Select

Advanced · Concurrency

select lets a goroutine wait on multiple channel operations, proceeding with whichever is ready. If several are ready it picks one at random; a default case makes it non-blocking.

• select1 — receive from whichever channel is ready
• select2 — timeout by racing a receive against time.After
• select3 — non-blocking receive with default

Resources

• Go by Example: Select
• Go by Example: Timeouts
• Go by Example: Non-Blocking Channel Operations

Exercises

select1 test

select waits on multiple channel operations and proceeds with whichever

Show hint

select chooses whichever case can proceed:

select {
case v := <-a: return v
case v := <-b: return v
}

Source

select2 test

Pairing a receive with time.After in a select implements a timeout.

Show hint

time.After(d) returns a channel that fires after d. Race it:

select {
case v := <-ch: return v, true
case <-time.After(d): return 0, false
}

Source

select3 test

A default case makes a select non-blocking: it runs when no other

Show hint

A default case runs when no other case is ready, so select never blocks:

select {
case v := <-ch: return v, true
default: return 0, false
}

Source