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// 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
}
}
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