'Emplace back thread on vector
Why this cause undefined behavior?
#include <iostream>
#include <thread>
#include <vector>
std::vector<std::thread> threads(3);
void task() { std::cout<<"Alive\n";}
void spawn() {
for(int i=0; i<threads.size(); ++i)
//threads[i] = std::thread(task);
threads.emplace_back(std::thread(task));
for(int i=0; i<threads.size(); ++i)
threads[i].join();
}
int main() {
spawn();
}
If I will create threads as in commented line thread is copied/moved assignment so its fine, but why is not working when creating thread in place?
Solution 1:[1]
What is happening in your code is that you construct three default threads, then add three further threads.
Change:
std::vector<std::thread> threads(3);
To:
std::vector<std::thread> threads;
const size_t number_of_threads = 3;
int main() {
threads.reserve(number_of_threads);
spawn();
}
And inside spawn
:
void spawn() {
for (int i = 0; i < number_of_threads; ++i) {
threads.emplace_back(std::thread(task));
}
for (int i = 0; i < threads.size(); ++i) {
threads[i].join();
}
}
When you are using emplace_back
or push_back
, you must not allocate the memory before, because that will call the constructor of threads. You should just reserve
it.
BTW, since you are using emplace_back
not push_back
you can directly write:
threads.emplace_back(task);
Sources
This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.
Source: Stack Overflow
Solution | Source |
---|---|
Solution 1 | Neonit |