57 lines
1.7 KiB
Java
57 lines
1.7 KiB
Java
// newio/LockingMappedFiles.java
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// (c)2016 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
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// Locking portions of a mapped file.
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import java.nio.*;
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import java.nio.channels.*;
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import java.io.*;
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public class LockingMappedFiles {
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static final int LENGTH = 0x8FFFFFF; // 128 MB
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static FileChannel fc;
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public static void main(String[] args) throws Exception {
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fc =
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new RandomAccessFile("test.dat", "rw").getChannel();
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MappedByteBuffer out =
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fc.map(FileChannel.MapMode.READ_WRITE, 0, LENGTH);
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for(int i = 0; i < LENGTH; i++)
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out.put((byte)'x');
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new LockAndModify(out, 0, 0 + LENGTH/3);
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new LockAndModify(out, LENGTH/2, LENGTH/2 + LENGTH/4);
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}
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private static class LockAndModify extends Thread {
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private ByteBuffer buff;
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private int start, end;
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LockAndModify(ByteBuffer mbb, int start, int end) {
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this.start = start;
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this.end = end;
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mbb.limit(end);
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mbb.position(start);
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buff = mbb.slice();
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start();
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}
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@Override
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public void run() {
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try {
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// Exclusive lock with no overlap:
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FileLock fl = fc.lock(start, end, false);
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System.out.println("Locked: "+ start +" to "+ end);
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// Perform modification:
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while(buff.position() < buff.limit() - 1)
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buff.put((byte)(buff.get() + 1));
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fl.release();
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System.out.println("Released: "+start+" to "+ end);
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} catch(IOException e) {
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throw new RuntimeException(e);
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}
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}
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}
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}
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/* Output:
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Locked: 75497471 to 113246206
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Locked: 0 to 50331647
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Released: 75497471 to 113246206
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Released: 0 to 50331647
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*/
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