// Copyright 2011 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

import (

// Cond implements a condition variable, a rendezvous point
// for goroutines waiting for or announcing the occurrence
// of an event.
// Each Cond has an associated Locker L (often a *Mutex or *RWMutex),
// which must be held when changing the condition and
// when calling the Wait method.
// A Cond must not be copied after first use.
// In the terminology of the Go memory model, Cond arranges that
// a call to Broadcast or Signal “synchronizes before” any Wait call
// that it unblocks.
// For many simple use cases, users will be better off using channels than a
// Cond (Broadcast corresponds to closing a channel, and Signal corresponds to
// sending on a channel).
// For more on replacements for sync.Cond, see [Roberto Clapis's series on
// advanced concurrency patterns], as well as [Bryan Mills's talk on concurrency
// patterns].
// [Roberto Clapis's series on advanced concurrency patterns]: https://blogtitle.github.io/categories/concurrency/
// [Bryan Mills's talk on concurrency patterns]: https://drive.google.com/file/d/1nPdvhB0PutEJzdCq5ms6UI58dp50fcAN/view
type Cond struct {
	noCopy noCopy

	// L is held while observing or changing the condition
	L Locker

	notify  notifyList
	checker copyChecker

// NewCond returns a new Cond with Locker l.
func ( Locker) *Cond {
	return &Cond{L: }

// Wait atomically unlocks c.L and suspends execution
// of the calling goroutine. After later resuming execution,
// Wait locks c.L before returning. Unlike in other systems,
// Wait cannot return unless awoken by Broadcast or Signal.
// Because c.L is not locked while Wait is waiting, the caller
// typically cannot assume that the condition is true when
// Wait returns. Instead, the caller should Wait in a loop:
//	c.L.Lock()
//	for !condition() {
//	    c.Wait()
//	}
//	... make use of condition ...
//	c.L.Unlock()
func ( *Cond) () {
	 := runtime_notifyListAdd(&.notify)
	runtime_notifyListWait(&.notify, )

// Signal wakes one goroutine waiting on c, if there is any.
// It is allowed but not required for the caller to hold c.L
// during the call.
// Signal() does not affect goroutine scheduling priority; if other goroutines
// are attempting to lock c.L, they may be awoken before a "waiting" goroutine.
func ( *Cond) () {

// Broadcast wakes all goroutines waiting on c.
// It is allowed but not required for the caller to hold c.L
// during the call.
func ( *Cond) () {

// copyChecker holds back pointer to itself to detect object copying.
type copyChecker uintptr

func ( *copyChecker) () {
	// Check if c has been copied in three steps:
	// 1. The first comparison is the fast-path. If c has been initialized and not copied, this will return immediately. Otherwise, c is either not initialized, or has been copied.
	// 2. Ensure c is initialized. If the CAS succeeds, we're done. If it fails, c was either initialized concurrently and we simply lost the race, or c has been copied.
	// 3. Do step 1 again. Now that c is definitely initialized, if this fails, c was copied.
	if uintptr(*) != uintptr(unsafe.Pointer()) &&
		!atomic.CompareAndSwapUintptr((*uintptr)(), 0, uintptr(unsafe.Pointer())) &&
		uintptr(*) != uintptr(unsafe.Pointer()) {
		panic("sync.Cond is copied")

// noCopy may be added to structs which must not be copied
// after the first use.
// See https://golang.org/issues/8005#issuecomment-190753527
// for details.
// Note that it must not be embedded, due to the Lock and Unlock methods.
type noCopy struct{}

// Lock is a no-op used by -copylocks checker from `go vet`.
func (*noCopy) ()   {}
func (*noCopy) () {}