std::shared_ptr<FenceTime> glCompositionDoneFenceTime; if (display && display->getCompositionDisplay()->getState().usesClientComposition) { glCompositionDoneFenceTime = std::make_shared<FenceTime>(display->getCompositionDisplay() ->getRenderSurface() ->getClientTargetAcquireFence()); } else { glCompositionDoneFenceTime = FenceTime::NO_FENCE; }

这段代码看起来是用来创建一个 std::shared_ptr<FenceTime> 对象，并根据条件赋值不同的值。如果 display 存在，并且它所对应的 CompositionDisplay 的状态使用了客户端组合，则创建一个新的 FenceTime 对象，并将其初始化为获取客户端目标采集 fence 的结果。否则，将 glCompositionDoneFenceTime 赋值为 FenceTime::NO_FENCE，即一个空的 FenceTime 对象。这段代码可能在图形界面的渲染过程中使用。

相关问题

std::atomic<std::shared_ptr<T>>

std::atomic is a C++ class template that provides atomic operations on its template parameter. In this case, the template parameter is std::shared_ptr<T>, which is a type of smart pointer that manages a reference-counted object.

The std::atomic<std::shared_ptr<T>> class template ensures that operations on the shared_ptr object are atomic, meaning that they are indivisible and cannot be interrupted by other threads. This prevents race conditions and ensures that the shared_ptr object is always in a consistent state.

The atomic operations provided by std::atomic<std::shared_ptr<T>> include load, store, and exchange. These operations allow multiple threads to access and modify the shared_ptr object without causing data races or other synchronization issues.

Overall, std::atomic<std::shared_ptr<T>> is a powerful tool for managing shared resources in a multithreaded environment, providing a safe and efficient way to share data between threads.

std::atomic<std::shared_ptr<T>>示例

std::atomic<std::shared_ptr<T>>是一个原子共享指针，可以在多线程环境下安全地访问和修改共享资源。以下是一个示例：

#include <atomic>
#include <iostream>
#include <memory>
#include <thread>

class Foo {
public:
    Foo() { std::cout << "Foo constructor" << std::endl; }
    ~Foo() { std::cout << "Foo destructor" << std::endl; }
    void bar() { std::cout << "Foo bar" << std::endl; }
};

std::atomic<std::shared_ptr<Foo>> ptr;

void thread_func() {
    std::shared_ptr<Foo> p(new Foo);
    ptr.store(p);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::shared_ptr<Foo> q = ptr.load();
    q->bar();
}

int main() {
    std::thread t(thread_func);
    std::shared_ptr<Foo> r = ptr.load();
    if (r) {
        r->bar();
    }
    t.join();
    return 0;
}

在这个示例中，我们创建了一个名为Foo的类，并在其中定义了一个名为bar的方法。然后，我们使用std::atomic<std::shared_ptr<Foo>>定义了一个原子共享指针ptr。在thread_func函数中，我们创建了一个指向Foo对象的共享指针p，并使用ptr.store(p)将其存储到ptr中。然后，我们等待1秒钟，使用ptr.load()获取ptr中存储的共享指针q，并调用它的bar方法。

在主函数中，我们使用ptr.load()获取ptr中存储的共享指针r，并调用它的bar方法。最后，我们使用t.join()等待线程t的结束。