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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < strong aria-hidd
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2022-08-24 10:48:15 +00:00
< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2022-08-04 06:59:33 +00:00
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< hr >
< h2 id = "114-基准测试" > < a class = "header" href = "#114-基准测试" > 11.4. 基准测试< / a > < / h2 >
< p > 基准测试是测量一个程序在固定工作负载下的性能。在Go语言中， ， ， < code > *testing.B< / code > 类型的参数；< code > *testing.B< / code > 参数除了提供和< code > *testing.T< / code > 类似的方法， ， < / p >
< p > 下面是IsPalindrome函数的基准测试， < / p >
< pre > < code class = "language-Go" > import " testing"
func BenchmarkIsPalindrome(b *testing.B) {
for i := 0; i < b.N; i++ {
IsPalindrome(" A man, a plan, a canal: Panama" )
}
}
< / code > < / pre >
< p > 我们用下面的命令运行基准测试。和普通测试不同的是，默认情况下不运行任何基准测试。我们需要通过< code > -bench< / code > 命令行标志参数手工指定要运行的基准测试函数。该参数是一个正则表达式，用于匹配要执行的基准测试函数的名字，默认值是空的。其中“.”模式将可以匹配所有基准测试函数，但因为这里只有一个基准测试函数，因此和< code > -bench=IsPalindrome< / code > 参数是等价的效果。< / p >
< pre > < code > $ cd $GOPATH/src/gopl.io/ch11/word2
$ go test -bench=.
PASS
BenchmarkIsPalindrome-8 1000000 1035 ns/op
ok gopl.io/ch11/word2 2.179s
< / code > < / pre >
< p > 结果中基准测试名的数字后缀部分， ， ， < / p >
< p > 报告显示每次调用IsPalindrome函数花费1.035微秒， ， ， < / p >
< p > 循环在基准测试函数内实现， ， ， ， ， < / p >
< p > 现在我们有了一个基准测试和普通测试， ， ： < / p >
< pre > < code class = "language-Go" > n := len(letters)/2
for i := 0; i < n; i++ {
if letters[i] != letters[len(letters)-1-i] {
return false
}
}
return true
< / code > < / pre >
< p > 不过很多情况下， < / p >
< pre > < code > $ go test -bench=.
PASS
BenchmarkIsPalindrome-8 1000000 992 ns/op
ok gopl.io/ch11/word2 2.093s
< / code > < / pre >
< p > 另一个改进想法是在开始为每个字符预先分配一个足够大的数组， ， ， ， < / p >
< pre > < code class = "language-Go" > letters := make([]rune, 0, len(s))
for _, r := range s {
if unicode.IsLetter(r) {
letters = append(letters, unicode.ToLower(r))
}
}
< / code > < / pre >
< p > 这个改进提升性能约35%， < / p >
< pre > < code > $ go test -bench=.
PASS
BenchmarkIsPalindrome-8 2000000 697 ns/op
ok gopl.io/ch11/word2 1.468s
< / code > < / pre >
< p > 如这个例子所示，快的程序往往是伴随着较少的内存分配。< code > -benchmem< / code > 命令行标志参数将在报告中包含内存的分配数据统计。我们可以比较优化前后内存的分配情况：< / p >
< pre > < code > $ go test -bench=. -benchmem
PASS
BenchmarkIsPalindrome 1000000 1026 ns/op 304 B/op 4 allocs/op
< / code > < / pre >
< p > 这是优化之后的结果：< / p >
< pre > < code > $ go test -bench=. -benchmem
PASS
BenchmarkIsPalindrome 2000000 807 ns/op 128 B/op 1 allocs/op
< / code > < / pre >
< p > 用一次内存分配代替多次的内存分配节省了75%的分配调用次数和减少近一半的内存需求。< / p >
< p > 这个基准测试告诉了我们某个具体操作所需的绝对时间， ， ， ？ ： ？ ： ？ < / p >
< p > 比较型的基准测试就是普通程序代码。它们通常是单参数的函数，由几个不同数量级的基准测试函数调用，就像这样：< / p >
< pre > < code class = "language-Go" > func benchmark(b *testing.B, size int) { /* ... */ }
func Benchmark10(b *testing.B) { benchmark(b, 10) }
func Benchmark100(b *testing.B) { benchmark(b, 100) }
func Benchmark1000(b *testing.B) { benchmark(b, 1000) }
< / code > < / pre >
< p > 通过函数参数来指定输入的大小， ， < / p >
< p > 比较型的基准测试反映出的模式在程序设计阶段是很有帮助的，但是即使程序完工了也应当保留基准测试代码。因为随着项目的发展，或者是输入的增加，或者是部署到新的操作系统或不同的处理器，我们可以再次用基准测试来帮助我们改进设计。< / p >
< p > < strong > 练习 11.6:< / strong > 为2.6.2节的练习2.4和练习2.5的PopCount函数编写基准测试。看看基于表格算法在不同情况下对提升性能会有多大帮助。< / p >
< p > < strong > 练习 11.7:< / strong > 为< code > *IntSet< / code > （ ） ， ？ ？ ？ < / p >
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