How use Waitpid Linux?
The call wait(&status) is equivalent to: waitpid(-1, &status, 0); The waitpid() system call suspends execution of the current process until a child specified by pid argument has changed state….wait() and waitpid()
| Tag | Description |
|---|---|
| > 0 | meaning wait for the child whose process ID is equal to the value of pid. |
Where can I use Waitpid?
WNOHANG WUNTRACED WCONTINUED
- Waitpid can used when you have more than one child for the process and you want to wait for particular child to get its execution done before parent resumes.
- waitpid supports job control.
- 3.it supports non blocking of the parent process.
What is Waitpid?
More precisely, waitpid() suspends the calling process until the system gets status information on the child. If pid is -1, waitpid() waits for any child process to end. If pid is less than -1, waitpid() waits for the termination of any child whose process group ID is equal to the absolute value of pid.
Is Waitpid better than wait?
waitpid is more flexible: If pid == -1, it waits for any child process. In this respect, waitpid is equivalent to wait. If pid == 0, it waits for any child whose process group ID equals that of the calling process.
Can Waitpid fail?
The waitpid() function shall fail if: ECHILD. The process specified by pid does not exist or is not a child of the calling process, or the process group specified by pid does not exist or does not have any member process that is a child of the calling process. EINTR.
How does Waitpid work?
Suspends the calling process until a child process ends or is stopped. More precisely, waitpid() suspends the calling process until the system gets status information on the child. If the system already has status information on an appropriate child when waitpid() is called, waitpid() returns immediately.
Why is Waitpid useful?
It’s used generally to wait until a specific process finishes (or otherwise changes state if you’re using special flags), based on its process ID (otherwise known as a pid ). It can also be used to wait for any of a group of child processes, either one from a specific process group or any child of the current process.
Does wait wait for grandchildren?
There is no way to wait for a grandchild; you need to implement the wait logic in each process. That way, each child will only exit after all it’s children have exited (and that will then include all grandchildren recusively).
Does Waitpid reap?
When a child process terminates it does not disappear entirely. The process of eliminating zombie processes is known as ‘reaping’. The simplest method is to call wait , but this will block the parent process if the child has not yet terminated. Alternatives are to use waitpid to poll or SIGCHLD to reap asynchronously.
What is the use of Waitpid system call?
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.
Which is an example of the use of waitpid ( )?
Syntax of waitpid(): pid_t waitpid(pid_t pid, int *status, int options); The value of pid can be: < -1: Wait for any child process whose process group ID is equal to the absolute value of pid. -1: Wait for any child process. 0: Wait for any child process whose process group ID is equal to that of the calling process.
What is the equivalent of waitpid in Linux?
It is exactly equivalent to “waitpid (-1, &status, 0)”. This exit status will be filled in the “status-ptr” argument. Below are some of the possible values: WIFEXITED: Returns a nonzero value if the child process terminated normally with exit or _exit.
Where to use waitpid ( PID, statusptr )?
For more help, use man waitpid. 1.where pid is the process of the child it should wait. 2.statusPtr is a pointer to the location where status information for the terminating process is to be stored. 3.specifies optional actions for the waitpid function.
What does waitid ( ) do in Linux 2.6?
The waitid () system call (available since Linux 2.6.9) provides more precise control over which child state changes to wait for. The idtype and id arguments select the child (ren) to wait for, as follows: Wait for the child whose process ID matches id. Wait for any child whose process group ID matches id.