inspector aborts when another process is running the inspector

[trevnorris]

• Version: 8.0.0-pre
• Platform: Linux
• Subsystem: inspector

Description:
Running node --inspect in the background causes make cctest to abort. The same thing for trying to run node --inspect twice.

Reproduction:
Run node --inspect in one window, and make cctest in another window. The test should fail with:

../test/cctest/test_inspector_socket_server.cc:381: Failure
Value of: server->Start(&loop)
  Actual: false
Expected: true
[--I] signal   0x6caf08
[-AI] async    0x6cad50
[---] <unknown> 0x7fff84cd1998
Makefile:117: recipe for target 'cctest' failed
make: *** [cctest] Segmentation fault (core dumped)

Alternative is to run node --inspect twice. Which gives me:

trevnorris:node (async-wrap-eps-impl) $ ./node --inspect
Unable to open devtools socket: address already in use
Unable to open devtools socket: Unknown system error 0
> /var/projects/node/out/Release/node[17258]: ../src/node.cc:3739:void node::EnableDebug(node::Environment *): Assertion `debugger_running' failed.
 1: node::Abort() [./node]
 2: 0x10abe44 [./node]
 3: 0x10b547b [./node]
 4: node::Start(v8::Isolate*, node::IsolateData*, int, char const* const*, int, char const* const*) [./node]
 5: node::Start(uv_loop_s*, int, char const* const*, int, char const* const*) [./node]
 6: node::Start(int, char**) [./node]
 7: __libc_start_main [/lib/x86_64-linux-gnu/libc.so.6]
 8: _start [./node]
Aborted (core dumped)

/cc @nodejs/v8-inspector

[eugeneo]

#10861 changes the test so it uses autodiscovered port (so it does not conflict with another instance of the test running or with node --inspect).

Not sure what is the desired behavior for running two instances of node with --inspect...

[joyeecheung]

IMO this should not abort, instead just exit normally (EDIT: I think --debug just throws an exception, doesn't exit, anyway if it does exit, should exit with a non-zero exit code) throw an exception with some message telling the address/socket is being used(unless people pass in --abort-on-uncaught-exceptions).

--debug uses Error: listen EADDRINUSE 127.0.0.1:5858, --inspect currently shows Unable to open devtools socket: address already in use but I would say mimicking the behavior of --debug is less confusing(more familiar) to users. And I think an additional hint like "Are you running another node instance with --inspect?" would be more friendly to beginners(googling for EADDRINUSE 5858 shows a lot of confused questions).

[eugeneo]

Assert was a bug, I created a pull request with a fix. That pull request also changes the message to be more in line with what the old debugger prints.

As to "Are you running another node instance with --inspect?" - the error message needs to be generic as the code does not know if the failure is because the port is bound or if there's some other failure.