| commit | fc75a64f36c931ec9d6e99ca19a753df1c53a70b | [log] [tgz] |
|---|---|---|
| author | Patrick Hiesel <hiesel@google.com> | Thu Apr 07 09:32:26 2022 +0200 |
| committer | Patrick Hiesel <hiesel@google.com> | Tue Apr 19 06:04:15 2022 +0000 |
| tree | d649099986b92b5ff621f31398794551e7598eee | |
| parent | 605261e7f47fdc836d7ea692d06488bd5be4c634 [diff] |
Fix threading issue in Diff cache We have observed occasional failures in computing diffs. The computation fails with a Zlib exception making it look like the pack file is currupted. Fsck, however, tells that the pack file is fine. Upon closer investigation, it seems like there is a case in the diff cache were we process on a different thread and cancel in case of a timeout. The objects we pass around (ObjectReader and DiffFormatter) are not thread safe. The JavaDoc of ObjectReader states that it is not thread safe and the Dfs implementation restates that. Checking the implementation also shows that it's not thread safe since it uses member variables to store intermediary results. Other implementations might be thread safe, but if the abstract class doesn't guarantee that, we can't rely on it. In Java, a timeout of a future does not guarantee to have actually terminated the work item when it occurs. So there could be a situation where the work item has timed out, but we are still processing anyway. The main thread then continues to process a different diff in a different region of the pack. The reused ObjectReader then gets confused as it races to read different parts of the pack. This is an attempt to fix the problem by using a pool to share DiffFormatter instances. DiffFormatters that are closed will be returned to the pool. If the pool itself is already closed, the a close call to the DiffFormatter's wrapper (Handle) will propagate to the DiffFormatter and consequently the ObjectReader). Closing the pool will close any resources currently in the pool. We run into this problem, because the diff cache uses getAll which sequentially loads many diffs for a single request. Google-Bug-Id: b/209491483 Release-Notes: Fix threading issue in diff cache Change-Id: I51bd1a73f573feab0eb58f825f28024852c17e47 (cherry picked from commit 4f5f8c7e80788b168a3a5d74568198d894019de4)
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