Attempts to acquire a lock on the given region of this channel's file.
This method does not block. An invocation 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.
The region specified by the
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
tryLock() method simply locks a region of size
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
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.
|The position at which the locked region is to start; must be non-negative|
| The size of the locked region; must be non-negative, and the sum
null if the lock could not be acquired
because another program holds an overlapping lock
|If the preconditions on the parameters do not hold|
|If this channel is closed|
|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 of the same file|
|If some other I/O error occurs|