这个bug搞了我两天， 大致就是说select 函数在linux 下 每次调用都会重置timeout参数值，
所以需要在每次调用select 函数之前， 重新设置timeout (window下面不会重置timeout)。
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On Linux, select() modifies timeout to reflect the amount of time not
slept; most other implementations do not do this. (POSIX.1-2001 per-
mits either behaviour.) This causes problems both when Linux code
which reads timeout is ported to other operating systems, and when code
is ported to Linux that reuses a struct timeval for multiple select()s
in a loop without reinitializing it. Consider timeout to be undefined
after select() returns.
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