我想了解condition_variables。線程鎖定互斥快於std :: conditional_variable :: wait()
我想我的代碼應該像:
1.主鎖MX
2.主要的wait()通知< =這裏鎖定解除
3.螺紋鎖MX
4線程發送通知
5線程解鎖mx
6.主等待()完成並鎖定mx
那麼爲什麼線程可以在通知後鎖定mx比wait()更快?
Example
#include <iostream>
#include <future>
#include <condition_variable>
#include <vector>
using namespace std::chrono_literals;
std::shared_future<void> ready;
std::mutex finish_mx;
std::condition_variable finish_cv;
int execute(int val, const std::shared_future<void> &ready){
ready.wait();
std::lock_guard<std::mutex> lock(finish_mx);
std::cout<<"Locked: "<<val<<std::endl;
finish_cv.notify_one();
return val;
}
int main()
{
std::promise<void> promise;
auto shared = promise.get_future().share();
std::vector<std::future<int>> pool;
for (int i=0; i<10; ++i){
auto fut = std::async(std::launch::async, execute, i, std::cref(shared));
pool.push_back(std::move(fut));
}
std::this_thread::sleep_for(100ms);
std::unique_lock<std::mutex> finish_lock(finish_mx);
promise.set_value();
for (int i=0; pool.size() > 0; ++i)
{
finish_cv.wait(finish_lock);
std::cout<<"Notifies: "<<i<<std::endl;
for (auto it = pool.begin(); it != pool.end(); ++it) {
auto state = it->wait_for(0ms);
if (state == std::future_status::ready) {
pool.erase(it);
break;
}
}
}
}
輸出示例:
Locked: 6
Locked: 7
Locked: 8
Locked: 9
Locked: 5
Locked: 4
Locked: 3
Locked: 2
Locked: 1
Notifies: 0
Locked: 0
Notifies: 1
編輯
for (int i=0; pool.size() > 0; ++i)
{
finish_cv.wait(finish_lock);
std::cout<<"Notifies: "<<i<<std::endl;
auto it = pool.begin();
while (it != pool.end()) {
auto state = it->wait_for(0ms);
if (state == std::future_status::ready) {
/* process result */
it = pool.erase(it);
} else {
++it;
}
}
}
那麼在notify_one()之後獲得結果的最好方法是檢查所有未來嗎? – Alex
我不明白你在問什麼,對不起。如果你想在'notify_one'調用和條件變量喚醒之間建立一對一的對應關係,那麼你需要使用多個條件變量或者不同形式的同步。 –