问题描述
我刚刚开始尝试在几天前的node.js。我已经意识到,当我的程序中有一个未处理的异常时,Node被终止。这与我已经暴露于正常的服务器容器不同,只有当工作线程在未处理的异常发生时才会死机,并且容器仍然能够接收到请求。这提出了一些问题:
- 是
process.on('uncaughtException')
唯一有效的方法来防范它? - 在执行异步进程期间,
process.on('uncaughtException')
会捕获未处理的异常? - 是否有一个已经建立的模块(如发送电子邮件或写入文件),我可以在未捕获的例外情况下利用这个模块?
我会感谢任何指针/文章,将显示在node.js中处理未捕获异常的常见最佳做法
更新:Joyent现在已经在中提及。以下信息是更多摘要:
安全地抛出错误
理想情况下,我们希望尽可能避免未捕获的错误,因此,根据我们的代码架构,我们可以使用以下方法之一安全地抛出错误,而不是直接抛出错误:
-
对于同步代码,如果发生错误,请返回错误:
//将分隔符定义为一个syncrhonous函数
var divideSync = function(x,y){
//如果错误条件?
if(y === 0){
//通过返回来安全地抛出错误
返回新错误(不能除以零)
}
else {
//没有错误发生,继续在
返回x / y
}
}
// Divide 4/2
var result = divideSync(4,2)
//发生错误?
if(result instanceof Error){
//安全处理错误
console.log('4/2 = err',result)
}
else {
//没有错误发生,继续在
console.log('4/2 ='+ result)
}
// Divide 4/0
result = divideSync(4,0)
//发生错误?
if(result instanceof Error){
//安全处理错误
console.log('4/0 = err',result)
}
else {
//没有错误发生,继续在
console.log('4/0 ='+ result)
}
-
对于基于回调(即异步)的代码,回调的第一个参数是
err
,if发生错误err
是错误,如果错误不会发生,那么err
是空
。任何其他参数都遵循err
参数:var divide = function x,y,next){
//如果错误条件?
if(y === 0){
//通过调用完成回调
//安全地抛出错误,第一个参数是错误
next(new错误(不能除以零)
}
else {
//没有错误发生,继续
next(null,x / y)
}
}
divide(4,2,function(err,result){
//发生错误
if(err){
//安全地处理错误
console.log('4/2 = err',err)
}
else {
//没有错误发生,继续在
console.log('4/2 ='+ result)
}
})
divide(4,0,function(err,result){
//发生错误
if(err){
//安全地处理错误
console.log('4/0 = err',err)
else {
//没有发生错误,继续在
console.log('4/0 ='+ result)
}
})
-
对于代码,错误可能发生在任何地方,而不是投掷错误,请中
var d = require('domain')。create()
d.on('error',function(err){
/ /安全处理错误
console.log(err)
})
//捕获此异步或同步代码块中未捕获的错误
d.run function(){
//我们要捕获的异步或同步代码抛出错误
var err = new Error('example')
throw err
})
-
如果我们知道发生错误的位置是同步代码,无论什么原因使用域(可能是旧版本的节点),我们可以使用try catch语句:
//捕获未知的错误同步代码块
// try catch语句只适用于同步代码
try {
//我们要捕获的同步代码抛出错误
var err = new Error('例子')
throw err
} catch(err){
//安全地处理错误
console.log(err)
}
但是,请注意不要在异步中使用
try ... catch
代码,作为异步抛出的错误不会被捕获:try {
setTimeout(function(){
var err = new Error('example')
throw err
},1000)
}
catch(err){
//示例错误赢得'被抓到这里...崩溃我们的应用程序
//因此需要域
}
另外需要注意的是,
try ... catch
是将try
语句如下:var divide = function(x,y,next){
//如果错误条件?
if(y === 0){
//通过调用完成回调
//安全地抛出错误,第一个参数是错误
next(new错误(不能除以零)
}
else {
//没有错误发生,继续
next(null,x / y)
}
}
var continueElsewhere = function(err,result){
throw new Error('others have failed')
}
try {
divide(4,2,continueElsewhere)
// ^执行分割,执行
// continueElsewhere将在try语句内
}
catch(err){
console.log(err.stack)
// ^将输出意外结果:其他地方失败
}
这个getcha很容易做,因为你的代码变得更加复杂。因此,最好是使用域或返回错误以避免(1)异步代码中未捕获的异常(2)try catch捕获您不希望执行的执行。在允许适当线程代替JavaScript的异步事件机器风格的语言中,这不是一个问题。
-
最后,在未捕获的错误的情况下发生在没有包装在域中的地方或try catch语句中,我们可以使用
uncaughtException
监听器使我们的应用程序不会崩溃(但是这样做可以使中的应用程序):
//捕获未包含在域中的未捕获的错误或尝试捕获语句
//不要在模块中使用此错误,而仅在应用程序中使用我们可以有多个这些绑定
process.on('uncaughtException',function(err){
//安全地处理错误
console.log(err)
})
//发出另外未捕获的错误的异步或同步代码
var err = new Error(例如)
掷ERR
I just started trying out node.js a few days ago. I've realized that the Node is terminated whenever I have an unhandled exception in my program. This is different than the normal server container that I have been exposed to where only the Worker Thread dies when unhandled exceptions occur and the container would still be able to receive the request. This raises a few questions:
- Is
process.on('uncaughtException')
the only effective way to guard against it? - Will
process.on('uncaughtException')
catch the unhandled exception during execution of asynchronous processes as well? - Is there a module that is already built (such as sending email or writing to a file) that I could leverage in the case of uncaught exceptions?
I would appreciate any pointer/article that would show me the common best practices for handling uncaught exceptions in node.js
解决方案 Update: Joyent now has their own guide mentioned in this answer. The following information is more of a summary:
Safely "throwing" errors
Ideally we'd like to avoid uncaught errors as much as possible, as such, instead of literally throwing the error, we can instead safely "throw" the error using one of the following methods depending on our code architecture:
For synchronous code, if an error happens, return the error:
// Define divider as a syncrhonous function
var divideSync = function(x,y) {
// if error condition?
if ( y === 0 ) {
// "throw" the error safely by returning it
return new Error("Can't divide by zero")
}
else {
// no error occured, continue on
return x/y
}
}
// Divide 4/2
var result = divideSync(4,2)
// did an error occur?
if ( result instanceof Error ) {
// handle the error safely
console.log('4/2=err', result)
}
else {
// no error occured, continue on
console.log('4/2='+result)
}
// Divide 4/0
result = divideSync(4,0)
// did an error occur?
if ( result instanceof Error ) {
// handle the error safely
console.log('4/0=err', result)
}
else {
// no error occured, continue on
console.log('4/0='+result)
}
For callback-based (ie. asynchronous) code, the first argument of the callback is err
, if an error happens err
is the error, if an error doesn't happen then err
is null
. Any other arguments follow the err
argument:
var divide = function(x,y,next) {
// if error condition?
if ( y === 0 ) {
// "throw" the error safely by calling the completion callback
// with the first argument being the error
next(new Error("Can't divide by zero"))
}
else {
// no error occured, continue on
next(null, x/y)
}
}
divide(4,2,function(err,result){
// did an error occur?
if ( err ) {
// handle the error safely
console.log('4/2=err', err)
}
else {
// no error occured, continue on
console.log('4/2='+result)
}
})
divide(4,0,function(err,result){
// did an error occur?
if ( err ) {
// handle the error safely
console.log('4/0=err', err)
}
else {
// no error occured, continue on
console.log('4/0='+result)
}
})
For eventful code, where the error may happen anywhere, instead of throwing the error, fire the error
event instead:
// Definite our Divider Event Emitter
var events = require('events')
var Divider = function(){
events.EventEmitter.call(this)
}
require('util').inherits(Divider, events.EventEmitter)
// Add the divide function
Divider.prototype.divide = function(x,y){
// if error condition?
if ( y === 0 ) {
// "throw" the error safely by emitting it
var err = new Error("Can't divide by zero")
this.emit('error', err)
}
else {
// no error occured, continue on
this.emit('divided', x, y, x/y)
}
// Chain
return this;
}
// Create our divider and listen for errors
var divider = new Divider()
divider.on('error', function(err){
// handle the error safely
console.log(err)
})
divider.on('divided', function(x,y,result){
console.log(x+'/'+y+'='+result)
})
// Divide
divider.divide(4,2).divide(4,0)
Safely "catching" errors
Sometimes though, there may still be code that throws an error somewhere which can lead to an uncaught exception and a potential crash of our application if we don't catch it safely. Depending on our code architecture we can use one of the following methods to catch it:
When we know where the error is occurring, we can wrap that section in a node.js domain
var d = require('domain').create()
d.on('error', function(err){
// handle the error safely
console.log(err)
})
// catch the uncaught errors in this asynchronous or synchronous code block
d.run(function(){
// the asynchronous or synchronous code that we want to catch thrown errors on
var err = new Error('example')
throw err
})
If we know where the error is occurring is synchronous code, and for whatever reason can't use domains (perhaps old version of node), we can use the try catch statement:
// catch the uncaught errors in this synchronous code block
// try catch statements only work on synchronous code
try {
// the synchronous code that we want to catch thrown errors on
var err = new Error('example')
throw err
} catch (err) {
// handle the error safely
console.log(err)
}
However, be careful not to use try...catch
in asynchronous code, as an asynchronously thrown error will not be caught:
try {
setTimeout(function(){
var err = new Error('example')
throw err
}, 1000)
}
catch (err) {
// Example error won't be caught here... crashing our app
// hence the need for domains
}
Another thing to be careful about with try...catch
is the risk of wrapping your completion callback inside the try
statement like so:
var divide = function(x,y,next) {
// if error condition?
if ( y === 0 ) {
// "throw" the error safely by calling the completion callback
// with the first argument being the error
next(new Error("Can't divide by zero"))
}
else {
// no error occured, continue on
next(null, x/y)
}
}
var continueElsewhere = function(err, result){
throw new Error('elsewhere has failed')
}
try {
divide(4, 2, continueElsewhere)
// ^ the execution of divide, and the execution of
// continueElsewhere will be inside the try statement
}
catch (err) {
console.log(err.stack)
// ^ will output the "unexpected" result of: elsewhere has failed
}
This gotcha is very easy to do as your code becomes more complex. As such, it is best to either use domains or to return errors to avoid (1) uncaught exceptions in asynchronous code (2) the try catch catching execution that you don't want it to. In languages that allow for proper threading instead of JavaScript's asynchronous event-machine style, this is less of an issue.
Finally, in the case where an uncaught error happens in a place that wasn't wrapped in a domain or a try catch statement, we can make our application not crash by using the uncaughtException
listener (however doing so can put the application in an unknown state):
// catch the uncaught errors that weren't wrapped in a domain or try catch statement
// do not use this in modules, but only in applications, as otherwise we could have multiple of these bound
process.on('uncaughtException', function(err) {
// handle the error safely
console.log(err)
})
// the asynchronous or synchronous code that emits the otherwise uncaught error
var err = new Error('example')
throw err
这篇关于Node.js最佳实践异常处理的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!