说明

Constructs the EvChild watcher object.

Call the callback when a status change for process ID pid (or any PID if pid is 0 ) has been received(a status change happens when the process terminates or is killed, or, when trace is true, additionally when it is stopped or continued). In other words, when the process receives a SIGCHLD , Ev will fetch the outstanding exit/wait status for all changed/zombie children and call the callback.

It is valid to install a child watcher after an EvChild has exited but before the event loop has started its next iteration. For example, first one calls fork , then the new child process might exit, and only then an EvChild watcher is installed in the parent for the new PID .

You can access both exit/tracing status and pid by using the rstatus and rpid properties of the watcher object.

The number of PID watchers per PID is unlimited. All of them will be called.

The EvChild::createStopped() method doesn't start(activate) the newly created watcher.