waitid - wait for a child process to change state
#include <sys/wait.h> int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
The waitid() function suspends the calling thread until one child of the process containing the calling thread changes state. It records the current state of a child in the structure pointed to by infop. If a child process changed state prior to the call to waitid(), waitid() returns immediately. If more than one thread is suspended in wait() or waitpid() waiting termination of the same process, exactly one thread will return the process status at the time of the target process termination
The idtype and id arguments are used to specify which children waitid() will wait for.
If idtype is P_PID, waitid() will wait for the child with a process ID equal to (pid_t)id.
If idtype is P_PGID, waitid() will wait for any child with a process group ID equal to (pid_t)id.
If idtype is P_ALL, waitid() will wait for any children and id is ignored.
The options argument is used to specify which state changes waitid() will wait for. It is formed by OR-ing together one or more of the following flags:
- Wait for processes that have exited.
- Status will be returned for any child that has stopped upon receipt of a signal.
- Status will be returned for any child that was stopped and has been continued.
- Return immediately if there are no children to wait for.
- Keep the process whose status is returned in infop in a waitable state. This will not affect the state of the process; the process may be waited for again after this call completes.
The infop argument must point to a siginfo_t structure. If waitid() returns because a child process was found that satisfied the conditions indicated by the arguments idtype and options, then the structure pointed to by infop will be filled in by the system with the status of the process. The si_signo member will always be equal to SIGCHLD.
If waitid() returns due to the change of state of one of its children, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The waitid() function will fail if:
- The calling process has no existing unwaited-for child processes.
- The waitid() function was interrupted by a signal.
- An invalid value was specified for options, or idtype and id specify an invalid set of processes.
exec, exit(), wait(), <sys/wait.h>.