// Copyright 2017 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 semaphore provides a weighted semaphore implementation.
package semaphore // import "golang.org/x/sync/semaphore"

import (
	"container/list"
	"context"
	"sync"
)

type waiter struct {
	n     int64
	ready chan<- struct{} // Closed when semaphore acquired.
}

func (conf *Config) alignof(T Type) int64 {
	f := stdSizes.Alignof
	if conf.Sizes != nil {
		f = conf.Sizes.Alignof
	}
	if a := f(T); a >= 1 {
		return a
	}
	panic("implementation of alignof returned an alignment < 1")
}

func (conf *Config) offsetsof(T *Struct) []int64 {
	var offsets []int64
	if T.NumFields() > 0 {
		// compute offsets on demand
		f := stdSizes.Offsetsof

// TypeList instead.
func (l *TypeList) list() []Type {
	if l == nil {
		return nil
	}
	return l.types
}

// ----------------------------------------------------------------------------
// Implementation

func bindTParams(list []*TypeParam) *TypeParamList {
	if len(list) == 0 {
		return nil
	}
	for i, typ := range list {
		if typ.index >= 0 {
			panic("type parameter bound more than once")
		}

TEXT ·Xchgint32(SB),NOSPLIT,$0-12
	B	·Xchg(SB)

TEXT ·Xchgint64(SB),NOSPLIT,$-4-20
	B	·Xchg64(SB)

// 64-bit atomics
// The native ARM implementations use LDREXD/STREXD, which are
// available on ARMv6k or later. We use them only on ARMv7.
// On older ARM, we use Go implementations which simulate 64-bit
// atomics with locks.
TEXT armCas64<>(SB),NOSPLIT,$0-21
	// addr is already in R1
	MOVW	old_lo+4(FP), R2

// necessary in order to make new(T) a valid implementation of arenas. Such a property
// is desirable to allow for a trivial implementation. (It also avoids complexities
// that arise from synchronization with the GC when trying to set the arena chunks to
// fault while the GC is active.)
//
// The implementation works in layers. At the bottom, arenas are managed in chunks.

	if len(nonce) != g.nonceSize {
		panic("crypto/cipher: incorrect nonce length given to GCM")
	}
	// Sanity check to prevent the authentication from always succeeding if an implementation
	// leaves tagSize uninitialized, for example.
	if g.tagSize < gcmMinimumTagSize {
		panic("crypto/cipher: incorrect GCM tag size")
	}

	if len(ciphertext) < g.tagSize {
		return nil, errOpen
	}

// protects some resource (e.g., allocmLock protects creation of new Ms). The
// read and write locks of that resource need to be represented in the lock
// rank.
//
// Internal ranking: as an implementation detail, rwmutex uses two mutexes:
// rLock and wLock. These have lock order requirements: wLock must be locked
// before rLock. This also needs to be represented in the lock rank.
//

	x+?            one or more x, prefer fewer
	x??            zero or one x, prefer zero
	x{n,m}?        n or n+1 or ... or m x, prefer fewer
	x{n,}?         n or more x, prefer fewer
	x{n}?          exactly n x

Implementation restriction: The counting forms x{n,m}, x{n,}, and x{n}
reject forms that create a minimum or maximum repetition count above 1000.
Unlimited repetitions are not subject to this restriction.

Grouping:

func (t *TypeParam) Underlying() Type {
	return t.iface()
}

func (t *TypeParam) String() string { return TypeString(t, nil) }

// ----------------------------------------------------------------------------
// Implementation

func (t *TypeParam) cleanup() {
	t.iface()
	t.check = nil
}

// iface returns the constraint interface of t.
func (t *TypeParam) iface() *Interface {
	bound := t.bound

	}
	if cmode != coverage.CtrModeAtomic {
		return fmt.Errorf("ClearCounters invoked for program built with -covermode=%s (please use -covermode=atomic)", cmode.String())
	}

	// Implementation note: this function would be faster and simpler
	// if we could just zero out the entire counter array, but for the
	// moment we go through and zero out just the slots in the array