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？
func connectToMongo(sess *mgo.Session, coll *mgo.Collection, sessionErr error) bool {
fmt.Println("enter main - connecting to mongo")
// 尝试这样做-不按预期工作
defer func() {
if r := recover(); r != nil {
var ok bool
err, ok := r.(error)
if !ok {
fmt.Printf("pkg: %v, error: %s", r, err)
}
}
return false
}()
maxWait := time.Duration(5 * time.Second)
sess, sessionErr = mgo.DialWithTimeout("localhost", maxWait)
if sessionErr == nil {
session.SetMode(mgo.Monotonic, true)
coll = session.DB("MyDB").C("MyCollection")
} else { // 永远不会执行到这里
fmt.Println("无法连接到本地Mongo实例！")
}
return true
}
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?
func connectToMongo(sess *mgo.Session, coll *mgo.Collection, sessionErr error) bool {
fmt.Println("enter main - connecting to mongo")
// tried doing this - doesn't work as intended
defer func() {
if r := recover(); r != nil {
var ok bool
err, ok := r.(error)
if !ok {
fmt.Printf("pkg: %v, error: %s", r, err)
}
}
return false
}()
maxWait := time.Duration(5 * time.Second)
sess, sessionErr = mgo.DialWithTimeout("localhost", maxWait)
if sessionErr == nil {
session.SetMode(mgo.Monotonic, true)
coll = session.DB("MyDB").C("MyCollection")
} else { // never gets here
fmt.Println("Unable to connect to local mongo instance!")
}
return true
}
答案1
得分: 4
请运行以下版本的代码：
package main
import (
"fmt"
"time"
)
import (
"labix.org/v2/mgo"
)
func connectToMongo() bool {
ret := false
fmt.Println("进入主函数 - 连接到MongoDB")
// 尝试这样做 - 不按预期工作
defer func() {
if r := recover(); r != nil {
fmt.Println("检测到恐慌")
var ok bool
err, ok := r.(error)
if !ok {
fmt.Printf("pkg: %v, 错误: %s", r, err)
}
}
}()
maxWait := time.Duration(5 * time.Second)
session, sessionErr := mgo.DialWithTimeout("localhost:27017", maxWait)
if sessionErr == nil {
session.SetMode(mgo.Monotonic, true)
coll := session.DB("MyDB").C("MyCollection")
if coll != nil {
fmt.Println("获得一个集合对象")
ret = true
}
} else { // 永远不会执行到这里
fmt.Println("无法连接到本地MongoDB实例！")
}
return ret
}
func main() {
if connectToMongo() {
fmt.Println("已连接")
} else {
fmt.Println("未连接")
}
}
当MongoDB运行时，你会看到：
进入主函数 - 连接到MongoDB
获得一个集合对象
已连接
当MongoDB关闭时，你会看到：
进入主函数 - 连接到MongoDB
无法连接到本地MongoDB实例！
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.
package main
import (
"fmt"
"time"
)
import (
"labix.org/v2/mgo"
)
func connectToMongo() bool {
ret := false
fmt.Println("enter main - connecting to mongo")
// tried doing this - doesn't work as intended
defer func() {
if r := recover(); r != nil {
fmt.Println("Detected panic")
var ok bool
err, ok := r.(error)
if !ok {
fmt.Printf("pkg: %v, error: %s", r, err)
}
}
}()
maxWait := time.Duration(5 * time.Second)
session, sessionErr := mgo.DialWithTimeout("localhost:27017", maxWait)
if sessionErr == nil {
session.SetMode(mgo.Monotonic, true)
coll := session.DB("MyDB").C("MyCollection")
if ( coll != nil ) {
fmt.Println("Got a collection object")
ret = true
}
} else { // never gets here
fmt.Println("Unable to connect to local mongo instance!")
}
return ret
}
func main() {
if ( connectToMongo() ) {
fmt.Println("Connected")
} else {
fmt.Println("Not Connected")
}
}
When MongoDB is up, I see:
enter main - connecting to mongo
Got a collection object
Connected
When MongoDB is down, I see:
enter main - connecting to mongo
Unable to connect to local mongo instance!
Not Connected
If you don't see the same behavior, post the output, including the panic you see.
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论