On return, fflags contains the events which triggered the filter. If a process can normally see another pro- cess, it can attach an event to it. The process has exited. On return, fflags contains the events which triggered the filter. Takes the signal number to monitor as the identifier and returns when the given signal is delivered to the process.
Event notification happens after normal signal delivery processing.
If there was an error creating the kernel event queue, a value of -1 is returned and errno set. Otherwise, -1 will be returned, and errno will be set to indicate the error condition. The kernel failed to allocate enough memory for the kernel queue. The per-process descriptor table is full. The system file table is full.