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Fix concurrent creation of fan-out object directories 

If multiple threads attempted to insert loose objects into the same new
fan-out directory, the creation of that directory was subject to a race
condition that could lead to an unnecessary IOException being thrown -
because an inserter could not 'create' a directory that had just been
generated by a different thread. All we require is that the directory
does indeed *exist*, so not being able to _create_ it is not actually a
fatal problem. Setting 'skipExisting' to 'true' on the call to mkdir()
fixes the issue.

I found this issue as a real world occurrence while working on The BFG
Repo Cleaner (https://github.com/rtyley/bfg-repo-cleaner), a tool which
concurrently performs a lot of object creation.

In order to demonstrate the problem here I've added a small test case
which reliably reproduces the issue on the few different hardware
systems I've tried. The error thrown when the race-condition arises is
this:

java.io.IOException: Creating directory /home/roberto/repo.git/objects/e6 failed
at org.eclipse.jgit.util.FileUtils.mkdir(FileUtils.java:182)
at org.eclipse.jgit.storage.file.ObjectDirectory.insertUnpackedObject(ObjectDirectory.java:590)
at org.eclipse.jgit.storage.file.ObjectDirectoryInserter.insertOneObject(ObjectDirectoryInserter.java:113)
at org.eclipse.jgit.storage.file.ObjectDirectoryInserter.insert(ObjectDirectoryInserter.java:91)
at org.eclipse.jgit.lib.ObjectInserter.insert(ObjectInserter.java:329)

Change-Id: I88eac49bc600c56ba9ad290e6133d8a7113125ab
This commit is contained in:
Roberto Tyley 2012-12-25 09:10:51 +00:00 committed by Gerrit Code Review @ Eclipse.org
parent 912ef3da19
commit 5dcc8693d7
2 changed files with 78 additions and 1 deletions
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77
org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/ObjectDirectoryTest.java Normal file
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@ -0,0 +1,77 @@
/*
* Copyright (C) 2012, Roberto Tyley <roberto.tyley@gmail.com>
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* - Neither the name of the Eclipse Foundation, Inc. nor the
* names of its contributors may be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.eclipse.jgit.storage.file;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.RepositoryTestCase;
import org.junit.Test;
import java.util.*;
import java.util.concurrent.*;
public class ObjectDirectoryTest extends RepositoryTestCase {
@Test
public void testConcurrentInsertionOfBlobsToTheSameNewFanOutDirectory()
throws Exception {
ExecutorService e = Executors.newCachedThreadPool();
for (int i=0; i < 100; ++i) {
ObjectDirectory db = createBareRepository().getObjectDatabase();
for (Future f : e.invokeAll(blobInsertersForTheSameFanOutDir(db))) {
f.get();
}
}
}
private Collection<Callable<ObjectId>> blobInsertersForTheSameFanOutDir(
final ObjectDirectory db) {
Callable<ObjectId> callable = new Callable<ObjectId>() {
public ObjectId call() throws Exception {
return db.newInserter().insert(Constants.OBJ_BLOB, new byte[0]);
}
};
return Collections.nCopies(4, callable);
}
}

2
org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
View File

@ -577,7 +577,7 @@ InsertLooseObjectResult insertUnpackedObject(File tmp, ObjectId id,
// directories are always lazily created. Note that we
// try the rename first as the directory likely does exist.
//
FileUtils.mkdir(dst.getParentFile());
FileUtils.mkdir(dst.getParentFile(), true);
if (tmp.renameTo(dst)) {
dst.setReadOnly();
unpackedObjectCache.add(id);