Re:Data Race Patterns in Go
by yencabulator on Saturday June 11, 2022 @02:59PM
(#31707157)
> If the Store() caller goes to sleep between setting the type and storing the pointer, it causes every Goroutine that calls Load() to block.
Where does this go to sleep: https://cs.opensource.google/go/go/+/refs/tags/go1.18.3:src/...
It looks like a CAS busy loop with preemption disabled, to me.
Re:Data Race Patterns in Go
by bumper_crop on Monday June 20, 2022 @09:06PM
(#31818489)
Make sure to read between the lines. It only looks like a busy loop. Remember, the OS can pause and preempt your thread at any time. This is a real and likely event.
By reading the lines and not between them, you could read these two lines: runtime_procPin() and runtime_procUnpin(). With explicit comments that these pause preemption.
> Pretty much every other language has atomic mean "one of these will win, one will lose"
Could you elaborate how "much every other language" implement it?
Re:Data Race Patterns in Go
by fastest963 on Friday June 10, 2022 @07:00PM
(#31700298)
This is why all the examples call Store immediately with a zero value of the type.
Re:Data Race Patterns in Go
by bumper_crop on Friday June 10, 2022 @07:22PM
(#31700441)
https://go.dev/play/p/xolc9oPwA0C
Interfaces don't have a zero type, which means that we can't have an atomic.Value which stores Shape. Atomic Value would be much easier to reason about if it had store semantics similar to a regular `var foo Shape = ...`. One of the other comment threads talked about generics helping this, so maybe there is hope.
Re:Data Race Patterns in Go
by yencabulator on Saturday June 11, 2022 @02:58PM
(#31707138)
Parent means
var bestShape atomic.Value
bestShape.Store((*Circle)(nil))Which will store it as a *Circle, and only allow more *Circles, not Shapes. That part of GP’s claim is correct.
It just had nothing to do with atomicity; it means something specific, not just “I like the failure mode.”
Re:Data Race Patterns in Go
by yencabulator on Sunday June 12, 2022 @11:36AM
(#31715293)
That's pretty easy to workaround:
type shapeContainer struct { Shape }
In fact, it's even worse than that. If the Store() caller goes to sleep between setting the type and storing the pointer, it causes every Goroutine that calls Load() to block. They can't make forward progress if the store caller hangs.