[libdispatch-changes] [132] trunk

[source_changes at macosforge.org]

Revision: 132
          http://trac.macosforge.org/projects/libdispatch/changeset/132
Author:   robert at fledge.watson.org
Date:     2009-11-04 14:44:23 -0800 (Wed, 04 Nov 2009)
Log Message:
-----------
Rework conversion of timeouts to sem_timedwait() arguments further:
reintroduce tests for CLOCK_UPTIME/CLOCK_MONOTONIC, and restore using
them for absolute times on non-Mac OS X systems; instead perform a
more mature but more costly conversion when calculating a timeout.

Perhaps we should cache the delta between our absolute clock and the
realtime clock to avoid a clock read each time we calculate a timeout.

This should re-eliminate the restriction that POSIX semaphores can't
be used on systems where we use mach_absolute_time().

Modified Paths:
--------------
    trunk/configure.ac
    trunk/src/shims/time.h
    trunk/src/time.c

Modified: trunk/configure.ac
===================================================================
--- trunk/configure.ac	2009-11-04 21:15:54 UTC (rev 131)
+++ trunk/configure.ac	2009-11-04 22:44:23 UTC (rev 132)
@@ -177,7 +177,8 @@
 #
 # Find functions and declarations we care about.
 #
-AC_CHECK_DECLS([CLOCK_REALTIME], [], [], [[#include <time.h>]])
+AC_CHECK_DECLS([CLOCK_UPTIME, CLOCK_MONOTONIC, CLOCK_REALTIME], [], [],
+  [[#include <time.h>]])
 AC_CHECK_DECLS([EVFILT_SESSION, NOTE_NONE, NOTE_REAP, NOTE_SIGNAL], [], [],
   [[#include <sys/event.h>]])
 AC_CHECK_DECLS([FD_COPY], [], [], [[#include <sys/select.h>]])

Modified: trunk/src/shims/time.h
===================================================================
--- trunk/src/shims/time.h	2009-11-04 21:15:54 UTC (rev 131)
+++ trunk/src/shims/time.h	2009-11-04 22:44:23 UTC (rev 132)
@@ -43,7 +43,13 @@
 	struct timespec ts;
 	int ret;
 
-	ret = clock_gettime(CLOCK_REALTIME, &ts);
+#if HAVE_DECL_CLOCK_UPTIME
+	ret = clock_gettime(CLOCK_UPTIME, &ts);
+#elif HAVE_DECL_CLOCK_MONOTONIC
+	ret = clock_gettime(CLOCK_MONOTONIC, &ts);
+#else
+#error "clock_gettime: no supported absolute time clock"
+#endif
 	(void)dispatch_assume_zero(ret);
 
 	/* XXXRW: Some kind of overflow detection needed? */

Modified: trunk/src/time.c
===================================================================
--- trunk/src/time.c	2009-11-04 21:15:54 UTC (rev 131)
+++ trunk/src/time.c	2009-11-04 22:44:23 UTC (rev 132)
@@ -184,44 +184,47 @@
 }
 
 #if USE_POSIX_SEM
-#ifdef HAVE_MACH_ABSOLUTE_TIME
-#error "Cannot currently use USE_POSIX_SEM and HAVE_MACH_ABSOLUTE_TIME together"
-#endif
 /*
  * Unlike Mach semaphores, POSIX semaphores take an absolute, real time as an
  * argument to sem_timedwait().  This routine converts from dispatch_time_t
  * but assumes the caller has already handled the possibility of
  * DISPATCH_TIME_FOREVER.
- *
- * XXXRW: Does not currently with with mach_absolute_time()/
  */
 struct timespec
 _dispatch_timeout_ts(dispatch_time_t when)
 {
-	struct timespec ts;
+	struct timespec ts_realtime;
+	uint64_t abstime;
 	int ret;
 
+	printf("_dispatch_timeout_ts: req %ld\n", (int64_t)when);
+
 	if (when == 0) {
-		when = _dispatch_absolute_time();
-		ts.tv_sec = when / NSEC_PER_SEC;
-		ts.tv_nsec = when % NSEC_PER_SEC;
-		return (ts);
+		ret = clock_gettime(CLOCK_REALTIME, &ts_realtime);
+		(void)dispatch_assume_zero(ret);
+		return (ts_realtime);
 	}
 	if ((int64_t)when < 0) {
-		when = -(int64_t)when + _dispatch_absolute_time();
-		ts.tv_sec = when / NSEC_PER_SEC;
-		ts.tv_nsec = when % NSEC_PER_SEC;
-		return (ts);
+		ret = clock_gettime(CLOCK_REALTIME, &ts_realtime);
+		(void)dispatch_assume_zero(ret);
+		when = -(int64_t)when + ts_realtime.tv_sec * NSEC_PER_SEC +
+		    ts_realtime.tv_nsec;
+		ts_realtime.tv_sec = when / NSEC_PER_SEC;
+		ts_realtime.tv_nsec = when % NSEC_PER_SEC;
+		return (ts_realtime);
 	}
 
 	/*
-	 * XXXRW: This code assumes that dispatch_time_t absolute times are
-	 * with respect to CLOCK_REALTIME.  If we want to support
-	 * USE_POSIX_SEM with mach_absolute_time(), a conversion is required
-	 * here.
+	 * Rebase 'when': (when - abstime) + realtime.
+	 *
+	 * XXXRW: Should we cache this delta to avoid system calls?
 	 */
-	ts.tv_sec = when / NSEC_PER_SEC;
-	ts.tv_nsec = when % NSEC_PER_SEC;
-	return (ts);
+	abstime = _dispatch_absolute_time();
+	ret = clock_gettime(CLOCK_REALTIME, &ts_realtime);
+	(void)dispatch_assume_zero(ret);
+	printf("now is %d.%lu\n", ts_realtime.tv_sec, ts_realtime.tv_nsec);
+	ts_realtime.tv_sec += (when - abstime) / NSEC_PER_SEC;
+	ts_realtime.tv_nsec += (when - abstime) % NSEC_PER_SEC;
+	return (ts_realtime);
 }
 #endif
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