Chapter 11. Nonblocking I/O

Compared to CPUs and memory or even disks, networks are slow. A high-end modern PC is capable of moving data between the CPU and main memory at speeds of around six gigabytes per second. It can move data to and from disk at the much slower but still respectable speed of about 150 megabytes per second.[3] By contrast, the theoretical maximum on today’s fastest local area networks tops out at about 150 megabytes per second, though many LANs only support speeds ten to a hundred times slower than that. And the speed across the public Internet is generally at least an order of magnitude smaller than what you see across a LAN. My faster than average FIOS connection promises 6 megabytes per second down and 3 megabytes per second up, about 5% of what my LAN can support. CPUs, disks, and networks are all speeding up over time. These numbers are all substantially higher than I reported in the third edition of this book 10 years ago. Nonetheless, CPUs and disks are likely to remain several orders of magnitude faster than networks for the foreseeable future. The last thing you want to do in these circumstances is make the blazingly fast CPU wait for the (relatively) molasses-slow network.

The traditional Java solution for allowing the CPU to race ahead of the network is a combination of buffering and multithreading. Multiple threads can generate data for several different connections at once and store that data in buffers until the network is actually ready to send ...

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