std::atomic_flag
std::atomic_flag是一个原子的布尔类型,可支持两种原子操作:
- test_and_set, 如果atomic_flag对象被设置,则返回true; 如果atomic_flag对象未被设置,则设置之,返回false
- clear. 清楚atomic_flag对象
std::atomic_flag可用于多线程之间的同步操作,类似于linux中的信号量。使用atomic_flag可实现mutex.
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#include <iostream>
#include <atomic>
#include <vector>
#include <thread>
#include <sstream>
std::atomic_flag lock = ATOMIC_FLAG_INIT;
std::stringstream stream;
void append_numer( int x)
{
while (lock.test_and_set());
stream << "thread#" << x << "\n" ;
lock.clear();
}
int main()
{
std::vector<std:: thread > ths;
for ( int i=0; i<10; i++)
ths.push_back(std:: thread (append_numer, i));
for ( int i=0; i<10; i++)
ths[i].join();
std::cout << stream.str();
return 0;
}
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std::atomic
std::atomic对int, char, bool等数据结构进行原子性封装,在多线程环境中,对std::atomic对象的访问不会造成竞争-冒险。利用std::atomic可实现数据结构的无锁设计。
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#include <iostream>
#include <atomic>
#include <vector>
#include <thread>
#include <sstream>
std::atomic< bool > ready( false );
std::atomic_flag winner = ATOMIC_FLAG_INIT;
void count1m( int i)
{
while (!ready);
for ( int i=0; i<1000000; i++);
if (!winner.test_and_set())
std::cout << "winner: " << i << std::endl;
}
int main()
{
std::vector<std:: thread > ths;
for ( int i=0; i<10; i++)
ths.push_back(std:: thread (count1m, i));
ready = true ;
for ( int i=0; i<10; i++)
ths[i].join();
return 0;
}
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在上例中,执行read=true之后,所有线程结束空等。winner被初始化为ATOMIC_FLAG_INIT,最先执行winner.test_and_set并返回false的线程为winner。
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#include <iostream>
#include <atomic>
#include <vector>
#include <thread>
#include <sstream>
std::atomic< int > foo(0);
void set_foo( int x)
{
foo = x;
}
void print_foo()
{
while (foo == 0)
{
std::this_thread::yield();
}
std::cout << "x: " << foo << std::endl;
}
int main()
{
std:: thread print_th(print_foo);
std:: thread set_th(set_foo, 10);
print_th.join();
set_th.join();
return 0;
}
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在上例总,set_foo用于设置atomic<int>对象的值,print_foo用于打印atomic<int>对象的值。std::atomic对象的值的读取和写入可使用load和store实现。
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#include <iostream>
#include <cassert>
#include <atomic>
#include <vector>
#include <unistd.h>
#include <thread>
#include <sstream>
std::atomic< int > foo(0);
std::atomic_flag lock = ATOMIC_FLAG_INIT;
void add_foo()
{
while (1)
{
foo++;
// foo = foo + 1;
while (lock.test_and_set());
std::cout << "add: " << foo << std::endl;
lock.clear();
usleep(1000);
}
}
void sub_foo()
{
while (1)
{
foo--;
// foo = foo - 1;
while (lock.test_and_set());
std::cout << "sub: " << foo << std::endl;
lock.clear();
usleep(1000);
}
}
int main()
{
std:: thread th2 = std:: thread (add_foo);
std:: thread th1 = std:: thread (sub_foo);
th1.join();
th2.join();
return 0;
}
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atomic<int>支持++和--的原子操作。
以上就是c++11 atomic的使用详解的详细内容,更多关于c++11 atomic的使用的资料请关注服务器之家其它相关文章!
原文链接:https://www.cnblogs.com/taiyang-li/p/5914331.html