Sets up a child setup function.
The child setup function will be called after fork but before exec on the child's side.
destroy_notify will not be automatically called on the child's side of the fork. It will only be called when
the last reference on the SubprocessLauncher is dropped or when a new child setup
function is given.
null can be given as child_setup to disable the functionality.
Child setup functions are only available on UNIX.
| this | |
| child_setup |
a SpawnChildSetupFunc to use as the child setup function |
| destroy_notify |
a DestroyNotify for |
| user_data |
user data for |