Repository: create-react-app
Issue: Killing the parent "yarn start" process leaves the sub-sub-process that actually listens to port 3000 still running
Labels: stale,needs triage,issue: bug report

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### Describe the bug

Programmatically trying to kill the "yarn start" process only kills some of the relevant processes.  In particular, the node sub-process that listens to port 3000 is left running, which in turn causes trouble on the next "yarn start" attempt.

### Did you try recovering your dependencies?

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Bug happens when running "yarn start" from fresh "npx create-react-app", so this should not be relevant.

### Which terms did you search for in User Guide?

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Tried searching for "stop", to see if there was some documented way of stopping the thing you start with "yarn start", but found nothing.

### Environment

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Environment Info:

  current version of create-react-app: 4.0.3
  running from /Users/hmeland/.npm/_npx/c67e74de0542c87c/node_modules/create-react-app

  System:
    OS: macOS 10.15.7
    CPU: (16) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
  Binaries:
    Node: 16.6.0 - /usr/local/bin/node
    Yarn: 1.22.10 - /usr/local/bin/yarn
    npm: 7.19.1 - /usr/local/bin/npm
  Browsers:
    Chrome: 92.0.4515.107
    Edge: Not Found
    Firefox: Not Found
    Safari: 14.1.2
  npmPackages:
    react: ^17.0.2 => 17.0.2
    react-dom: ^17.0.2 => 17.0.2
    react-scripts: 4.0.3 => 4.0.3
  npmGlobalPackages:
    create-react-app: Not Found

### Steps to reproduce

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To reproduce (I'm on OSX, don't know whether other OSes are also affected):

    $ npx create-react-app repro
    $ cd repro/
    $ yarn
    $ yarn start &
    [1] 94708
      # Now, wait for browser page to open and start working...
   
    $ pstree 94708
    -+= 94708 hmeland node /usr/local/Cellar/yarn/1.22.10/libexec/bin/yarn.js start
     \-+- 94730 hmeland /usr/local/Cellar/node/16.6.0/bin/node /private/tmp/repro/node_modules/.bin/react-scripts start
       \--- 94731 hmeland /usr/local/Cellar/node/16.6.0/bin/node /private/tmp/repro/node_modules/react-scripts/scripts/start.js

    $ sudo lsof -i :3000 | grep LISTEN
    node    94731 hmeland   27u  IPv4 0xe4aa337aee33c393      0t0  TCP *:hbci (LISTEN)
      # Note that the process listening to port 3000 (pid 94708)
      # is not the master "yarn start" process (pid 94731)
    
      # If we had run "yarn start" in the foreground, and quit it with
      # Control-C, that ends up killing both all of the relevant processes.
      # However, I'm trying to script starting/stopping the development
      # web server in concert with my backend service, so naively I only
      # have the master "yarn start" process to work with (unless I want
      # to put my hands into a hornets' nest of OS-specific
      # workarounds).
    
    $ kill 94708
    [1]+  Terminated: 15          yarn start
    $ pstree 94708
      # No output, as the parent process has been killed
      # ... but the listening node subprocess is still running:
    $ sudo lsof -i :3000 | grep LISTEN
    node    94731 hmeland   27u  IPv4 0xe4aa337af94349b3      0t0  TCP *:hbci (LISTEN)


### Expected behavior

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Killing the parent process should also cause the listening sub-process to get killed.

### Actual behavior

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