Ref-count the runtime from RubyLandProxy.

By storing a reference to the runtime in a long-lived location while
there are live proxies, we can ensure the proxies will be collected
first. Otherwise, when the whole proxy+runtime chain becomes
unreachable, they could be collected in any order... and having the
runtime go away while we still have proxies around makes SpiderMonkey
quite upset.

ext/spidermonkey/ruby_land_proxy.c

@@ -462,6 +462,8 @@ static void finalize(RubyLandProxy* proxy)
   {
     // remove our GC handle on the JS value
     JS_RemoveRootRT(proxy->runtime->js, &(proxy->key));
+
+    johnson_runtime_unref(proxy->runtime);
   }
 
   free(proxy);
@@ -519,7 +521,9 @@ VALUE make_ruby_land_proxy(JohnsonRuntime* runtime, jsval value, const char cons
 
     // put the proxy OID in the id map
     JCHECK(JS_HashTableAdd(runtime->jsids, (void *)value, (void *)proxy));
-
+
+    johnson_runtime_ref(runtime);
+
     JRETURN_RUBY(proxy);
   }
 }

ext/spidermonkey/runtime.c

@@ -6,6 +6,8 @@
 #include "jroot.h"
 #include "ruby_land_proxy.h"
 
+static VALUE live_runtimes;
+
 /*
  * call-seq:
  *   global
@@ -270,6 +272,8 @@ initialize_native(VALUE self, VALUE UNUSED(options))
   JohnsonRuntime* runtime;
   Data_Get_Struct(self, JohnsonRuntime, runtime);
 
+  runtime->refs = 0;
+
   if ((runtime->js = JS_NewRuntime(0x100000))
     && (runtime->jsids = create_id_hash())
     && (runtime->rbids = create_id_hash()))
@@ -306,6 +310,26 @@ JSContext* johnson_get_current_context(JohnsonRuntime * runtime)
   return context->js;
 }
 
+void johnson_runtime_ref(JohnsonRuntime* runtime)
+{
+  runtime->refs++;
+  if (runtime->refs == 1)
+  {
+    VALUE self = (VALUE)JS_GetRuntimePrivate(runtime->js);
+    rb_hash_aset(live_runtimes, self, Qtrue);
+  }
+}
+
+void johnson_runtime_unref(JohnsonRuntime* runtime)
+{
+  runtime->refs--;
+  if (runtime->refs == 0)
+  {
+    VALUE self = (VALUE)JS_GetRuntimePrivate(runtime->js);
+    rb_hash_delete(live_runtimes, self);
+  }
+}
+
 static void deallocate(JohnsonRuntime* runtime)
 {
   // our gc callback can create ruby objects, so disable it
@@ -334,6 +358,9 @@ void init_Johnson_SpiderMonkey_Runtime(VALUE spidermonkey)
 {
   VALUE klass = rb_define_class_under(spidermonkey, "Runtime", rb_cObject);
 
+  live_runtimes = rb_hash_new();
+  rb_iv_set(klass, "@live_runtimes", live_runtimes);
+
   rb_define_alloc_func(klass, allocate);
   rb_define_private_method(klass, "initialize_native", initialize_native, 1);
 

ext/spidermonkey/runtime.h

@@ -19,9 +19,14 @@ typedef struct {
 
   JSHashTable *jsids; // jsid -> rbid
   JSHashTable *rbids; // rbid -> jsid
+
+  int refs;
 } JohnsonRuntime;
 
 JSContext* johnson_get_current_context(JohnsonRuntime* runtime);
 void init_Johnson_SpiderMonkey_Runtime(VALUE spidermonkey);
 
+void johnson_runtime_ref(JohnsonRuntime* runtime);
+void johnson_runtime_unref(JohnsonRuntime* runtime);
+
 #endif