avoid setitimer on OS X, because we can use a pthread instead

svn: r3986

src/mzscheme/include/scheme.h

@@ -73,7 +73,7 @@
 # undef USE_ITIMER
 #endif
 
-#if defined(USE_ITIMER) || defined(USE_WIN32_THREAD_TIMER)
+#if defined(USE_ITIMER) || defined(USE_WIN32_THREAD_TIMER) || defined(USE_PTHREAD_THREAD_TIMER)
 # define FUEL_AUTODECEREMENTS
 #endif
 

src/mzscheme/sconfig.h

@@ -631,6 +631,9 @@
 # define SYSTEM_TYPE_NAME "macosx"
 #endif
 
+# undef USE_ITIMER
+# define USE_PTHREAD_THREAD_TIMER
+
 # define USE_MAP_ANON
 
 # define USE_CARBON_FP_PREDS
@@ -1044,6 +1047,12 @@
     MzScheme-implemented threads). Define MZ_THREAD_QUANTUM_USEC to
     set the base time in usec allocated to each thread. */
 
+ /* USE_WIN32_THREAD_TIMER uses a background Windows thread to implement
+    tread pre-emption. */
+
+ /* USE_PTHREAD_THREAD_TIMER uses a background pthread to implement
+    tread pre-emption. */
+
  /* SIGSET_IS_SIGNAL uses signal() in place of sigset() for Unix. This 
     flag is often paired with SIGSET_NEEDS_REINSTALL for traditional
     Unix systems. */

src/mzscheme/src/port.c

@@ -7949,6 +7949,67 @@ void scheme_start_itimer_thread(long usec)
 
 #endif
 
+#ifdef USE_PTHREAD_THREAD_TIMER
+
+#include <pthread.h>
+
+static int itimer = 0, itimer_continue = 0;
+static pthread_mutex_t itimer_mutex;
+static pthread_cond_t itimer_cond;
+static volatile long itimer_delay;
+
+#ifdef MZ_XFORM
+START_XFORM_SKIP;
+#endif
+static void *run_itimer(void *p)
+{
+  while (1) {
+    usleep(itimer_delay);
+    scheme_fuel_counter = 0;
+    
+    pthread_mutex_lock(&itimer_mutex);
+    if (itimer_continue) {
+      itimer_continue = 0;
+    } else {
+      itimer_continue = -1;
+      pthread_cond_wait(&itimer_cond, &itimer_mutex);
+    }
+    pthread_mutex_unlock(&itimer_mutex);
+  }
+}
+#ifdef MZ_XFORM
+END_XFORM_SKIP;
+#endif
+
+void scheme_start_itimer_thread(long usec)
+{
+  itimer_delay = usec;
+
+  if (!itimer) {
+    pthread_t t;
+    pthread_mutex_init(&itimer_mutex, NULL);
+    pthread_cond_init(&itimer_cond, NULL);
+    pthread_create(&t, NULL, run_itimer,  NULL);
+    itimer = 1;
+  } else {
+    pthread_mutex_lock(&itimer_mutex);
+    if (!itimer_continue) {
+      /* itimer thread is currently running working */
+      itimer_continue = 1;
+    } else if (itimer_continue < 0) {
+      /* itimer thread is waiting on cond */
+      itimer_continue = 0;
+      pthread_cond_signal(&itimer_cond);
+    } else {
+      /* itimer thread is working, and we've already
+         asked it to continue */
+    }
+    pthread_mutex_unlock(&itimer_mutex);
+  }
+}
+
+#endif
+
 /*========================================================================*/
 /*                       memory debugging help                            */
 /*========================================================================*/

src/mzscheme/src/thread.c

@@ -3722,6 +3722,8 @@ void scheme_thread_block(float sleep_time)
   if (do_atomic)
     missed_context_switch = 1;
 
+  MZTHREADELEM(p, fuel_counter) = p->engine_weight;
+
 #ifdef USE_ITIMER
   {
     struct itimerval t, old;
@@ -3739,14 +3741,12 @@ void scheme_thread_block(float sleep_time)
     setitimer(ITIMER_PROF, &t, &old);
   }
 #endif
-#ifdef USE_WIN32_THREAD_TIMER
+#if defined(USE_WIN32_THREAD_TIMER) || defined(USE_PTHREAD_THREAD_TIMER)
   scheme_start_itimer_thread(MZ_THREAD_QUANTUM_USEC);
 #endif
 
   /* Check scheduled_kills early and often. */
   check_scheduled_kills();
-
-  MZTHREADELEM(p, fuel_counter) = p->engine_weight;
 }
 
 void scheme_making_progress()