详解js中的异步异常处理与使用domian教程

try {
 process.nextTick(function () {
  foo.bar();
 });
} catch (err) {
 //can not catch it
}

//express风格的路由
app.get('/index', function (req, res) {
 try {
  //业务逻辑
 } catch (err) {
  logger.error(err);
  res.statusCode = 500;
  return res.json({success: false, message: '服务器异常'});
 }
});

app.get('/index', function (req, res) {
 // 业务逻辑 
});

process.on('uncaughtException', function (err) {
 logger.error(err);
});

var domain = require('domain');

//引入一个domain的中间件，将每一个请求都包裹在一个独立的domain中
//domain来处理异常
app.use(function (req,res, next) {
 var d = domain.create();
 //监听domain的错误事件
 d.on('error', function (err) {
  logger.error(err);
  res.statusCode = 500;
  res.json({sucess:false, messag: '服务器异常'});
  d.dispose();
 });
 
 d.add(req);
 d.add(res);
 d.run(next);
});

app.get('/index', function (req, res) {
 //处理业务
});

var http = require('http');
var connect = require('connect');
var RedisStore = require('connect-redis')(connect);
var domainMiddleware = require('domain-middleware');

var server = http.createServer();
var app = connect();
app.use(connect.session({
 key: 'key',
 secret: 'secret',
 store: new RedisStore(6379, 'localhost')
}));
//domainMiddleware的使用可以看前面的链接
app.use(domainMiddleware({
 server: server,
 killTimeout: 30000
}));

var domain = require('domain');
var redis = require('redis');
var cache = redis.createClient(6379, 'localhost');

function error() {
 cache.get('a', function () {
  throw new Error('something wrong');
 });
}

function ok () {
 setTimeout(function () {
  throw new Error('something wrong');
 }, 100);
}
var d = domain.create();
d.on('error', function (err) {
 console.log(err);
});

d.run(ok);  //domain捕获到异常
d.run(error); //异常被抛出

function laterCall() {
 console.log('print me later');
}

process.nextTick(laterCallback);
console.log('print me first');

//简化后的domain传递部分代码
function nextDomainTick(callback) {
 nextTickQueue.push({callback: callback, domain: process.domain});
}

function _tickDomainCallback() {
 var tock = nextTickQueue.pop();
 //设置process.domain = tock.domain
 tock.domain && tock.domain.enter();
 callback();
 //清除process.domain
 tock.domain && tock.domain.exit();    
 }
};

 if (exports.usingDomains) {
  // if there is an active domain, then attach to it.
  domain = domain || require('domain');
  if (domain.active && !(this instanceof domain.Domain)) {
   this.domain = domain.active;
  }
 }

 if (process.domain) timer.domain = process.domain;

// create a top-level domain for the server
var serverDomain = domain.create();
serverDomain.run(function() {
 // server is created in the scope of serverDomain
 http.createServer(function(req, res) {
  // req and res are also created in the scope of serverDomain
  // however, we'd prefer to have a separate domain for each request.
  // create it first thing, and add req and res to it.
  var reqd = domain.create();
  reqd.add(req);
  reqd.add(res);
  reqd.on('error', function(er) {
   console.error('Error', er, req.url);
   try {
    res.writeHead(500);
    res.end('Error occurred, sorry.');
   } catch (er) {
    console.error('Error sending 500', er, req.url);
   }
  });
 }).listen(1337);
});

var domain = require('domain');
var EventEmitter = require('events').EventEmitter;

var e = new EventEmitter();

var timer = setTimeout(function () {
 e.emit('data'); 
}, 10);

function next() {
 e.once('data', function () {
  throw new Error('something wrong here');
 });
}

var d = domain.create();
d.on('error', function () {
 console.log('cache by domain');
});

d.run(next);

d.add(timer);
//or
d.add(e);