What is Signalfd in Linux?
signalfd() creates a file descriptor that can be used to accept signals targeted at the caller. This provides an alternative to the use of a signal handler or sigwaitinfo(2), and has the advantage that the file descriptor may be monitored by select(2), poll(2), and epoll(7).
Is Waitpid a system call?
The waitpid() system call suspends execution of the current process until a child specified by pid argument has changed state.
What is epoll in Linux?
epoll is a Linux kernel system call for a scalable I/O event notification mechanism, first introduced in version 2.5. Its function is to monitor multiple file descriptors to see whether I/O is possible on any of them.
What is Sigchld signal?
The SIGCHLD signal is the only signal that the z/TPF system sends to a process. Sends a SIGCHLD signal to the parent process to indicate that the child process has ended. Saves the exit status of the child process so that the parent process can identify which child process (by process ID) ended and its exit status.
What is exec close?
The close-on-exec flag for a file descriptor tells whether the file descriptor should remain open across exec-calls. So when the Tcl interpreter has heaps of files open and the close-on-exec flag is not set, the exec’ed command will inherit all these file descriptors.
What is Eventfd?
eventfd() creates an “eventfd object” that can be used as an event wait/notify mechanism by user-space applications, and by the kernel to notify user-space applications of events. The object contains an unsigned 64-bit integer (uint64_t) counter that is maintained by the kernel.
What is Waitpid function?
The waitpid() function allows the calling thread to obtain status information for one of its child processes. A suspended waitpid() function call can be interrupted by the delivery of a signal whose action is either to run a signal-catching function or to terminate the process.
What does Waitpid return Linux?
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.
Why is epoll used?
epoll stands for event poll and is a Linux specific construct. It allows for a process to monitor multiple file descriptors and get notifications when I/O is possible on them. It allows for both edge-triggered as well as level-triggered notifications.
Is epoll synchronous?
Yes. You call the epoll_wait function, and it waits until any FD is ready, and then tells you which FDs are ready. Depends what you mean by “synchronous”. epoll_wait will wait, unless you give it a timeout of 0 milliseconds.
How do I use Sigint in Linux?
The SIGINT signal is sent to a process by its controlling terminal when a user wishes to interrupt the process. This is typically initiated by pressing Ctrl-C, but on some systems, the “delete” character or “break” key can be used. The SIGKILL signal is sent to a process to cause it to terminate immediately (kill).
How does waitpid ( ) work in a system call?
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 happens if SIGCHLD is blocked because of waitpid?
Otherwise, if SIGCHLD is blocked, if wait () or waitpid () return because the status of a child process is available, any pending SIGCHLD signal shall be cleared unless the status of another child process is available. For all other conditions, it is unspecified whether child status will be available when a SIGCHLD signal is delivered.
When to return errno in waitpid ( ) function?
If wait () or waitpid () returns because the status of a child process is available, these functions shall return a value equal to the process ID of the child process for which status is reported. If wait () or waitpid () returns due to the delivery of a signal to the calling process, -1 shall be returned and errno set to [EINTR].
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.