inspector: crash on debugger connection if JS session is already active

[ofrobots]

Found this on googleapis/cloud-debug-nodejs#356 originally.

// Flags: --inspect=9229
const inspector = require('inspector');
const session = new inspector.Session();
session.connect();

setInterval(() => { console.log('jello')}, 2000);

setTimeout(() => {
 require('child_process').spawn(process.execPath, [
 'inspect',
 'localhost:9229'
 ])
}, 1000);

Crashes with:

$ ./node_g --inspect ~/tmp/test/test.js
Debugger listening on ws://127.0.0.1:9229/8c72c164-5fc4-41b9-af56-8a8c4cf95cb7
For help see https://nodejs.org/en/docs/inspector
jello
Debugger attached.
/Users/ofrobots/src/node/out/Debug/node[35110]: ../src/inspector_agent.cc:347:void node::inspector::NodeInspectorClient::connectFrontend(node::inspector::InspectorSessionDelegate *): Assertion `(channel_) == (nullptr)' failed.
 1: node::Abort() [/Users/ofrobots/src/node/./node_g]
 2: node::(anonymous namespace)::DomainEnter(node::Environment*, v8::Local<v8::Object>) [/Users/ofrobots/src/node/./node_g]
 3: node::inspector::NodeInspectorClient::connectFrontend(node::inspector::InspectorSessionDelegate*) [/Users/ofrobots/src/node/./node_g]
 4: node::inspector::Agent::Connect(node::inspector::InspectorSessionDelegate*) [/Users/ofrobots/src/node/./node_g]
 5: node::inspector::InspectorIo::DispatchMessages() [/Users/ofrobots/src/node/./node_g]
 6: node::inspector::DispatchMessagesTask::Run() [/Users/ofrobots/src/node/./node_g]
 7: node::RunForegroundTask(v8::Task*) [/Users/ofrobots/src/node/./node_g]
 8: node::NodePlatform::FlushForegroundTasksInternal() [/Users/ofrobots/src/node/./node_g]
 9: node::FlushTasks(uv_async_s*) [/Users/ofrobots/src/node/./node_g]
10: uv__async_io [/Users/ofrobots/src/node/./node_g]
11: uv__io_poll [/Users/ofrobots/src/node/./node_g]
12: uv_run [/Users/ofrobots/src/node/./node_g]
13: node::Start(v8::Isolate*, node::IsolateData*, int, char const* const*, int, char const* const*) [/Users/ofrobots/src/node/./node_g]
14: node::Start(uv_loop_s*, int, char const* const*, int, char const* const*) [/Users/ofrobots/src/node/./node_g]
15: node::Start(int, char**) [/Users/ofrobots/src/node/./node_g]
16: main [/Users/ofrobots/src/node/./node_g]
17: start [/Users/ofrobots/src/node/./node_g]
[1] 35110 abort ./node_g --inspect ~/tmp/test/test.js

This affects master, 9.x and 8.x.

/cc @nodejs/v8-inspector

[TimothyGu]

Seems to be a duplicate of #14745. Specifically #14745 (comment)

[auchenberg]

@ofrobots @eugeneo What should happen here? Should the port automatically be incremented? I assume it crashes as port 9922 is already used by the main process?

[eugeneo]

This is a bug in the Node inspector code. There is an assertion thrown when WS session is connected while there's a JS bindings session.

I tried to fix it in the past, but it requires a rework of the WS connection process that is currently happening on another thread but now will need a roundtrip to the main thread.

Chrome is currently launching support for the multiple concurrent Inspector sessions. Once that support is stable and Node moves on a compatible V8, this assertion will be removed. There will likely be a need to do some other work in Node.js to support concurrent sessions - but at least this bug will be auto-fixed.

[eugeneo]

I am still planning to take another look at this bug later this week, time permitting - I think there might be a reasonable fix.

[heisian]

Node is wonderful, we get the opportunity to debug the debugger.