Atomicity of 32bit read on multicore CPU

Question

(Note: I\'ve added tags to this question based on where I feel will people will be who are likely to be able to help, so please don\'t shout:))

In my VS 2017 64bit p

Answer 1

As I posted here, this question was never about protecting a critical section of code, it was purely about avoiding torn read/writes. user3386109 posted a comment here which I ended up using, but declined posting it as an answer here. Thus I am providing the solution I ended up using for completeness of this question; maybe it will help someone in the future.

The following shows the atomic setting and testing of m_lClosed:

long m_lClosed = 0;

Thread 1

// Set flag to closed
if (InterlockedCompareExchange(&m_lClosed, 1, 0) == 0)
    cout << "Closed OK!\n";

Thread 2

This code replaces if (!m_lClosed)

if (InterlockedCompareExchange(&m_lClosed, 0, 0) == 0)
    cout << "Not closed!";