Improve worker exited unexpectedly error

[stefanpenner]

When a worker exits unexpectedly, it can be tricky to figure out why.
To improve debugging, I've added some additional information to the existing error message:

• the status code or signal code
• that workerpools script
• spawnargs
• spawnfile
• stdout
• stderr

example output:

Error: Workerpool Worker terminated Unexpectedly
    exitCode: `12`
    workerpool.script: `/Users/spenner/src/josdejong/workerpool/lib/worker.js`
    spawnArgs: `/usr/local/Cellar/node/11.10.0/bin/node,--inspect=43210,/Users/spenner/src/josdejong/workerpool/lib/worker.js`
    spawnfile: `/usr/local/Cellar/node/11.10.0/bin/node`
    stdout: `null`
    stderr: `null`

    at ChildProcess.<anonymous> (/Users/spenner/src/josdejong/workerpool/lib/WorkerHandler.js:263:13)
    at ChildProcess.emit (events.js:197:13)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:254:12)

[stefanpenner]

I suspect the issue is, we have 1 incrementing ID per pool

workerpool/lib/Pool.js

Line 246 in da0c602

debugPort: this.debugPortStart + workers.length,

so if we have 2 pools they will conflict.

[stefanpenner]

Some ideas:

• don't propagate --inspector ports to child processes (likely not a great idea)
• partition the child process inspector ports like: this.debugPortStart = (options.debugPortStart || 43210) + (1000 * POOL_COUNT); <-- confirmed this works
• have a shared port allocator, that ensures all provided ports are unique and reclaimed during terminate <-- likely the best idea

[josdejong]

Thanks for improving the error reporting! 👍