Go Memory Model Checkpoint

Happens-before, synchronization, and atomic publication.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. A goroutine sets x=42 and closes done. Another receives from the now-closed, unbuffered done channel and then reads x. There are no other writes. What can it rely on?

Select one answer.

The read may legally observe an arbitrary value because x is not atomic Closing done automatically orders reads that occurred before the receive The read observes 42 through the close/receive ordering No ordering exists unless done carries x as a value

2. A buffered channel already contains a token. A writer later changes shared state and closes it. A reader receives the old token and immediately reads state. What assumption is unsafe?

Select one answer.

That receiving the earlier buffered token necessarily observed the later close That the channel can retain a value before closure That reading a buffered token removes it That a receive can occur before the writer closes

3. A fully initialized struct containing a map is published with atomic.Pointer. The writer then mutates the same map while readers access it. Is pointer publication enough?

Select one answer.

Yes; an atomic pointer makes all reachable objects atomic No; it does not synchronize later mutation of the pointed-to map Yes; maps only race when their pointers change No; atomic.Pointer cannot publish any struct

4. For a mutex-protected value, the visibility edge pairs a prior Unlock with a later successful operation named what?

5. A cell starts at5. Two concurrent swaps install7 and9; both return5. What does this reveal? Select one answer.

Select one answer.

Swap was not one atomic replacement, even if individual loads/stores were atomic Any legal swap ordering can return5 twice The test must assume a specific goroutine start order Immutable snapshots prevent this observation automatically

6. A cell starts at2. Swaps install6 and10; final value is6. What predecessor did the swap-to6 return? Enter one integer.

Auto-advance on pass

Join Discord