1 files changed, 100 insertions, 0 deletions
diff --git a/src/sync/oncefunc.go b/src/sync/oncefunc.go
new file mode 100644
index 0000000..db28628
--- /dev/null
+++ b/src/sync/oncefunc.go
@@ -0,0 +1,100 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+// OnceFunc returns a function that invokes f only once. The returned function
+// may be called concurrently.
+//
+// If f panics, the returned function will panic with the same value on every call.
+func OnceFunc(f func()) func() {
+	var (
+		once  Once
+		valid bool
+		p     any
+	)
+	// Construct the inner closure just once to reduce costs on the fast path.
+	g := func() {
+		defer func() {
+			p = recover()
+			if !valid {
+				// Re-panic immediately so on the first call the user gets a
+				// complete stack trace into f.
+				panic(p)
+			}
+		}()
+		f()
+		f = nil      // Do not keep f alive after invoking it.
+		valid = true // Set only if f does not panic.
+	}
+	return func() {
+		once.Do(g)
+		if !valid {
+			panic(p)
+		}
+	}
+}
+
+// OnceValue returns a function that invokes f only once and returns the value
+// returned by f. The returned function may be called concurrently.
+//
+// If f panics, the returned function will panic with the same value on every call.
+func OnceValue[T any](f func() T) func() T {
+	var (
+		once   Once
+		valid  bool
+		p      any
+		result T
+	)
+	g := func() {
+		defer func() {
+			p = recover()
+			if !valid {
+				panic(p)
+			}
+		}()
+		result = f()
+		f = nil
+		valid = true
+	}
+	return func() T {
+		once.Do(g)
+		if !valid {
+			panic(p)
+		}
+		return result
+	}
+}
+
+// OnceValues returns a function that invokes f only once and returns the values
+// returned by f. The returned function may be called concurrently.
+//
+// If f panics, the returned function will panic with the same value on every call.
+func OnceValues[T1, T2 any](f func() (T1, T2)) func() (T1, T2) {
+	var (
+		once  Once
+		valid bool
+		p     any
+		r1    T1
+		r2    T2
+	)
+	g := func() {
+		defer func() {
+			p = recover()
+			if !valid {
+				panic(p)
+			}
+		}()
+		r1, r2 = f()
+		f = nil
+		valid = true
+	}
+	return func() (T1, T2) {
+		once.Do(g)
+		if !valid {
+			panic(p)
+		}
+		return r1, r2
+	}
+}