C# performance optimization best practices

1. The explicitly registered EvenHandler must be explicitly unregistered to avoid memory leaks

Registering a member method to an event of an object will cause the latter to hold A reference to the former. The former will not be garbage collected until the event is logged out.

##

private void Form1_Load()
{
  ……
  //注册事件
  CommandRemotingContext.CmdChanged += new ReciverCmdStateChangedEventHandler(this.CommandRemotingContext_CmdChanged);
  ……
}
private void Form1_FromClosed()
{
  ……
  //关闭窗体时及时释放事件
  CommandRemotingContext.CmdChanged -= new ReciverCmdStateChangedEventHandler(this.CommandRemotingContext_CmdChanged);
  ……
}

Memory leak problem caused by events:

• Object A subscribes to events in object B

• The life cycle of object A is much longer than that of object B

• Object A does not unsubscribe from object B

• Eventually, object B cannot be released

2. Batch operations on the data source bound to the control should avoid automatic refresh

• When the client operates data in batches, the refresh operation of the control will cause unnecessary time consumption
  

• When the data source (such as When a DataTable, Array, List, ObservableCollection or other IListSource, etc.) is bound to a control, you should disconnect the binding or suspend the refresh of the control when operating data in batches.

  this.gcBillList.DataSource = null;
  DataRowCollection rows = this.ds.Tables[0].Rows;
  foreach (DataRow row in rows)
  {
      // DataRow数据操作
  }
  this.gcBillList.DataSource = this.ds.Tables[0].DefaultView;

3. Reduce the number of communications between the client and the server

• The fewer WebService calls, the better. If the amount of data to be transmitted is large, consider splitting it into multiple calls.
  

• For short WebService calls, they should be merged as much as possible to reduce the number of interactions

  //多次调用了相同的WS  
  txtCompanyName.Text=SCPubFunctionClient.PublicWSCal<string>(“ForTest”, “GetCompanyNameByID”,“0001”);  txtCompanyInnerName.Text=SCPubFunctionClient.PublicWSCal<string>(“ForTest”, “GetCompanyInnerNameByID”,“0001”);
  //合并相邻的WS  
  string[] result=SCPubFunctionClient.PublicWSCal<string>(“ForTest”, “GetCompanyNameAndInnerNameByID”,“0001”);
  txtCompanyName.Text=result[0];
  txtCompanyInnerName.Text= result[1];

4. Reduce the number of communications between the client and the server

If not necessary, try to avoid calling WebService repeatedly in the loop body

##

//循环调用了相同的WS  
List<Person> persons;
……
foreach(string personID in personIDs)
{
	person=HRPubWsClient.getPerson(personID);
	persons.Add(person);
}
//合并WS  
List<Person> persons;
……
persons =HRPubWsClient.getPersonList(personIDs);

5. Use generics to avoid boxing and unboxing operations (reduce garbage collection pressure)

• Boxing operations will cause GC pressure; if it occurs in a collection , should be avoided by using generic collections.

  
  

• For collections of value types, use List instead of ArrayList, and use Dictionary instead of Hashtable.

  ArrayList h=new ArrayList();  //不建议
  h.Add(1);
   
  List<object> h = new List<object>();  //不建议
  h.Add(1);
   
  List<int> h = new List<int>();    //建议
  h.Add(1);

6. String operation:

C# String operation--reduce Garbage collection pressure7. Use constants to avoid creating objects

• In the following example, there are a lot of new decimal(0) codes in the program, which will cause small Objects are created and recycled frequently; the correct approach is to use the Decimal.Zero constant.

  private string CurrencyCalc()
  {
      if (firstValue == new decimal(0))  ……
      if (secondValue == new decimal(0)) ……
      if (thirdValue == new decimal(0)) ……
      if (fourthValue == new decimal(0)) ……
      ……
  }

8. Avoid unnecessary exception throwing

C# Exception handling ( Catch Throw) IL analysis

9. Use RemoveAll instead of RemoveAt to delete multiple elements

• When using the RemoveAll method to delete multiple elements in a collection (such as a List) at one time, only one resize operation will be performed on the internal array of the List, which is significantly more efficient than calling RemoveAt in a loop.

  List<string>  lst = new List<string> {"1", "2", "3", "1", "2", "4"};
  //不建议：
  for (int i = lst.Count - 1; i >= 0; i--)
  {
      if (lst[i] == "1" || lst[i] == "2")
      {
          lst.RemoveAt(i);
       }
  }
   
  //建议：
  lst.RemoveAll(s => s == "1" || s == "2");

10. C# DataSet performance best practices

11. Reflection and dynamic binding--reduce CPU Occupy

• # Reflection technology converts static binding during compilation into dynamic binding that is delayed to runtime.

  
  

• C# mainly supports 5 ways to dynamically create objects (the time consumption comes from the network, which is quite different from my actual measurement. See the specific test below) :

动态创建对象的方式	与Direct Create
1.Type.InvokeMember	慢40倍以上
2.ContructorInfo.Invoke	慢40倍以上
3.Activator.CreateInstance(Type)	慢7倍
4.Activator.CreateInstance(assemblyName, typeName)	慢1000倍以上
5.Assembly.CreateInstance(typeName)	慢40倍以上

• 应尽量避免使用反射和动态绑定；如必须使用，要遵循以下原则：

1． 使用接口调用方式将动态绑定改造为早期绑定（Direct Call）
2． 使用 Activator.CreateInstance(Type)方式动态创建对象

3． 使用typeof操作符代替GetType调用

小注：

通过循环创建实例记录时间如下：

加载程序集、获取类型在循环外部时间如下（这时不同创建方式消耗时间差距挺大）：

代码如下：

 public void TestCreateInstance()
        {
            Stopwatch watch1 = new Stopwatch();
            var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
            Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
            int num = 100000;
            watch1.Start();

            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                Activator.CreateInstance(type);
            }
            watch1.Stop();
            label1.Text = "Activator.CreateInstance(Type type)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                Activator.CreateInstance("ReflectiveClassLibrary", "ReflectiveClassLibrary.TestClass");
            }
            watch1.Stop();
            label2.Text = "Activator.CreateInstance(string assemblyName,string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //加载程序集                
                asmb.CreateInstance("TestClass");
            }
            watch1.Stop();
            label3.Text = "assembly.CreateInstance(string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                object obj = type.InvokeMember(null, BindingFlags.Public |
               BindingFlags.Instance | BindingFlags.CreateInstance, null, null, null);
            }
            watch1.Stop();
            label4.Text = "Type.InvokeMember(string name, BindingFlags invokeAttr, Binder binder, object target, object[] args)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                ConstructorInfo constructorInfo = type.GetConstructors()[0];
                constructorInfo.Invoke(null);
            }
            watch1.Stop();
            label5.Text = "ContructorInfo.Invoke(object[] parameters)时间：" + watch1.ElapsedMilliseconds + "毫秒";

        }

加载程序集、获取类型在循环内部时间如下（这时不同创建方式消耗时间差距比较小）：

代码如下：

 public void TestCreateInstance()
        {
            Stopwatch watch1 = new Stopwatch();
            //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
            //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
            int num = 100000;
            watch1.Start();

            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                Activator.CreateInstance(type);
            }
            watch1.Stop();
            label1.Text = "Activator.CreateInstance(Type type)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                Activator.CreateInstance("ReflectiveClassLibrary", "ReflectiveClassLibrary.TestClass");
            }
            watch1.Stop();
            label2.Text = "Activator.CreateInstance(string assemblyName,string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //加载程序集                
                asmb.CreateInstance("TestClass");
            }
            watch1.Stop();
            label3.Text = "assembly.CreateInstance(string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                object obj = type.InvokeMember(null, BindingFlags.Public |
               BindingFlags.Instance | BindingFlags.CreateInstance, null, null, null);
            }
            watch1.Stop();
            label4.Text = "Type.InvokeMember(string name, BindingFlags invokeAttr, Binder binder, object target, object[] args)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                ConstructorInfo constructorInfo = type.GetConstructors()[0];
                constructorInfo.Invoke(null);
            }
            watch1.Stop();
            label5.Text = "ContructorInfo.Invoke(object[] parameters)时间：" + watch1.ElapsedMilliseconds + "毫秒";

        }

测试代码如下：

c# 反射测试demo

12、序列化与反序列化

• 相对于XML、二进制序列化方式，Protobuf效率较高，支持数据量较大
  

• protobuf序列化后的大小是json的1/10，xml格式的1/20，是二进制序列化的1/10

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