unix/mpthreadport: Use named semaphores on Mac OS X.

Unnamed semaphores (via sem_init) are not supported on this OS.  See #4465.

ports/unix/mpthreadport.c

@@ -34,6 +34,7 @@
 
 #if MICROPY_PY_THREAD
 
+#include <fcntl.h>
 #include <signal.h>
 #include <sched.h>
 #include <semaphore.h>
@@ -54,7 +55,12 @@ STATIC thread_t *thread;
 
 // this is used to synchronise the signal handler of the thread
 // it's needed because we can't use any pthread calls in a signal handler
+#if defined(__APPLE__)
+STATIC char thread_signal_done_name[25];
+STATIC sem_t *thread_signal_done_p;
+#else
 STATIC sem_t thread_signal_done;
+#endif
 
 // this signal handler is used to scan the regs and stack of a thread
 STATIC void mp_thread_gc(int signo, siginfo_t *info, void *context) {
@@ -71,7 +77,11 @@ STATIC void mp_thread_gc(int signo, siginfo_t *info, void *context) {
         void **ptrs = (void**)(void*)MP_STATE_THREAD(pystack_start);
         gc_collect_root(ptrs, (MP_STATE_THREAD(pystack_cur) - MP_STATE_THREAD(pystack_start)) / sizeof(void*));
         #endif
+        #if defined (__APPLE__)
+        sem_post(thread_signal_done_p);
+        #else
         sem_post(&thread_signal_done);
+        #endif
     }
 }
 
@@ -85,7 +95,13 @@ void mp_thread_init(void) {
     thread->ready = 1;
     thread->arg = NULL;
     thread->next = NULL;
+
+    #if defined(__APPLE__)
+    snprintf(thread_signal_done_name, sizeof(thread_signal_done_name), "micropython_sem_%d", (int)thread->id);
+    thread_signal_done_p = sem_open(thread_signal_done_name, O_CREAT | O_EXCL, 0666, 0);
+    #else
     sem_init(&thread_signal_done, 0, 0);
+    #endif
 
     // enable signal handler for garbage collection
     struct sigaction sa;
@@ -104,6 +120,10 @@ void mp_thread_deinit(void) {
         free(th);
     }
     pthread_mutex_unlock(&thread_mutex);
+    #if defined(__APPLE__)
+    sem_close(thread_signal_done_p);
+    sem_unlink(thread_signal_done_name);
+    #endif
     assert(thread->id == pthread_self());
     free(thread);
 }
@@ -125,7 +145,11 @@ void mp_thread_gc_others(void) {
             continue;
         }
         pthread_kill(th->id, SIGUSR1);
+        #if defined(__APPLE__)
+        sem_wait(thread_signal_done_p);
+        #else
         sem_wait(&thread_signal_done);
+        #endif
     }
     pthread_mutex_unlock(&thread_mutex);
 }