Improve the exponential backoff algorithm in spin-lock

internal/spinlock.go

@@ -12,13 +12,18 @@ import (
 
 type spinLock uint32
 
+const maxBackoff = 64
+
 func (sl *spinLock) Lock() {
 	backoff := 1
 	for !atomic.CompareAndSwapUint32((*uint32)(sl), 0, 1) {
+		// Leverage the exponential backoff algorithm, see https://en.wikipedia.org/wiki/Exponential_backoff.
 		for i := 0; i < backoff; i++ {
 			runtime.Gosched()
 		}
-		backoff <<= 1
+		if backoff < maxBackoff {
+			backoff <<= 1
+		}
 	}
 }
 

internal/spinlock_test.go

@@ -11,6 +11,17 @@ import (
 	"testing"
 )
 
+/*
+Benchmark result for three types of locks:
+	goos: darwin
+	goarch: amd64
+	pkg: github.com/panjf2000/ants/v2/internal
+	cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
+	BenchmarkMutex-12              	20549502	        71.84 ns/op	       0 B/op	       0 allocs/op
+	BenchmarkSpinLock-12           	58629697	        20.02 ns/op	       0 B/op	       0 allocs/op
+	BenchmarkBackOffSpinLock-12    	72523454	        15.74 ns/op	       0 B/op	       0 allocs/op
+*/
+
 type originSpinLock uint32
 
 func (sl *originSpinLock) Lock() {