libcurl与CLOSE_WAIT

调用libcurl下载，然后使用netstat查看发现有大量的TCP连接保持在CLOSE_WAIT状态
查看libcurl的文档说明，有这样一个选项：

CURLOPT_FORBID_REUSE

Pass a long. Set to 1 to make the next transfer explicitly close the connection when done. Normally, libcurl keeps all connections alive when done with one transfer in case a succeeding one follows that can re-use them. This option should be used with caution and only if you understand what it does. Set to 0 to have libcurl keep the connection open for possible later re-use (default behavior).

也就是说，默认情况下libcurl完成一个任务以后，出于重用连接的考虑不会马上关闭
如果没有新的TCP请求来重用这个连接，那么只能等到CLOSE_WAIT超时，这个时间默认在7200秒甚至更高，太多的CLOSE_WAIT连接会导致性能问题

解决方法：

最好再修改一下TCP参数调低CLOSE_WAIT和TIME_WAIT的超时时间

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