需求是现在有80G的日志，需要把这些日志按照某个规则，分类放到另外的8个文件里面去，每个文件代表一种类型的日志。
我的做法是起8个线程a[8]分析日志，8个线程b[8]写文件。这样a和b就是一个多对多的关系。对每一个a[i]，b[0]到b[7]都回向它发送数据。如果使用vector或者是数组之类的结构的话，还得自己考虑锁的问题。
而如果使用pipe的话，a[i]负责往对应的pipe中写，b[i]在8个pipe上select或者epoll，就能很好避免掉自己管理各种竞态条件或者死锁。
唯一需要注意的问题是：每次读写的数据必须是小于PIPE_BUF的，这样才能保证读写的原子性。linux2.6.11之后PIPE_BUF的大小是65536。（参看 man 7 pipe）
另外，具体设计的时候，还需要考虑读写是否需要设置非阻塞等等。因为如果pipe的容量只有PIPE_BUF，如果满了，而且是阻塞式的写的话，当前线程式会阻塞在write操作上的。
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