vm_core.h (rb_thread_t): use 32-bit running_time_us

The current range based current values of:

	TIME_QUANTUM_USEC=100000
	RUBY_THREAD_PRIORITY_MAX=3
	RUBY_THREAD_PRIORITY_MIN=-3

Gives a range of 12500..800000, plenty enough for a 32-bit
integer.  Clamping this also reduces potential implementation
bugs between 32-bit and 64-bit platforms.

I may consider a further reduction to uint16_t in the future
for M:N threading, but some users may want slightly larger
time quantums.

* vm_core.h (rb_thread_t): use 32-bit running_time_us

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58591 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread.c

@@ -1247,7 +1247,7 @@ rb_thread_sleep(int sec)
 }
 
 static void
-rb_thread_schedule_limits(unsigned long limits_us)
+rb_thread_schedule_limits(uint32_t limits_us)
 {
     thread_debug("rb_thread_schedule\n");
     if (!rb_thread_alone()) {
@@ -2085,7 +2085,7 @@ rb_threadptr_execute_interrupts(rb_thread_t *th, int blocking_timing)
 	}
 
 	if (timer_interrupt) {
-	    unsigned long limits_us = TIME_QUANTUM_USEC;
+	    uint32_t limits_us = TIME_QUANTUM_USEC;
 
 	    if (th->priority > 0)
 		limits_us <<= th->priority;

vm_core.h

@@ -816,7 +816,7 @@ typedef struct rb_thread_struct {
 #ifdef USE_SIGALTSTACK
     void *altstack;
 #endif
-    unsigned long running_time_us;
+    uint32_t running_time_us; /* 12500..800000 */
     VALUE name;
 } rb_thread_t;