epoll_create - Linux
Overview
The epoll_create
command is a Linux system call used for creating an epoll instance. epoll is an I/O multiplexing mechanism that scales to a large number of file descriptors. The primary purpose of epoll_create
is to create a "listening post" that allows applications to efficiently monitor multiple file descriptors for events like data arrival, socket connection, disconnection, and various other system events.
Syntax
#include <sys/epoll.h>
int epoll_create(int flags);
Parameters:
- flags: Specifies additional flags to modify the behavior of the epoll instance. Currently, there are no flags defined. The value should always be 0.
Return Value:
- A non-negative file descriptor representing the created epoll instance if successful.
- -1 if the call fails, with
errno
set to indicate the error.
Options/Flags
There are no options or flags available for epoll_create
.
Examples
Simple Usage:
#include <sys/epoll.h>
int main() {
// Create an epoll instance
int epoll_fd = epoll_create(0);
if (epoll_fd == -1) {
perror("epoll_create");
exit(EXIT_FAILURE);
}
// Use the epoll instance to monitor file descriptors
// ...
return 0;
}
Complex Usage:
#include <sys/epoll.h>
int main() {
// Create an epoll instance with a large maximum event size
int epoll_fd = epoll_create(EPOLL_CLOEXEC); // Use EPOLL_CLOEXEC to automatically close the epoll instance on exec()
if (epoll_fd == -1) {
perror("epoll_create");
exit(EXIT_FAILURE);
}
// Add multiple file descriptors to the epoll instance
struct epoll_event events[10]; // Array to store up to 10 events
int num_events = epoll_wait(epoll_fd, events, 10, 5000); // Wait for events for 5 seconds
if (num_events == -1) {
perror("epoll_wait");
exit(EXIT_FAILURE);
}
// Process the events returned by epoll_wait
for (int i = 0; i < num_events; i++) {
if (events[i].events & EPOLLIN) {
// Handle data arrival for the file descriptor
// ...
} else if (events[i].events & EPOLLHUP) {
// Handle socket disconnection for the file descriptor
// ...
}
}
return 0;
}
Common Issues
- Incorrect flags: Using non-zero flags can lead to unexpected behavior.
Integration
epoll_create
is often used in conjunction with other system calls:
- epoll_ctl: Add, modify, or remove file descriptors from the epoll instance.
- epoll_wait: Wait for events to occur on any of the registered file descriptors.
Related Commands
- select: Another I/O multiplexing mechanism, but less scalable than epoll.
- poll: Similar to select, but uses polling instead of a "listening post" like epoll.