time() function: return current time.
+
+Files:
+lib/time.c
+m4/time.m4
+
+Depends-on:
+time-h
+
+configure.ac:
+gl_FUNC_TIME
+gl_CONDITIONAL([GL_COND_OBJ_TIME], [test $REPLACE_TIME = 1])
+AM_COND_IF([GL_COND_OBJ_TIME], [
+  gl_PREREQ_TIME
+])
+gl_TIME_MODULE_INDICATOR([time])
+
+Makefile.am:
+if GL_COND_OBJ_TIME
+lib_SOURCES += time.c
+endif
+
+Include:
+<time.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+all
diff --git a/modules/time-h b/modules/time-h
index 75ff3a4d8c..5b0fc3feae 100644
--- a/modules/time-h
+++ b/modules/time-h
@@ -38,6 +38,7 @@ time.h: time.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H) $(
 	      -e 's/@''GNULIB_NANOSLEEP''@/$(GNULIB_NANOSLEEP)/g' \
 	      -e 's/@''GNULIB_STRFTIME''@/$(GNULIB_STRFTIME)/g' \
 	      -e 's/@''GNULIB_STRPTIME''@/$(GNULIB_STRPTIME)/g' \
+	      -e 's/@''GNULIB_TIME''@/$(GNULIB_TIME)/g' \
 	      -e 's/@''GNULIB_TIMEGM''@/$(GNULIB_TIMEGM)/g' \
 	      -e 's/@''GNULIB_TIMESPEC_GET''@/$(GNULIB_TIMESPEC_GET)/g' \
 	      -e 's/@''GNULIB_TIMESPEC_GETRES''@/$(GNULIB_TIMESPEC_GETRES)/g' \
@@ -59,6 +60,7 @@ time.h: time.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H) $(
 	      -e 's|@''REPLACE_MKTIME''@|$(REPLACE_MKTIME)|g' \
 	      -e 's|@''REPLACE_NANOSLEEP''@|$(REPLACE_NANOSLEEP)|g' \
 	      -e 's|@''REPLACE_STRFTIME''@|$(REPLACE_STRFTIME)|g' \
+	      -e 's|@''REPLACE_TIME''@|$(REPLACE_TIME)|g' \
 	      -e 's|@''REPLACE_TIMEGM''@|$(REPLACE_TIMEGM)|g' \
 	      -e 's|@''REPLACE_TIMESPEC_GET''@|$(REPLACE_TIMESPEC_GET)|g' \
 	      -e 's|@''REPLACE_TZSET''@|$(REPLACE_TZSET)|g' \
diff --git a/tests/test-time-h-c++.cc b/tests/test-time-h-c++.cc
index 70b2a0f0c7..13cb436e1b 100644
--- a/tests/test-time-h-c++.cc
+++ b/tests/test-time-h-c++.cc
@@ -28,6 +28,10 @@
 SIGNATURE_CHECK (GNULIB_NAMESPACE::timespec_get, int, (struct timespec *, int));
 #endif
 
+#if GNULIB_TEST_TIME
+SIGNATURE_CHECK (GNULIB_NAMESPACE::time, time_t, (time_t *));
+#endif
+
 #if GNULIB_TEST_NANOSLEEP
 SIGNATURE_CHECK (GNULIB_NAMESPACE::nanosleep, int,
                  (struct timespec const *, struct timespec *));
-- 
2.34.1


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From 8e356e3d3dd556b2716216fdc7a1bbafe29c8ccb Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Wed, 8 Mar 2023 17:02:38 +0100
Subject: [PATCH 2/3] time: Add tests.

* tests/test-time.c: New file.
* modules/time-tests: New file.
---
 ChangeLog          |  4 ++++
 modules/time-tests | 13 ++++++++++++
 tests/test-time.c  | 49 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)
 create mode 100644 modules/time-tests
 create mode 100644 tests/test-time.c

diff --git a/ChangeLog b/ChangeLog
index d65b3393c4..580b78c331 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2023-03-08  Bruno Haible  <bruno@clisp.org>
 
+	time: Add tests.
+	* tests/test-time.c: New file.
+	* modules/time-tests: New file.
+
 	time: New module.
 	* lib/time.in.h (time): New declaration.
 	* lib/time.c: New file.
diff --git a/modules/time-tests b/modules/time-tests
new file mode 100644
index 0000000000..e817f332cb
--- /dev/null
+++ b/modules/time-tests
@@ -0,0 +1,13 @@
+Files:
+tests/test-time.c
+tests/signature.h
+tests/macros.h
+
+Depends-on:
+gettimeofday
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-time
+check_PROGRAMS += test-time
diff --git a/tests/test-time.c b/tests/test-time.c
new file mode 100644
index 0000000000..3986ee2f3d
--- /dev/null
+++ b/tests/test-time.c
@@ -0,0 +1,49 @@
+/* Test of time() function.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible.  */
+
+#include <config.h>
+
+#include <time.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (time, time_t, (time_t *));
+
+#include <sys/time.h>
+
+#include "macros.h"
+
+int
+main (void)
+{
+  /* Check consistency of time() with gettimeofday().tv_sec.  */
+  struct timeval tv1;
+  struct timeval tv2;
+  time_t tt3;
+
+  /* Wait until gettimeofday() reports an increase in tv_sec.  */
+  ASSERT (gettimeofday (&tv1, NULL) == 0);
+  do
+    ASSERT (gettimeofday (&tv2, NULL) == 0);
+  while (tv2.tv_sec == tv1.tv_sec);
+  /* We are now at the beginning of a second.  Test whether time() reports
+     the new second or the previous one.  */
+  tt3 = time (NULL);
+  ASSERT (tt3 >= tv2.tv_sec);
+
+  return 0;
+}
-- 
2.34.1


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From 570d7dbfff17995c9999ec9ab3d7296d960f1e46 Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Wed, 8 Mar 2023 17:09:37 +0100
Subject: [PATCH 3/3] gettimeofday, timespec_get tests: Avoid test failure on
 glibc/Linux.

* modules/gettimeofday-tests (Depends-on): Add 'time'.
* modules/timespec_get-tests (Depends-on): Likewise.
* tests/test-gettimeofday.c (test_consistency): Update comment.
* tests/test-timespec_get.c (main): Likewise.
---
 ChangeLog                  | 6 ++++++
 modules/gettimeofday-tests | 1 +
 modules/timespec_get-tests | 1 +
 tests/test-gettimeofday.c  | 3 ++-
 tests/test-timespec_get.c  | 3 ++-
 5 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 580b78c331..fc3bf8e087 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2023-03-08  Bruno Haible  <bruno@clisp.org>
 
+	gettimeofday, timespec_get tests: Avoid test failure on glibc/Linux.
+	* modules/gettimeofday-tests (Depends-on): Add 'time'.
+	* modules/timespec_get-tests (Depends-on): Likewise.
+	* tests/test-gettimeofday.c (test_consistency): Update comment.
+	* tests/test-timespec_get.c (main): Likewise.
+
 	time: Add tests.
 	* tests/test-time.c: New file.
 	* modules/time-tests: New file.
diff --git a/modules/gettimeofday-tests b/modules/gettimeofday-tests
index 83c7c4b363..a08631d836 100644
--- a/modules/gettimeofday-tests
+++ b/modules/gettimeofday-tests
@@ -4,6 +4,7 @@ tests/signature.h
 tests/macros.h
 
 Depends-on:
+time
 
 configure.ac:
 
diff --git a/modules/timespec_get-tests b/modules/timespec_get-tests
index 7784792196..bb11062cb0 100644
--- a/modules/timespec_get-tests
+++ b/modules/timespec_get-tests
@@ -4,6 +4,7 @@ tests/signature.h
 tests/macros.h
 
 Depends-on:
+time
 
 configure.ac:
 
diff --git a/tests/test-gettimeofday.c b/tests/test-gettimeofday.c
index 6daf069339..d1d5206709 100644
--- a/tests/test-gettimeofday.c
+++ b/tests/test-gettimeofday.c
@@ -70,7 +70,8 @@ test_consistency ()
   ASSERT (tt2 <= tt4);
 
   /* Verify that the tv_sec field of the result is the same as time(NULL).  */
-  /* Note: This assertion sometimes fails on glibc systems, see
+  /* Note: It's here that the dependency to the 'time' module is needed.
+     Without it, this assertion would sometimes fail on glibc systems, see
      https://sourceware.org/bugzilla/show_bug.cgi?id=30200  */
   ASSERT (tv1.tv_sec <= tt2);
   ASSERT (tt2 <= tv3.tv_sec);
diff --git a/tests/test-timespec_get.c b/tests/test-timespec_get.c
index 69b98c5c64..a7e927cf62 100644
--- a/tests/test-timespec_get.c
+++ b/tests/test-timespec_get.c
@@ -46,7 +46,8 @@ main (void)
   ASSERT (tt2 <= tt4);
 
   /* Verify that the tv_sec field of the result is the same as time(NULL).  */
-  /* Note: This assertion sometimes fails on glibc systems, see
+  /* Note: It's here that the dependency to the 'time' module is needed.
+     Without it, this assertion would sometimes fail on glibc systems, see
      https://sourceware.org/bugzilla/show_bug.cgi?id=30200  */
   ASSERT (ts1.tv_sec <= tt2);
   ASSERT (tt2 <= ts3.tv_sec);
-- 
2.34.1