Bug 184442 – Bmalloc should have its own lockers instead of lock_guard and unique_lock

• Component: JavaScriptCore
• Status: NEW

[Saam Barati]

std::unique_lock and std::lock_guard are incompatible types. With bug #184176, I need to use unique_lock in just a few places since we may drop it to wait on a condition variable. However, since we pass this locker to things we call, I need to change the function of a bunch of signatures that don't actually need the API unique_lock provides. Same with things that call this API, they now need to pass in unique_lock.

A lot less code would be changed if we just had a class hierarchy like this:

```
// I'm just picking same names as std, but we could do something different.
template <typename Lock>
class LockGuard {
public:
    LockGuard(Lock& lock) 
        : m_lock(lock)
   {
       m_lock.lock();
   }
   ~LockGuard(Lock& lock)
   {
       if (m_locked)
           m_lock.unlock();
   }
protected:
    Lock& m_lock;
    bool m_locked { true };
};

template <typename Lock>
class UniqueLock : public LockGuard<Lock> {
    using Base = LockGuard<Lock>;
public:
    UniqueLock(Lock& l) : Base(l) { }
    void lock() { m_locked = true; m_lock.lock(); }
    void unlock() { m_locked = false; m_lock.unlock(); }
};
```

Or something along those lines.