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From "Johannes Scharf (JIRA)" <j...@apache.org>
Subject [jira] Commented: (VFS-293) FtpFileSystem causes deadlock
Date Fri, 08 Jan 2010 14:12:54 GMT

    [ https://issues.apache.org/jira/browse/VFS-293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12798020#action_12798020
] 

Johannes Scharf commented on VFS-293:
-------------------------------------

I've found a possible solution for this bug.
Simply synchronize the getClient and putClient methods themselves on "this" and remove the
synchronized block inside the methods which synchronzes on "idleClientSync".

{code:java}
@Override
	public synchronized FtpClient getClient() throws FileSystemException {
		if (idleClient == null || !idleClient.isConnected()) {
			if (log.isDebugEnabled()) {
				log.debug("getClient(): Returning new FtpClient...");
			}
			FtpClient ftpClient = new FtpClientWrapper(
					(GenericFileName) getRoot().getName(),
					getFileSystemOptions());
			return ftpClient;
		} else {
			if (log.isDebugEnabled()) {
				log.debug("getClient(): Returning idle FtpClient...");
			}
			final FtpClient client = idleClient;
			idleClient = null;
			return client;
		}
	}

        public synchronized void putClient(final FtpClient client) {
		if (idleClient == null) {
			if (log.isDebugEnabled()) {
				log.debug("Pooling used FtpClient...");
			}
			// Hang on to client for later
			idleClient = client;
		} else {
			if (log.isDebugEnabled()) {
				log.debug("Disposing used FtpClient...");
			}
			// Close the client
			closeConnection(client);
		}
	}
{code}

> FtpFileSystem causes deadlock
> -----------------------------
>
>                 Key: VFS-293
>                 URL: https://issues.apache.org/jira/browse/VFS-293
>             Project: Commons VFS
>          Issue Type: Bug
>    Affects Versions: 1.0
>            Reporter: Johannes Scharf
>
> I use Commons VFS to access FTP from multiple threads. In each thread I create directories
and copy files on the FTP server.
> Nearly everytime when i run the program  a deadlock occurs which causes all threads to
hang. I've created a stacktrace with "jstack" which clearly shows where the deadlock is happening.
> Stacktrace:
> {noformat}
> Found one Java-level deadlock:
> =============================
> "pool-1-thread-5":
>   waiting to lock monitor 0x030813b4 (object 0x22f972e8, a org.apache.commons.vfs.provider.ftp.FtpFileSystem),
>   which is held by "pool-1-thread-2"
> "pool-1-thread-2":
>   waiting to lock monitor 0x03082c7c (object 0x22f999e0, a java.lang.Object),
>   which is held by "pool-1-thread-4"
> "pool-1-thread-4":
>   waiting to lock monitor 0x030813b4 (object 0x22f972e8, a org.apache.commons.vfs.provider.ftp.FtpFileSystem),
>   which is held by "pool-1-thread-2"
> Java stack information for the threads listed above:
> ===================================================
> "pool-1-thread-5":
> 	at org.apache.commons.vfs.provider.AbstractFileSystem.streamOpened(AbstractFileSystem.java:569)
> 	- waiting to lock <0x22f972e8> (a org.apache.commons.vfs.provider.ftp.FtpFileSystem)
> 	at org.apache.commons.vfs.provider.DefaultFileContent.streamOpened(DefaultFileContent.java:92)
> 	at org.apache.commons.vfs.provider.DefaultFileContent.getOutputStream(DefaultFileContent.java:377)
> 	at at.js.jtransporter.transporter.VFSTransporter.createFile(VFSTransporter.java:119)
> 	at at.js.jtransporter.worker.resource.ResourceWorker.createFile(ResourceWorker.java:80)
> 	at at.js.jtransporter.worker.resource.ResourceWorker.processJob(ResourceWorker.java:51)
> 	at at.js.jtransporter.worker.AbstractRunnableWorker.run(AbstractRunnableWorker.java:82)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
> 	at java.lang.Thread.run(Thread.java:619)
> "pool-1-thread-2":
> 	at org.apache.commons.vfs.provider.ftp.FtpFileSystem.putClient(FtpFileSystem.java:137)
> 	- waiting to lock <0x22f999e0> (a java.lang.Object)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileObject.doGetChildren(FtpFileObject.java:158)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileObject.getChildFile(FtpFileObject.java:103)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileObject.getInfo(FtpFileObject.java:181)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileObject.refresh(FtpFileObject.java:208)
> 	at org.apache.commons.vfs.provider.AbstractFileSystem.resolveFile(AbstractFileSystem.java:319)
> 	- locked <0x22f972e8> (a org.apache.commons.vfs.provider.ftp.FtpFileSystem)
> 	at org.apache.commons.vfs.provider.AbstractFileSystem.resolveFile(AbstractFileSystem.java:267)
> 	- locked <0x22f972e8> (a org.apache.commons.vfs.provider.ftp.FtpFileSystem)
> 	at org.apache.commons.vfs.provider.AbstractFileObject.getParent(AbstractFileObject.java:512)
> 	- locked <0x22f972e8> (a org.apache.commons.vfs.provider.ftp.FtpFileSystem)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileObject.getInfo(FtpFileObject.java:177)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileObject.refresh(FtpFileObject.java:208)
> 	at org.apache.commons.vfs.provider.AbstractFileSystem.resolveFile(AbstractFileSystem.java:319)
> 	- locked <0x22f972e8> (a org.apache.commons.vfs.provider.ftp.FtpFileSystem)
> 	at org.apache.commons.vfs.provider.AbstractFileSystem.resolveFile(AbstractFileSystem.java:267)
> 	- locked <0x22f972e8> (a org.apache.commons.vfs.provider.ftp.FtpFileSystem)
> 	at org.apache.commons.vfs.provider.AbstractFileObject.resolveFile(AbstractFileObject.java:670)
> 	at at.js.jtransporter.transporter.VFSTransporter.createFile(VFSTransporter.java:118)
> 	at at.js.jtransporter.worker.resource.ResourceWorker.createFile(ResourceWorker.java:80)
> 	at at.js.jtransporter.worker.resource.ResourceWorker.processJob(ResourceWorker.java:51)
> 	at at.js.jtransporter.worker.AbstractRunnableWorker.run(AbstractRunnableWorker.java:82)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
> 	at java.lang.Thread.run(Thread.java:619)
> "pool-1-thread-4":
> 	at org.apache.commons.vfs.provider.AbstractFileSystem.resolveFile(AbstractFileSystem.java:267)
> 	- waiting to lock <0x22f972e8> (a org.apache.commons.vfs.provider.ftp.FtpFileSystem)
> 	at org.apache.commons.vfs.provider.AbstractFileSystem.getRoot(AbstractFileSystem.java:242)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileSystem.getClient(FtpFileSystem.java:108)
> 	- locked <0x22f999e0> (a java.lang.Object)
> 	at org.apache.commons.vfs.provider.ftp.FtpFileObject.doGetOutputStream(FtpFileObject.java:490)
> 	at org.apache.commons.vfs.provider.AbstractFileObject.getOutputStream(AbstractFileObject.java:1219)
> 	at org.apache.commons.vfs.provider.DefaultFileContent.getOutputStream(DefaultFileContent.java:373)
> 	at at.js.jtransporter.transporter.VFSTransporter.createFile(VFSTransporter.java:119)
> 	at at.js.jtransporter.worker.resource.ResourceWorker.createFile(ResourceWorker.java:80)
> 	at at.js.jtransporter.worker.resource.ResourceWorker.processJob(ResourceWorker.java:51)
> 	at at.js.jtransporter.worker.AbstractRunnableWorker.run(AbstractRunnableWorker.java:82)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
> 	at java.lang.Thread.run(Thread.java:619)
> Found 1 deadlock.
> {noformat}

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