Wait for one or more child process to change its state
#include <sys/wait.h> #include <sys/resource.h> pid_t wait4( pid_t pid, int * stat_loc, int options, struct rusage * resource_usage );
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The wait4() function suspends execution of the calling thread until status information from one of its terminated child processes is available, or until the delivery of a signal whose action is either to terminate the process or execute a signal handler. If status information is available prior to the call to wait4(), the return is immediate.
|If the parent process sets the action for SIGCHLD to SIG_IGN, its children won't enter the zombie state, and it won't be able to use the wait*() functions to wait on their deaths.|
The wait4() function behaves the same as the wait() function when passed a pid argument of -1, and the options argument has a value of zero.
Only one of the WIFEXITED(stat_val) and WIFSIGNALED(stat_val) macros can evaluate to a nonzero value.
The following call:
wait3( stat_loc, options, resource_usage );
is equivalent to the call:
waitpid( (pid_t)-1, stat_loc, options );
except that on successful completion, if the resource_usage argument to wait3() isn't a NULL pointer, the rusage structure that the third argument points to is filled in for the child process identified by the return value.
It's also equivalent to:
wait4( (pid_t)-1, stat_loc, options, resource_usage );
The waitpid() function is POSIX: wait3() and wait4() are BSD extensions.
If successful, wait4() returns the process ID of the terminating child process. If wait4() was invoked with WNOHANG set in options, it has at least one child process specified by pid for which status is not available, and status is not available for any process specified by pid, a value of zero is returned. On delivery of a signal waitpid() returns -1, and errno is set to EINTR.
exit(), fork(), pause(), wait(), wait3(), waitid(), waitpid()
“Detecting process termination” in the “Processes” chapter of the QNX Neutrino Programmer's Guide