What does that mean in practice? Can I perform expensive calculations in parallel exhausting all cores?
package main
import (
"time"
"runtime"
)
func main(){
for i := runtime.NumCPU(); i > 0; i-- {
go func() {
for {}
}()
}
time.Sleep(time.Second)
println("bye")
}For example, as of now, the standard release note url for 1.14 currently 404s: https://golang.org/doc/go1.14
Anyone happen to know why there used to be overhead here/what changed?
From my comfortable sofa, it seems that there should be little difference between a defer-ed and direct call?
The full design doc is here: https://github.com/golang/proposal/blob/master/design/34481-...
> Go 1.13 implements the defer statement by calling into the runtime to push a "defer object" onto the defer chain. Then, in any function that contains defer statements, the compiler inserts a call to runtime.deferreturn at every function exit point to unwind that function's defers.
> We propose optimizing deferred calls in functions where every defer is executed at most once (specifically, a defer may be on a conditional path, but is never in a loop in the control-flow graph). In this optimization, the compiler assigns a bit for every defer site to indicate whether that defer had been reached or not. The defer statement itself simply sets the corresponding bit and stores all necessary arguments in specific stack slots. Then, at every exit point of the function, the compiler open-codes each deferred call, protected by (and clearing) each corresponding bit.
Selected changes:
- This release improves the performance of most uses of defer to incur almost zero overhead compared to calling the deferred function directly. As a result, defer can now be used in performance-critical code without overhead concerns.
- Goroutines are now asynchronously preemptible. As a result, loops without function calls no longer potentially deadlock the scheduler or significantly delay garbage collection.
- Per the overlapping interfaces proposal, Go 1.14 now permits embedding of interfaces with overlapping method sets: methods from an embedded interface may have the same names and identical signatures as methods already present in the (embedding) interface. This solves problems that typically (but not exclusively) occur with diamond-shaped embedding graphs. Explicitly declared methods in an interface must remain unique, as before.