What does it mean if a call to Waitpid does not block?

What does it mean if a call to Waitpid does not block?

3 Answers. Show activity on this post. The WNOHANG flag (set in the options argument) will make the call to waitpid() non-blocking. You’ll have to call it periodically to check if the child is finished yet.

What does Waitpid mean?

The waitpid() system call suspends execution of the current process until a child specified by pid argument has changed state. By default, waitpid() waits only for terminated children, but this behaviour is modifiable via the options argument, as described below.

What is 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 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 does Waitpid work?

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.

What is the difference between wait and Waitpid?

Difference between wait and waitpid(): Wait() waits for any child process but waitpid() waits for a specific child equal to pid. By default waitpid() waits for the only terminated child where as wait() waits for both terminated or a signaled child.

What are Waitpid options?

options. (Input) An integer field containing flags that define how waitpid() should operate. The pid argument specifies a set of child processes for which status is requested.

How do I check the status of my child process?

The parent can use the system call wait() or waitpid() along with the macros WIFEXITED and WEXITSTATUS with it to learn about the status of its stopped child. (*)wait() system call : It suspends execution of the calling process until one of its children terminates. Syntax of wait() system call: pid_t wait(int *status);

Does Waitpid block?

waitpid can be either blocking or non-blocking: If options is 0, then it is blocking.

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.

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.

How use Waitpid Linux?

General description

1. If pid is greater than 0, waitpid() waits for termination of the specific child whose process ID is equal to pid.
2. If pid is equal to zero, waitpid() waits for termination of any child whose process group ID is equal to that of the caller.
3. If pid is -1, waitpid() waits for any child process to end.

What is the difference between waitpid and wnohang?

Normally, a call to waitpid causes the calling process to be blocked until status information from the specified process is available; the WNOHANG option prevents the calling process from being blocked. If status information is not available, waitpid returns a 0 .

What is waitpid-1&status 0?

waitpid (-1, &status, 0); The waitpid () system call suspends execution of the current process until a child specified by pid argument has changed state. By default, waitpid () waits only for terminated children, but this behaviour is modifiable via the options argument, as described below. The value of pid can be:

Why does waitpid () return 0?

If WNOHANG was given, and if there is at least one process (usually a child) whose status information is not available, waitpid () returns 0.

Where does wait () and waitpid () store status information?

If status is not NULL, wait () and waitpid () store status information in the int to which it points. This integer can be inspected with the following macros (which take the integer itself as an argument, not a pointer to it, as is done in wait () and waitpid ()!):