// atomic_flag as a spinning lock
#include <iostream> // std::cout
#include <atomic> // std::atomic_flag
#include <thread> // std::thread
#include <vector> // std::vector
#include <sstream> // std::stringstream
std::atomic_flag lock_stream = ATOMIC_FLAG_INIT;
std::stringstream stream;
void append_number(int x) {
while (lock_stream.test_and_set()) {
}
stream << "thread #" << x << '\n';
lock_stream.clear();
}
int main()
{
std::vector<std::thread> threads;
for (int i = 1; i <= 10; ++i) threads.push_back(std::thread(append_number, i));
for (auto& th : threads) th.join();
std::cout << stream.str();
return 0;
}
The above is atomic_flaga simple spin lock implemented using www.cplusplus.comthe example program given.
std::amotic_flagThe member function test_and_set()that has always been well understood is not in place. You can think in another way.
std::atomic_flag lock_stream = ATOMIC_FLAG_INIT;After being initialized , it is when it is falsecalled test_and_set(). If it lock_streamis false, set it to true, and then the function returns false; if it lock_streamis true, do not set it (because it is already true) and return true.
void append_number(int x)In the function, when the lock_streamlock is acquired (that is, the lock_stream is false before and is set to true), it lock_stream.test_and_set()returns false, exits the while() loop, and executes the following code. Other threads lock_stream.test_and_set()return because they have not acquired the lock, trueand then loop to try until the lock is acquired and exit the loop.