.

vendor/github.com/valyala/fasthttp/stackless/func.go

@@ -0,0 +1,80 @@
+package stackless
+
+import (
+	"runtime"
+	"sync"
+)
+
+// NewFunc returns stackless wrapper for the function f.
+//
+// Unlike f, the returned stackless wrapper doesn't use stack space
+// on the goroutine that calls it.
+// The wrapper may save a lot of stack space if the following conditions
+// are met:
+//
+//   - f doesn't contain blocking calls on network, I/O or channels;
+//   - f uses a lot of stack space;
+//   - the wrapper is called from high number of concurrent goroutines.
+//
+// The stackless wrapper returns false if the call cannot be processed
+// at the moment due to high load.
+func NewFunc(f func(ctx any)) func(ctx any) bool {
+	if f == nil {
+		// developer sanity-check
+		panic("BUG: f cannot be nil")
+	}
+
+	funcWorkCh := make(chan *funcWork, runtime.GOMAXPROCS(-1)*2048)
+	onceInit := func() {
+		n := runtime.GOMAXPROCS(-1)
+		for i := 0; i < n; i++ {
+			go funcWorker(funcWorkCh, f)
+		}
+	}
+	var once sync.Once
+
+	return func(ctx any) bool {
+		once.Do(onceInit)
+		fw := getFuncWork()
+		fw.ctx = ctx
+
+		select {
+		case funcWorkCh <- fw:
+		default:
+			putFuncWork(fw)
+			return false
+		}
+		<-fw.done
+		putFuncWork(fw)
+		return true
+	}
+}
+
+func funcWorker(funcWorkCh <-chan *funcWork, f func(ctx any)) {
+	for fw := range funcWorkCh {
+		f(fw.ctx)
+		fw.done <- struct{}{}
+	}
+}
+
+func getFuncWork() *funcWork {
+	v := funcWorkPool.Get()
+	if v == nil {
+		v = &funcWork{
+			done: make(chan struct{}, 1),
+		}
+	}
+	return v.(*funcWork)
+}
+
+func putFuncWork(fw *funcWork) {
+	fw.ctx = nil
+	funcWorkPool.Put(fw)
+}
+
+var funcWorkPool sync.Pool
+
+type funcWork struct {
+	ctx  any
+	done chan struct{}
+}