Prototype of a GChildWatchSource callback, called when a child process has exited.
To interpret wait_status, see the documentation for
check_wait_status. In particular, on Unix platforms, note that it is usually not equal to the integer passed to `exit()` or returned
from `main()`.
| pid |
the process id of the child process |
| wait_status |
Status information about the child process, encoded in a platform-specific manner |
| user_data |
user data passed to |