今天同事做培训讲到了线程同步的方法， 其中一个就是用到Semaphore。 Semaphore可以用在不同进程之间的线程同步， 若是在单进程中的线程同步， 使用lock或是Monitor就足够了。 正如其名 旗语就是存在多个任务， 每个任务上都插一个小旗作为互斥信号， 当有一个线程去访问该任务时， 就拔掉小旗 以示其他线程不能访问， 访问完成后再插回小旗使其他线程可以访问。
Demo:
代码
1
using System;
2using System.Collections.Generic;
3using System.Text;
4using System.Threading;
5using System.Diagnostics;
6
7namespace ConsoleApplication1
8
{
9
10 class Resources
11
{
12 public string Name;
13
14 public bool isInUse;
15
}
16 class Program
17 {
18 public static Semaphore m_Semaphore;
19 public static List<Resources> m_ResourceList = new List<Resources>();
20 static Random m_Random = new Random();
21
22 public static void ThreadFunc()
23 {
24 while (true)
25 {
26 int resourceID = 0;
27 m_Semaphore.WaitOne();
28
29 for (int i = 0; i < m_ResourceList.Count; i++)
30 {
31 lock (m_ResourceList[i])
32 {
33 if (!m_ResourceList[i].isInUse)
34 {
35 resourceID = i;
36 m_ResourceList[i].isInUse = true;
37 break;
38 }
39 }
40 }
41 Console.WriteLine(string.Format("Thread {0} is using Resource {1}", Thread.CurrentThread.Name, m_ResourceList[resourceID].Name));
42
43 Thread.Sleep(m_Random.Next(10) * 100);
44
45 lock (m_ResourceList[resourceID])
46 {
47 m_ResourceList[resourceID].isInUse = false;
48 }
49
50 m_Semaphore.Release();
51 }
52
53 }
54
55 static void Main(string[] args)
56 {
57 m_Semaphore = new Semaphore(5, 5);
58 //Add five resources to the resource list
59 for (int i = 0; i < 5; i++)
60 {
61 Resources r = new Resources();
62 r.Name = string.Format("{0}", i + 1);
63 r.isInUse = false;
64 m_ResourceList.Add(r);
65 }
66
67 //New 6 threads to access the resources list
68 for (int i = 0; i < 6; i++)
69 {
70 Thread th = new Thread(ThreadFunc);
71 th.Name = string.Format("{0}", i + 1);
72 th.Start();
73 }
74 }
75 }
76
}
77
78
using System;2
using System.Collections.Generic;3
using System.Text;4
using System.Threading;5
using System.Diagnostics;6
7
namespace ConsoleApplication18
{9
10
class Resources11
{12
public string Name;13
14
public bool isInUse;15
}16
class Program17
{18
public static Semaphore m_Semaphore;19
public static List<Resources> m_ResourceList = new List<Resources>();20
static Random m_Random = new Random();21
22
public static void ThreadFunc()23
{24
while (true)25
{26
int resourceID = 0;27
m_Semaphore.WaitOne();28
29
for (int i = 0; i < m_ResourceList.Count; i++)30
{31
lock (m_ResourceList[i])32
{33
if (!m_ResourceList[i].isInUse)34
{35
resourceID = i;36
m_ResourceList[i].isInUse = true;37
break;38
}39
}40
}41
Console.WriteLine(string.Format("Thread {0} is using Resource {1}", Thread.CurrentThread.Name, m_ResourceList[resourceID].Name));42
43
Thread.Sleep(m_Random.Next(10) * 100);44
45
lock (m_ResourceList[resourceID])46
{47
m_ResourceList[resourceID].isInUse = false;48
}49
50
m_Semaphore.Release();51
}52
53
}54
55
static void Main(string[] args)56
{57
m_Semaphore = new Semaphore(5, 5);58
//Add five resources to the resource list59
for (int i = 0; i < 5; i++)60
{61
Resources r = new Resources();62
r.Name = string.Format("{0}", i + 1);63
r.isInUse = false;64
m_ResourceList.Add(r);65
}66
67
//New 6 threads to access the resources list68
for (int i = 0; i < 6; i++)69
{70
Thread th = new Thread(ThreadFunc);71
th.Name = string.Format("{0}", i + 1);72
th.Start();73
}74
}75
}76
}77
78