How to Acquire a Lock with a Deadline in Go?

Acquiring Lock with Deadline in Go

In Go, the sync.Mutex type only provides Lock() and Unlock() methods. For scenarios where a lock acquisition should be attempted within a deadline, or potentially aborted immediately, there is no built-in solution.

Proposed Solution: Channel as Mutex

An alternative approach is to use a channel with a buffer size of one to simulate a mutex. By sending and receiving a single empty struct value (struct{}{}), lock and unlock operations can be performed.

Lock:

<code class="go">l := make(chan struct{}, 1)
l <- struct{}{}</code>

Unlock:

<code class="go"><-l</code>

Try Lock:

<code class="go">select {
case l <- struct{}{}:
    // lock acquired
    <-l
default:
    // lock not acquired
}</code>

Try Lock with Timeout:

<code class="go">select {
case l <- struct{}{}:
    // lock acquired
    <-l
case <-time.After(time.Minute):
    // lock not acquired
}</code>

In the provided examples, s.someObj is assumed to be a map from key to value.

Example 1: LockBefore() for Latency Sensitive Code

<code class="go">// DoTheThing locks before performing expensive computations.
func (s *RPCService) DoTheThing(ctx context.Context, ...) ... {
    l := make(chan struct{}, 1)
    select {
    case l <- struct{}{}:
        defer <-l
        ... expensive computation based on internal state ...
    default:
        return s.cheapCachedResponse[req.Parameter]
    }
}</code>

Example 2: TryLock() for Updating Stats

<code class="go">// updateObjStats attempts to lock and update stats.
func (s *StatsObject) updateObjStats(key, value interface{}) {
    l := make(chan struct{}, 1)
    select {
    case l <- struct{}{}:
        defer <-l
        ... update stats ...
        ... fill in s.cheapCachedResponse ...
    default:
        // skip locked object
    }
}

// UpdateStats attempts to lock and update stats for all objects.
func (s *StatsObject) UpdateStats() {
    s.someObj.Range(s.updateObjStats)
}</code>

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