Avoid deadlock during GC. Check for GC_DONT_GC environment variable at startup rather than during collection with world stopped since g_hasenv may take OS locks and encounter deadlock. (case 1077203)

Author: joncham

mono/metadata/boehm-gc.c

@@ -60,6 +60,7 @@ void *pthread_get_stackaddr_np(pthread_t);
 
 static gboolean gc_initialized = FALSE;
 static gboolean gc_strict_wbarriers = FALSE;
+static gboolean gc_dont_gc_env = FALSE;
 static mono_mutex_t mono_gc_lock;
 
 typedef void (*GC_push_other_roots_proc)(void);
@@ -208,6 +209,9 @@ mono_gc_base_init (void)
 		g_free (debug_opts);
 	}
 
+	/* cache value rather than calling during collection since g_hasenv may take locks and can deadlock */
+	gc_dont_gc_env = g_hasenv ("GC_DONT_GC");
+
 	GC_init ();
 
 	GC_set_warn_proc (mono_gc_warning);
@@ -1539,7 +1543,7 @@ mono_gc_is_moving (void)
 gboolean
 mono_gc_is_disabled (void)
 {
-	if (GC_dont_gc || g_hasenv ("GC_DONT_GC"))
+	if (GC_dont_gc || gc_dont_gc_env)
 		return TRUE;
 	else
 		return FALSE;