Go 下一步计划，新标准库 sync/v2！

func OnceFunc(f func()) func()
func OnceValue[T any](f func( "T any") T) func() T
func OnceValues[T1, T2 any](f func( "T1, T2 any") (T1, T2)) func() (T1, T2)
type Cond struct{ ... }
    func NewCond(l Locker) *Cond
type Locker interface{ ... }
type Mutex struct{ ... }
type Once struct{ ... }
type RWMutex struct{ ... }
type WaitGroup struct{ ... }
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// Map is like a Go map[K]V but is safe for concurrent use
// by multiple goroutines without additional locking or coordination.
// ...and so forth
type Map[K comparable, V any] struct { ... }

// Load returns the value stored in the map for a key, or the zero value if no
// value is present.
// The ok result indicates whether value was found in the map.
func (m *Map[K, V]) Load(key K) (value V, ok bool)

// Store sets the value for a key.
func (m *Map[K, V]) Store(key K, value V)

// LoadOrStore returns the existing value for the key if present.
// Otherwise, it stores and returns the given value.
// The loaded result is true if the value was loaded, false if stored.
func (m *Map[K, V]) LoadOrStore(key K, value V) (actual V, loaded bool)

// LoadAndDelete deletes the value for a key, returning the previous value if any.
// The loaded result reports whether the key was present.
func (m *Map[K, V]) LoadAndDelete(key K) (value V, loaded bool)

// Delete deletes the value for a key.
func (m *Map[K, V]) Delete(key K)

// Swap swaps the value for a key and returns the previous value if any.
// The loaded result reports whether the key was present.
func (m *Map[K, V]) Swap(key K, value V) (previous V, loaded bool)

// CompareAndDelete deletes the entry for key if its value is equal to old.
// This panics if V is not a comparable type.
//
// If there is no current value for key in the map, CompareAndDelete
// returns false.
func (m *Map[K, V]) CompareAndDelete(key K, old V) (deleted bool)

// CompareAndSwap swaps the old and new values for key
// if the value stored in the map is equal to old.
// This panics if V is not a comparable type.
func (m *Map[K, V]) CompareAndSwap(key K, old, new V) (swapped bool)

// Clear deletes all the entries, resulting in an empty Map.
func (m *Map[K, V]) Clear()

// All returns an iterator over the keys and values in the map.
// ... and so forth
func (m *Map[K, V]) All() iter.Seq2[K, V]

// TODO: Consider Keys and Values methods that return iterators, like maps.Keys and maps.Values.
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// A Pool is a set of temporary objects of type T that may be individually saved and retrieved.
// ...and so forth
type Pool[T any] struct {
    ...
}

// NewPool returns a new pool. If the newf argument is not nil, then when the pool is empty,
// newf is called to fetch a new value. This is useful when the values in the pool should be initialized.
func NewPool[T any] (newf func() T) *Pool[T]

// Put adds x to the pool.
func (p *Pool[T]) Put(x T)

// Get selects an arbitrary item from the Pool, removes it from the
// Pool, and returns it to the caller.
// ...and so forth
//
// If Get does not have a value to return, and p was created with a call to [NewPool] with a non-nil argument,
// Get returns the result of calling the function passed to [NewPool].
func (p *Pool[T]) Get() T
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