DATAREDIS-1117 - Improve doLock method to atomic.

[joongsoo]

Related tickets: DATAREDIS-1117.

• doLock method is not guarantee to acquire lock, so improved it.

• Improved doLock method is guarantee to acquire lock, so wasLocked variable is unnecessary. I removed it.

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[joongsoo]

@christophstrobl Hi! I need feedback. is this pr has problem?

[mp911de]

Thanks for your pull request. There's indeed a loophole where checkAndPotentiallyWaitUntilUnlocked waits for unlocking but the lock acquisition happens later and potentially when someone has acquired the lock.

With locking, it makes sense to reduce the handling into a single place. Instead of modifying doLock, it makes sense to put the concept of locking directly into the execute method by passing a boolean flag, whether the execute callback requires a lock so execute and checkAndPotentiallyWaitUntilUnlocked can evaluate that flag and handle locking appropriately.

[joongsoo]

@mp911de Hi. I refactored the code based on your review. Thank you.

• All actions need locking for atomic processing. So handled lock in the execute method. (If "put" and "putIfAbsent" are called at the same time, can broken the atomic. because put is not guarantee applied the lock. I attached scenario image)
• Because the code for judging locks has been separated, each method can only have its own responsibility.