What is a context in Go? What is it used for, what types are there, and what patterns exist for working with it?

In Go, the context (package context) is a mechanism for passing cancellation signals, deadlines, and other values between goroutines.

Purpose:

• Managing the lifetime of operations (e.g., canceling an HTTP request on timeout).
• Passing cross-cutting data (e.g., request identifiers for logging).

Types of context:

• context.Background() — the root, empty context.
• context.TODO() — used when the context is not yet defined.
• Contexts with cancellation (WithCancel), with timeout (WithTimeout), with deadline (WithDeadline), with values (WithValue).

Working patterns:

• Pass the context as the first parameter to functions.
• Do not store the context in structures, pass it explicitly.
• Check for cancellation via <-ctx.Done().

Example:

ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
 defer cancel()

select {
case <-time.After(time.Second * 10):
    fmt.Println("operation finished")
case <-ctx.Done():
    fmt.Println("operation cancelled or timed out")
}