Await all futures being resolved before shutdown is resolved.

packages/services/src/kernel/default.ts

@@ -377,16 +377,15 @@ export class DefaultKernel implements Kernel.IKernel {
    * The promise will be rejected if the kernel status is `Dead` or if the
    * request fails or the response is invalid.
    */
-  shutdown(): Promise<void> {
+  async shutdown(): Promise<void> {
     if (this.status === 'dead') {
       this._clearSocket();
-      this._clearState();
+      await this._clearState();
       return;
     }
-    return Private.shutdownKernel(this.id, this.serverSettings).then(() => {
-      this._clearState();
-      this._clearSocket();
-    });
+    await Private.shutdownKernel(this.id, this.serverSettings);
+    await this._clearState();
+    this._clearSocket();
   }
 
   /**
@@ -851,11 +850,13 @@ export class DefaultKernel implements Kernel.IKernel {
   /**
    * Clear the internal state.
    */
-  private _clearState(): void {
+  private async _clearState(): Promise<void> {
     this._isReady = false;
     this._pendingMessages = [];
+    const futuresResolved: Promise<KernelMessage.IShellMessage>[] = [];
     this._futures.forEach(future => {
       future.dispose();
+      futuresResolved.push(future.done);
     });
     this._comms.forEach(comm => {
       comm.dispose();
@@ -866,6 +867,10 @@ export class DefaultKernel implements Kernel.IKernel {
     this._comms = new Map<string, Kernel.IComm>();
     this._displayIdToParentIds.clear();
     this._msgIdToDisplayIds.clear();
+
+    await Promise.all(futuresResolved).catch(() => {
+      /* no-op */
+    });
   }
 
   /**