Golang / MGO — 报错：没有可达的服务器

huangapple
go评论118阅读模式
英文:

Golang / MGO -- panic: no reachable servers

问题

我有以下连接到Mongo的函数。为了测试，我关闭了mongod，并希望在没有Mongo可用时允许程序继续运行。似乎如果无法连接到服务器，MGO会引发panic，所以我写了一个defer/recover，但panic仍然导致程序退出。从这种情况中恢复的正确方法是什么？

  1. func connectToMongo(sess *mgo.Session, coll *mgo.Collection, sessionErr error) bool {
  2.     fmt.Println("enter main - connecting to mongo")
  4.     // 尝试这样做-不按预期工作
  5.     defer func() {
  6.         if r := recover(); r != nil {
  7.             var ok bool
  8.             err, ok := r.(error)
  9.             if !ok {
  10.                 fmt.Printf("pkg: %v, error: %s", r, err)
  11.             }
  12.         }
  13.         return false
  14.     }()
  16.     maxWait := time.Duration(5 * time.Second)
  17.     sess, sessionErr = mgo.DialWithTimeout("localhost", maxWait)
  18.     if sessionErr == nil {
  19.         session.SetMode(mgo.Monotonic, true)
  20.         coll = session.DB("MyDB").C("MyCollection")
  21.     } else { // 永远不会执行到这里
  22.         fmt.Println("无法连接到本地Mongo实例！")
  23.     }
  24.     return true
  25. }
英文:

I have the following function that connects to Mongo. For testing, I shutdown mongod, and want to allow the program to continue w/0 mongo if it's not available. It seems that MGO throws a panic if the server can't be connected, so I wrote a defer/recover below, but the panic still causes the program to exit. What's the proper way to recover from this?

  1. func connectToMongo(sess *mgo.Session, coll *mgo.Collection, sessionErr error) bool {
  2. 	fmt.Println("enter main - connecting to mongo")
  4. 	// tried doing this - doesn't work as intended
  5. 	defer func() {
  6. 		if r := recover(); r != nil {
  7. 			var ok bool
  8. 			err, ok := r.(error)
  9. 			if !ok {
  10. 				fmt.Printf("pkg:  %v,  error: %s", r, err)
  11. 			}
  12. 		}
  13. 		return false
  14. 	}()
  16. 	maxWait := time.Duration(5 * time.Second)
  17. 	sess, sessionErr = mgo.DialWithTimeout("localhost", maxWait)
  18. 	if sessionErr == nil {
  19. 		session.SetMode(mgo.Monotonic, true)
  20. 		coll = session.DB("MyDB").C("MyCollection")
  21. 	} else { // never gets here
  22. 		fmt.Println("Unable to connect to local mongo instance!")
  23. 	}
  24. 	return true
  25. }

答案1

得分: 4

请运行以下版本的代码：

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"time"
  6. )
  8. import (
  9. 	"labix.org/v2/mgo"
  10. )
  12. func connectToMongo() bool {
  13. 	ret := false
  14. 	fmt.Println("进入主函数 - 连接到MongoDB")
  16. 	// 尝试这样做 - 不按预期工作
  17. 	defer func() {
  18. 		if r := recover(); r != nil {
  19. 			fmt.Println("检测到恐慌")
  20. 			var ok bool
  21. 			err, ok := r.(error)
  22. 			if !ok {
  23. 				fmt.Printf("pkg: %v, 错误: %s", r, err)
  24. 			}
  25. 		}
  26. 	}()
  28. 	maxWait := time.Duration(5 * time.Second)
  29. 	session, sessionErr := mgo.DialWithTimeout("localhost:27017", maxWait)
  30. 	if sessionErr == nil {
  31. 		session.SetMode(mgo.Monotonic, true)
  32. 		coll := session.DB("MyDB").C("MyCollection")
  33. 		if coll != nil {
  34. 			fmt.Println("获得一个集合对象")
  35. 			ret = true
  36. 		}
  37. 	} else { // 永远不会执行到这里
  38. 		fmt.Println("无法连接到本地MongoDB实例！")
  39. 	}
  40. 	return ret
  41. }
  43. func main() {
  44. 	if connectToMongo() {
  45. 		fmt.Println("已连接")
  46. 	} else {
  47. 		fmt.Println("未连接")
  48. 	}
  49. }

当MongoDB运行时，你会看到：

  1. 进入主函数 - 连接到MongoDB
  2. 获得一个集合对象
  3. 已连接

当MongoDB关闭时，你会看到：

  1. 进入主函数 - 连接到MongoDB
  2. 无法连接到本地MongoDB实例！
  3. 未连接

如果你没有看到相同的行为，请发布输出，包括你看到的恐慌信息。

英文:

Run the following version of your posted code.
Try to not modify the code, at least not changing the position of the line numbers. That way, if you post a stacktrace, the numbers will match.

  1. package main
  3. import (
  4.     "fmt"
  5.     "time"
  6. )
  8. import (
  9.     "labix.org/v2/mgo"
  10. )
  12. func connectToMongo() bool {
  13.     ret := false
  14.     fmt.Println("enter main - connecting to mongo")
  16.     // tried doing this - doesn't work as intended
  17.     defer func() {
  18.         if r := recover(); r != nil {
  19.             fmt.Println("Detected panic")
  20.             var ok bool
  21.             err, ok := r.(error)
  22.             if !ok {
  23.                 fmt.Printf("pkg:  %v,  error: %s", r, err)
  24.             }
  25.         }
  26.     }()
  28.     maxWait := time.Duration(5 * time.Second)
  29.     session, sessionErr := mgo.DialWithTimeout("localhost:27017", maxWait)
  30.     if sessionErr == nil {
  31.         session.SetMode(mgo.Monotonic, true)
  32.         coll := session.DB("MyDB").C("MyCollection")
  33.         if ( coll != nil ) {
  34.             fmt.Println("Got a collection object")
  35.             ret = true
  36.         }
  37.     } else { // never gets here
  38.         fmt.Println("Unable to connect to local mongo instance!")
  39.     }
  40.     return ret
  41. }
  43. func main() {
  44.     if ( connectToMongo() ) {
  45.         fmt.Println("Connected")
  46.     } else {
  47.         fmt.Println("Not Connected")
  48.     }
  49. }

When MongoDB is up, I see:

  1. enter main - connecting to mongo
  2. Got a collection object
  3. Connected

When MongoDB is down, I see:

  1. enter main - connecting to mongo
  2. Unable to connect to local mongo instance!
  3. Not Connected

If you don't see the same behavior, post the output, including the panic you see.

huangapple
  • 本文由 发表于 2014年1月7日 23:52:28
  • 转载请务必保留本文链接：https://go.coder-hub.com/20976030.html
  • go
  • mgo
  • mongodb
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