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< title > 示例: 併發的字典遍歷 | Go编程语言< / title >
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< div class = "book" data-level = "8.8" data-chapter-title = "示例: 併發的字典遍歷" data-filepath = "ch8/ch8-08.md" data-basepath = ".." data-revision = "Fri Dec 25 2015 12:32:44 GMT+0800 (中国标准时间)" >
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前言
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< b > 0.1.< / b >
Go語言起源
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< b > 0.2.< / b >
Go語言項目
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< b > 0.3.< / b >
本書的組織
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< b > 0.4.< / b >
更多的信息
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< b > 0.5.< / b >
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致謝
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< b > 1.< / b >
入門
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< b > 1.1.< / b >
Hello, World
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< b > 1.2.< / b >
命令行參數
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< b > 1.3.< / b >
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査找重複的行
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< / li >
< li class = "chapter " data-level = "1.4" data-path = "ch1/ch1-04.html" >
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< b > 1.4.< / b >
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GIF動畵
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< b > 1.5.< / b >
穫取URL
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< b > 1.6.< / b >
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併發穫取多個URL
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< b > 1.7.< / b >
Web服務
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< b > 1.8.< / b >
本章要點
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< b > 2.< / b >
程序結構
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< b > 2.1.< / b >
命名
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< b > 2.2.< / b >
聲明
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< b > 2.3.< / b >
變量
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< b > 2.4.< / b >
賦值
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< b > 2.5.< / b >
類型
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< b > 2.6.< / b >
包和文件
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< b > 2.7.< / b >
作用域
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< b > 3.< / b >
基礎數據類型
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< b > 3.1.< / b >
整型
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< b > 3.2.< / b >
浮點數
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< li class = "chapter " data-level = "3.3" data-path = "ch3/ch3-03.html" >
< a href = "../ch3/ch3-03.html" >
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< b > 3.3.< / b >
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複數
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< li class = "chapter " data-level = "3.4" data-path = "ch3/ch3-04.html" >
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< b > 3.4.< / b >
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布爾型
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< b > 3.5.< / b >
字符串
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< b > 3.6.< / b >
常量
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< b > 4.< / b >
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複合數據類型
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< ul class = "articles" >
< li class = "chapter " data-level = "4.1" data-path = "ch4/ch4-01.html" >
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< b > 4.1.< / b >
數組
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< b > 4.2.< / b >
切片
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< b > 4.3.< / b >
字典
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< b > 4.4.< / b >
結構體
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< b > 4.5.< / b >
JSON
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< b > 4.6.< / b >
文本和HTML模闆
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< li class = "chapter " data-level = "5" data-path = "ch5/ch5.html" >
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< b > 5.< / b >
函數
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< b > 5.1.< / b >
函數聲明
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< b > 5.2.< / b >
遞歸
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< b > 5.3.< / b >
多返迴值
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< li class = "chapter " data-level = "5.4" data-path = "ch5/ch5-04.html" >
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< b > 5.4.< / b >
錯誤
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< li class = "chapter " data-level = "5.5" data-path = "ch5/ch5-05.html" >
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< b > 5.5.< / b >
函數值
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< li class = "chapter " data-level = "5.6" data-path = "ch5/ch5-06.html" >
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< b > 5.6.< / b >
匿名函數
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< b > 5.7.< / b >
可變參數
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< b > 5.8.< / b >
Deferred函數
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< b > 5.9.< / b >
Panic異常
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< li class = "chapter " data-level = "5.10" data-path = "ch5/ch5-10.html" >
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< b > 5.10.< / b >
Recover捕穫異常
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< b > 6.< / b >
方法
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< b > 6.1.< / b >
方法聲明
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< b > 6.2.< / b >
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基於指針對象的方法
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< li class = "chapter " data-level = "6.3" data-path = "ch6/ch6-03.html" >
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< b > 6.3.< / b >
通過嵌入結構體來擴展類型
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< li class = "chapter " data-level = "6.4" data-path = "ch6/ch6-04.html" >
< a href = "../ch6/ch6-04.html" >
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< b > 6.4.< / b >
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方法值和方法表達式
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< li class = "chapter " data-level = "6.5" data-path = "ch6/ch6-05.html" >
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< b > 6.5.< / b >
示例: Bit數組
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< b > 6.6.< / b >
封裝
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< b > 7.< / b >
接口
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< b > 7.1.< / b >
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接口是合約
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< b > 7.2.< / b >
接口類型
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< b > 7.3.< / b >
實現接口的條件
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< b > 7.4.< / b >
flag.Value接口
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< b > 7.5.< / b >
接口值
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< b > 7.6.< / b >
sort.Interface接口
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< b > 7.7.< / b >
http.Handler接口
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< b > 7.8.< / b >
error接口
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< b > 7.9.< / b >
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示例: 表達式求值
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< b > 7.10.< / b >
類型斷言
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< b > 7.11.< / b >
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基於類型斷言識别錯誤類型
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< b > 7.12.< / b >
通過類型斷言査詢接口
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< b > 7.13.< / b >
類型分支
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< b > 7.14.< / b >
示例: 基於標記的XML解碼
< / a >
< / li >
< li class = "chapter " data-level = "7.15" data-path = "ch7/ch7-15.html" >
< a href = "../ch7/ch7-15.html" >
< i class = "fa fa-check" > < / i >
< b > 7.15.< / b >
補充幾點
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "8" data-path = "ch8/ch8.html" >
< a href = "../ch8/ch8.html" >
< i class = "fa fa-check" > < / i >
< b > 8.< / b >
Goroutines和Channels
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "8.1" data-path = "ch8/ch8-01.html" >
< a href = "../ch8/ch8-01.html" >
< i class = "fa fa-check" > < / i >
< b > 8.1.< / b >
Goroutines
< / a >
< / li >
< li class = "chapter " data-level = "8.2" data-path = "ch8/ch8-02.html" >
< a href = "../ch8/ch8-02.html" >
< i class = "fa fa-check" > < / i >
< b > 8.2.< / b >
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示例: 併發的Clock服務
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< / a >
< / li >
< li class = "chapter " data-level = "8.3" data-path = "ch8/ch8-03.html" >
< a href = "../ch8/ch8-03.html" >
< i class = "fa fa-check" > < / i >
< b > 8.3.< / b >
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示例: 併發的Echo服務
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< / a >
< / li >
< li class = "chapter " data-level = "8.4" data-path = "ch8/ch8-04.html" >
< a href = "../ch8/ch8-04.html" >
< i class = "fa fa-check" > < / i >
< b > 8.4.< / b >
Channels
< / a >
< / li >
< li class = "chapter " data-level = "8.5" data-path = "ch8/ch8-05.html" >
< a href = "../ch8/ch8-05.html" >
< i class = "fa fa-check" > < / i >
< b > 8.5.< / b >
併行的循環
< / a >
< / li >
< li class = "chapter " data-level = "8.6" data-path = "ch8/ch8-06.html" >
< a href = "../ch8/ch8-06.html" >
< i class = "fa fa-check" > < / i >
< b > 8.6.< / b >
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示例: 併發的Web爬蟲
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< / a >
< / li >
< li class = "chapter " data-level = "8.7" data-path = "ch8/ch8-07.html" >
< a href = "../ch8/ch8-07.html" >
< i class = "fa fa-check" > < / i >
< b > 8.7.< / b >
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基於select的多路複用
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< / a >
< / li >
< li class = "chapter active" data-level = "8.8" data-path = "ch8/ch8-08.html" >
< a href = "../ch8/ch8-08.html" >
< i class = "fa fa-check" > < / i >
< b > 8.8.< / b >
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示例: 併發的字典遍歷
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< / a >
< / li >
< li class = "chapter " data-level = "8.9" data-path = "ch8/ch8-09.html" >
< a href = "../ch8/ch8-09.html" >
< i class = "fa fa-check" > < / i >
< b > 8.9.< / b >
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併發的退齣
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< / a >
< / li >
< li class = "chapter " data-level = "8.10" data-path = "ch8/ch8-10.html" >
< a href = "../ch8/ch8-10.html" >
< i class = "fa fa-check" > < / i >
< b > 8.10.< / b >
示例: 聊天服務
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "9" data-path = "ch9/ch9.html" >
< a href = "../ch9/ch9.html" >
< i class = "fa fa-check" > < / i >
< b > 9.< / b >
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基於共享變量的併發
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< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "9.1" data-path = "ch9/ch9-01.html" >
< a href = "../ch9/ch9-01.html" >
< i class = "fa fa-check" > < / i >
< b > 9.1.< / b >
競爭條件
< / a >
< / li >
< li class = "chapter " data-level = "9.2" data-path = "ch9/ch9-02.html" >
< a href = "../ch9/ch9-02.html" >
< i class = "fa fa-check" > < / i >
< b > 9.2.< / b >
sync.Mutex互斥鎖
< / a >
< / li >
< li class = "chapter " data-level = "9.3" data-path = "ch9/ch9-03.html" >
< a href = "../ch9/ch9-03.html" >
< i class = "fa fa-check" > < / i >
< b > 9.3.< / b >
sync.RWMutex讀寫鎖
< / a >
< / li >
< li class = "chapter " data-level = "9.4" data-path = "ch9/ch9-04.html" >
< a href = "../ch9/ch9-04.html" >
< i class = "fa fa-check" > < / i >
< b > 9.4.< / b >
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內存同步
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< / a >
< / li >
< li class = "chapter " data-level = "9.5" data-path = "ch9/ch9-05.html" >
< a href = "../ch9/ch9-05.html" >
< i class = "fa fa-check" > < / i >
< b > 9.5.< / b >
sync.Once初始化
< / a >
< / li >
< li class = "chapter " data-level = "9.6" data-path = "ch9/ch9-06.html" >
< a href = "../ch9/ch9-06.html" >
< i class = "fa fa-check" > < / i >
< b > 9.6.< / b >
競爭條件檢測
< / a >
< / li >
< li class = "chapter " data-level = "9.7" data-path = "ch9/ch9-07.html" >
< a href = "../ch9/ch9-07.html" >
< i class = "fa fa-check" > < / i >
< b > 9.7.< / b >
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示例: 併發的非阻塞緩存
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< / a >
< / li >
< li class = "chapter " data-level = "9.8" data-path = "ch9/ch9-08.html" >
< a href = "../ch9/ch9-08.html" >
< i class = "fa fa-check" > < / i >
< b > 9.8.< / b >
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Goroutines和線程
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< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "10" data-path = "ch10/ch10.html" >
< a href = "../ch10/ch10.html" >
< i class = "fa fa-check" > < / i >
< b > 10.< / b >
包和工具
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "10.1" data-path = "ch10/ch10-01.html" >
< a href = "../ch10/ch10-01.html" >
< i class = "fa fa-check" > < / i >
< b > 10.1.< / b >
簡介
< / a >
< / li >
< li class = "chapter " data-level = "10.2" data-path = "ch10/ch10-02.html" >
< a href = "../ch10/ch10-02.html" >
< i class = "fa fa-check" > < / i >
< b > 10.2.< / b >
導入路徑
< / a >
< / li >
< li class = "chapter " data-level = "10.3" data-path = "ch10/ch10-03.html" >
< a href = "../ch10/ch10-03.html" >
< i class = "fa fa-check" > < / i >
< b > 10.3.< / b >
包聲明
< / a >
< / li >
< li class = "chapter " data-level = "10.4" data-path = "ch10/ch10-04.html" >
< a href = "../ch10/ch10-04.html" >
< i class = "fa fa-check" > < / i >
< b > 10.4.< / b >
導入聲明
< / a >
< / li >
< li class = "chapter " data-level = "10.5" data-path = "ch10/ch10-05.html" >
< a href = "../ch10/ch10-05.html" >
< i class = "fa fa-check" > < / i >
< b > 10.5.< / b >
匿名導入
< / a >
< / li >
< li class = "chapter " data-level = "10.6" data-path = "ch10/ch10-06.html" >
< a href = "../ch10/ch10-06.html" >
< i class = "fa fa-check" > < / i >
< b > 10.6.< / b >
包和命名
< / a >
< / li >
< li class = "chapter " data-level = "10.7" data-path = "ch10/ch10-07.html" >
< a href = "../ch10/ch10-07.html" >
< i class = "fa fa-check" > < / i >
< b > 10.7.< / b >
工具
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "11" data-path = "ch11/ch11.html" >
< a href = "../ch11/ch11.html" >
< i class = "fa fa-check" > < / i >
< b > 11.< / b >
測試
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "11.1" data-path = "ch11/ch11-01.html" >
< a href = "../ch11/ch11-01.html" >
< i class = "fa fa-check" > < / i >
< b > 11.1.< / b >
go test
< / a >
< / li >
< li class = "chapter " data-level = "11.2" data-path = "ch11/ch11-02.html" >
< a href = "../ch11/ch11-02.html" >
< i class = "fa fa-check" > < / i >
< b > 11.2.< / b >
測試函數
< / a >
< / li >
< li class = "chapter " data-level = "11.3" data-path = "ch11/ch11-03.html" >
< a href = "../ch11/ch11-03.html" >
< i class = "fa fa-check" > < / i >
< b > 11.3.< / b >
測試覆蓋率
< / a >
< / li >
< li class = "chapter " data-level = "11.4" data-path = "ch11/ch11-04.html" >
< a href = "../ch11/ch11-04.html" >
< i class = "fa fa-check" > < / i >
< b > 11.4.< / b >
基準測試
< / a >
< / li >
< li class = "chapter " data-level = "11.5" data-path = "ch11/ch11-05.html" >
< a href = "../ch11/ch11-05.html" >
< i class = "fa fa-check" > < / i >
< b > 11.5.< / b >
剖析
< / a >
< / li >
< li class = "chapter " data-level = "11.6" data-path = "ch11/ch11-06.html" >
< a href = "../ch11/ch11-06.html" >
< i class = "fa fa-check" > < / i >
< b > 11.6.< / b >
示例函數
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "12" data-path = "ch12/ch12.html" >
< a href = "../ch12/ch12.html" >
< i class = "fa fa-check" > < / i >
< b > 12.< / b >
反射
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "12.1" data-path = "ch12/ch12-01.html" >
< a href = "../ch12/ch12-01.html" >
< i class = "fa fa-check" > < / i >
< b > 12.1.< / b >
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爲何需要反射?
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< / a >
< / li >
< li class = "chapter " data-level = "12.2" data-path = "ch12/ch12-02.html" >
< a href = "../ch12/ch12-02.html" >
< i class = "fa fa-check" > < / i >
< b > 12.2.< / b >
reflect.Type和reflect.Value
< / a >
< / li >
< li class = "chapter " data-level = "12.3" data-path = "ch12/ch12-03.html" >
< a href = "../ch12/ch12-03.html" >
< i class = "fa fa-check" > < / i >
< b > 12.3.< / b >
Display遞歸打印
< / a >
< / li >
< li class = "chapter " data-level = "12.4" data-path = "ch12/ch12-04.html" >
< a href = "../ch12/ch12-04.html" >
< i class = "fa fa-check" > < / i >
< b > 12.4.< / b >
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示例: 編碼S表達式
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< / a >
< / li >
< li class = "chapter " data-level = "12.5" data-path = "ch12/ch12-05.html" >
< a href = "../ch12/ch12-05.html" >
< i class = "fa fa-check" > < / i >
< b > 12.5.< / b >
通過reflect.Value脩改值
< / a >
< / li >
< li class = "chapter " data-level = "12.6" data-path = "ch12/ch12-06.html" >
< a href = "../ch12/ch12-06.html" >
< i class = "fa fa-check" > < / i >
< b > 12.6.< / b >
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示例: 解碼S表達式
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< / a >
< / li >
< li class = "chapter " data-level = "12.7" data-path = "ch12/ch12-07.html" >
< a href = "../ch12/ch12-07.html" >
< i class = "fa fa-check" > < / i >
< b > 12.7.< / b >
穫取結構體字段標識
< / a >
< / li >
< li class = "chapter " data-level = "12.8" data-path = "ch12/ch12-08.html" >
< a href = "../ch12/ch12-08.html" >
< i class = "fa fa-check" > < / i >
< b > 12.8.< / b >
顯示一個類型的方法集
< / a >
< / li >
< li class = "chapter " data-level = "12.9" data-path = "ch12/ch12-09.html" >
< a href = "../ch12/ch12-09.html" >
< i class = "fa fa-check" > < / i >
< b > 12.9.< / b >
幾點忠告
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "13" data-path = "ch13/ch13.html" >
< a href = "../ch13/ch13.html" >
< i class = "fa fa-check" > < / i >
< b > 13.< / b >
底層編程
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "13.1" data-path = "ch13/ch13-01.html" >
< a href = "../ch13/ch13-01.html" >
< i class = "fa fa-check" > < / i >
< b > 13.1.< / b >
unsafe.Sizeof, Alignof 和 Offsetof
< / a >
< / li >
< li class = "chapter " data-level = "13.2" data-path = "ch13/ch13-02.html" >
< a href = "../ch13/ch13-02.html" >
< i class = "fa fa-check" > < / i >
< b > 13.2.< / b >
unsafe.Pointer
< / a >
< / li >
< li class = "chapter " data-level = "13.3" data-path = "ch13/ch13-03.html" >
< a href = "../ch13/ch13-03.html" >
< i class = "fa fa-check" > < / i >
< b > 13.3.< / b >
示例: 深度相等判斷
< / a >
< / li >
< li class = "chapter " data-level = "13.4" data-path = "ch13/ch13-04.html" >
< a href = "../ch13/ch13-04.html" >
< i class = "fa fa-check" > < / i >
< b > 13.4.< / b >
通過cgo調用C代碼
< / a >
< / li >
< li class = "chapter " data-level = "13.5" data-path = "ch13/ch13-05.html" >
< a href = "../ch13/ch13-05.html" >
< i class = "fa fa-check" > < / i >
< b > 13.5.< / b >
幾點忠告
< / a >
< / li >
< / ul >
< / li >
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< li class = "chapter " data-level = "14" data-path = "CONTRIBUTORS.html" >
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< a href = "../CONTRIBUTORS.html" >
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< i class = "fa fa-check" > < / i >
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< b > 14.< / b >
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附録
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< / a >
< / li >
< li class = "divider" > < / li >
< li >
< a href = "https://www.gitbook.com" target = "blank" class = "gitbook-link" >
本書使用 GitBook 釋出
< / a >
< / li >
< / ul >
< / nav >
< / div >
< div class = "book-body" >
< div class = "body-inner" >
< div class = "book-header" role = "navigation" >
<!-- Actions Left -->
<!-- Title -->
< h1 >
< i class = "fa fa-circle-o-notch fa-spin" > < / i >
< a href = "../" > Go编程语言< / a >
< / h1 >
< / div >
< div class = "page-wrapper" tabindex = "-1" role = "main" >
< div class = "page-inner" >
< section class = "normal" id = "section-" >
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< h2 id = "88-示例-併發的字典遍歷" > 8.8. 示 例 : 併 發 的 字 典 遍 歷 < / h2 >
< p > 在 本 小 節 中 ， 我 們 會 創 建 一 個 程 序 來 生 成 指 定 目 録 的 硬 盤 使 用 情 況 報 告 ， 這 個 程 序 和 Unix里 的 du工 具 比 較 相 似 。 大 多 數 工 作 用 下 面 這 個 walkDir函 數 來 完 成 ， 這 個 函 數 使 用 dirents函 數 來 枚 舉 一 個 目 録 下 的 所 有 入 口 。 < / p >
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< pre > < code class = "lang-go" > gopl.io/ch8/du1
< span class = "hljs-comment" > // walkDir recursively walks the file tree rooted at dir< / span >
< span class = "hljs-comment" > // and sends the size of each found file on fileSizes.< / span >
< span class = "hljs-keyword" > func< / span > walkDir(dir < span class = "hljs-typename" > string< / span > , fileSizes < span class = "hljs-keyword" > chan< / span > < - < span class = "hljs-typename" > int64< / span > ) {
< span class = "hljs-keyword" > for< / span > _, entry := < span class = "hljs-keyword" > range< / span > dirents(dir) {
< span class = "hljs-keyword" > if< / span > entry.IsDir() {
subdir := filepath.Join(dir, entry.Name())
walkDir(subdir, fileSizes)
} < span class = "hljs-keyword" > else< / span > {
fileSizes < - entry.Size()
}
}
}
< span class = "hljs-comment" > // dirents returns the entries of directory dir.< / span >
< span class = "hljs-keyword" > func< / span > dirents(dir < span class = "hljs-typename" > string< / span > ) []os.FileInfo {
entries, err := ioutil.ReadDir(dir)
< span class = "hljs-keyword" > if< / span > err != < span class = "hljs-constant" > nil< / span > {
fmt.Fprintf(os.Stderr, < span class = "hljs-string" > " du1: %v\n" < / span > , err)
< span class = "hljs-keyword" > return< / span > < span class = "hljs-constant" > nil< / span >
}
< span class = "hljs-keyword" > return< / span > entries
}
< / code > < / pre >
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< p > ioutil.ReadDir函 數 會 返 迴 一 個 os.FileInfo類 型 的 slice， os.FileInfo類 型 也 是 os.Stat這 個 函 數 的 返 迴 值 。 對 每 一 個 子 目 録 而 言 ， walkDir會 遞 歸 地 調 用 其 自 身 ， 併 且 會 對 每 一 個 文 件 也 遞 歸 調 用 。 walkDir函 數 會 向 fileSizes這 個 channel發 送 一 條 消 息 。 這 條 消 息 包 含 了 文 件 的 字 節 大 小 。 < / p >
< p > 下 面 的 主 函 數 ， 用 了 兩 個 goroutine。 後 颱 的 goroutine調 用 walkDir來 遍 歷 命 令 行 給 齣 的 每 一 個 路 徑 併 最 終 關 閉 fileSizes這 個 channel。 主 goroutine會 對 其 從 channel中 接 收 到 的 文 件 大 小 進 行 纍 加 ， 併 輸 齣 其 和 。 < / p >
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< pre > < code class = "lang-go" > < span class = "hljs-keyword" > package< / span > main
< span class = "hljs-keyword" > import< / span > (
< span class = "hljs-string" > " flag" < / span >
< span class = "hljs-string" > " fmt" < / span >
< span class = "hljs-string" > " io/ioutil" < / span >
< span class = "hljs-string" > " os" < / span >
< span class = "hljs-string" > " path/filepath" < / span >
)
< span class = "hljs-keyword" > func< / span > main() {
< span class = "hljs-comment" > // Determine the initial directories.< / span >
flag.Parse()
roots := flag.Args()
< span class = "hljs-keyword" > if< / span > < span class = "hljs-built_in" > len< / span > (roots) == < span class = "hljs-number" > 0< / span > {
roots = []< span class = "hljs-typename" > string< / span > {< span class = "hljs-string" > " ." < / span > }
}
< span class = "hljs-comment" > // Traverse the file tree.< / span >
fileSizes := < span class = "hljs-built_in" > make< / span > (< span class = "hljs-keyword" > chan< / span > < span class = "hljs-typename" > int64< / span > )
< span class = "hljs-keyword" > go< / span > < span class = "hljs-keyword" > func< / span > () {
< span class = "hljs-keyword" > for< / span > _, root := < span class = "hljs-keyword" > range< / span > roots {
walkDir(root, fileSizes)
}
< span class = "hljs-built_in" > close< / span > (fileSizes)
}()
< span class = "hljs-comment" > // Print the results.< / span >
< span class = "hljs-keyword" > var< / span > nfiles, nbytes < span class = "hljs-typename" > int64< / span >
< span class = "hljs-keyword" > for< / span > size := < span class = "hljs-keyword" > range< / span > fileSizes {
nfiles++
nbytes += size
}
printDiskUsage(nfiles, nbytes)
}
< span class = "hljs-keyword" > func< / span > printDiskUsage(nfiles, nbytes < span class = "hljs-typename" > int64< / span > ) {
fmt.Printf(< span class = "hljs-string" > " %d files %.1f GB\n" < / span > , nfiles, < span class = "hljs-typename" > float64< / span > (nbytes)/< span class = "hljs-number" > 1e9< / span > )
}
< / code > < / pre >
< p > 這 個 程 序 會 在 打 印 其 結 果 之 前 卡 住 很 長 時 間 。 < / p >
< pre > < code > $ go build gopl.io/ch8/du1
$ ./du1 $HOME /usr /bin /etc
213201 files 62.7 GB
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< / code > < / pre > < p > 如 果 在 運 行 的 時 候 能 夠 讓 我 們 知 道 處 理 進 度 的 話 想 必 更 好 。 但 是 ， 如 果 簡 單 地 把 printDiskUsage函 數 調 用 移 動 到 循 環 里 會 導 致 其 打 印 齣 成 百 上 韆 的 輸 齣 。 < / p >
< p > 下 面 這 個 du的 變 種 會 間 歇 打 印 內 容 ， 不 過 隻 有 在 調 用 時 提 供 了 -v的 flag纔 會 顯 示 程 序 進 度 信 息 。 在 roots目 録 上 循 環 的 後 颱 goroutine在 這 里 保 持 不 變 。 主 goroutine現 在 使 用 了 計 時 器 來 每 500ms生 成 事 件 ， 然 後 用 select語 句 來 等 待 文 件 大 小 的 消 息 來 更 新 總 大 小 數 據 ， 或 者 一 個 計 時 器 的 事 件 來 打 印 當 前 的 總 大 小 數 據 。 如 果 -v的 flag在 運 行 時 沒 有 傳 入 的 話 ， tick這 個 channel會 保 持 爲 nil， 這 樣 在 select里 的 case也 就 相 當 於 被 禁 用 了 。 < / p >
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< pre > < code class = "lang-go" > gopl.io/ch8/du2
< span class = "hljs-keyword" > var< / span > verbose = flag.Bool(< span class = "hljs-string" > " v" < / span > , < span class = "hljs-constant" > false< / span > , < span class = "hljs-string" > " show verbose progress messages" < / span > )
< span class = "hljs-keyword" > func< / span > main() {
< span class = "hljs-comment" > // ...start background goroutine...< / span >
< span class = "hljs-comment" > // Print the results periodically.< / span >
< span class = "hljs-keyword" > var< / span > tick < -< span class = "hljs-keyword" > chan< / span > time.Time
< span class = "hljs-keyword" > if< / span > *verbose {
tick = time.Tick(< span class = "hljs-number" > 500< / span > * time.Millisecond)
}
< span class = "hljs-keyword" > var< / span > nfiles, nbytes < span class = "hljs-typename" > int64< / span >
loop:
< span class = "hljs-keyword" > for< / span > {
< span class = "hljs-keyword" > select< / span > {
< span class = "hljs-keyword" > case< / span > size, ok := < -fileSizes:
< span class = "hljs-keyword" > if< / span > !ok {
< span class = "hljs-keyword" > break< / span > loop < span class = "hljs-comment" > // fileSizes was closed< / span >
}
nfiles++
nbytes += size
< span class = "hljs-keyword" > case< / span > < -tick:
printDiskUsage(nfiles, nbytes)
}
}
printDiskUsage(nfiles, nbytes) < span class = "hljs-comment" > // final totals< / span >
}
< / code > < / pre >
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< p > 由 於 我 們 的 程 序 不 再 使 用 range循 環 ， 第 一 個 select的 case必 鬚 顯 式 地 判 斷 fileSizes的 channel是 不 是 已 經 被 關 閉 了 ， 這 里 可 以 用 到 channel接 收 的 二 值 形 式 。 如 果 channel已 經 被 關 閉 了 的 話 ， 程 序 會 直 接 退 齣 循 環 。 這 里 的 break語 句 用 到 了 標 籤 break， 這 樣 可 以 同 時 終 結 select和 for兩 個 循 環 ； 如 果 沒 有 用 標 籤 就 break的 話 隻 會 退 齣 內 層 的 select循 環 ， 而 外 層 的 for循 環 會 使 之 進 入 下 一 輪 select循 環 。 < / p >
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< p > 現 在 程 序 會 悠 閒 地 爲 我 們 打 印 更 新 流 ： < / p >
< pre > < code > $ go build gopl.io/ch8/du2
$ ./du2 -v $HOME /usr /bin /etc
28608 files 8.3 GB
54147 files 10.3 GB
93591 files 15.1 GB
127169 files 52.9 GB
175931 files 62.2 GB
213201 files 62.7 GB
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< / code > < / pre > < p > 然 而 這 個 程 序 還 是 會 花 上 很 長 時 間 纔 會 結 束 。 無 法 對 walkDir做 併 行 化 處 理 沒 什 麽 别 的 原 因 ， 無 非 是 因 爲 磁 盤 繫 統 併 行 限 製 。 下 面 這 個 第 三 個 版 本 的 du， 會 對 每 一 個 walkDir的 調 用 創 建 一 個 新 的 goroutine。 它 使 用 sync.WaitGroup (§ 8.5)來 對 仍 舊 活 躍 的 walkDir調 用 進 行 計 數 ， 另 一 個 goroutine會 在 計 數 器 減 爲 零 的 時 候 將 fileSizes這 個 channel關 閉 。 < / p >
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< pre > < code class = "lang-go" > gopl.io/ch8/du3
< span class = "hljs-keyword" > func< / span > main() {
< span class = "hljs-comment" > // ...determine roots...< / span >
< span class = "hljs-comment" > // Traverse each root of the file tree in parallel.< / span >
fileSizes := < span class = "hljs-built_in" > make< / span > (< span class = "hljs-keyword" > chan< / span > < span class = "hljs-typename" > int64< / span > )
< span class = "hljs-keyword" > var< / span > n sync.WaitGroup
< span class = "hljs-keyword" > for< / span > _, root := < span class = "hljs-keyword" > range< / span > roots {
n.Add(< span class = "hljs-number" > 1< / span > )
< span class = "hljs-keyword" > go< / span > walkDir(root, & n, fileSizes)
}
< span class = "hljs-keyword" > go< / span > < span class = "hljs-keyword" > func< / span > () {
n.Wait()
< span class = "hljs-built_in" > close< / span > (fileSizes)
}()
< span class = "hljs-comment" > // ...select loop...< / span >
}
< span class = "hljs-keyword" > func< / span > walkDir(dir < span class = "hljs-typename" > string< / span > , n *sync.WaitGroup, fileSizes < span class = "hljs-keyword" > chan< / span > < - < span class = "hljs-typename" > int64< / span > ) {
< span class = "hljs-keyword" > defer< / span > n.Done()
< span class = "hljs-keyword" > for< / span > _, entry := < span class = "hljs-keyword" > range< / span > dirents(dir) {
< span class = "hljs-keyword" > if< / span > entry.IsDir() {
n.Add(< span class = "hljs-number" > 1< / span > )
subdir := filepath.Join(dir, entry.Name())
< span class = "hljs-keyword" > go< / span > walkDir(subdir, n, fileSizes)
} < span class = "hljs-keyword" > else< / span > {
fileSizes < - entry.Size()
}
}
}
< / code > < / pre >
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< p > 由 於 這 個 程 序 在 高 峯 期 會 創 建 成 百 上 韆 的 goroutine， 我 們 需 要 脩 改 dirents函 數 ， 用 計 數 信 號 量 來 阻 止 他 同 時 打 開 太 多 的 文 件 ， 就 像 我 們 在 8.7節 中 的 併 發 爬 蟲 一 樣 ： < / p >
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< pre > < code class = "lang-go" > < span class = "hljs-comment" > // sema is a counting semaphore for limiting concurrency in dirents.< / span >
< span class = "hljs-keyword" > var< / span > sema = < span class = "hljs-built_in" > make< / span > (< span class = "hljs-keyword" > chan< / span > < span class = "hljs-keyword" > struct< / span > {}, < span class = "hljs-number" > 20< / span > )
< span class = "hljs-comment" > // dirents returns the entries of directory dir.< / span >
< span class = "hljs-keyword" > func< / span > dirents(dir < span class = "hljs-typename" > string< / span > ) []os.FileInfo {
sema < - < span class = "hljs-keyword" > struct< / span > {}{} < span class = "hljs-comment" > // acquire token< / span >
< span class = "hljs-keyword" > defer< / span > < span class = "hljs-keyword" > func< / span > () { < -sema }() < span class = "hljs-comment" > // release token< / span >
< span class = "hljs-comment" > // ...< / span >
< / code > < / pre >
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< p > 這 個 版 本 比 之 前 那 個 快 了 好 幾 倍 ， 盡 管 其 具 體 效 率 還 是 和 你 的 運 行 環 境 ， 機 器 配 置 相 關 。 < / p >
< p > 練 習 8.9: 編 寫 一 個 du工 具 ， 每 隔 一 段 時 間 將 root目 録 下 的 目 録 大 小 計 算 併 顯 示 齣 來 。 < / p >
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< / section >
< / div >
< / div >
< / div >
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< a href = "../ch8/ch8-07.html" class = "navigation navigation-prev " aria-label = "Previous page: 基於select的多路複用" > < i class = "fa fa-angle-left" > < / i > < / a >
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< a href = "../ch8/ch8-09.html" class = "navigation navigation-next " aria-label = "Next page: 併發的退齣" > < i class = "fa fa-angle-right" > < / i > < / a >
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< / div >
< / div >
< script src = "../gitbook/app.js" > < / script >
< script src = "../gitbook/plugins/gitbook-plugin-sharing/buttons.js" > < / script >
< script src = "../gitbook/plugins/gitbook-plugin-fontsettings/buttons.js" > < / script >
< script >
require(["gitbook"], function(gitbook) {
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var config = {"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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gitbook.start(config);
});
< / script >
< / body >
< / html >
