Attempts to acquire in shared mode. This method should query if
the state of the object permits it to be acquired in the shared
mode, and if so to acquire it.
<p>This method is always invoked by the thread performing
acquire. If this method reports failure, the acquire method
may queue the thread, if it is not already queued, until it is
signalled by a release from some other thread.
@param arg the acquire argument. This value is always the one
passed to an acquire method, or is the value saved on entry
to a condition wait. The value is otherwise uninterpreted
and can represent anything you like.
@return a negative value on failure; zero if acquisition in shared
mode succeeded but no subsequent shared-mode acquire can
succeed; and a positive value if acquisition in shared
mode succeeded and subsequent shared-mode acquires might
also succeed, in which case a subsequent waiting thread
must check availability. (Support for three different
return values enables this method to be used in contexts
where acquires only sometimes act exclusively.) Upon
success, this object has been acquired.
@throws IllegalMonitorStateException if acquiring would place this
synchronizer in an illegal state. This exception must be
thrown in a consistent fashion for synchronization to work
correctly.
@throws UnsupportedOperationException if shared mode is not supported
Attempts to acquire in shared mode. This method should query if the state of the object permits it to be acquired in the shared mode, and if so to acquire it.
<p>This method is always invoked by the thread performing acquire. If this method reports failure, the acquire method may queue the thread, if it is not already queued, until it is signalled by a release from some other thread.
<p>The default implementation throws {@link UnsupportedOperationException}.
@param arg the acquire argument. This value is always the one passed to an acquire method, or is the value saved on entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like. @return a negative value on failure; zero if acquisition in shared mode succeeded but no subsequent shared-mode acquire can succeed; and a positive value if acquisition in shared mode succeeded and subsequent shared-mode acquires might also succeed, in which case a subsequent waiting thread must check availability. (Support for three different return values enables this method to be used in contexts where acquires only sometimes act exclusively.) Upon success, this object has been acquired. @throws IllegalMonitorStateException if acquiring would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly. @throws UnsupportedOperationException if shared mode is not supported