I have 2 threads that concurrently access the same large file(.txt).
1st Thread is reading from the File. 2nd Thread is writing to the File.
Both threads access the same block e.g. (start:0, blocksize:10), but with different channel & Buffer instances
Reader:
{
int BLOCK_SIZE = 10;
byte[] bytesArr = new byte[BLOCK_SIZE];
File file = new File("/db.txt");
RandomAccessFile randomFile = new RandomAccessFile(file, "r");
FileChannel channel = randomFile.getChannel();
MappedByteBuffer map = channel.map(FileChannel.MapMode.READ_ONLY, 0, BLOCK_SIZE);
map.get(bytesArr , 0, BLOCK_SIZE);
channel.close();
}
Writer:
{
int BLOCK_SIZE = 10;
File file = new File("/db.txt");
RandomAccessFile randomFile = new RandomAccessFile(file, "rw");
FileChannel channel = randomFile.getChannel();
MappedByteBuffer map = channel.map(FileChannel.MapMode.READ_WRITE, 0, BLOCK_SIZE);
map.put(bytesToWrite);
channel.close();
}
I know that if both starts at the same time, I will get Overlapping Exceptions! BUT what I would like to know, at which point exactly the Overlapping is happing? I mean when occurs the "lock" exactly? Example: lets say the writer get access first, then if reader try to access, at which point is it possible?:
FileChannel channel = randomFile.getChannel();
// 1- can reader access here?
MappedByteBuffer map = channel.map(FileChannel.MapMode.READ_WRITE, 0, BLOCK_SIZE);
// 2- can reader access here?
map.put(bytesToWrite);
// 3- can reader access here?
channel.close();
// 4- can reader access here?
1, 2, 3 or 4?
No 4 is sure, because the channel is been closed! What about the other points?
Thanks!
