I/O (Input/Output) operations involve reading from or writing to external resources like networks, file systems, or databases. These operations are commonly slow and block programs while waiting for the external resource to respond.
A common workaround is threading, which allows programs to do multiple things simultaneously. In Ruby Concurrency Mechanisms, threads remain useful for I/O-bound work despite the Global Interpreter Lock.
Why Threads Work for I/O
The key insight: threads waiting on I/O operations are considered idle by the GIL. While one thread waits for a network response or disk read, other threads can execute Ruby code. This enables Concurrency where one thread executes code while another waits on a slow external resource.
This pattern appears throughout Ruby’s concurrency mechanisms:
- Threads: Automatic context switching during I/O waits
- Fibers: Explicit yielding during blocking operations
- Ractors: Better suited for CPU-bound tasks, not I/O optimization
The Async Ruby framework leverages fibers to handle thousands of concurrent I/O operations efficiently, demonstrating how cooperative multitasking excels at I/O-heavy workloads.