span之高效能字串操作實測
.net中的字串操作效能問題由來已久,幸運的是微軟推出了span<T>高效能指標操作封裝工具類。這個類到底有多高的效能呢?網上傳言反正很高,但是實際上在網上很難找到合適的測試例項,這讓本人實在無力吐槽。經不住高效能這三個字的誘惑,本人還是瞭解了一番後做了幾個簡單樣例來測試一番,下面列出幾種字串常見操作的測試程式碼及其執行結果。
一、String.Index 測試
1var t1 = StopWacherHelper.DoTimer(() => 2{ 3for (int i = 0; i < count; i++) 4{ 5str.IndexOf(subStr); 6} 7}); 8 9Console.WriteLine($"string.IndexOf {count} 次用時:{t1} 毫秒");
1var t2 = StopWacherHelper.DoTimer(() => 2{ 3var strSpan = str.AsSpan(); 4 5var subStrSpan = subStr.AsSpan(); 6 7for (int i = 0; i < count; i++) 8{ 9strSpan.IndexOf(subStrSpan); 10} 11}); 12 13Console.WriteLine($"Span<T>.IndexOf {count} 次用時:{t2} 毫秒");
二、String.Substring 測試
1var t1 = StopWacherHelper.DoTimer(() => 2{ 3for (int i = 0; i < count; i++) 4{ 5str.Substring(0, str.IndexOf(subStr)); 6} 7}); 8 9Console.WriteLine($"String.Substring {count} 次用時:{t1} 毫秒");
1var t2 = StopWacherHelper.DoTimer(() => 2{ 3var strSpan = str.AsSpan(); 4 5var subStrSpan = subStr.AsSpan(); 6 7var index = strSpan.IndexOf(subStrSpan); 8 9for (int i = 0; i < count; i++) 10{ 11strSpan.Slice(0, strSpan.IndexOf(subStrSpan)); 12} 13});
三、String.Split 測試
1var t1 = StopWacherHelper.DoTimer(() => 2{ 3for (int i = 0; i < count; i++) 4{ 5var arr = str.Split(new string[] { splitStr }, StringSplitOptions.None); 6} 7}); 8 9Console.WriteLine($"String.Split {count} 次用時:{t1} 毫秒");
1var t2 = StopWacherHelper.DoTimer(() => 2{ 3var strSpan = str.AsSpan(); 4 5var splitSapn = splitStr.AsSpan(); 6 7int m = 0, n = 0; 8 9for (int i = 0; i < count; i++) 10{ 11List<string> arr = new List<string>(); 12 13while (true) 14{ 15m = n; 16n = strSpan.IndexOf(splitSapn); 17if (n > -1) 18{ 19arr.Add(strSpan.Slice(0, n).ToString()); 20strSpan = strSpan.Slice(n + splitSapn.Length); 21} 22else 23{ 24break; 25} 26} 27 28} 29}); 30 31Console.WriteLine($"Span<T>.Split {count} 次用時:{t2} 毫秒");
四、String.Replace 測試
1var t1 = StopWacherHelper.DoTimer(() => 2{ 3for (int i = 0; i < count; i++) 4{ 5str.Replace(splitStr, replaceStr); 6} 7}); 8 9Console.WriteLine($"String.Replace {count} 次用時:{t1} 毫秒");
1var t2 = StopWacherHelper.DoTimer(() => 2{ 3var strSpan = str.AsSpan(); 4 5var splitSapn = splitStr.AsSpan(); 6 7int m = 0, n = 0; 8 9for (int i = 0; i < count; i++) 10{ 11List<string> arr = new List<string>(); 12 13while (true) 14{ 15m = n; 16n = strSpan.IndexOf(splitSapn); 17if (n > -1) 18{ 19arr.Add(strSpan.Slice(0, n).ToString()); 20strSpan = strSpan.Slice(n + splitSapn.Length); 21} 22else 23{ 24break; 25} 26} 27string.Join(replaceStr, arr); 28} 29}); 30 31Console.WriteLine($"Span<T>.Replace {count} 次用時:{t2} 毫秒");
怎麼樣,經過上面的測試,是不是覺的Span<T>確實是名不虛傳?的確,在上面幾個常見場景中,Span<T>的高效能確實不同凡響,差不多是10倍的效能優勢!看到這裡,小夥伴們是不是覺的字串操作全改成Span<T>就行了?那下面的兩個測試會讓大家看清現實,在String.Contains中表現還不如原生的。
一、String.Contains 測試
1var t1 = StopWacherHelper.DoTimer(() => 2{ 3for (int i = 0; i < count; i++) 4{ 5str.Contains(subStr); 6} 7}); 8 9Console.WriteLine($"string.Contains {count} 次用時:{t1} 毫秒");
1var t2 = StopWacherHelper.DoTimer(() => 2{ 3var strSpan = str.AsSpan(); 4 5var subStrSpan = subStr.AsSpan(); 6 7for (int i = 0; i < count; i++) 8{ 9strSpan.Contains(subStrSpan, StringComparison.CurrentCulture); 10} 11}); 12 13Console.WriteLine($"Span<T>.Contains {count} 次用時:{t2} 毫秒");
仔細一看,不對啊,Span<T>的Contains裡面有其它的大小寫和語言相關的判斷啊。好,那再換一個原生方法對比測試一下。
二、String.Compare 測試
1var t1 = StopWacherHelper.DoTimer(() => 2{ 3for (int i = 0; i < count; i++) 4{ 5string.Compare(str, subStr, true); 6} 7}); 8 9Console.WriteLine($"string.Compare {count} 次用時:{t1} 毫秒");
1var t2 = StopWacherHelper.DoTimer(() => 2{ 3var strSpan = str.AsSpan(); 4 5var subStrSpan = subStr.AsSpan(); 6 7for (int i = 0; i < count; i++) 8{ 9strSpan.Contains(subStrSpan, StringComparison.CurrentCultureIgnoreCase); 10} 11}); 12 13Console.WriteLine($"Span<T>.Contains {count} 次用時:{t2} 毫秒");
還是被反殺了,這說明Span<T>的這個Contains方法可能真的只能在某些地方才能用,不然效能反而會有所下降。