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  1. Commons VFS
  2. VFS-25

[vfs] Deadly embrace between AbstractFileProvider and SoftRefFilesCache

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Critical
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: None
    • Labels:
      None
    • Environment:

      Operating System: All
      Platform: All

    • Bugzilla Id:
      37374

      Description

      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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            • Assignee:
              Unassigned
              Reporter:
              fdutton@bellsouth.net Faron Dutton
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              Dates

              • Created:
                Updated:
                Resolved: