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Java Forum / General / January 2006writing to sockets
In non-blocking NIO, why do I need the OP_WRITE flag to be set in an interest set ever? I understand that OP_READ indicates that new data is ready to be read. But for writing, should I not only need to do Channel.write(buffer) whenever I feel for it? In nonblocking mode, if the write buffer of the socket is full, just "blasting away" with writes will cause a large number of zero-length writes. If inside a tight loop, you would effectively busy-wait for sending of data, which would clear some of the buffer (much like not looking at a selector, and just calling read() repeatedly would busy-wait for arrival of data). Gotcha, so I can have my data (can be huge) stored into Collections, then when WRITE is ready, move it over to a ByteBuffer and output to the channel. That is the best strategy? The reason I am having the Collections is that I want to have a per connection buffer (for simple design), if I would allocate big ByteBuffers for each connection, that would give me memory problems when I have many connections (a few thousands). So Collections resize nicely, then use ByteBuffers and feed the channel... > In nonblocking mode, if the write buffer of the socket is full, just > "blasting away" with writes will cause a large number of zero-length > writes. If inside a tight loop, you would effectively busy-wait for > sending of data, which would clear some of the buffer (much like not > looking at a selector, and just calling read() repeatedly would > busy-wait for arrival of data). Page 134 of Java NIO (Ron Hitchens, O'Reilly) calls sayHello(channel) which does write without checking for readiness. Is this bad programming style? > In nonblocking mode, if the write buffer of the socket is full, just > "blasting away" with writes will cause a large number of zero-length > writes. If inside a tight loop, you would effectively busy-wait for > sending of data, which would clear some of the buffer (much like not > looking at a selector, and just calling read() repeatedly would > busy-wait for arrival of data). Well, that depends: If the channel is in blocking mode, the call is just fine. If however, the call is made in nonblocking mode, only part of the data (possibly none) might be written, which is not a good thing. > In non-blocking NIO, why do I need the OP_WRITE flag to be set in an > interest set ever? I understand that OP_READ indicates that new data > is ready to be read. But for writing, should I not only need to do > Channel.write(buffer) whenever I feel for it? You can write without OP_WRITE as long as write() succeeds. When write() returns 0, wait until OP_WRITE is indicated before attempting to write again. /gordon  Signature[ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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