Monitors

I/O operation monitors, often referred to simply as I/O monitors or event monitors, are mechanisms used in computer systems to efficiently manage and handle I/O (input/output) operations, such as reading from or writing to files, sockets, or other I/O devices. These monitors are crucial for event-driven programming, where applications need to react to various events asynchronously.

There are several types of I/O operation monitors, each with its own implementation and usage characteristics. Some common ones include:

1. Polling: In polling-based I/O monitors, the application continuously checks the status of I/O operations to determine if they are ready to perform data transfer. This approach can be inefficient because it involves active waiting and can lead to high CPU utilization.

2. Select: The select system call is available on many Unix-like operating systems. It allows applications to monitor multiple file descriptors for various types of events (e.g., readability, writability, exceptions) in a single call. However, select suffers from certain limitations, such as scalability issues with a large number of file descriptors.

3. Poll: The poll system call is an alternative to select and provides similar functionality. It can monitor multiple file descriptors for events and is more scalable than select because it does not have the same limitations on the maximum number of file descriptors.

4. Epoll: epoll is a scalable I/O event notification mechanism available on Linux systems. It allows applications to monitor large numbers of file descriptors efficiently. Unlike select and poll, which have O(n) complexity, epoll has O(1) complexity, making it suitable for high-performance applications with many file descriptors.

5. kqueue: kqueue is a similar event notification mechanism available on BSD-based operating systems (e.g., FreeBSD, macOS). It provides efficient monitoring of file descriptors and other kernel events. Like epoll, kqueue has O(1) complexity, making it suitable for high-performance applications.

These I/O operation monitors are essential for building efficient and scalable event-driven systems, such as network servers, real-time applications, and multimedia applications. The choice of which monitor to use depends on factors such as the operating system, the specific requirements of the application, and performance considerations.

Monitors Library

Monitors is a C++ library that provides various I/O monitoring mechanisms, each implemented as a separate class. These classes allow developers to efficiently monitor file descriptors for events such as readability or writability.

Features

• Poller: Implements polling-based I/O monitoring.
• Epoller: Provides I/O monitoring using the epoll mechanism on Linux systems.
• Selector: Implements I/O monitoring using the select system call.
• KQueuer: Provides I/O monitoring using the kqueue mechanism on BSD-based systems.

Each monitoring mechanism is encapsulated within its own class and implements the IMonitor interface, allowing for a consistent interface across different platforms.

Usage

Poller

The Poller class provides polling-based I/O monitoring. To use it, follow these steps:

1. Create an instance of the Poller class.
2. Use the push method to add file descriptors to monitor for events.
3. Use the pop method to remove file descriptors from monitoring.
4. Use the is_readable and is_writeable methods to check for readability and writability of file descriptors.
5. Use the wait method to wait for events on monitored file descriptors.
6. Use the wait method to wait for events on monitored file descriptors.
7. Event flags for setting events (for all Monitors):
   • EVENT_READ: Set to monitor readability of the file descriptor.
   • EVENT_WRITE: Set to monitor writability of the file descriptor.
   • EVENT_RW: Set to monitor both readability and writability of the file descriptor.

Example:

#include "monitors.hpp"

IMonitor* monitor = new Poller();

// Add file descriptor to monitor
monitor->push(fd, EVENT_READ);
// Remove file descriptor from monitor
monitor->pop(fd);

// Wait for events on monitored fds
monitor->wait(timeout_in_sec);

// Check if file descriptor is readable
if (monitor->is_readable(fd)) {
    // Perform read operation
}
// Check if file descriptor is writeable
if (monitor->is_writeable(fd)) {
    // Perform read operation
}