Test.cpp

#include <iostream>
#include <mutex>

std::mutex globalMutex;

class CustomScopedLock {
public:
  CustomScopedLock(std::mutex &m) : m_(m) {
    std::cout << "CustomScopedLock locking mutex..." << std::endl;
    m_.lock();
    std::cout << "CustomScopedLock has locked mutex!" << std::endl;
  };

  ~CustomScopedLock() {
    m_.unlock();
    std::cout << "CustomScopedLock has unlocked mutex" << std::endl;
  };

private:
  std::mutex &m_;
};

void lockMutexBad(bool shouldThrow) {
  std::cout << "Locking mutex manually..." << std::endl;
  globalMutex.lock();
  std::cout << "Mutex is locked!" << std::endl;

  // Could also imagine this as an early return. If you use a plain old
  // mutex, you have to remember to manually unlock before every return...
  // and it's quite easy to forget.
  if (shouldThrow) {
    std::cout << "Throwing exception" << std::endl;
    throw 1;
  }

  globalMutex.unlock();
  std::cout << "Mutex has been unlocked manually" << std::endl;
}

void lockMutexBadExample() {
  try {
    lockMutexBad(true);
  } catch (...) {
    std::cout << "Caught exception" << std::endl;
  }
  lockMutexBad(false);
}

void lockMutexGood(bool shouldThrow) {
  std::cout << "Locking mutex with scoped_lock..." << std::endl;
  std::scoped_lock lock(globalMutex);
  std::cout << "Mutex is locked!" << std::endl;

  if (shouldThrow) {
    std::cout << "Throwing exception" << std::endl;
    throw 1;
  }
}

void lockMutexGoodExample() {
  try {
    lockMutexGood(true);
  } catch (...) {
    std::cout << "Caught exception" << std::endl;
  }
  lockMutexGood(false);
}

void lockMutexCustomScopeLock(bool shouldThrow) {
  CustomScopedLock lock(globalMutex);

  if (shouldThrow) {
    std::cout << "Throwing exception" << std::endl;
    throw 1;
  }
}

void lockMutexCustomScopeLock() {
  try {
    lockMutexCustomScopeLock(true);
  } catch (...) {
    std::cout << "Caught exception" << std::endl;
  }
  lockMutexCustomScopeLock(false);
}

int main() {
  lockMutexBadExample();
  // lockMutexGoodExample();
  // lockMutexCustomScopeLock();

  return 0;
}