Wait exposes some internals of the implementation of wait and wait_untraced. Those functions return a deferred that becomes determined when a particular child process exits. The implementation, by default, installs a signal handler for SIGCHLD that calls check_all, which considers all undetermined wait results, calls wait_nohang, and fills them in if appropriate. If OCaml is being used as a plugin in some other process that is already managing signals, e.g. in Ecaml, then we can't install a signal handler. So, we expose do_not_handle_sigchld, which the plugin should call before any call to wait, and will prevent the SIGCHLD handler from being installed. It is then the responsibility of the plugin to call check_all regularly, so that child processes created by Async are reaped and the corresponding deferreds become determined.