Refactor DetermineSleepTime() to use milliseconds.

Since we're not using select() anymore, we don't need to bother with
struct timeval.  We can work directly in milliseconds, which the latch
API wants.

Discussion: https://postgr.es/m/CA%2BhUKG%2BZ-HpOj1JsO9eWUP%2Bar7npSVinsC_npxSy%2BjdOMsx%3DGg%40mail.gmail.com

Author: macdice

src/backend/postmaster/postmaster.c

@@ -1586,16 +1586,16 @@ checkControlFile(void)
 }
 
 /*
- * Determine how long should we let ServerLoop sleep.
+ * Determine how long should we let ServerLoop sleep, in milliseconds.
  *
  * In normal conditions we wait at most one minute, to ensure that the other
  * background tasks handled by ServerLoop get done even when no requests are
  * arriving.  However, if there are background workers waiting to be started,
  * we don't actually sleep so that they are quickly serviced.  Other exception
  * cases are as shown in the code.
  */
-static void
-DetermineSleepTime(struct timeval *timeout)
+static int
+DetermineSleepTime(void)
 {
 	TimestampTz next_wakeup = 0;
 
@@ -1608,26 +1608,20 @@ DetermineSleepTime(struct timeval *timeout)
 	{
 		if (AbortStartTime != 0)
 		{
+			int			seconds;
+
 			/* time left to abort; clamp to 0 in case it already expired */
-			timeout->tv_sec = SIGKILL_CHILDREN_AFTER_SECS -
+			seconds = SIGKILL_CHILDREN_AFTER_SECS -
 				(time(NULL) - AbortStartTime);
-			timeout->tv_sec = Max(timeout->tv_sec, 0);
-			timeout->tv_usec = 0;
+
+			return Max(seconds * 1000, 0);
 		}
 		else
-		{
-			timeout->tv_sec = 60;
-			timeout->tv_usec = 0;
-		}
-		return;
+			return 60 * 1000;
 	}
 
 	if (StartWorkerNeeded)
-	{
-		timeout->tv_sec = 0;
-		timeout->tv_usec = 0;
-		return;
-	}
+		return 0;
 
 	if (HaveCrashedWorker)
 	{
@@ -1665,26 +1659,14 @@ DetermineSleepTime(struct timeval *timeout)
 
 	if (next_wakeup != 0)
 	{
-		long		secs;
-		int			microsecs;
-
-		TimestampDifference(GetCurrentTimestamp(), next_wakeup,
-							&secs, &microsecs);
-		timeout->tv_sec = secs;
-		timeout->tv_usec = microsecs;
-
-		/* Ensure we don't exceed one minute */
-		if (timeout->tv_sec > 60)
-		{
-			timeout->tv_sec = 60;
-			timeout->tv_usec = 0;
-		}
-	}
-	else
-	{
-		timeout->tv_sec = 60;
-		timeout->tv_usec = 0;
+		/* Ensure we don't exceed one minute, or go under 0. */
+		return Max(0,
+				   Min(60 * 1000,
+					   TimestampDifferenceMilliseconds(GetCurrentTimestamp(),
+													   next_wakeup)));
 	}
+
+	return 60 * 1000;
 }
 
 /*
@@ -1743,12 +1725,9 @@ ServerLoop(void)
 	for (;;)
 	{
 		time_t		now;
-		struct timeval timeout;
-
-		DetermineSleepTime(&timeout);
 
 		nevents = WaitEventSetWait(pm_wait_set,
-								   timeout.tv_sec * 1000 + timeout.tv_usec / 1000,
+								   DetermineSleepTime(),
 								   events,
 								   lengthof(events),
 								   0 /* postmaster posts no wait_events */ );