File size: 2,343 Bytes
e36aeda | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 | // 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() {
// Use a struct so that there's a single heap allocation.
d := struct {
f func()
once Once
valid bool
p any
}{
f: f,
}
return func() {
d.once.Do(func() {
defer func() {
d.f = nil // Do not keep f alive after invoking it.
d.p = recover()
if !d.valid {
// Re-panic immediately so on the first
// call the user gets a complete stack
// trace into f.
panic(d.p)
}
}()
d.f()
d.valid = true // Set only if f does not panic.
})
if !d.valid {
panic(d.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 {
// Use a struct so that there's a single heap allocation.
d := struct {
f func() T
once Once
valid bool
p any
result T
}{
f: f,
}
return func() T {
d.once.Do(func() {
defer func() {
d.f = nil
d.p = recover()
if !d.valid {
panic(d.p)
}
}()
d.result = d.f()
d.valid = true
})
if !d.valid {
panic(d.p)
}
return d.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) {
// Use a struct so that there's a single heap allocation.
d := struct {
f func() (T1, T2)
once Once
valid bool
p any
r1 T1
r2 T2
}{
f: f,
}
return func() (T1, T2) {
d.once.Do(func() {
defer func() {
d.f = nil
d.p = recover()
if !d.valid {
panic(d.p)
}
}()
d.r1, d.r2 = d.f()
d.valid = true
})
if !d.valid {
panic(d.p)
}
return d.r1, d.r2
}
}
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