DO NOT REPLY [Bug 37374] New: - Deadly embrace between AbstractFileProvider and SoftRefFilesCache

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http://issues.apache.org/bugzilla/show_bug.cgi?id=37374

           Summary: Deadly embrace between AbstractFileProvider and
                    SoftRefFilesCache
           Product: Commons
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: critical
          Priority: P2
         Component: VFS
        AssignedTo: commons-dev@jakarta.apache.org
        ReportedBy: fdutton@bellsouth.net


Lock contention occurs when one thread attempts to retreave a FileSystem from
the cache at the same time that the SoftRefFilesCache thread is attempting to
close a FileSystem. SoftRefFilesCache locaks itself and then calls
FileSystem.close(), which attempts to acquire a lock on the
AbstractFileProvider. AbstractFileProvider locks itself before calling
SoftRefFilesCache.

To fix:
1) Remove 'synchronized' from AbstractLayeredFileProvider.createfileSystem()
2) Replace AbstractFileProvider with the following:
/*
 * Copyright 2002-2005 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.vfs.provider;

import java.util.Collections;
import java.util.Map;
import java.util.TreeMap;

import org.apache.commons.vfs.FileName;
import org.apache.commons.vfs.FileObject;
import org.apache.commons.vfs.FileSystem;
import org.apache.commons.vfs.FileSystemConfigBuilder;
import org.apache.commons.vfs.FileSystemException;
import org.apache.commons.vfs.FileSystemOptions;
import org.apache.commons.vfs.provider.local.GenericFileNameParser;

/**
 * A partial {@link FileProvider} implementation.  Takes care of managing the
 * file systems created by the provider.
 *
 * @author <a href="mailto:adammurdoch@apache.org">Adam Murdoch</a>
 * @version $Revision: 191323 $ $Date: 2005-06-19 03:25:16 -0400 (Sun, 19 Jun
2005) $
 */
public abstract class AbstractFileProvider
    extends AbstractVfsContainer
    implements FileProvider
{
    private FileNameParser parser;

    public AbstractFileProvider()
    {
        parser = GenericFileNameParser.getInstance();
    }

    protected FileNameParser getFileNameParser()
    {
        return parser;
    }

    protected void setFileNameParser(FileNameParser parser)
    {
        this.parser = parser;
    }

    /**
     * The cached file systems.  This is a mapping from root URI to
     * FileSystem object.
     */
    // private final Map fileSystems = new HashMap();
    private final Map fileSystems = Collections.synchronizedMap(new TreeMap());

    /**
     * Closes the file systems created by this provider.
     */
    public void close()
    {
        fileSystems.clear();
        super.close();
    }

    /**
     * Creates a layered file system.  This method throws a 'not supported'
exception.
     */
    public FileObject createFileSystem(final String scheme, final FileObject
file, final FileSystemOptions properties)
        throws FileSystemException
    {
        // Can't create a layered file system
        throw new FileSystemException("vfs.provider/not-layered-fs.error", scheme);
    }

    /**
     * Adds a file system to those cached by this provider.  The file system
     * may implement {@link VfsComponent}, in which case it is initialised.
     */
    protected void addFileSystem(final Comparable key, final FileSystem fs)
        throws FileSystemException
    {
        // Add to the cache
        addComponent(fs);

        FileSystemKey treeKey = new FileSystemKey(key, fs.getFileSystemOptions());
        ((AbstractFileSystem) fs).setCacheKey(treeKey);
        fileSystems.put(treeKey, fs);
    }

    /**
     * Locates a cached file system
     *
     * @return The provider, or null if it is not cached.
     */
    protected FileSystem findFileSystem(final Comparable key, final
FileSystemOptions fileSystemProps)
    {
        FileSystemKey treeKey = new FileSystemKey(key, fileSystemProps);
        return (FileSystem) fileSystems.get(treeKey);
    }

    public FileSystemConfigBuilder getConfigBuilder()
    {
        return null;
    }

    public void freeUnusedResources()
    {
        Object[] item = fileSystems.values().toArray();
        for (int i = 0; i < item.length; ++i)
        {
            AbstractFileSystem fs = (AbstractFileSystem) item[i];
            if (fs.isReleaseable())
            {
                fs.closeCommunicationLink();
            }
        }
    }

    public void closeFileSystem(final FileSystem filesystem)
    {
        AbstractFileSystem fs = (AbstractFileSystem) filesystem;

        fileSystems.remove(fs.getCacheKey());
        removeComponent(fs /*fileSystems*/);
        fs.close();
    }

    /**
     * Parses an absolute URI.
     *
     * @param base The base file - if null the <code>uri</code> needs to be absolute
     * @param uri The URI to parse.
     */
    public FileName parseUri(FileName base, String uri) throws FileSystemException
    {
        if (getFileNameParser() != null)
        {
            return getFileNameParser().parseUri(getContext(), base, uri);
        }

        throw new FileSystemException("vfs.provider/filename-parser-missing.error");
        // return GenericFileName.parseUri(getFileNameParser(), uri, 0);
    }
}

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