public abstract FileLock lock (long position, long size, boolean shared) throws IOException

Acquires a lock on the given region of this channel's file.

An invocation of this method will block until the region can be locked, this channel is closed, or the invoking thread is interrupted, whichever comes first.

If this channel is closed by another thread during an invocation of this method then an AsynchronousCloseException will be thrown.

If the invoking thread is interrupted while waiting to acquire the lock then its interrupt status will be set and a FileLockInterruptionException will be thrown. If the invoker's interrupt status is set when this method is invoked then that exception will be thrown immediately; the thread's interrupt status will not be changed.

The region specified by the position and size parameters need not be contained within, or even overlap, the actual underlying file. Lock regions are fixed in size; if a locked region initially contains the end of the file and the file grows beyond the region then the new portion of the file will not be covered by the lock. If a file is expected to grow in size and a lock on the entire file is required then a region starting at zero, and no smaller than the expected maximum size of the file, should be locked. The zero-argument lock() method simply locks a region of size Long.MAX_VALUE.

Some operating systems do not support shared locks, in which case a request for a shared lock is automatically converted into a request for an exclusive lock. Whether the newly-acquired lock is shared or exclusive may be tested by invoking the resulting lock object's isShared method.

File locks are held on behalf of the entire Java virtual machine. They are not suitable for controlling access to a file by multiple threads within the same virtual machine.

position     The position at which the locked region is to start; must be non-negative
size     The size of the locked region; must be non-negative, and the sum position +  size must be non-negative
shared     true to request a shared lock, in which case this channel must be open for reading (and possibly writing); false to request an exclusive lock, in which case this channel must be open for writing (and possibly reading)

Returns:  A lock object representing the newly-acquired lock

IllegalArgumentException     If the preconditions on the parameters do not hold
ClosedChannelException     If this channel is closed
AsynchronousCloseException     If another thread closes this channel while the invoking thread is blocked in this method
FileLockInterruptionException     If the invoking thread is interrupted while blocked in this method
OverlappingFileLockException     If a lock that overlaps the requested region is already held by this Java virtual machine, or if another thread is already blocked in this method and is attempting to lock an overlapping region
NonReadableChannelException     If shared is true this channel was not opened for reading
NonWritableChannelException     If shared is false but this channel was not opened for writing
IOException     If some other I/O error occurs

See also:
lock(), tryLock(), tryLock(long,long,boolean)