Fix portability problems in mythread.h.

Use gettimeofday() if clock_gettime() isn't available
(e.g. Darwin).

The test for availability of pthread_condattr_setclock()
and CLOCK_MONOTONIC was incorrect. Instead of fixing the
#ifdefs, use an Autoconf test. That way if there exists a
system that supports them but doesn't specify the matching
POSIX #defines, the features will still get detected.

Don't try to use pthread_sigmask() on OpenVMS. It doesn't
have that function.

Guard mythread.h against being #included multiple times.

configure.ac

@@ -435,7 +435,14 @@ if test "x$enable_threads" = xyes; then
 	LIBS="$LIBS $PTHREAD_LIBS"
 	AM_CFLAGS="$AM_CFLAGS $PTHREAD_CFLAGS"
 	CC="$PTHREAD_CC"
+
+	# These are nice to have but not mandatory.
+	OLD_CFLAGS=$CFLAGS
+	CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
 	AC_SEARCH_LIBS([clock_gettime], [rt])
+	AC_CHECK_FUNCS([clock_gettime pthread_condattr_setclock])
+	AC_CHECK_DECLS([CLOCK_MONOTONIC], [], [], [[#include <time.h>]])
+	CFLAGS=$OLD_CFLAGS
 fi
 AM_CONDITIONAL([COND_THREADS], [test "x$ax_pthread_ok" = xyes])
 

src/common/mythread.h

@@ -10,6 +10,9 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
+#ifndef MYTHREAD_H
+#define MYTHREAD_H
+
 #include "sysdefs.h"
 
 
@@ -19,19 +22,23 @@
 // Using pthreads //
 ////////////////////
 
+#include <sys/time.h>
 #include <pthread.h>
 #include <signal.h>
 #include <time.h>
-#include <unistd.h>
 
 
+#ifdef __VMS
+// Do nothing on OpenVMS. It doesn't have pthread_sigmask().
+#define mythread_sigmask(how, set, oset) do { } while (0)
+#else
 /// \brief      Set the process signal mask
 ///
 /// If threads are disabled, sigprocmask() is used instead
 /// of pthread_sigmask().
 #define mythread_sigmask(how, set, oset) \
 	pthread_sigmask(how, set, oset)
-
+#endif
 
 /// \brief      Call the given function once
 ///
@@ -96,7 +103,9 @@ typedef struct {
 static inline int
 mythread_cond_init(mythread_cond *mycond)
 {
-#if defined(_POSIX_CLOCK_SELECTION) && defined(_POSIX_MONOTONIC_CLOCK)
+#ifdef HAVE_CLOCK_GETTIME
+	// NOTE: HAVE_DECL_CLOCK_MONOTONIC is always defined to 0 or 1.
+#	if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK) && HAVE_DECL_CLOCK_MONOTONIC
 	struct timespec ts;
 	pthread_condattr_t condattr;
 
@@ -122,6 +131,8 @@ mythread_cond_init(mythread_cond *mycond)
 #	endif
 
 	mycond->clk_id = CLOCK_REALTIME;
+#endif
+
 	return pthread_cond_init(&mycond->cond, NULL);
 }
 
@@ -133,11 +144,21 @@ mythread_cond_init(mythread_cond *mycond)
 static inline void
 mythread_cond_abstime(const mythread_cond *mycond, struct timespec *ts)
 {
+#ifdef HAVE_CLOCK_GETTIME
 	struct timespec now;
 	clock_gettime(mycond->clk_id, &now);
 
 	ts->tv_sec += now.tv_sec;
 	ts->tv_nsec += now.tv_nsec;
+#else
+	(void)mycond;
+
+	struct timeval now;
+	gettimeofday(&now, NULL);
+
+	ts->tv_sec += now.tv_sec;
+	ts->tv_nsec += now.tv_usec * 1000L;
+#endif
 
 	// tv_nsec must stay in the range [0, 999_999_999].
 	if (ts->tv_nsec >= 1000000000L) {
@@ -200,3 +221,5 @@ do { \
 } while (0)
 
 #endif
+
+#endif