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Date: Fri, 24 Mar 2006 13:43:21 +0000 (GMT)
From: "Anton Luht (JIRA)" <jira@apache.org>
To: harmony-commits@incubator.apache.org
Subject: [jira] Created: (HARMONY-246)
 java.nio.channels.FileChannel.tryLock() should be non-blocking
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java.nio.channels.FileChannel.tryLock() should be non-blocking
--------------------------------------------------------------

         Key: HARMONY-246
         URL: http://issues.apache.org/jira/browse/HARMONY-246
     Project: Harmony
        Type: Bug
  Components: Classlib  
 Environment: Windows, Linux
    Reporter: Anton Luht


j2se 1.4.2 spec for java.nio.channels.FileChannel says: 

tryLock(..) 

Attempts to acquire a lock on the given region of this channel's file. 
This method does not block. An invocation of this always returns immediately, either having acquired a lock on the requested region or having failed to do so. If it fails to acquire a lock because an overlapping lock is held by another program then it returns null. If it fails to acquire a lock for any other reason then an appropriate exception is thrown. 

in Harmony code this method blocks 

Suggested fix (naive): always use O_NONBLOCK in fcntl

Code to reproduce:

import java.io.*;

public class Test {
  public static void main(String args[]) throws Exception {
     File f = new File("abcd");
     f.deleteOnExit();
   
     new FileOutputStream(f, true).getChannel().tryLock();
       
     System.err.println("locked OK");

     String javaCmd = System.getProperty("java.home") + 
                        File.separator +
			"bin" + 
			File.separator + 
			"java";

    if(args.length == 0) {
            Process p = Runtime.getRuntime().exec(new String[] { javaCmd, 
            "-cp",
            System.getProperty("java.class.path"),
            "Test", "foo" } );
      
            String line;

            InputStream is = p.getInputStream();
            BufferedReader input = new BufferedReader(new InputStreamReader(p
                    .getErrorStream()));
            while ((line = input.readLine()) != null) {
                System.err.println("Child prints: " + line);
            }
           input.close();
    }
  }
}

Steps to reproduce:
1. Build Harmony j2se subset as described in README.txt. 
2. Compile Test.java using BEA 1.4 javac 
> javac Test.java 
3. Run java using compatible VM (J9) 
> java Test

Output :
java version "1.4.2_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_04-b05)
BEA WebLogic JRockit(TM) 1.4.2_04 JVM  (build ari-31788-20040616-1132-win-ia32,
Native Threads, GC strategy: parallel)

locked OK
Child prints: locked OK

Output in Harmony:
locked OK
<here test hangs>

JUnit test:

---------------FileLockTest.java------------

import java.io.*;

import junit.framework.*;

public class FileLockTest extends TestCase {
	static boolean childVM = false;

	public static void main(String[] args) {
		childVM = args.length > 0;
		junit.textui.TestRunner.run(FileLockTest.class);
	}

	public void testFileLock() throws Exception {
		File f = new File("abcd");
                                           f.deleteOnExit();


		new FileOutputStream(f, true).getChannel().tryLock();

		System.err.println("locked OK");

		String javaCmd = System.getProperty("java.home") + File.separator
				+ "bin" + File.separator + "java";

		if (!childVM) {
			Process p = Runtime.getRuntime().exec(
					new String[] { javaCmd, "-cp",
							System.getProperty("java.class.path"),
							this.getClass().getName(), "foo" });

			String line;

			BufferedReader input = new BufferedReader(new InputStreamReader(p
					.getErrorStream()));
			while ((line = input.readLine()) != null) {
				System.err.println("Child prints: " + line);
			}
			input.close();
		}

	}
}


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