参考链接:
线程支持库:https://zh.cppreference.com/w/cpp/thread 若能懂此链接,下面都不用看
1. https://blog.csdn.net/coolwriter/article/details/79883253
2. https://blog.csdn.net/coolwriter/article/details/79884298
thread:构造线程
#include <iostream> // std::cout
#include <thread> // std::thread
void thr_function1()
{
for (int i = 0; i != 10; ++i)
{
std::cout << "thread 1 print " << i << std::endl;
}
}
void thr_function2(int n)
{
std::cout << "thread 1 print " << n << std::endl;
}
int main()
{
std::thread t1(thr_function1); // spawn new thread that calls foo()
std::thread t2(thr_function2, 111); // spawn new thread that calls bar(0)
std::cout << "main, foo and bar now execute concurrently...\n";
// synchronize threads:
t1.join(); // pauses until first finishes 主线程等待t1线程结束
t2.join(); // pauses until second finishes 主线程等待t2线程结束
std::cout << "thread 1 and htread 2 completed.\n";
return 0;
}
class thread
member: http://www.cplusplus.com/reference/thread/thread/
Member types
get_id //Thread id (public member type )
native_handle_type //Native handle type (public member type )
Member functions:
Construct thread (public member function )
Thread destructor (public member function )
operator= // Move-assign thread (public member function )
get_id // Get thread id (public member function )
joinable //Check if joinable (public member function )
join //Join thread (public member function )
detach //Detach thread (public member function )
swap //Swap threads (public member function )
native_handle //Get native handle (public member function )
hardware_concurrency [static] //Detect hardware concurrency (public static member function )
多线程变量安全
方式一: 原子操作
方式二: std::mutex 互斥量
std::mutex 互斥量: https://zh.cppreference.com/w/cpp/thread/mutex
#include <iostream> // std::cout
#include <thread> // std::thread
#include <mutex> // std::mutex
std::mutex mtx; // mutex for critical section
void print_block(int n, char c) {
// critical section (exclusive access to std::cout signaled by locking mtx):
// mtx.try_lock //尝试锁定互斥,若互斥不可用,则返回
mtx.lock(); //锁定互斥,若互斥不可用则阻塞
for (int i = 0; i<n; ++i) { std::cout << c; }
std::cout << '\n';
mtx.unlock(); //解开互斥
}
int main()
{
std::thread th1(print_block, 50, '*');
std::thread th2(print_block, 50, '$');
th1.join();
th2.join();
return 0;
}
mutex类4种
std::mutex,最基本的 Mutex 类。
std::recursive_mutex,递归 Mutex 类。
std::time_mutex,定时 Mutex 类。
std::recursive_timed_mutex,定时递归 Mutex 类。
recursive_mutex: https://zh.cppreference.com/w/cpp/thread/recursive_mutex
std::recursive_mutex 与 std::mutex一样,也是一种可以被上锁的对象,但是和 std::mutex 不同的是,std::recursive_mutex 允许同一个线程对互斥量多次上锁(即递归上锁),
来获得对互斥量对象的多层所有权,std::recursive_mutex 释放互斥量时需要调用与该锁层次深度相同次数的 unlock(),可理解为 lock() 次数和 unlock() 次数相同,除此之外,
std::recursive_mutex 的特性和 std::mutex 大致相同。
time_mutex: //https://zh.cppreference.com/w/cpp/thread/timed_mutex
std::time_mutex 比 std::mutex 多了两个成员函数:
try_lock_for(): //尝试锁定互斥,若互斥在指定的时限时期中不可用则返回
try_lock_until(): //尝试锁定互斥,若直至抵达指定时间点互斥不可用则返回
#include <iostream> // std::cout
#include <chrono> // std::chrono::milliseconds
#include <thread> // std::thread
#include <mutex> // std::timed_mutex
std::timed_mutex mtx;
void fireworks() {
// waiting to get a lock: each thread prints "-" every 200ms:
while (!mtx.try_lock_for(std::chrono::milliseconds(200))) {
std::cout << "-";
}
// got a lock! - wait for 1s, then this thread prints "*"
std::this_thread::sleep_for(std::chrono::milliseconds(1000));
std::cout << "*\n";
mtx.unlock();
}
int main ()
{
std::thread threads[10];
// spawn 10 threads:
for (int i=0; i<10; ++i)
threads[i] = std::thread(fireworks);
for (auto& th : threads) th.join();
return 0;
}
Lock 类(两种)
std::lock_guard: //https://zh.cppreference.com/w/cpp/thread/lock_guard
与 Mutex RAII 相关,方便线程对互斥量上锁。 //https://zh.cppreference.com/w/cpp/thread/lock_guard
值得注意的是,lock_guard 对象并不负责管理 Mutex 对象的生命周期,lock_guard 对象只是简化了 Mutex 对象的上锁和解锁操作,
: 方便线程对互斥量上锁,即在某个 lock_guard 对象的声明周期内,它所管理的锁对象会一直保持上锁状态;
*: 而 lock_guard 的生命周期结束之后,它所管理的锁对象会被解锁。
#include <iostream> // std::cout
#include <thread> // std::thread
#include <mutex> // std::mutex, std::lock_guard, std::adopt_lock
std::mutex mtx; // mutex for critical section
void print_thread_id(int id) {
mtx.lock();
std::lock_guard<std::mutex> lck(mtx, std::adopt_lock); //= mtx.lock() 且在lck 析构时,mtk.unlock
std::cout << "thread #" << id << '\n';
}
int main()
{
std::thread threads[10];
// spawn 10 threads:
for (int i = 0; i<10; ++i)
threads[i] = std::thread(print_thread_id, i + 1);
for (auto& th : threads) th.join();
return 0;
}
**** scope_lock:构造时是否加锁是可选的(不加锁时假定当前线程已经获得锁的所有权),析构时自动释放锁,所有权不可转移,对象生存期内不允许手动加锁和释放锁。
std::unique_lock: //https://zh.cppreference.com/w/cpp/thread/unique_lock
与 Mutex RAII 相关,方便线程对互斥量上锁,但提供了更好的上锁和解锁控制。
类 unique_lock 是通用互斥包装器,允许延迟锁定、锁定的有时限尝试、递归锁定、所有权转移和与条件变量一同使用。
unique_lock比lock_guard使用更加灵活,功能更加强大。
使用unique_lock需要付出更多的时间、性能成本。所以能用lock_guard时,用lock_guard
class LogFile {
std::mutex _mu;
ofstream f;
public:
LogFile() {
f.open("log.txt");
}
~LogFile() {
f.close();
}
void shared_print(string msg, int id) {
std::unique_lock<std::mutex> guard(_mu);//如果 guard(_mu, std::defer_lock); 表示不上锁
//do something 1
guard.unlock(); //临时解锁
//do something 2
guard.lock(); //继续上锁
// do something 3
f << msg << id << endl;
cout << msg << id << endl;
// 结束时析构guard会临时解锁
// 这句话可要可不要,不写,析构的时候也会自动执行
// guard.ulock();
}
};
condition_variable
类是同步原语 //https://zh.cppreference.com/w/cpp/thread/condition_variable
能用于阻塞一个线程,或同时阻塞多个线程,直至另一线程修改共享变量(条件)并通知 condition_variable 。
当 std::condition_variable 对象的某个 wait 函数被调用的时候,它使用 std::unique_lock(通过 std::mutex) 来锁住当前线程。当前线程会一直被阻塞,直到另外一个线程在相同的 std::condition_variable 对象上调用了 notification 函数来唤醒当前线程。
#include <iostream> // std::cout
#include <thread> // std::thread
#include <mutex> // std::mutex, std::unique_lock
#include <condition_variable> // std::condition_variable
std::mutex mtx; // 全局互斥锁.
std::condition_variable cv; // 全局条件变量.
bool ready = false; // 全局标志位.
void do_print_id(int id)
{
std::unique_lock <std::mutex> lck(mtx);
while (!ready) // 如果标志位不为 true, 则等待...
cv.wait(lck); // 当前线程被阻塞, 当全局标志位变为 true 之后,此外还有 wait for ,wait until 等语句
// 线程被唤醒, 继续往下执行打印线程编号id.
std::cout << "thread " << id << '\n';
}
void go()
{
std::unique_lock <std::mutex> lck(mtx);
ready = true; // 设置全局标志位为 true.
cv.notify_all(); // 唤醒所有线程.
//notify_one 通知一个等待的线程
}
int main()
{
std::thread threads[10];
// spawn 10 threads:
for (int i = 0; i < 10; ++i)
threads[i] = std::thread(do_print_id, i);
std::cout << "10 threads ready to race...\n";
go(); // go!
for (auto & th:threads)
th.join();
return 0;
}
结果:
10 threads ready to race...
thread 1
thread 0
thread 2
thread 3
thread 4
thread 5
thread 6
thread 7
thread 8
thread 9
原文链接: https://www.cnblogs.com/heimazaifei/p/12176724.html
欢迎关注
微信关注下方公众号,第一时间获取干货硬货;公众号内回复【pdf】免费获取数百本计算机经典书籍
原创文章受到原创版权保护。转载请注明出处:https://www.ccppcoding.com/archives/191728
非原创文章文中已经注明原地址,如有侵权,联系删除
关注公众号【高性能架构探索】,第一时间获取最新文章
转载文章受原作者版权保护。转载请注明原作者出处!