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Port
In a manner similar to processes, Ports should be considered. Ports are a datatype that encompasses all kinds of connections and sockets opened to the outside world: TCP sockets, UDP sockets, SCTP sockets, file descriptors, and so on.
?There is a general function (again, similar to processes) to count them: length(erlang:ports()) . However, this function merges in all types of ports into a single entity. Instead, one can use recon to get them sorted by type:
端口(ports)和进程的行为模式是很相近的，是一种包含了连接和sockets的数据类型：TCP sockets,UDP sockets，SCTP sockets，文件描述符等等。
?有一个通用的函数(和进程的processes()类似)来计算端口总数量：length(erlang:ports())。但这个函数的输出包含了所有的端口类型的总和，因此你无法获知某个特定类型端口的具体数目，可以使用recon的port_type来根据端口类型排序他们。---------------------------------------------------------1> recon:port_types().[{"tcp_inet",21480},{"efile",2},{"udp_inet",2},{"0/1",1},{"2/2",1},{"inet_gethost 4 ",1}]
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?This list contains the types and the count for each type of port. The type name is a string and is defined by the Erlang VM itself.
?All the *_inet ports are usually sockets, where the prefix is the protocol used (TCP, UDP, SCTP). The efile type is for files, while "0/1" and "2/2" are file descriptors for standard I/O channels (stdin and stdout) and standard error channels (stderr), respectively. Most other types will be given names of the driver they’re talking to, and will be examples of port programs 14 or port drivers 15.
?Again, tracking these can be useful to assess load or usage of a system, detect leaks, and so on.?上面这个列表包含了每种类型的端口和数量。端口类型名是Erlang VM自定义的字符串。所有以XXX_inet的端口通常都是sockets，其中XXX前缀就是所使用的协议(TCP,UDP,SCTP)。efile类型是针对文件的，"0/1" 和 "2/2" 就是标准I/O(stdin和stdout),和错误处理(stderr)的文件描述符。大多数其它的port类型在与驱动(dirver)交互时会给定一个名字，代表了相应的port programs14或port drivers15。
全程跟踪端口数会对诊断负载或进程泄漏有极大的帮助。
[14] http://www.erlang.org/doc/tutorial/c_port.html
[15] http://www.erlang.org/doc/tutorial/c_portdriver.html
[14] http://www.erlang.org/doc/tutorial/c_port.html
[15] http://www.erlang.org/doc/tutorial/c_portdriver.html