48 lines
1.4 KiB
Java
48 lines
1.4 KiB
Java
//: io/LockingMappedFiles.java
|
|
// Locking portions of a mapped file.
|
|
// {RunByHand}
|
|
import java.nio.*;
|
|
import java.nio.channels.*;
|
|
import java.io.*;
|
|
|
|
public class LockingMappedFiles {
|
|
static final int LENGTH = 0x8FFFFFF; // 128 MB
|
|
static FileChannel fc;
|
|
public static void main(String[] args) throws Exception {
|
|
fc =
|
|
new RandomAccessFile("test.dat", "rw").getChannel();
|
|
MappedByteBuffer out =
|
|
fc.map(FileChannel.MapMode.READ_WRITE, 0, LENGTH);
|
|
for(int i = 0; i < LENGTH; i++)
|
|
out.put((byte)'x');
|
|
new LockAndModify(out, 0, 0 + LENGTH/3);
|
|
new LockAndModify(out, LENGTH/2, LENGTH/2 + LENGTH/4);
|
|
}
|
|
private static class LockAndModify extends Thread {
|
|
private ByteBuffer buff;
|
|
private int start, end;
|
|
LockAndModify(ByteBuffer mbb, int start, int end) {
|
|
this.start = start;
|
|
this.end = end;
|
|
mbb.limit(end);
|
|
mbb.position(start);
|
|
buff = mbb.slice();
|
|
start();
|
|
}
|
|
public void run() {
|
|
try {
|
|
// Exclusive lock with no overlap:
|
|
FileLock fl = fc.lock(start, end, false);
|
|
System.out.println("Locked: "+ start +" to "+ end);
|
|
// Perform modification:
|
|
while(buff.position() < buff.limit() - 1)
|
|
buff.put((byte)(buff.get() + 1));
|
|
fl.release();
|
|
System.out.println("Released: "+start+" to "+ end);
|
|
} catch(IOException e) {
|
|
throw new RuntimeException(e);
|
|
}
|
|
}
|
|
}
|
|
} ///:~
|