摘要：場景使用搭建應用時，常常遇到并發問題導致創建一條數據的時候會同時創建多條。通過方法配合選項即可實現鎖機制。主要的方法有三個加鎖解鎖更改鎖過期時間用法支持實現比較簡單，行內，有興趣的可以在這里查看源碼

場景：使用node+mongo搭建web應用時，常常遇到并發問題導致創建一條數據的時候會同時創建多條。

通過redis set 方法 配合 ‘NX’ 選項即可實現鎖機制。

主要的方法有三個：

lock(加鎖)

unlock(解鎖)

extend(更改鎖過期時間)

Redlock.prototype.lock = function(resource,ttl,callback){
  var self = this;
  var _val = _random();
  return new Promise(function(resolve, reject) {
    var lock = new Lock(self, resource, _val);
    self.client.SET(resource,_val,"EX",ttl,"NX",function(err,data){
      if(!err && data === "OK"){
        return resolve(lock);
      }else{
        var err = err || "resource: "+resource+" is locked.";
        self.emit("lockError", err);
        return reject(err);
      }
    })
  }).asCallback(callback);
}

Redlock.prototype.unlock = function(lock,callback){
  var self = this;
  return new Promise(function(resolve, reject) {
    if(typeof lock !== "object") return reject("unlockError:lock is not object.");
    self.client.GET(lock.resource,function(err,data){
      if(!err && data === lock.value){
        self.client.DEL(lock.resource,function(err){
          if(err){
            self.emit("unlockError",err);
            return reject("unlockError:"+err);
          }else{
            return resolve(lock);
          }     
        })
      }else{
        self.emit("unlockError",err || "resource:" + lock.resource + " unable to unlock.")
        return reject("unlockError:" + err || ("resource:" + lock.resource + " unable to unlock."));
      }
    })
  }).asCallback(callback);
}

Redlock.prototype.extend = function(lock,ttl,callback){
  var self = this;
  return new Promise(function(resolve, reject){
    if(typeof lock !== "object") return reject("unlockError:lock is not object.");
    self.client.GET(lock.resource,function(err,data){
      if(!err && data === lock.value){
        self.client.expire(lock.resource,ttl,function(err,data){
          if(!err && data === 1){
            return resolve(lock);
          }else{
            self.emit("extendError", err);
            return reject("extendError:"+err);
          }          
        });
      }else{
        self.emit("extendError", err);
        return reject("extendError:"+err);
      }
    })
  }).asCallback(callback);
}

var client = require("redis").createClient("port","host");
var redlock = new RedLock(client);
var lock;

`callback`:

//lock
redlock.lock("test-resource-lock",3,function(err,lockInstance){
  lock = lockInstance;
  done(err);
});
//unlock
redlock.unlock(lock,function(err,data){
  done(err);
});


`promise`:

redlock.lock("test-resource-lock-promise",3).done(
  function(lock){
    //todo
    redlock.unlock(lock);
  },
  function(){
  }
) 

PS:支持callback and promise.

實現比較簡單，100行內，有興趣的可以在 這里https://github.com/navyxie/redlock-node 查看源碼