Epoll is a Linux kernel interface for efficient I/O event notification by allowing user-space applications to monitor multiple file descriptors or sockets for events.
Epoll works by registering a set of file descriptors with the kernel, and then waiting for events to occur on those descriptors. It uses a "polling" approach, where the application waits for the kernel to signal that events are ready, rather than actively polling the file descriptors itself.
The epoll API provides three system calls:
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epoll_create: creates a new epoll instance and returns a file descriptor that can be used to refer to it. -
epoll_ctl: modifies the set of file descriptors that are being monitored by the epoll instance. It can be used to add or remove file descriptors from the set, or to change the events that the kernel should watch for (e.g., read, write, or error). -
epoll_wait: waits for events to occur on the file descriptors that are being monitored by the epoll instance. It blocks until at least one event occurs, and then returns information about the file descriptor(s) that triggered the event.
One of the main advantages of epoll over other I/O notification mechanisms (such as select and poll) is its ability to scale well in high-concurrency scenarios, where there are many file descriptors being monitored at once. Epoll achieves this scalability by using a "red-black" tree data structure to efficiently keep track of the set of file descriptors, rather than linearly searching through them like select and poll do.
Rust is able to interact with the operating system interfaces for input-output (I/O) operations, specifically with the epoll interface and epoll crate.