IsReady Pattern

While back, I found something like following code from production and quite a bit surprised. IsReady or IsDirty function is very frequently called from main thread which enters a lock to check a shared boolean value. Yes, it was before C++11 and we didn’t have common framework for async task scheduling. Quick fix was just removing lock for m_isReady and added volatile specifier. However, volatile is not really synchronization primitive. Moreover, Visual Studio had different behavior in different versions back then.

// IsDirty called from main thread frequently.
bool Foo::IsDirty()
{
    ScopedLock(m_aLock);
    return m_isReady;
}

// Process run worker thread.
void Foo::Process()
{
    ScopedLock(m_aLock);
   
    // Do expensive work here. 
    
    // Write result to shared variable.
    
    m_isReady = true;
}