Daily bit(e) of C++ | std::mutex

Daily bit(e) of C++ #12, The mutual exclusion lock std::mutex

std::mutex is a mutual exclusion lock that permits only one owner to hold the lock. A successive attempt at obtaining the lock will block until the previous owner of the lock releases it.

While the mutex can be locked and unlocked manually, it is desirable to use the RAII-based std::unique_lock instead, which will always correctly release a held lock, preventing accidental deadlocks.

#include <mutex>
#include <thread>
#include <chrono>
using namespace std::chrono_literals;

struct Shared {
    int value;
    std::mutex mux;
};
Shared shared{0,{}};

{
auto t1 = std::jthread([&shared]{
  for (int i = 0; i < 10; i++) {
    // obtain lock
    std::unique_lock lock(shared.mux);
    // modify shared state
    shared.value += 10;
  } // mutex unlocks as std::unique_lock is destroyed
});
auto t2 = std::jthread([&shared]{
  for (int i = 0; i < 10; i++) {
    // obtain lock
    std::unique_lock lock(shared.mux);
    // modify shared state
    shared.value += 1;
  } // mutex unlocks as std::unique_lock is destroyed
});
} // t1 && t2 a destroyed and joined

// shared.value == 110

Open the example in Compiler Explorer.