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  • Java FileLock for Reading and Writing

    - by bobtheowl2
    I have a process that will be called rather frequently from cron to read a file that has certain move related commands in it. My process needs to read and write to this data file - and keep it locked to prevent other processes from touching it during this time. A completely separate process can be executed by a user to (potential) write/append to this same data file. I want these two processes to play nice and only access the file one at a time. The nio FileLock seemed to be what I needed (short of writing my own semaphore type files), but I'm having trouble locking it for reading. I can lock and write just fine, but when attempting to create lock when reading I get a NonWritableChannelException. Is it even possible to lock a file for reading? Seems like a RandomAccessFile is closer to what I need, but I don't see how to implement that. Here is the code that fails: FileInputStream fin = new FileInputStream(f); FileLock fl = fin.getChannel().tryLock(); if(fl != null) { System.out.println("Locked File"); BufferedReader in = new BufferedReader(new InputStreamReader(fin)); System.out.println(in.readLine()); ... The exception is thrown on the FileLock line. java.nio.channels.NonWritableChannelException at sun.nio.ch.FileChannelImpl.tryLock(Unknown Source) at java.nio.channels.FileChannel.tryLock(Unknown Source) at Mover.run(Mover.java:74) at java.lang.Thread.run(Unknown Source) Looking at the JavaDocs, it says Unchecked exception thrown when an attempt is made to write to a channel that was not originally opened for writing. But I don't necessarily need to write to it. When I try creating a FileOutpuStream, etc. for writing purposes it is happy until I try to open a FileInputStream on the same file.

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  • In Java What is the guaranteed way to get a FileLock from FileChannel while accessing a RandomAcces

    - by narasimha.bhat
    I am trying to use FileLock lock(long position, long size,boolean shared) in FileChannel object As per the javadoc it can throw OverlappingFileLockException. When I create a test program with 2 threads lock method seems to be waiting to acquire the lock (both exclusive and non exclusive) But when the number threads increases in the acutal scenario over lapping file lock exception is thrown and processing slows down due the block at File lock table. What is the best way to acquire lock avoiding the OverlappingFileLockException ?

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  • FileStream to save file then immediately unlock in C# ?

    - by aron
    Hello, I have this code that saves a pdf file. FileStream fs = new FileStream(SaveLocation, FileMode.Create); fs.Write(result.DocumentBytes, 0, result.DocumentBytes.Length); fs.Flush(); fs.Close(); It works fine. However sometimes it does not release the lock right away and that causes file locking exceptions with functions run after this one run. Is there a ideal way to release the file lock right after the fs.Close() thanks!

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  • Cannot delete an image file that is shown in a listview

    - by Enrico
    Hello all, In my listview I show thumbnails of small images in a certain folder. I setup the listview as follows: var imageList = new ImageList(); foreach (var fileInfo in dir.GetFiles()) { try { var image = Image.FromFile(fileInfo.FullName); imageList.Images.Add(image); } catch { Console.WriteLine("error"); } } listView.View = View.LargeIcon; imageList.ImageSize = new Size(64, 64); listView.LargeImageList = imageList; for (int j = 0; j < imageList.Images.Count; j++) { var item = new ListViewItem {ImageIndex = j, Text = "blabla"}; listView.Items.Add(item); } The user can rightclick on an image in the listview to remove it. I remove it from the listview and then I want to delete this image from the folder. Now I get the error that the file is in use. Of course this is logical since the imagelist is using the file. I tried to first remove the image from the imagelist, but I keep on having the file lock. Can somebody tell me what I am doing wrong? Thanks!

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  • Safest way to copy a file

    - by aron
    Hello, I need to merg two PDF files. However sometimes a file might be locked up I wrote this code, but I'm wondering if it's not the smartest solution: private static int FILE_LOCKED_WAIT_PERIOD = 1000; while (true) { // If the file is in use, IOException will be thrown. // If file is not permitted to be opened because of Permission // Restrictions, UnauthorizedAccessException will be thrown. // For all other, Use normal Exception. try { inputDocument1 = PdfReader.Open(fileToMerge, PdfDocumentOpenMode.Import); break; } catch (IOException) { Thread.Sleep(FILE_LOCKED_WAIT_PERIOD); } catch (UnauthorizedAccessException) { Thread.Sleep(FILE_LOCKED_WAIT_PERIOD); } catch (Exception) { Thread.Sleep(FILE_LOCKED_WAIT_PERIOD); } }

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  • Java: opening and reading from a file without locking it.

    - by rogue780
    I need to be able to mimic 'tail -f' with Java. I'm trying to read a log file as it's being written by another process, but when I open the file to read it, it locks the file and the other process can't write to it anymore. Any help would be greatly appreciated! Here is the code that I'm using currently: public void read(){ Scanner fp = null; try{ fp = new Scanner(new FileReader(this.filename)); fp.useDelimiter("\n"); }catch(java.io.FileNotFoundException e){ System.out.println("java.io.FileNotFoundException e"); } while(true){ if(fp.hasNext()){ this.parse(fp.next()); } } }

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  • FileStream to save file then immediately unlock in .NET ?

    - by aron
    I have this code that saves a pdf file. FileStream fs = new FileStream(SaveLocation, FileMode.Create); fs.Write(result.DocumentBytes, 0, result.DocumentBytes.Length); fs.Flush(); fs.Close(); It works fine. However sometimes it does not release the lock right away and that causes file locking exceptions with functions run after this one run. Is there a ideal way to release the file lock right after the fs.Close()

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  • File Encrypt/Decrypt under load?

    - by chopps
    I found an interesting article about encrypting and decrypting files but since it uses a file.dat to store the key this will run into problems when theres alot of users on the site dealing with alot of files. http://www.codeproject.com/KB/security/VernamEncryption.aspx?display=Print Should a new file be created every time a file needs decrypting or would there be a better way to do this? UPDATE: Here is what im using to avoid the locking problems. using (Mutex FileLock = new Mutex(true, System.Guid.NewGuid().ToString())) { try { FileLock.WaitOne(); using (FileStream fs = new FileStream(keyFile, FileMode.Open)) { keyBytes = new byte[fs.Length]; fs.Read(keyBytes, 0, keyBytes.Length); } } catch (Exception ex) { EventLog.LogEvent(ex); } finally { FileLock.ReleaseMutex(); } } I tested it on 1000 TIFFs doing both encryption and decryption without any errors.

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  • Better documentation for tasks waiting on resources

    - by SQLOS Team
    The sys.dm_os_waiting_tasks DMV contains a wealth of useful information about tasks waiting on a resource, but until now detailed information about the resource being consumed - sys.dm_os_waiting_tasks.resource_description - hasn't been documented, apart from a rather self-evident "Description of the resource that is being consumed."   Thanks to a recent Connect suggestion this column will get more information added. Here is a summary of the possible values that can appear in this column - Note this information is current for SQL Server 2008 R2 and Denali:   Thread-pool resource owner:•       threadpool id=scheduler<hex-address> Parallel query resource owner:•       exchangeEvent id={Port|Pipe}<hex-address> WaitType=<exchange-wait-type> nodeId=<exchange-node-id> Exchange-wait-type can be one of the following.•       e_waitNone•       e_waitPipeNewRow•       e_waitPipeGetRow•       e_waitSynchronizeConsumerOpen•       e_waitPortOpen•       e_waitPortClose•       e_waitRange Lock resource owner:<type-specific-description> id=lock<lock-hex-address> mode=<mode> associatedObjectId=<associated-obj-id>               <type-specific-description> can be:• For DATABASE: databaselock subresource=<databaselock-subresource> dbid=<db-id>• For FILE: filelock fileid=<file-id> subresource=<filelock-subresource> dbid=<db-id>• For OBJECT: objectlock lockPartition=<lock-partition-id> objid=<obj-id> subresource=<objectlock-subresource> dbid=<db-id>• For PAGE: pagelock fileid=<file-id> pageid=<page-id> dbid=<db-id> subresource=<pagelock-subresource>• For Key: keylock  hobtid=<hobt-id> dbid=<db-id>• For EXTENT: extentlock fileid=<file-id> pageid=<page-id> dbid=<db-id>• For RID: ridlock fileid=<file-id> pageid=<page-id> dbid=<db-id>• For APPLICATION: applicationlock hash=<hash> databasePrincipalId=<role-id> dbid=<db-id>• For METADATA: metadatalock subresource=<metadata-subresource> classid=<metadatalock-description> dbid=<db-id>• For HOBT: hobtlock hobtid=<hobt-id> subresource=<hobt-subresource> dbid=<db-id>• For ALLOCATION_UNIT: allocunitlock hobtid=<hobt-id> subresource=<alloc-unit-subresource> dbid=<db-id> <mode> can be:• Sch-S• Sch-M• S• U• X• IS• IU• IX• SIU• SIX• UIX• BU• RangeS-S• RangeS-U• RangeI-N• RangeI-S• RangeI-U• RangeI-X• RangeX-S• RangeX-U• RangeX-X External resource owner:•       External ExternalResource=<wait-type> Generic resource owner:•       TransactionMutex TransactionInfo Workspace=<workspace-id>•       Mutex•       CLRTaskJoin•       CLRMonitorEvent•       CLRRWLockEvent•       resourceWait Latch resource owner:•       <db-id>:<file-id>:<page-in-file>•       <GUID>•       <latch-class> (<latch-address>)   Further Information Slava Oks's weblog: sys.dm_os_waiting_tasks.Informit.com: Identifying Blocking Using sys.dm_os_waiting_tasks - Ken Henderson   - Guy

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  • Is it possible for competing file access to cause deadlock in Java?

    - by BlairHippo
    I'm chasing a production bug that's intermittent enough to be a real bastich to diagnose properly but frequent enough to be a legitimate nuisance for our customers. While I'm waiting for it to happen again on a machine set to spam the logfile with trace output, I'm trying to come up with a theory on what it could be. Is there any way for competing file read/writes to create what amounts to a deadlock condition? For instance, let's say I have Thread A that occasionally writes to config.xml, and Thread B that occasionally reads from it. Is there a set of circumstances that would cause Thread B to prevent Thread A from proceeding? My thanks in advance to anybody who helps with this theoretical fishing expedition. Edit: To answer Pyrolistical's questions: the code isn't using Filelock, and is running on a WinXP machine.

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