Don't dispose a serial session if it's not open (#66)

* Don't dispose a serial session if it's not open

Respect the number of serial listeners and only start and stop
serial when required.

Author: microbit-robert

lib/usb-radio-bridge.ts

@@ -83,7 +83,10 @@ class MicrobitRadioBridgeConnectionImpl
     const currentStatus = this.status;
     if (e.status !== ConnectionStatus.CONNECTED) {
       this.setStatus(e.status);
-      this.serialSession?.dispose();
+      if (this.serialSessionOpen) {
+        // If the session is already closed we don't need to dispose.
+        this.serialSession?.dispose();
+      }
     } else {
       this.status = ConnectionStatus.DISCONNECTED;
       if (

lib/usb.ts

@@ -564,11 +564,10 @@ class MicrobitWebUSBConnectionImpl
   protected eventActivated(type: string): void {
     switch (type as keyof SerialConnectionEventMap) {
       case "serialdata": {
-        // Prevent starting serial when flashing.
-        if (!this.flashing) {
+        // Prevent starting serial if already started and when flashing.
+        if (!this.addedListeners.serialdata && !this.flashing) {
           this.startSerialInternal();
         }
-        // Allows for reinstating serial after flashing.
         this.addedListeners.serialdata++;
         break;
       }
@@ -578,8 +577,10 @@ class MicrobitWebUSBConnectionImpl
   protected async eventDeactivated(type: string) {
     switch (type as keyof SerialConnectionEventMap) {
       case "serialdata": {
-        this.stopSerialInternal();
         this.addedListeners.serialdata--;
+        if (!this.addedListeners.serialdata) {
+          this.stopSerialInternal();
+        }
         break;
       }
     }