Relationship between sigchld and wait/waipid Functions

1. Sigchild is only a signal value sent to the parent process when the child process exits. This is a way to asynchronously notify the parent process. the parent process can capture and ignore this signal. The default action is to ignore this signal.
2. Generally, when a sigchild signal occurs, the main process calls waitpid or wait in the signal processing function of sigchild to reclaim the end state of the sub-process. But you need to understand:Waitpid or wait does not rely on the arrival of the sigchld signal to determine whether the sub-process is terminated. (It may be determined by checking the sub-process status through round-robin. It can be determined only by checking the specific code implementation ), that is, the wait/waitpid does not depend on the sigchild signal.In the sigchild signal processing function, wait/waitpid is often called to reclaim the sub-process status to avoid unnecessary round patrols of wait/waitpid. It is a method to save resources, but this is not necessary.