FileLocking Example

Author: dalmia

10-File Systems/FileLocking.java

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+import java.io.*;
+import java.nio.channels.*;
+
+public class FileLocking{
+ public static final boolean EXCLUSIVE = false;
+ public static final boolean SHARED = true;
+
+ public static void main(String args[]) throws IOException {
+ FileLock sharedLock = null;
+ FileLock exclusiveLock = null;
+
+ try{
+ RandomAccessFile raf = new RandomAccessFile("file.txt", "rw");
+
+ // get the channel for the file
+ FileChannel ch = raf.getChannel();
+
+ // this locks the first half of the file - exclusive
+ exclusiveLock = ch.lock(0, raf.length()/2, EXCLUSIVE);
+
+ /** Now modify the data **/
+
+ // release the lock
+ exclusiveLock.release();
+
+ // this locks the second half of the file - shared
+ sharedLock = ch.lock(raf.length()/2 + 1, raf.length(), SHARED);
+
+ /** Now read the data **/
+
+ // release the lock
+ sharedLock.release();
+ } catch(java.io.IOException ioe){
+ System.err.println(ioe);
+ } finally{
+ if (exclusiveLock != null) exclusiveLock.release();
+ if (sharedLock != null) sharedLock.release()
+ }
+ }
+}

10-File Systems/file.txt

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+This is a dummy file.