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线程同步之lock学习

news 来源：原创 2024/5/19 1:00:51

在应用程序中使用多个线程的一个好处是每个线程都可以异步执行。然而，线程的异步特性意味着必须协调对资源（如文件句柄、网络连接和内存）的访问。否则，两个或更多的线程可能在同一时间访问相同的资源，而每个线程都不知道其他线程的操作。结果将产生不可预知的数据损坏。这个时候我们就需要lock上场了。

Lock的作用

Lock获取给定对象的互斥锁，保证相应的代码块运行时，不会被其他线程中断;直到该对象被释放时其他线程才能访问相应的代码块；

Lock实现本质

通过System.Threading.Monitor的enter和exit方法实现的

代码实例如下

View Code

1 public void PrintByInnerObj( object greating)
2        {
3            Console.WriteLine(greating + " -- before lock " );
4             object obj = new object ();
5             lock (obj)
6            {
7                Console.WriteLine(greating + " -- is locking " );
8                Console.WriteLine(greating.ToString());
9                System.Threading.Thread.Sleep( 10000 );
10            }
11            Console.WriteLine(greating + " --  has unlock " );
12        }

对应的MSIL代码如下

View Code

1 .method public hidebysig instance void   PrintByInnerObj( object greating) cil managed
2 {
3    // Code size       116 (0x74)
4    .maxstack    2
5    .locals init ([ 0 ] object obj,
6            [ 1 ] bool ' <>s__LockTaken0 ' ,
7            [ 2 ] object CS$ 2 $ 0000 ,
8            [ 3 ] bool CS$ 4 $ 0001 )
9    IL_0000:    nop
10    IL_0001:    ldarg.1
11    IL_0002:    ldstr        " -- before lock "
12    IL_0007:    call         string [mscorlib]System.String::Concat( object ,
13                                                                object )
14    IL_000c:    call         void [mscorlib]System.Console::WriteLine( string )
15    IL_0011:    nop
16    IL_0012:    newobj       instance void [mscorlib]System.Object::.ctor()
17    IL_0017:    stloc.0
18    IL_0018:    ldc.i4.0
19    IL_0019:    stloc.1
20   .try
21   {
22      IL_001a:    ldloc.0
23      IL_001b:    dup
24      IL_001c:    stloc.2
25      IL_001d:    ldloca.s     ' <>s__LockTaken0 '
26      IL_001f:    call         void [mscorlib]System.Threading.Monitor::Enter( object ,
27                                                                          bool &)
28      IL_0024:    nop
29      IL_0025:    nop
30      IL_0026:    ldarg.1
31      IL_0027:    ldstr        " -- is locking "
32      IL_002c:    call         string [mscorlib]System.String::Concat( object ,
33                                                                  object )
34      IL_0031:    call         void [mscorlib]System.Console::WriteLine( string )
35      IL_0036:    nop
36      IL_0037:    ldarg.1
37      IL_0038:    callvirt     instance string [mscorlib]System.Object::ToString()
38      IL_003d:    call         void [mscorlib]System.Console::WriteLine( string )
39      IL_0042:    nop
40      IL_0043:    ldc.i4       0x2710
41      IL_0048:    call         void [mscorlib]System.Threading.Thread::Sleep( int32 )
42      IL_004d:    nop
43      IL_004e:    nop
44      IL_004f:    leave .s    IL_0061
45   }   // end .try
46   finally
47   {
48      IL_0051:    ldloc.1
49      IL_0052:    ldc.i4.0
50      IL_0053:   ceq
51      IL_0055:    stloc.3
52      IL_0056:    ldloc.3
53      IL_0057:    brtrue.s    IL_0060
54      IL_0059:    ldloc.2
55      IL_005a:    call         void [mscorlib]System.Threading.Monitor::Exit( object )
56      IL_005f:    nop
57      IL_0060:    endfinally
58   }   // end handler
59    IL_0061:    nop
60    IL_0062:    ldarg.1
61    IL_0063:    ldstr        " --  has unlock "
62    IL_0068:    call         string [mscorlib]System.String::Concat( object ,
63                                                                object )
64    IL_006d:    call         void [mscorlib]System.Console::WriteLine( string )
65    IL_0072:    nop
66    IL_0073:    ret
67 } // end of method MyLockTest::PrintByInnerObj

Lock的锁定范围

Lock的参数必须为引用类型的对象，该对象代表了锁定的范围，对象不同锁定的范围也不同。

锁定参数为待锁定代码块内声明的对象，锁定范围为该代码块

View Code

1 public void PrintByInnerObj(objectgreating)
2
3 {
4
5 Console.WriteLine(greating + " -- before lock " );
6
7 object obj = newobject();
8
9 lock (obj)
10
11 {
12
13 Console.WriteLine(greating + " -- is locking " );
14
15 Console.WriteLine(greating.ToString());
16
17 System.Threading.Thread.Sleep( 10000 );
18
19 }
20
21 Console.WriteLine(greating + " -- has unlock " );
22
23 }

锁定参数为待锁定代码块所在类的私有字段，锁定范围为该类具体的一个实例

View Code

1 public void PrintByInstanceObj(objectgreating)
2
3 {
4
5 Console.WriteLine(greating + " -- before lock " );
6
7 lock (instanceObj)
8
9 {
10
11 Console.WriteLine(greating + " -- is locking " );
12
13 Console.WriteLine(greating.ToString());
14
15 System.Threading.Thread.Sleep( 10000 );
16
17 }
18
19 Console.WriteLine(greating + " -- has unlock " );
20
21 }

锁定参数为待锁定代码块所在类的私有静态字段，锁定范围为该类所有的实例

View Code

1 public void PrintLockByStaticObj(objectgreating)
2
3 {
4
5 Console.WriteLine(greating + " -- before lock " );
6
7 lock (staticObj)
8
9 {
10
11 Console.WriteLine(greating + " -- is locking " );
12
13 Console.WriteLine(greating.ToString());
14
15 Thread.Sleep( 10000 );
16
17 }
18
19 Console.WriteLine(greating + " -- has unlock " );
20
21 }

锁定参数为某一字符串，锁定范围为与该字符串值相等的所有字符串

View Code

1 public void PrintLockByStringObj(objectgreating)
2
3 {
4
5 Console.WriteLine(greating + " -- before lock " );
6
7 lock (stringObj)
8
9 {
10
11 Console.WriteLine(greating + " -- is locking " );
12
13 Console.WriteLine(greating.ToString());
14
15 System.Threading.Thread.Sleep( 10000 );
16
17 }
18
19 Console.WriteLine(greating + " --has unlock " );
20
21 }
22
23
24 public void PrintLockByString(objectgreating)
25
26 {
27
28 Console.WriteLine(greating + " -- before lock " );
29
30 lock ( " lock " )
31
32 {
33
34 Console.WriteLine(greating + " -- is locking " );
35
36 Console.WriteLine(greating.ToString());
37
38 System.Threading.Thread.Sleep( 10000 );
39
40 }
41
42 Console.WriteLine(greating + " --has unlock " );
43
44 }

锁定参数为this，锁定范围为所有能访问到this的地方

View Code

1 public void PrintLockByThis(objectgreating)
2
3 {
4
5 Console.WriteLine(greating + " -- before lock " );
6
7 lock ( this )
8
9 {
10
11 Console.WriteLine(greating + " -- is locking " );
12
13 Console.WriteLine(greating.ToString());
14
15 System.Threading.Thread.Sleep( 10000 );
16
17 }
18
19 Console.WriteLine(greating + " --has unlock " );
20
21 }

锁定参数为某个类的System.Type的实例，锁定范围为所有的地方

锁定public的实例字段，锁定范围同锁定this

View Code

1 public void PrintLockByPublicInstanceObj(objectgreating)
2
3 {
4
5 Console.WriteLine(greating + " -- before lock " );
6
7 lock (publicInstanceObj)
8
9 {
10
11 Console.WriteLine(greating + " -- is locking " );
12
13 Console.WriteLine(greating.ToString());
14
15 System.Threading.Thread.Sleep( 10000 );
16
17 }
18
19 Console.WriteLine(greating + " --has unlock " );
20
21 }

锁定参数为public的静态字段，锁定范围与锁定system.type相同

View Code

1 public void PrintLockByPublicStaticObj(objectgreating)
2
3 {
4
5 Console.WriteLine(greating + " -- before lock " );
6
7 lock (publicStaticObj)
8
9 {
10
11 Console.WriteLine(greating + " -- is locking " );
12
13 Console.WriteLine(greating.ToString());
14
15 System.Threading.Thread.Sleep( 10000 );
16
17 }
18
19 Console.WriteLine(greating + " --has unlock " );
20
21 }

整个类的代码如下

View Code

  1 using System;
  2 using System.Collections.Generic;
  3 using System.Linq;
  4 using System.Text;
  5 using System.Threading;
  6
  7 namespace LockCVolatileCA
  8 {
  9     public class MyLockTest
10     {
11         private static object staticObj = new object ();
12         private object instanceObj = new object ();
13         public static object publicStaticObj = new object ();
14         public object publicInstanceObj = new object ();
15         private string stringObj = " lock " ;
16         private static Int32 i = new int ()  ;
17
18         public void PrintByInnerObj( object greating)
19        {
20            Console.WriteLine(greating + " -- before lock " );
21             object obj = new object ();
22             lock (obj)
23            {
24                Console.WriteLine(greating + " -- is locking " );
25                Console.WriteLine(greating.ToString());
26                System.Threading.Thread.Sleep( 10000 );
27            }
28            Console.WriteLine(greating + " --  has unlock " );
29        }
30
31         public void PrintByInstanceObj( object greating)
32        {
33            Console.WriteLine(greating + " -- before lock " );
34             lock (instanceObj)
35            {
36                Console.WriteLine(greating + " -- is locking " );
37                Console.WriteLine(greating.ToString());
38                System.Threading.Thread.Sleep( 10000 );
39            }
40            Console.WriteLine(greating + " --  has unlock " );
41        }
42
43         public void PrintLockByStaticObj( object greating)
44        {
45            Console.WriteLine(greating + " -- before lock " );
46             lock (staticObj)
47            {
48                Console.WriteLine(greating + " -- is locking " );
49                Console.WriteLine(greating.ToString());
50                Thread.Sleep( 10000 );
51            }
52            Console.WriteLine(greating + " -- has unlock " );
53        }
54
55         public void PrintLockByClass( object greating)
56        {
57            Console.WriteLine(greating + " -- before lock " );
58             lock ( typeof (MyLockTest))
59            {
60                Console.WriteLine(greating + " -- is locking " );
61                Console.WriteLine(greating.ToString());
62                Thread.Sleep( 1000 );
63            }
64            Console.WriteLine(greating + " -- has unlock " );
65        }
66
67         public void PrintLockByThis( object greating)
68        {
69            Console.WriteLine(greating + " -- before lock " );
70             lock ( this )
71            {
72                Console.WriteLine(greating + " -- is locking " );
73                Console.WriteLine(greating.ToString());
74                System.Threading.Thread.Sleep( 10000 );
75            }
76            Console.WriteLine(greating + " --has unlock " );
77        }
78
79         public void PrintLockByStringObj( object greating)
80        {
81            Console.WriteLine(greating + " -- before lock " );
82             lock (stringObj)
83            {
84                Console.WriteLine(greating + " -- is locking " );
85                Console.WriteLine(greating.ToString());
86                System.Threading.Thread.Sleep( 10000 );
87            }
88            Console.WriteLine(greating + " --has unlock " );
89        }
90
91         public void PrintLockByString( object greating)
92        {
93            Console.WriteLine(greating + " -- before lock " );
94             lock ( " lock " )
95            {
96                Console.WriteLine(greating + " -- is locking " );
97                Console.WriteLine(greating.ToString());
98                System.Threading.Thread.Sleep( 10000 );
99            }
100            Console.WriteLine(greating + " --has unlock " );
101        }
102
103         public void PrintLockByPublicStaticObj( object greating)
104        {
105            Console.WriteLine(greating + " -- before lock " );
106             lock (publicStaticObj)
107            {
108                Console.WriteLine(greating + " -- is locking " );
109                Console.WriteLine(greating.ToString());
110                System.Threading.Thread.Sleep( 10000 );
111            }
112            Console.WriteLine(greating + " --has unlock " );
113        }
114
115         public void PrintLockByPublicInstanceObj( object greating)
116        {
117            Console.WriteLine(greating + " -- before lock " );
118             lock (publicInstanceObj)
119            {
120                Console.WriteLine(greating + " -- is locking " );
121                Console.WriteLine(greating.ToString());
122                System.Threading.Thread.Sleep( 10000 );
123            }
124            Console.WriteLine(greating + " --has unlock " );
125        }
126     }
127 }