Refactor globallock

[wolfogre]

Follow #31908. The main refactor is that it has removed the returned context of Lock.

The returned context of Lock in old code is to provide a way to let callers know that they have lost the lock. But in most cases, callers shouldn't cancel what they are doing even it has lost the lock. And the design would confuse developers and make them use it incorrectly.

See the discussion history: #31813 (comment) and #31813 (comment)

It's a breaking change, but since the new module hasn't been used yet, I think it's OK to not add the pr/breaking label.

Design principles

It's almost copied from #31908, but with some changes.

Use spinlock even in memory implementation (unchanged)

In actual use cases, users may cancel requests. sync.Mutex will block the goroutine until the lock is acquired even if the request is canceled. And the spinlock is more suitable for this scenario since it's possible to give up the lock acquisition.

Although the spinlock consumes more CPU resources, I think it's acceptable in most cases.

Do not expose the mutex to callers (unchanged)

If we expose the mutex to callers, it's possible for callers to reuse the mutex, which causes more complexity.

For example:

lock := GetLocker(key)
lock.Lock()
// ...
// even if the lock is unlocked, we cannot GC the lock,
// since the caller may still use it again.
lock.Unlock()
lock.Lock()
// ...
lock.Unlock()

// callers have to GC the lock manually.
RemoveLocker(key)

That's why #31813 (comment)

In this PR, we only expose ReleaseFunc to callers. So callers just need to call ReleaseFunc to release the lock, and do not need to care about the lock's lifecycle.

release, err := locker.Lock(ctx, key)
if err != nil {
    return err
}
// ...
release()

// if callers want to lock again, they have to re-acquire the lock.
release, err := locker.Lock(ctx, key)
// ...

In this way, it's also much easier for redis implementation to extend the mutex automatically, so that callers do not need to care about the lock's lifecycle. See also #31813 (comment)

Use "release" instead of "unlock" (unchanged)

For "unlock", it has the meaning of "unlock an acquired lock". So it's not acceptable to call "unlock" when failed to acquire the lock, or call "unlock" multiple times. It causes more complexity for callers to decide whether to call "unlock" or not.

So we use "release" instead of "unlock" to make it clear. Whether the lock is acquired or not, callers can always call "release", and it's also safe to call "release" multiple times.

But the code DO NOT expect callers to not call "release" after acquiring the lock. If callers forget to call "release", it will cause resource leak. That's why it's always safe to call "release" without extra checks: to avoid callers to forget to call it.

Acquired locks could be lost, but the callers shouldn't stop

Unlike sync.Mutex which will be locked forever once acquired until calling Unlock, for distributed lock, the acquired lock could be lost.

For example, the caller has acquired the lock, and it holds the lock for a long time since auto-extending is working for redis. However, it lost the connection to the redis server, and it's impossible to extend the lock anymore.

In #31908, it will cancel the context to make the operation stop, but it's not safe. Many operations are not revert-able. If they have been interrupted, then the instance goes corrupted. So Lock won't return ctx anymore in this PR.

Multiple ways to use the lock

1. Regular way

release, err := Lock(ctx, key)
if err != nil {
    return err
}
defer release()
// ...

2. Early release

release, err := Lock(ctx, key)
if err != nil {
    return err
}
defer release()
// ...
// release the lock earlier
release()
// continue to do something else
// ...

3. Functional way

if err := LockAndDo(ctx, key, func(ctx context.Context) error {
    // ...
    return nil
}); err != nil {
    return err
}

[wolfogre]

Maybe we can add a new method in the future, like

LockAndWatch(ctx context.Context, key string) (context.Context, ReleaseFunc, error)

For some operations which are revertable and care about lock losing, if they really exist.