Is Waitpid the same as wait?
The waitpid() function shall be equivalent to wait() if the pid argument is (pid_t)-1 and the options argument is 0. Otherwise, its behavior shall be modified by the values of the pid and options arguments. The pid argument specifies a set of child processes for which status is requested.
What is Waitpid Wnohang?
WNOHANG. This flag specifies that waitpid should return immediately instead of waiting, if there is no child process ready to be noticed. WUNTRACED. This flag specifies that waitpid should report the status of any child processes that have been stopped as well as those that have terminated.
How do I use Waitpid and wait?
The wait() system call suspends execution of the current process until one of its children terminates. The call wait(&status) is equivalent to: waitpid(-1, &status, 0);…wait() and waitpid()
| Tag | Description |
|---|---|
| < -1 | meaning wait for any child process whose process group ID is equal to the absolute value of pid. |
What does Waitpid return with Wnohang?
Returned value If successful, waitpid() returns a value of the process (usually a child) whose status information has been obtained. If WNOHANG was given, and if there is at least one process (usually a child) whose status information is not available, waitpid() returns 0.
Which is correct parameter of Waitpid?
Basically you have 3 parameters: pid_t waitpid(pid_t pid, int *status, int options); pid is the process you are waiting for. Unless you are waiting for multiple children (in which case specify 0, -1, or a number less than -1 – details in the manpage), specify the pid of your process here.
What is status in Waitpid?
WSTOPSIG(status) returns the number of the signal which caused the child to stop. This macro should only be employed if WIF- STOPPED returned true.
What does Waitpid 1 mean?
From the linux manual : The pid parameter specifies the set of child processes for which to wait. If pid is -1, the call waits for any child process.
Does Waitpid return anything?
RETURN VALUES If waitpid() returns because the status of a child process is available, it returns a value equal to the process ID of the child process for which status is reported.
What is the use of Waitpid?
The waitpid() function allows the calling thread to obtain status information for one of its child processes. The calling thread suspends processing until status information is available for the specified child process, if the options argument is 0.
What is the status in Waitpid?
Only one status is returned per waitpid function call. If pid is equal to -1, status is requested for any child process. If status information is available for two or more processes, the order in which their status is reported is not specified. If pid is greater than 0, status is requested for a single process.
What are Waitpid options?
What does Wifsignaled mean?
WIFSIGNALED(status) returns true if the child process was terminated by a signal. WTERMSIG(status) returns the number of the signal that caused the child process to terminate. This macro should only be employed if WIFSIGNALED returned true. WCOREDUMP(status) returns true if the child produced a core dump.
How does wnohang prevent waitpid / waitpid from blocking?
That’s what WNOHANG is for. It prevents wait()/waitpid() from blocking so that your process can go on with other tasks. If a child died, its pid will be returned by wait()/waitpid() and your process can act on that. If nothing died, then the returned pid is 0.
When to use errno or 0 in C-waitpid?
If not, either 0 is returned (if unterminated children exist) or -1 is returned (if not) and ERRNO is set to ECHILD (No child processes). This is useful if you want to find out if any of your children recently died without having to wait for one of them to die.
What does waitpid with PID OF-1 mean?
As I understand, waitpid with a pid of -1 means that I wait for all child’s to finish but if I add an option to the waitpid of WNOHANG, that options says to exit immediately if none have finished…These seems extremely confusing.
When does a non-blocking wait return a PID?
Waits for a particular child process to terminate and returns the pid of the deceased process, or -1 if there is no such child process. A non-blocking wait (with WNOHANG in FLAGS) can return 0 if there are child processes matching PID but none have terminated yet.