Explain: Don't communicate by sharing memory; share memory by communicating

Question

I wonder what is the most down to earth explanation of this famous quote:

Don\'t communicate by sharing memory; share memory by communicating. (R. Pik

Answer 1

In essence, yes. Any values that are assigned to variables before the channel send are eligible to be observed after the channel read, since the channel operation imposes an ordering constraint. But it's important to remember the other part of the equation: if you want to guarantee that those values are observed, you have to make sure that no one else can write to those variables in between the write and the read. Obviously using locks would be possible, but pointless at the same time because if you're already combining locks and cross-thread memory modification, what benefit are you getting from channels? You could pass around something as simple as a boolean, as a token allowing exclusive access to the global data, and it would be 100% correct in terms of the memory model guarantees (as long as your code didn't have bugs), it would just probably be a bad design because you would be making things all implicit and action-at-a-distance-y without a good reason; passing the data explicitly is usually going to be clearer and less error-prone.