- Channels - communication channels, associated with an underlying socket connection
- Selectors - Object through which a single thread can monitor and service multiple channels
- SelectionKeys - Each channel registered with the selector has an associated key
- Interest Set
- What kind of activity the selector will monitor for
- Ready Set
- What operations the channel associated with the key is ready for
- Interest Set
- When you register a chanel with the selector you need to set what the selector will monitor
for
- Connect, Accept, Read, Write
- The server socket channel will be registered with accept for example
- A key is associated with each registered channel
- You may set multiple interests for each key (read and write)
- Interest set
- Select monitors all channels
- Interest set
- Takes action when there is activity on any one channel (ready set)
- Writing to and reading from a channel are independent of the interest set
- The interest is only used by the selector
- If you do not register write interest with the interest set, you can still write to the channel from any random thread
- When
channel.write()returns 0, this means 0 bytes were written and the channel is not currently writable- Could be full
- Rather than spinning in the while loop, you can register write interest with the selector
, then when the channel does become writable the
selector.select()call will pick it up - Rare situation
- Remember to turn off write interest when done so the selector does not continuosly loop
ByteBuffer buffer = ByteBuffer.wrap(byteArray);
while (true) {
socketChannel.write(buffer);
} selector.select()blocks,selector.selectNow()does not block- Clients registered for read interest
- Channels will typically always be writable
- Registering write interest will mean there is almost always activity on that channel
- Could de-registering read interest after you already know there is something to read so the selector does not keep looping
- Not writable: buffer is full