[C#] Try Catch Finally issue

• try-catch
• 超出一般控制流程的程式碼會處理這些例外狀況
• throw 
• 在程式執行期間發出出現例外狀況的訊號
• 拋出捕抓到的例外
• Code

            try
            {
                // throw 的訊息會導引至 catch 中顯示
                if (sName.Equals("Lyndon"))
                    throw new ApplicationException("DemoError");
            }
            catch (Exception e)
            {
                Console.WriteLine("Error: {0}", e.Message);
            }

• try-catch-finally
• finally 
• 選擇性區塊
• finally 中的程式無論如何都會執行 
• 通常將釋放資源的程式寫在 finally 中
• Code

            try
            {
                // try 區塊中的資源、處理
            }
            catch (Exception e)
            {
                // catch 區塊中的例外情況
            }
            finally
            {
                // 釋放 try 區塊中所使用的資源
                // 撰寫 finally 區塊
                // 1. 程式執行順序最後一定會跑至 finally 區塊
                // 2. 如 try / catch 區塊中，使用 return，finally 區塊還是會被執行
            }

• try-catch block
• Code

public class TryCatchPerformanceLib
    {
public int nCount = 1000000;
        public long lSum = 0;
        public bool flag = false;
        public int nDiv = 100000;
        public int nDiv2 = 200000;

        /// 

        /// Case1: no try catch
        /// 
        /// Sum number
        public long Case1()
        {
            lSum = 0;
            for (int i = 0; i < nCount; i++)
            {
                lSum += i;
                if (i % nDiv == 0)
                    flag = true;
            }

            return lSum;
        }

        /// 

        /// Case2: try catch
        /// 
        /// Sum number
        public long Case2()
        {
            lSum = 0;
            for (int i = 0; i < nCount; i++)
            {
                try
                {
                    lSum += i;
                    if (i % nDiv == 0)
                        flag = true;
                }
                catch (Exception e)
                {
                    Console.WriteLine("Error: {0}", e.Message);
                }
            }

            return lSum;
        }

        /// 

        /// Case2: try catch and one exception
        /// 
        /// Sum number
        public long Case3()
        {
            lSum = 0;
            for (int i = 0; i < nCount; i++)
            {
                try
                {
                    lSum += i;
                    if (i % nDiv == 0)
                        throw new ApplicationException("DemoError");
                }
                catch (Exception e)
                {
                    Console.WriteLine("Error: {0}", e.Message);
                }
            }

            return lSum;
        }

        /// 

        /// Case2: try catch and one exception (reduce frequency)
        /// 
        /// Sum number
        public long Case4()
        {
            lSum = 0;
            for (int i = 0; i < nCount; i++)
            {
                try
                {
                    lSum += i;
                    if (i % nDiv2 == 0)
                        throw new ApplicationException("DemoError");
                }
                catch (Exception e)
                {
                    Console.WriteLine("Error: {0}", e.Message);
                }
            }

            return lSum;
        }
    }

• Result
• Case1 Sum=499,999,500,000 Time=11ms
• Case2 Sum=499,999,500,000 Time=11ms
• Case3 Sum=499,999,500,000 Time=121ms
• Case4 Sum=499,999,500,000 Time=45ms
1. try…catch 只有在發生 Exception 時才會影響效能
2. 當 catch 越頻繁影響效能越嚴重
• Ref:
• http://blog.darkthread.net/post-2009-12-20-try-catch-performance.aspx
• http://blog.darkthread.net/blogs/darkthreadtw/archive/2007/11/14/kb-how-avoidable-try-catch-tortures-your-machine.aspx
• https://dotblogs.com.tw/yc421206/archive/2011/06/09/27445.aspx
• https://docs.microsoft.com/zh-tw/dotnet/csharp/language-reference/keywords/exception-handling-statements
• http://teddy-chen-tw.blogspot.tw/2013/11/javatrycatchfinally1java-se-7.html