Concurrency & Threads
std::thread, mutex, lock_guard, atomics and std::async.
Key PointsAlways lock mutexes via RAII guards (lock_guard/unique_lock), never raw lock/unlock.
C++
#include <thread>
#include <mutex>
#include <atomic>
#include <iostream>
std::mutex m;
int counter = 0;
void bump() {
for (int i = 0; i < 10000; ++i) {
std::lock_guard lock(m);
++counter;
}
}
int main() {
std::thread t1(bump), t2(bump);
t1.join(); t2.join();
std::cout << counter << '\n'; // 20000
}For plain counters prefer std::atomic<int> over a mutex - it is lock-free.
C++
#include <thread>
#include <mutex>
#include <atomic>
#include <iostream>
std::mutex m;
int counter = 0;
void bump() {
for (int i = 0; i < 10000; ++i) {
std::lock_guard lock(m);
++counter;
}
}
int main() {
std::thread t1(bump), t2(bump);
t1.join(); t2.join();
std::cout << counter << '\n'; // 20000
}简单计数器优先用 std::atomic<int>，比互斥锁更轻。