commit | 96d9e3eb197c2cd95fc5277b71d8f03f1893bcda | [log] [tgz] |
---|---|---|
author | Matthias Sohn <matthias.sohn@sap.com> | Thu Mar 30 13:43:17 2023 +0200 |
committer | Matthias Sohn <matthias.sohn@sap.com> | Wed Apr 19 16:29:44 2023 +0200 |
tree | 02bbb3f8f23ba91cb7fa1b6e11996b9459ee8be7 | |
parent | f371bfb3eb9b212c735aa7985b98eff89e34da80 [diff] |
Prevent infinite loop rescanning the pack list on PackMismatchException We found, when analysing an incident where Gerrit's gc runner thread got stuck, that we can end up in an infinite loop in ObjectDirectory#openPackedObject which tries to rescan the pack list and starts over trying to open a packed object in an unconfined loop if it catches a PackMismatchException. Here the relevant part of a thread dump we created while the gc runner was stuck: "WorkQueue-2[java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask@350812a3[Not completed, task = java.util.concurrent.Executors$RunnableAdapter@5425d7ee]]" #72 tid=0x00007f73cee1c800 nid=0x584 runnable [0x00007f7392d57000] java.lang.Thread.State: RUNNABLE at org.eclipse.jgit.internal.storage.file.WindowCache.removeAll(WindowCache.java:716) at org.eclipse.jgit.internal.storage.file.WindowCache.purge(WindowCache.java:399) at org.eclipse.jgit.internal.storage.file.PackFile.close(PackFile.java:296) at org.eclipse.jgit.internal.storage.file.ObjectDirectory.reuseMap(ObjectDirectory.java:973) at org.eclipse.jgit.internal.storage.file.ObjectDirectory.scanPacksImpl(ObjectDirectory.java:904) at org.eclipse.jgit.internal.storage.file.ObjectDirectory.scanPacks(ObjectDirectory.java:895) - locked <0x000000050a498f60> (a java.util.concurrent.atomic.AtomicReference) at org.eclipse.jgit.internal.storage.file.ObjectDirectory.searchPacksAgain(ObjectDirectory.java:794) at org.eclipse.jgit.internal.storage.file.ObjectDirectory.openPackedObject(ObjectDirectory.java:465) at org.eclipse.jgit.internal.storage.file.ObjectDirectory.openPackedFromSelfOrAlternate(ObjectDirectory.java:417) at org.eclipse.jgit.internal.storage.file.ObjectDirectory.openObject(ObjectDirectory.java:408) at org.eclipse.jgit.internal.storage.file.WindowCursor.open(WindowCursor.java:132) at org.eclipse.jgit.lib.ObjectReader$1.open(ObjectReader.java:279) at org.eclipse.jgit.revwalk.RevWalk$2.next(RevWalk.java:1031) at org.eclipse.jgit.internal.storage.pack.PackWriter.findObjectsToPack(PackWriter.java:1911) at org.eclipse.jgit.internal.storage.pack.PackWriter.preparePack(PackWriter.java:960) at org.eclipse.jgit.internal.storage.pack.PackWriter.preparePack(PackWriter.java:876) at org.eclipse.jgit.internal.storage.file.GC.writePack(GC.java:1168) at org.eclipse.jgit.internal.storage.file.GC.repack(GC.java:852) at org.eclipse.jgit.internal.storage.file.GC.doGc(GC.java:269) at org.eclipse.jgit.internal.storage.file.GC.gc(GC.java:220) at org.eclipse.jgit.api.GarbageCollectCommand.call(GarbageCollectCommand.java:179) at com.google.gerrit.server.git.GarbageCollection.run(GarbageCollection.java:112) at com.google.gerrit.server.git.GarbageCollection.run(GarbageCollection.java:75) at com.google.gerrit.server.git.GarbageCollection.run(GarbageCollection.java:71) at com.google.gerrit.server.git.GarbageCollectionRunner.run(GarbageCollectionRunner.java:76) at com.google.gerrit.server.logging.LoggingContextAwareRunnable.run(LoggingContextAwareRunnable.java:103) at java.util.concurrent.Executors$RunnableAdapter.call(java.base@11.0.18/Executors.java:515) at java.util.concurrent.FutureTask.runAndReset(java.base@11.0.18/FutureTask.java:305) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(java.base@11.0.18/ScheduledThreadPoolExecutor.java:305) at com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:612) at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base@11.0.18/ThreadPoolExecutor.java:1128) at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base@11.0.18/ThreadPoolExecutor.java:628) at java.lang.Thread.run(java.base@11.0.18/Thread.java:829) The code in ObjectDirectory#openPackedObject [1] apparently assumes that this is caused by a transient problem which it can resume from by retrying. We use `core.trustFolderStat = false` on this server since it uses NFS. The incident we had showed that we can enter into an infinite loop here if there is a permanent mismatch between a pack file and its corresponding pack index. I am not yet sure how this can happen. Break the infinite loop by limiting the number of attempts rescanning the pack list to 5 retries. When we exceed this threshold set the type of the PackMismatchException to permanent and rethrow it which breaks the infinite loop. Also apply the same limit in #getPackedObjectSize and #selectObjectRepresentation where we use similar retry loops. [1] https://git.eclipse.org/r/plugins/gitiles/jgit/jgit/+/011c26ff36b9e76c84fc2459e337f159c0f55a9a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java#465 Change-Id: I20fb63bcc1fdc3a03d39b963f06a90e6f0ba73dc
An implementation of the Git version control system in pure Java.
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org.eclipse.jgit
A pure Java library capable of being run standalone, with no additional support libraries. It provides classes to read and write a Git repository and operate on a working directory.
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