JS: Add concept of js_closethread

In order to better model content close vs destroy, add the concept
of closing a thread to the JS interface.

Signed-off-by: Daniel Silverstone <dsilvers@digital-scurf.org>

content/handlers/javascript/duktape/dukky.c

@@ -754,6 +754,26 @@ nserror js_newthread(jsheap *heap, void *win_priv, void *doc_priv, jsthread **th
 #undef CTX
 #define CTX (thread->ctx)
 
+/* exported interface documented in js.h */
+nserror js_closethread(jsthread *thread)
+{
+	/* We can always close down a thread, it might just confuse
+	 * the code running, though we don't mind since we're in the
+	 * process of destruction at this point
+	 */
+	duk_int_t top = duk_get_top(CTX);
+
+	/* Closing down the extant thread */
+	NSLOG(dukky, DEBUG, "Closing down extant thread %p in heap %p", thread, thread->heap);
+	duk_get_global_string(CTX, MAGIC(closedownThread));
+	dukky_pcall(CTX, 0, true);
+
+	/* Restore whatever stack we had */
+	duk_set_top(CTX, top);
+
+	return NSERROR_OK;
+}
+
 /**
  * Destroy a Duktape thread
  */

content/handlers/javascript/js.h

@@ -96,15 +96,28 @@ void js_destroyheap(jsheap *heap);
  */
 nserror js_newthread(jsheap *heap, void *win_priv, void *doc_priv, jsthread **thread);
 
+/**
+ * Close a javascript thread
+ *
+ * This should be called when the HTML content which owns the thread is
+ * being closed.  This is a separate process from destroying the thread
+ * and merely disconnects any callbacks and thus hopefully stops
+ * additional JS things from triggering.  If any code runs and attempts to
+ * register callbacks after closedown, they will fail.
+ *
+ * \param thread The thread to close down
+ * \return NSERROR_OK on success, appropriate error otherwise
+ */
+nserror js_closethread(jsthread *thread);
+
 /**
  * Destroy a javascript thread
  *
  * This should be called when the browsing context is done with the thread.
  *
- * Essentially it should be called when the content is about to be destroyed
- * but in reality it can be called when the browser window relinquishes its
- * handle on the content since nominally the browser window itself owns
- * the thread.
+ * This will be called when the HTML content associated with the browsing
+ * context is being destroyed.  The thread should have already been closed
+ * down during the HTML content close.
  *
  * \param thread The thread to be destroyed
  */

content/handlers/javascript/none/none.c

@@ -51,6 +51,11 @@ nserror js_newthread(jsheap *heap, void *win_priv, void *doc_priv, jsthread **th
 	return NSERROR_NOT_IMPLEMENTED;
 }
 
+nserror js_closethread(jsthread *thread)
+{
+	return NSERROR_OK;
+}
+
 void js_destroythread(jsthread *thread)
 {
 }