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.