suppress resumed events while interrupted (firefox-devtools#4972)

Author: jasonLaster

src/client/README.md

@@ -0,0 +1,53 @@
+# Debugger Client
+
+The Debugger client is responsible for managing the communication between the
+client application and JS server.
+
+* When the server sends a notification to the client, the client receives an
+  "event" and notifies the application via redux actions.
+* When the application, wants to send a command to the server, it invokes
+  "commands" in the client.
+
+The Debugger supports a Firefox and a Chrome client, which lets it attach and
+debug Firefox, Chrome, and Node contexts. The clients are defined in
+`src/client` and have an `onConnect` function, and a `commands` and `events`
+module.
+
+Both clients implement client adapters for translating commands and events into
+JSON packets. The chrome client debugger adapter is defined in
+[chrome-remote-interface][chrome-remote-interface]. The Firefox client adapters
+are defined in two places:
+
+* The launchpad client adapter is maintained in the package
+  [devtools-connection][dt-connect].
+* The panel client adapter is maintained in
+  [devtools-client.js][devtools-client.js].
+
+## Firefox
+
+### Remote Debugger Protocol
+
+The [Remote Debugger Protocol][protocol] specifies the client / server API.
+
+### Interrupt
+
+When the client wants to add a breakpoint, it avoids race conditions by doing
+temporary pauses called interrupts.
+
+We want to do these interrupts transparently, so we've decided that the client
+should not notify the application that the thread has been paused or resumed.
+
+[protocol]: https://searchfox.org/mozilla-central/source/devtools/docs/backend/protocol.md
+[dt-connect]: https://github.com/devtools-html/devtools-core/tree/master/packages/devtools-connection
+[devtools-client.js]: https://searchfox.org/mozilla-central/source/devtools/shared/client/debugger-client.js
+
+## Chrome
+
+### Chrome Debugger Protocol
+
+The chrome debugger protocol is available [here][devtools-protocol-viewer]. And
+is maintained in the devtools-protocol [repo][devtools-protocol-gh].
+
+[chrome-remote-interface]: https://github.com/cyrus-and/chrome-remote-interface
+[devtools-protocol-viewer]: https://chromedevtools.github.io/devtools-protocol/
+[devtools-protocol-gh]: https://github.com/ChromeDevTools/devtools-protocol

src/client/firefox/events.js

@@ -27,6 +27,7 @@ type Dependencies = {
 let threadClient: ThreadClient;
 let actions: Actions;
 let supportsWasm: boolean;
+let isInterrupted: boolean;
 
 function setupEvents(dependencies: Dependencies) {
   threadClient = dependencies.threadClient;
@@ -47,6 +48,7 @@ async function paused(_: "paused", packet: PausedPacket) {
   // breakpoints, ignore the event.
   const { why } = packet;
   if (why.type === "interrupted" && !packet.why.onNext) {
+    isInterrupted = true;
     return;
   }
 
@@ -61,6 +63,14 @@ async function paused(_: "paused", packet: PausedPacket) {
 }
 
 function resumed(_: "resumed", packet: ResumedPacket) {
+  // NOTE: the client suppresses resumed events while interrupted
+  // to prevent unintentional behavior.
+  // see [client docs](../README.md#interrupted) for more information.
+  if (isInterrupted) {
+    isInterrupted = false;
+    return;
+  }
+
   actions.resumed(packet);
 }