Erlang错误处理翻译片断

Before we go into details of the supervision and error handling in an Erlang system, we need see how Erlang processes terminate, or in Erlang terminology, exit.

咱们先来看看Erlang进程如何结束，或者说先来研究一下Erlang的关键字： exit.

A process which executes exit(normal) or simply runs out of things to do has a normal exit.

当进程经过执行exit(normal)或者进程全部代码都执行完成时，进程正常结束。

A process which encounters a runtime error (e.g. divide by zero, bad match, trying to call a function which doesn't exist etc) exits with an error, i.e. has an abnormal exit. A process which executes exit(Reason) where Reason is any Erlang term except the atom normal, also has an abnormal exit.

当进程遇到运行时错误（好比除0，非法匹配或者试图调用一个不存在的函数）会终止并产生一个错误，也就是说进程非正常终止。当进程经过执行exit(Reason),Reasons是指除了normal的其余任何Erlang term,也会使进程非正常终止。

An Erlang process can set up links to other Erlang processes. If a process calls link(Other_Pid) it sets up a bidirectional link between itself and the process called Other_Pid. When a process terminates, it sends something called a signal to all the processes it has links to.

Erlang进程能够链接到其余的Erlang进程。若是一个进程调用了link(Other_Pid)函数，这个进程就建立了一个它本身与进程Other_Pid之间的一个双向链接。当一个进程结束，它会发送一个信号给链接到它的进程。

The signal carries information about the pid it was sent from and the exit reason.

信号里面包含发送进程的PID以及终止缘由。

The default behaviour of a process which receives a normal exit is to ignore the signal.

当一个进程收到一个正常终止信号时，它的默认处理方式是忽略这个信号。

The default behaviour in the two other cases (i.e. abnormal exit) above is to bypass all messages to the receiving process and to kill it and to propagate the same error signal to the killed process' links. In this way you can connect all processes in a transaction together using links and if one of the processes exits abnormally, all the processes in the transaction will be killed. As we often want to create a process and link to it at the same time, there is a special BIF, spawn_link which does the same as spawn, but also creates a link to the spawned process.

当一个进程收到一个非正常终止信号时，他的默认处理方式是忽略全部其余消息而且杀掉本身，而后发送一个一样的终止信号给链接到它的其余进程。（也就是玉石俱焚！！多浪漫的基情 ：P）经过这种方式，你可使用link把一个事务里面的全部进程链接在一块儿，这样的话，当他们中有一个进程非正常终止，事务中的全部其余进程都会被杀掉。因为咱们常常须要在建立一个进程的同时链接到它，因此Erlang提供了一个内置函数spawn_link，他的功能基本与spawn相同，惟一不一样的是会建立一个链接到spawn出来的进程。

It is possible to modify the default behaviour of a process so that it does not get killed when it receives abnormal exit signals, but all signals will be turned into normal messages on the format {'EXIT',FromPID,Reason} and added to the end of the receiving processes message queue. This behaviour is set by:

process_flag(trap_exit, true)

为了让进程收到非正常终止信号时不杀掉本身，咱们有必要改变进程的默认处理方式。经过调用
process_flag(trap_exit, true)函数，全部的异常终止信号都会被转换成普通的消息，消息格式为：{'EXIT',FromPID,Reason}，这些消息会被添加到接收进程的消息队列。

There are several other process flags, see erlang(3). Changing the default behaviour of a process in this way is usually not done in standard user programs, but is left to the supervisory programs in OTP (but that's another tutorial). 

经过这种方式改变进程的默认处理方式通常不会出如今标准的用户程序当中，这种方式常常使用的地方是在OPT的监督程序当中。