Very limited shared promotion

[Walter Bright]

On 6/18/2019 6:29 AM, Steven Schveighoffer wrote:
> Seems like it would be safe,

When dealing with concurrency, that's like throwing a bunch of chemicals into a 
vat and saying it seems safe to drink :-)

Just remember that doubled checked locking fooled a lot of very smart people for 
many years. I got snookered by it, too.

Not sure where I read about it recently, but some expert had come up with a lock 
free algorithm, and the bug was only discovered a couple years later.

Unless you are really, really good at concurrency, it's best to stick with 
atomics and locks, every time.