Clarify acquiring index shard permit #24971
Merged
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
In previous work, we refactored the delay mechanism in index shard operation permits to allow for async delaying of acquisition. This refactoring made explicit when permit acquisition is disabled whereas previously we were relying on an implicit condition, namely that all permits were acquired by the thread trying to delay acquisition. When using the implicit mechanism, we tried to acquire a permit and if this failed, we returned a null releasable as an indication that our operation should be queued. Yet, now we know when we are delayed and we should not even try to acquire a permit. If we try to acquire a permit and one is not available, we know that we are not delayed, and so acquisition should be successful. If it is not successful, something is deeply wrong. This commit takes advantage of this refactoring to simplify the internal implementation.
bleskes
approved these changes
May 30, 2017
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
In previous work, we refactored the delay mechanism in index shard operation permits to allow for async delaying of acquisition. This refactoring made explicit when permit acquisition is disabled whereas previously we were relying on an implicit condition, namely that all permits were acquired by the thread trying to delay acquisition. When using the implicit mechanism, we tried to acquire a permit and if this failed, we returned a null releasable as an indication that our operation should be queued. Yet, now we know when we are delayed and we should not even try to acquire a permit. If we try to acquire a permit and one is not available, we know that we are not delayed, and so acquisition should be successful. If it is not successful, something is deeply wrong. This commit takes advantage of this refactoring to simplify the internal implementation.
Relates #24925