小编典典

解析性能(If,TryParse,Try-Catch)

c#

我对处理信息解析文本的不同方法了解很多。例如,对于解析整数,可以期待什么样的性能。我想知道是否有人知道这一点。我正在从测试过的人那里寻找一些实数。

在哪种情况下,哪一个提供最佳性能?

Parse(...)  // Crash if the case is extremely rare .0001%

If (SomethingIsValid) // Check the value before parsing
    Parse(...)

TryParse(...) // Using TryParse

try
{
    Parse(...)
}
catch
{
    // Catch any thrown exceptions
}

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2020-05-19

共1个答案

小编典典

始终使用 T.TryParse(string str,out T value) 。抛出异常的代价很高,如果可以 先验地
处理异常,则应避免抛出异常。使用try-
catch块来“节省”性能(因为无效数据速率较低)会滥用异常处理,但会牺牲可维护性和良好的编码习惯。遵循良好的软件工程开发实践,编写测试案例,运行应用程序,然后进行基准测试并进行优化。

“我们应该忘记效率低下的问题,大约有97%的时间是这样: 过早的优化是万恶之源 。但是,我们不应该在那3%的临界水平上放弃自己的机会。”
-Donald Knuth

因此,就像在碳信用额度中一样,您任意分配try-catch 的性能 较差 ,而TryParse的性能则 更好
。只有在运行了应用程序并确定我们有某种类型的wrt字符串解析速度减慢之后,我们才考虑使用TryParse以外的任何方法。

(编辑:由于提问者似乎希望定时数据与好的建议一起使用,因此这是请求的定时数据)

用户(对于非信徒)10,000个输入上的各种故障率的时间:

Failure Rate      Try-Catch          TryParse        Slowdown
  0%           00:00:00.0131758   00:00:00.0120421      0.1
 10%           00:00:00.1540251   00:00:00.0087699     16.6
 20%           00:00:00.2833266   00:00:00.0105229     25.9
 30%           00:00:00.4462866   00:00:00.0091487     47.8
 40%           00:00:00.6951060   00:00:00.0108980     62.8
 50%           00:00:00.7567745   00:00:00.0087065     85.9
 60%           00:00:00.7090449   00:00:00.0083365     84.1
 70%           00:00:00.8179365   00:00:00.0088809     91.1
 80%           00:00:00.9468898   00:00:00.0088562    105.9
 90%           00:00:01.0411393   00:00:00.0081040    127.5
100%           00:00:01.1488157   00:00:00.0078877    144.6


/// <param name="errorRate">Rate of errors in user input</param>
/// <returns>Total time taken</returns>
public static TimeSpan TimeTryCatch(double errorRate, int seed, int count)
{
    Stopwatch stopwatch = new Stopwatch();
    Random random = new Random(seed);
    string bad_prefix = @"X";

    stopwatch.Start();
    for(int ii = 0; ii < count; ++ii)
    {
        string input = random.Next().ToString();
        if (random.NextDouble() < errorRate)
        {
           input = bad_prefix + input;
        }

        int value = 0;
        try
        {
            value = Int32.Parse(input);
        }
        catch(FormatException)
        {
            value = -1; // we would do something here with a logger perhaps
        }
    }
    stopwatch.Stop();

    return stopwatch.Elapsed;
}

/// <param name="errorRate">Rate of errors in user input</param>
/// <returns>Total time taken</returns>
public static TimeSpan TimeTryParse(double errorRate, int seed, int count)
{
    Stopwatch stopwatch = new Stopwatch();
    Random random = new Random(seed);
    string bad_prefix = @"X";

    stopwatch.Start();
    for(int ii = 0; ii < count; ++ii)
    {
        string input = random.Next().ToString();
        if (random.NextDouble() < errorRate)
        {
           input = bad_prefix + input;
        }

        int value = 0;
        if (!Int32.TryParse(input, out value))
        {
            value = -1; // we would do something here with a logger perhaps
        }
    }
    stopwatch.Stop();

    return stopwatch.Elapsed;
}

public static void TimeStringParse()
{
    double errorRate = 0.1; // 10% of the time our users mess up
    int count = 10000; // 10000 entries by a user

    TimeSpan trycatch = TimeTryCatch(errorRate, 1, count);
    TimeSpan tryparse = TimeTryParse(errorRate, 1, count);

    Console.WriteLine("trycatch: {0}", trycatch);
    Console.WriteLine("tryparse: {0}", tryparse);
}
2020-05-19