首页 › 未分类 › Linux平台用C++封装线程读写锁

Linux平台用C++封装线程读写锁

第七根弦 2014 年 5 月 30 日 未分类 发表评论 (0)

在Linux平台上已经有现成的线程读写锁pthread_rwlock_t以及相关API，现将这些API封装成与Win32平台上相同的接口，以便于编写跨平台程序。这些API包括pthread_rwlock_init，pthread_rwlock_rdlock，pthread_rwlock_tryrdlock，pthread_rwlock_wrlock，pthread_rwlock_trywrlock，pthread_rwlock_unlock，pthread_rwlock_destroy，可在Linux在线手册上查阅它们的说明。下边的代码在VS2005中编辑，在Fedora 13虚拟机中编译，测试通过。

C++
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
//RWLockImpl.h
 
#ifndef _RWLockImpl_Header
#define _RWLockImpl_Header
 
#include <iostream>
#include <pthread.h>
#include <errno.h>
#include <assert.h>
 
using namespace std;
 
/*
读写锁允许当前的多个读用户访问保护资源，但只允许一个写读者访问保护资源
*/
 
//-----------------------------------------------------------------
class CRWLockImpl
{
protected:
CRWLockImpl();
~CRWLockImpl();
void ReadLockImpl();
bool TryReadLockImpl();
void WriteLockImpl();
bool TryWriteLockImpl();
void UnlockImpl();
 
private:
pthread_rwlock_t m_rwl;
};
 
//-----------------------------------------------------------------
 
class CMyRWLock: private CRWLockImpl
{
public:
 
//创建读/写锁
CMyRWLock(){};
 
//销毁读/写锁
~CMyRWLock(){};
 
//获取读锁
//如果其它一个线程占有写锁，则当前线程必须等待写锁被释放，才能对保护资源进行访问
void ReadLock();
 
//尝试获取一个读锁
//如果获取成功，则立即返回true，否则当另一个线程占有写锁，则返回false
bool TryReadLock();
 
//获取写锁
//如果一个或更多线程占有读锁，则必须等待所有锁被释放
//如果相同的一个线程已经占有一个读锁或写锁，则返回结果不确定
void WriteLock();
 
//尝试获取一个写锁
//如果获取成功，则立即返回true，否则当一个或更多其它线程占有读锁，返回false
//如果相同的一个线程已经占有一个读锁或写锁，则返回结果不确定
bool TryWriteLock();
 
//释放一个读锁或写锁
void Unlock();
 
private:
CMyRWLock(const CMyRWLock&);
CMyRWLock& operator = (const CMyRWLock&);
};
 
inline void CMyRWLock::ReadLock()
{
ReadLockImpl();
}
 
inline bool CMyRWLock::TryReadLock()
{
return TryReadLockImpl();
}
 
inline void CMyRWLock::WriteLock()
{
WriteLockImpl();
}
 
inline bool CMyRWLock::TryWriteLock()
{
return TryWriteLockImpl();
}
 
inline void CMyRWLock::Unlock()
{
UnlockImpl();
}
 
#endif

C++
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
//RWLockImpl.cpp
 
#include "RWLockImpl.h"
 
CRWLockImpl::CRWLockImpl()
{
if (pthread_rwlock_init(&m_rwl, NULL))
cout<<"cannot create reader/writer lock"<<endl;
}
 
CRWLockImpl::~CRWLockImpl()
{
pthread_rwlock_destroy(&m_rwl);
}
 
void CRWLockImpl::ReadLockImpl()
{
if (pthread_rwlock_rdlock(&m_rwl))
cout<<"cannot lock reader/writer lock"<<endl;
}
 
bool CRWLockImpl::TryReadLockImpl()
{
int rc = pthread_rwlock_tryrdlock(&m_rwl);
if (rc == 0)
return true;
else if (rc == EBUSY)
return false;
else
cout<<"cannot lock reader/writer lock"<<endl;
 
return false;
}
 
void CRWLockImpl::WriteLockImpl()
{
if (pthread_rwlock_wrlock(&m_rwl))
cout<<"cannot lock reader/writer lock"<<endl;
}
 
bool CRWLockImpl::TryWriteLockImpl()
{
int rc = pthread_rwlock_trywrlock(&m_rwl);
if (rc == 0)
return true;
else if (rc == EBUSY)
return false;
else
cout<<"cannot lock reader/writer lock"<<endl;
return false;
}
 
void CRWLockImpl::UnlockImpl()
{
if (pthread_rwlock_unlock(&m_rwl))
cout<<"cannot unlock reader/writer lock"<<endl;
}

下边是测试代码

C++
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
// pthread_rwlock.cpp : 定义控制台应用程序的入口点。
//
 
#include "RWLockImpl.h"
 
//创建一个读写锁对象
CMyRWLock g_myRWLock;
volatile int g_counter = 0;
 
//线程函数
void * StartThread(void *pParam)
{
int lastCount = 0;
for (int i = 0; i < 10000; ++i)
{
g_myRWLock.ReadLock();
lastCount = g_counter;
//在读锁域，两个线程不断循环交替访问全局变量g_counter
for (int k = 0; k < 100; ++k)
{
if (g_counter != lastCount)
cout<<"the value of g_counter has been updated."<<endl;
sleep(0);
}
g_myRWLock.Unlock();
 
 
g_myRWLock.WriteLock();
//在写锁域，只有一个线程可以修改全局变量g_counter的值
for (int k = 0; k < 100; ++k)
{
--g_counter;
sleep(0);
}
for (int k = 0; k < 100; ++k)
{
++g_counter;
sleep(0);
}
++g_counter;
if (g_counter <= lastCount)
cout<<"the value of g_counter is error."<<endl;
g_myRWLock.Unlock();
}
 
return (void *)0;
}
 
int main(int argc, char* argv[])
{
pthread_t thread1,thread2;
pthread_attr_t attr1,attr2;
 
//创建两个工作线程
pthread_attr_init(&attr1);
pthread_attr_setdetachstate(&attr1,PTHREAD_CREATE_JOINABLE);
if (pthread_create(&thread1,&attr1, StartThread,0) == -1)
{
cout<<"Thread 1: create failed"<<endl;
}
pthread_attr_init(&attr2);
pthread_attr_setdetachstate(&attr2,PTHREAD_CREATE_JOINABLE);
if (pthread_create(&thread2,&attr2, StartThread,0) == -1)
{
cout<<"Thread 2: create failed"<<endl;
}
 
//等待线程结束
void *result;
pthread_join(thread1,&result);
pthread_join(thread2,&result);
 
//关闭线程，释放资源
pthread_attr_destroy(&attr1);
pthread_attr_destroy(&attr2);
 
cout<<"the g_counter = "<<g_counter<<endl;
 
int iWait;
cin>>iWait;
 
return 0;
}

编译，运行
运行结果与在Win32下用C++实现多线程读写锁的相同。

|

发表评论