Rewrite how updates are triggered (closes #1504036):

(update_init, update_sched, update_run, update_wait): Don't create a
separate UpdateSched thread, run update_sched() in the Update thread.
Run the update by calling update_run() instead of by signalling its
thread.  update_run() replaces update_wait(); it just runs the update
and returns instead of waiting for the signal to update in a loop.
Move initialization of the Update thread's *player to its new thread
entry point.
(update_sem, update_init): Remove update_sem.
(update_thread): New.
(update_init): Initialize it.
(update_forced): New.
(update_trigger, update_force): Wake up update_thread with
update_force set.
(update_sched): Reset it before sleep, test it after sleep so that
schedule checking is only done for scheduled updates, not forced
updates.

(update_sched, update_init): Move sanity test of s_p_etu to
update_init().

src/server/update.c

@@ -48,14 +48,15 @@
 #include "prototypes.h"
 #include "server.h"
 
-empth_sem_t *update_sem;
+static empth_t *update_thread;
 empth_rwlock_t *update_lock;
 int update_pending;
 time_t update_time;
+static int update_forced;
 
 static void update_sched(void *);
 static void update_force(void *);
-static void update_wait(void *unused);
+static void update_run(void);
 static int run_hook(char *cmd, char *name);
 
 void
@@ -64,9 +65,14 @@ update_init(void)
     struct player *dp;
     int stacksize;
 
-    update_sem = empth_sem_create("Update", 0);
+    if (s_p_etu <= 0) {
+	logerror("bad value for s_p_etu (%d)", s_p_etu);
+	s_p_etu = 2 * 60;
+	logerror("setting s_p_etu to %d", s_p_etu);
+    }
+
     update_lock = empth_rwlock_create("Update");
-    if (!update_sem || !update_lock)
+    if (!update_lock)
 	exit_nomem();
 
     dp = player_new(-1);
@@ -76,12 +82,9 @@ update_init(void)
     stacksize = 100000 +
 /* finish_sects */ WORLD_X * WORLD_Y * (2 * sizeof(double) +
 					sizeof(char *));
-    if (!empth_create(PP_UPDATE, update_wait, stacksize, 0,
+    update_thread = empth_create(PP_UPDATE, update_sched, stacksize, 0,
-		      "Update", dp))
+				 "Update", dp);
-	exit_nomem();
+    if (!update_thread)
-
-    if (!empth_create(PP_SCHED, update_sched, 50 * 1024, 0,
-		      "UpdateSched", NULL))
 	exit_nomem();
 }
 
@@ -92,12 +95,11 @@ update_sched(void *unused)
     int wind;
     time_t now, delta;
 
-    if (s_p_etu <= 0) {
+    player->proc = empth_self();
-	logerror("bad value for s_p_etu (%d)", s_p_etu);
+    player->cnum = 0;
-	s_p_etu = 2 * 60;
+    player->god = 1;
-	logerror("setting s_p_etu to %d", s_p_etu);
+
-    }
+    for (;;) {
-    while (1) {
 	time(&now);
 	next_update_time(&now, &update_time, &delta);
 	if (update_window > 0) {
@@ -108,7 +110,9 @@ update_sched(void *unused)
 	logerror("Next update at %s", ctime(&update_time));
 	logerror("Next update in %ld seconds", (long)delta);
 	/* sleep until update is scheduled to go off */
+	update_forced = 0;
 	empth_sleep(update_time);
+	if (!update_forced) {
 	    time(&now);
 	    now += adj_update;
 	    if (!gamehours(now)) {
@@ -123,7 +127,8 @@ update_sched(void *unused)
 		logerror("Updates disabled...skipping update");
 		continue;
 	    }
-	empth_sem_signal(update_sem);
+	}
+	update_run();
     }
     /*NOTREACHED*/
 }
@@ -141,7 +146,8 @@ update_trigger(time_t secs_from_now)
 	return -1;
 
     if (secs_from_now == 0) {
-	empth_sem_signal(update_sem);
+	update_forced = 1;
+	empth_wakeup(update_thread);
 	return 0;
     }
 
@@ -163,23 +169,17 @@ update_force(void *seconds)
 
     time(&now);
     empth_sleep(now + *(time_t *)seconds);
-    empth_sem_signal(update_sem);
+    update_forced = 1;
+    empth_wakeup(update_thread);
     free(seconds);
     empth_exit();
 }
 
-/*ARGSUSED*/
 static void
-update_wait(void *unused)
+update_run(void)
 {
     struct player *p;
 
-    player->proc = empth_self();
-    player->cnum = 0;
-    player->god = 1;
-
-    while (1) {
-	empth_sem_wait(update_sem);
     update_pending = 1;
     for (p = player_next(0); p != 0; p = player_next(p)) {
 	if (p->state != PS_PLAYING)
@@ -195,15 +195,13 @@ update_wait(void *unused)
 	if (run_hook(pre_update_hook, "pre-update")) {
 	    update_pending = 0;
 	    empth_rwlock_unlock(update_lock);
-		continue;
+	    return;
 	}
     }
     update_main();
     update_pending = 0;
     empth_rwlock_unlock(update_lock);
 }
-    /*NOTREACHED*/
-}
 
 static int
 run_hook(char *cmd, char *name)