runtime.Gosched
- Go course
- Expert
- Lesson 21/34
- 4 min
Learn to voluntarily yield a goroutine with Gosched.
runtime.Gosched
runtime.Gosched() yields the current goroutine and puts it back on the queue; the P runs another goroutine, and then its turn comes again. The goroutine doesn't block, it just yields.
runtime.GOMAXPROCS(1)
go fmt.Println("goroutine")
runtime.Gosched() // give the other one a chance
fmt.Println("main")Since preemption arrived in Go 1.14 it's rarely needed in real code; you see it in tests and tight-loop experiments.
Don't use it for synchronization
The assumption "I called Gosched, so the goroutine must have run" is wrong; the scheduler doesn't guarantee it, and behavior changes on multi-core machines. To know that work has finished use real synchronization tools such as channels, sync.WaitGroup or sync.Once.
Practice Wait for the flag
Declare var hazir atomic.Bool. A goroutine sets the flag to true. main calls runtime.Gosched() in a loop until the flag is true, then prints "hazır".
Starter code
package main
import (
"fmt"
"runtime"
"sync/atomic"
)
func main() {
// buraya yaz
}Sample solution
package main
import (
"fmt"
"runtime"
"sync/atomic"
)
func main() {
var hazir atomic.Bool
go hazir.Store(true)
for !hazir.Load() {
runtime.Gosched()
}
fmt.Println("hazır")
}Expected output
hazır
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the key difference between Gosched and time.Sleep(0)?
- They are identical
- Sleep(0) panics
- Gosched ends the program
- Gosched returns to the queue right away; Sleep goes through the timer Correct answer
Explanation: Gosched only yields; it is not a synchronization tool. For ordering guarantees use channels or a WaitGroup.
2 Yield
for !hazir.Load() {
runtime.____()
}for !hazir.Load() {
runtime.Gosched()
}Explanation: Gosched lets other goroutines use the P while the loop waits.
3 Tool and guarantee
| Term | Meaning |
|---|---|
Gosched |
Only yields |
Channel |
Ordering guarantee |
WaitGroup |
Waits for completion |
atomic.Bool |
Safe flag |