Wrapper doesn't exit upon SIGTERM when coprocess running in foreground

[dekobon]

When the wrapper is configured to use coprocesses, restarts are set to unlimited and backgrounding is disabled, when the wrapper receives a SIGTERM it fails to exit. Only after a second SIGTERM or SIGINT does the wrapper exit.

To Reproduce
Set a coprocess config block like the following and run.

"coprocess": {
    "blank": {
      "name": "blank",
      "exec": [ "echo", "''" ],
      "restarts": "unlimited",
      "background": "true",
      "exec_event": "pre-start",
      "stop_event": "exit"
    }
}

Expected behavior
The wrapper should exit when it receives the first SIGTERM.

Your environment

• Version of the NGINX Wrapper: v0.0.1
• Version of NGINX: nginx/1.19.0 (nginx-plus-r22)
• Using NGINX or NGINX Plus: plus
• Go version used to build: 1.15
• OS and distribution: Linux/Ubuntu/18.04
• Containerization or Virtualization environment: None

[dekobon]

I'm unable to reproduce this in the master branch. There is however a long delay between the time SIGTERM is issued and when the process exits.