>From f3243f20107435f620338aa15e1fdd5779d639fe Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Sun, 16 Feb 2020 12:47:52 -0800
Subject: [PATCH] xnanosleep: prefer pause, and get remaining time

Problem reported by Vladimir Panteleev in:
https://lists.gnu.org/r/bug-gnulib/2020-02/msg00052.html
* lib/xnanosleep.c: Include intprops.h, unistd.h.
(xnanosleep) [HAVE_PAUSE]: Prefer pause when sleeping infinitely.
(xnanosleep): Obtain remaining time when nanosleep is interrupted.
* m4/xnanosleep.m4 (gl_XNANOSLEEP): Check for 'pause'.
* modules/xnanosleep (Depends-on): Add intprops, unistd.
---
 ChangeLog          | 11 +++++++++++
 lib/xnanosleep.c   | 22 ++++++++++++++++++++--
 m4/xnanosleep.m4   |  4 ++--
 modules/xnanosleep |  2 ++
 4 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index beacc0926..4e3f51ba2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2020-02-16  Paul Eggert  <address@hidden>
+
+	xnanosleep: prefer pause, and get remaining time
+	Problem reported by Vladimir Panteleev in:
+	https://lists.gnu.org/r/bug-gnulib/2020-02/msg00052.html
+	* lib/xnanosleep.c: Include intprops.h, unistd.h.
+	(xnanosleep) [HAVE_PAUSE]: Prefer pause when sleeping infinitely.
+	(xnanosleep): Obtain remaining time when nanosleep is interrupted.
+	* m4/xnanosleep.m4 (gl_XNANOSLEEP): Check for 'pause'.
+	* modules/xnanosleep (Depends-on): Add intprops, unistd.
+
 2020-02-16  Bruno Haible  <address@hidden>
 
 	lchmod: Improve cross-compilation guess.
diff --git a/lib/xnanosleep.c b/lib/xnanosleep.c
index 5774f75f3..8619c6df6 100644
--- a/lib/xnanosleep.c
+++ b/lib/xnanosleep.c
@@ -22,10 +22,12 @@
 
 #include "xnanosleep.h"
 
+#include <intprops.h>
 #include <timespec.h>
 
 #include <errno.h>
 #include <time.h>
+#include <unistd.h>
 
 /* Sleep until the time (call it WAKE_UP_TIME) specified as
    SECONDS seconds after the time this function is called.
@@ -37,6 +39,17 @@
 int
 xnanosleep (double seconds)
 {
+#if HAVE_PAUSE
+  if (1.0 + TYPE_MAXIMUM (time_t) <= seconds)
+    {
+      do
+        pause ();
+      while (errno == EINTR);
+
+      /* pause failed (!); fall back on repeated nanosleep calls.  */
+    }
+#endif
+
   struct timespec ts_sleep = dtotimespec (seconds);
 
   for (;;)
@@ -46,9 +59,14 @@ xnanosleep (double seconds)
          set errno to EINTR.  nanosleep from linux-2.6.10, as well as
          implementations by (all?) other vendors, doesn't return -1
          in that case;  either it continues sleeping (if time remains)
-         or it returns zero (if the wake-up time has passed).  */
+         or it returns zero (if the wake-up time has passed).
+
+         Gnulib's replacement nanosleep sometimes does not update
+         TS_SLEEP, and it is possible some kernels have a similar bug.
+         However, this merely causes xnanosleep to sleep longer than
+         necessary, which is not a correctness bug.  */
       errno = 0;
-      if (nanosleep (&ts_sleep, NULL) == 0)
+      if (nanosleep (&ts_sleep, &ts_sleep) == 0)
         break;
       if (errno != EINTR && errno != 0)
         return -1;
diff --git a/m4/xnanosleep.m4 b/m4/xnanosleep.m4
index 5f305f864..88454ae01 100644
--- a/m4/xnanosleep.m4
+++ b/m4/xnanosleep.m4
@@ -1,4 +1,4 @@
-#serial 5
+#serial 6
 dnl Copyright (C) 2005-2006, 2009-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -8,5 +8,5 @@ dnl Written by Paul Eggert.
 
 AC_DEFUN([gl_XNANOSLEEP],
 [
-  :
+  AC_CHECK_FUNCS_ONCE([pause])
 ])
diff --git a/modules/xnanosleep b/modules/xnanosleep
index 0a2b373ea..cc9069cb2 100644
--- a/modules/xnanosleep
+++ b/modules/xnanosleep
@@ -8,8 +8,10 @@ m4/xnanosleep.m4
 
 Depends-on:
 dtotimespec
+intprops
 nanosleep
 time
+unistd
 
 configure.ac:
 gl_XNANOSLEEP
-- 
2.17.1