Currently, getContentSummary takes two phases to complete:
- phase1. check the permission of the entire subtree. If any subdirectory does not have READ_EXECUTE, an access control exception is thrown and getContentSummary terminates here (unless it's super user).
- phase2. If phase1 passed, it will then traverse the entire tree recursively to get the actual content summary.
An issue is, both phases currently hold the fs lock.
Phase 2 has already been written that, it will yield the fs lock over time, such that it does not block other operations for too long. However phase 1 does not yield. Meaning it's possible that the permission check phase still blocks things for long time.
One fix is to add lock yield to phase 1. But a simpler fix is to merge phase 1 into phase 2. Namely, instead of doing a full traversal for permission check first, we start with phase 2 directly, but for each directory, before obtaining its summary, check its permission first. This way we take advantage of existing lock yield in phase 2 code and still able to check permission and terminate on access exception.
Thanks Tsz-wo Sze for the offline discussions!