Go的錯誤處理機制介紹 Defer, Panic與Recover

package main

import "fmt"

func main() {
	f()
	fmt.Println("Returned normally from f.")
}

func f() {
// 被推延至結束才執行，並且recover() 會接受panic所傳遞的參數
	defer func() {
		if r := recover(); r != nil {
			fmt.Println("Recovered in f", r)
		}
	}()
	fmt.Println("Calling g.")
	g(0)
	fmt.Println("Returned normally from g.")
}

func g(i int) {
	if i > 3 {
		fmt.Println("Panicking!")
		panic(fmt.Sprintf("%v", i))
	}
        // 將 印出“Defer in g"這段訊息 延後印出，直到panic觸發或是程式結束才會被印出來
        // 先被defer的會最晚被印出來，為Last in first out !
	defer fmt.Println("Defer in g", i)
	fmt.Println("Printing in g", i)
	g(i + 1)
}

func someFunction() {
	var err error

	mongo, err := getMongoSession() // 回傳一個mongo的instance
	mongo.SetSocketTimeout(1 * time.Hour)
	//session.SetSocketTimeout(1 * time.Hour)

	if err != nil {
		errors := common.Error{
			ErrorType:        1,
			ErrorDescription: err.Error(),
		}
		logger.Console().Panic(errors)
		logger.File().Error(err)
	}

        // 將關閉mongo的動作推延至 該function執行玩return後執行
	defer mongo.Close()

	collection := mongo.DB(dbName).C(collectionName.BsBlocks)
	result := []blockStrcut.BlockWithOnlyTxHashesIntNum{}
	err = collection.Find(conditions).All(&result)

	return result, err
}