Context

Advanced · Concurrency

context.Context carries cancellation signals, deadlines, and request-scoped values across API boundaries and goroutines. Convention: pass it as the first argument, named ctx.

• context1 — cancellation via context.WithCancel + ctx.Done()
• context2 — timeouts via context.WithTimeout; return ctx.Err()
• context3 — request-scoped values via WithValue / ctx.Value

Resources

• Go blog: Go Concurrency Patterns: Context
• pkg.go.dev: context
• Go by Example: Context

Exercises

context1 test

A context.Context lets a caller signal cancellation to running work.

Show hint

A select can wait on multiple channels at once.

Add `case <-ctx.Done(): return count` so the loop exits when cancelled.

Source

context2 test

context.WithTimeout cancels itself after a duration.

Show hint

Race the work against the context using select:

select {
case <-time.After(d): return nil
case <-ctx.Done(): return ctx.Err()
}

Source

context3 test

Contexts can carry request-scoped values down a call chain.

Show hint

ctx.Value returns interface{}. Use the comma-ok type assertion:

if u, ok := ctx.Value(userKey).(string); ok { return u }
return "anonymous"

Source