我在两种不同情况下使用互斥量:-第一个示例:我将互斥锁与unique_lock一起使用,以确保线程不会同时访问同一资源-第二个示例:我将第一个示例扩展为使用condition_variable,以便所有线程都等到这个附加线程通知它们。
这是我的第一个例子
#include <thread>
#include <mutex>
#include <condition_variable>
#include <iostream>
using namespace std;
mutex Mutex;
condition_variable cv;
bool ready = false;
void print(const char* ThreadName,int WaitTime)
{
cout << ThreadName << " : Waiting to get lock!" << endl;
unique_lock<mutex> lock(Mutex);
cout << ThreadName << " : Got the lock" << endl;
this_thread::sleep_for(chrono::milliseconds(WaitTime));
while (!ready)
{
cv.wait(lock);
}
cout<< ThreadName << " : thread is finishing now...." << endl;
}
void execute(const char* ThreadName)
{
this_thread::sleep_for(chrono::milliseconds(2000));
cout<< ThreadName << "Thready is ready to be executed!" << endl;
ready = true;
cv.notify_all();
}
int main()
{
thread t1(print, "Print1",200);
thread t2(print, "Print2",1000);
thread t3(print, "Print3",500);
thread t4(print, "Print4",10);
thread te(execute, "Execute");
t1.join();
t2.join();
t3.join();
t4.join();
te.join();
return 0;
}
其结果是:
Print1Print3 : Waiting to get lock!Print2 : Waiting to get lock!
Print2 : Got the lock
Print4 : Waiting to get lock!
: Waiting to get lock!
Print2 : thread is finishing now....
Print3 : Got the lock
Print3 : thread is finishing now....
Print4 : Got the lock
Print4 : thread is finishing now....
Print1 : Got the lock
Print1 : thread is finishing now....
我们看到拥有互斥量的第一个线程可以做他的事,只有完成后,下一个线程才能超越unique_lock lock(Mutex);语句
现在我扩展此示例以使用condition_variable
#include <thread>
#include <mutex>
#include <condition_variable>
#include <iostream>
using namespace std;
mutex Mutex;
condition_variable cv;
bool ready = false;
void print(const char* ThreadName,int WaitTime)
{
cout << ThreadName << " : Waiting to get lock!" << endl;
unique_lock<mutex> lock(Mutex);
cout << ThreadName << " : Got the lock" << endl;
this_thread::sleep_for(chrono::milliseconds(WaitTime));
while (!ready)
{
cv.wait(lock);
}
cout<< ThreadName << " : thread is finishing now...." << endl;
}
void execute(const char* ThreadName)
{
this_thread::sleep_for(chrono::milliseconds(2000));
cout<< ThreadName << "Thready is ready to be executed!" << endl;
ready = true;
cv.notify_all();
}
int main()
{
thread t1(print, "Print1",200);
thread t2(print, "Print2",1000);
thread t3(print, "Print3",500);
thread t4(print, "Print4",10);
thread te(execute, "Execute");
t1.join();
t2.join();
t3.join();
t4.join();
te.join();
return 0;
}
此输出为
Print1Print3: Waiting to get lock!
: Waiting to get lock!
Print2 : Waiting to get lock!
Print4 : Waiting to get lock!
Print3 : Got the lock
Print1 : Got the lock
Print4 : Got the lock
Print2 : Got the lock
ExecuteThready is ready to be executed!
Print2 : thread is finishing now....
Print4 : thread is finishing now....
Print1 : thread is finishing now....
Print3 : thread is finishing now....
我不明白的是,所有4个线程如何在互斥锁上获得锁定,而condition_variable和互斥锁之间没有链接?
...... condition_variable和互斥量之间无处可链接?
链接在这里:
cv.wait(lock);
wait
函数在返回之前会做三件事:它
- 解锁给定的
它等待其他线程调用lock
,cv.notify_all()
,然后- 它重新锁定
lock
。