If the GC runs before the Mutex's are initialised then we get a crash in pthread_mutex_lock.

It is possible for GC to run during initialisation due to objects being allocated

Author: eightbitraptor

inits.c

@@ -20,6 +20,7 @@ static void Init_builtin_prelude(void);
 void
 rb_call_inits(void)
 {
+    CALL(Thread_Mutex);
 #if USE_TRANSIENT_HEAP
     CALL(TransientHeap);
 #endif

thread.c

@@ -5259,6 +5259,16 @@ rb_thread_backtrace_locations_m(int argc, VALUE *argv, VALUE thval)
     return rb_vm_thread_backtrace_locations(argc, argv, thval);
 }
 
+void
+Init_Thread_Mutex()
+{
+    rb_thread_t *th = GET_THREAD();
+
+    rb_native_mutex_initialize(&th->vm->waitpid_lock);
+    rb_native_mutex_initialize(&th->vm->workqueue_lock);
+    rb_native_mutex_initialize(&th->interrupt_lock);
+}
+
 /*
  *  Document-class: ThreadError
  *
@@ -5378,9 +5388,6 @@ Init_Thread(void)
 	    /* acquire global vm lock */
 	    gvl_init(th->vm);
 	    gvl_acquire(th->vm, th);
-            rb_native_mutex_initialize(&th->vm->waitpid_lock);
-            rb_native_mutex_initialize(&th->vm->workqueue_lock);
-            rb_native_mutex_initialize(&th->interrupt_lock);
 
 	    th->pending_interrupt_queue = rb_ary_tmp_new(0);
 	    th->pending_interrupt_queue_checked = 0;