core: tweak runtime destruction sequence

Objects might need to be freed after the JS context is gone, so delay
destroying the runtime until the very end.

This is tricky, however, since it means bindings need to make sure not
to use js_free but rather do js_free_rt when releasing resources late.

src/vm.c

@@ -228,25 +228,28 @@ TJSRuntime *TJS_NewRuntimeInternal(bool is_worker, TJSRunOptions *options) {
 }
 
 void TJS_FreeRuntime(TJSRuntime *qrt) {
+    JS_FreeValue(qrt->ctx, JS_GetException(qrt->ctx));
+    JS_FreeContext(qrt->ctx);
+    qrt->ctx = NULL;
     JS_RunGC(qrt->rt);
 
-    /* Close all loop handles. */
+    /* Close all core loop handles. */
     uv_close((uv_handle_t *) &qrt->jobs.prepare, NULL);
     uv_close((uv_handle_t *) &qrt->jobs.idle, NULL);
     uv_close((uv_handle_t *) &qrt->jobs.check, NULL);
     uv_close((uv_handle_t *) &qrt->stop, NULL);
-
-    JS_FreeContext(qrt->ctx);
-    JS_FreeRuntime(qrt->rt);
-
-    /* Destroy CURLM handle. */
     if (qrt->curl_ctx.curlm_h) {
-        curl_multi_cleanup(qrt->curl_ctx.curlm_h);
         uv_close((uv_handle_t *) &qrt->curl_ctx.timer, NULL);
     }
 
     /* Destroy WASM runtime. */
     m3_FreeEnvironment(qrt->wasm_ctx.env);
+    qrt->wasm_ctx.env = NULL;
+
+    /* Give close handles a chance to run. */
+    for (int i = 0; i < 5; i++) {
+        uv_run(&qrt->loop, UV_RUN_NOWAIT);
+    }
 
     uv_walk(&qrt->loop, uv__walk, NULL);
 
@@ -267,6 +270,15 @@ void TJS_FreeRuntime(TJSRuntime *qrt) {
     (void)closed;
 #endif
 
+    /* Destroy CURLM handle. */
+    if (qrt->curl_ctx.curlm_h) {
+        curl_multi_cleanup(qrt->curl_ctx.curlm_h);
+        qrt->curl_ctx.curlm_h = NULL;
+    }
+
+    JS_FreeRuntime(qrt->rt);
+    qrt->rt = NULL;
+
     free(qrt);
 }