Base implementation class for interruptible channels.
This class encapsulates the low-level machinery required to implement the asynchronous closing and interruption of channels. A concrete channel class must invoke the begin
and end
methods before and after, respectively, invoking an I/O operation that might block indefinitely. In order to ensure that the end
method is always invoked, these methods should be used within a try
... finally
block:
boolean completed = false;
try {
begin();
completed = ...; // Perform blocking I/O operation
return ...; // Return result
} finally {
end(completed);
}
The completed
argument to the end
method tells whether or not the I/O operation actually completed, that is, whether it had any effect that would be visible to the invoker. In the case of an operation that reads bytes, for example, this argument should be true
if, and only if, some bytes were actually transferred into the invoker's target buffer.
A concrete channel class must also implement the implCloseChannel
method in such a way that if it is invoked while another thread is blocked in a native I/O operation upon the channel then that operation will immediately return, either by throwing an exception or by returning normally. If a thread is interrupted or the channel upon which it is blocked is asynchronously closed then the channel's end
method will throw the appropriate exception.
This class performs the synchronization required to implement the Channel
specification. Implementations of the implCloseChannel
method need not synchronize against other threads that might be attempting to close the channel.