Implementation(System call/API)

1、下面是 libevent – an event notification library 总结的当前各种OS 中，IO multiplexing的implementation:

/dev/poll, kqueue(2), event ports, POSIX select(2), Windows select(), poll(2), and epoll(4).

2、下面是 "libuv Design overview¶ # The I/O loop¶ "总结的:

The event loop follows the rather usual single threaded asynchronous I/O approach: all (network) I/O is performed on non-blocking sockets which are polled using the best mechanism available on the given platform:

epoll on Linux,

kqueue on OSX and other BSDs,

event ports on SunOS and

IOCP on Windows.

执行implementation的共同点:

支持设置timeout(system call with timeout)

1、这一点非常重要，它是实现"Multiplex on file and time event"的基础

2、在APUE 14.4.1 select and pselect Functions 中有对timeout参数的说明，可以作为参考

Wait the specified number of seconds and microseconds.

Return is made when one of the specified descriptors is ready or when the timeout value expires.

If the timeout expires before any of the descriptors is ready, the return value is 0.(If the system doesn’t provide microsecond resolution, the tvptr−>tv_usec value is rounded up to the nearest supported value.)

As with the first condition, this wait can also be interrupted by a caught signal.

Any (or all) of the middle three arguments to select (the pointers to the descriptor sets) can be null pointers if we’re not interested in that condition.

If all three pointers are NULL, then we have a higher-precision timer than is provided by sleep. (Recall from Section 10.19 that sleep waits for an integral number of seconds.

With select, we can wait for intervals less than one second; the actual resolution depends on the system’s clock.) Exercise 14.5 shows such a function.

支持同时管理多个file descriptor

Concurrent programming

广泛用于Concurrent programming，能够用于解决C10K问题。

参见工程parallel-computing的The-C10K-problem章节。