//	} else
//		return 0;
TEXT ·Cas(SB), NOSPLIT, $0-17
	MOVD	ptr+0(FP), R3
	MOVWZ	old+8(FP), R4
	MOVWZ	new+12(FP), R5
	LWSYNC
cas_again:
	LWAR	(R3), R6
	CMPW	R6, R4
	BNE	cas_fail
	STWCCC	R5, (R3)
	BNE	cas_again
	MOVD	$1, R3
	LWSYNC
	MOVB	R3, ret+16(FP)
	RET
cas_fail:
	LWSYNC
	MOVB	R0, ret+16(FP)
	RET

// bool	·Cas64(uint64 *ptr, uint64 old, uint64 new)
// Atomically:
//	if(*val == old){

//go:build ppc64 || ppc64le

#include "textflag.h"

TEXT ·publicationBarrier(SB),NOSPLIT|NOFRAME,$0-0
	// LWSYNC is the "export" barrier recommended by Power ISA
	// v2.07 book II, appendix B.2.2.2.
	// LWSYNC is a load/load, load/store, and store/store barrier.
	LWSYNC

		p1.To.Reg = out
		// BNE
		p2 := s.Prog(ppc64.ABNE)
		p2.To.Type = obj.TYPE_BRANCH
		// ISYNC
		pisync := s.Prog(ppc64.AISYNC)
		pisync.To.Type = obj.TYPE_NONE
		p2.To.SetTarget(pisync)

	case ssa.OpPPC64LoweredAtomicStore8,
		ssa.OpPPC64LoweredAtomicStore32,
		ssa.OpPPC64LoweredAtomicStore64:
		// SYNC or LWSYNC
		// MOVB/MOVW/MOVD arg1,(arg0)
		st := ppc64.AMOVD
		switch v.Op {

	"SUBECC",
	"SUBEV",
	"SUBEVCC",
	"SUBZE",
	"SUBZECC",
	"SUBZEVCC",
	"SUBZEV",
	"SYNC",
	"XOR",
	"XORCC",
	"XORIS",
	"DCBF",
	"DCBI",
	"DCBST",
	"DCBT",
	"DCBTST",
	"DCBZ",
	"EIEIO",
	"ICBI",
	"ISYNC",
	"PTESYNC",
	"TLBIE",
	"TLBIEL",
	"TLBSYNC",
	"TW",
	"SYSCALL",
	"WORD",
	"RFCI",
	"FCPSGN",
	"FCPSGNCC",
	"FRES",
	"FRESCC",

	case PASTECC:
		// paste. has two input registers, and an L field, unlike other 3 operand instructions.
		return op + " " + args[0] + "," + args[1] + "," + args[2]
	case SYNC:
		if args[0] == "$1" {
			return "LWSYNC"
		}
		return "HWSYNC"

	case ISEL:
		return "ISEL " + args[3] + "," + args[1] + "," + args[2] + "," + args[0]

	// store instructions always have the memory operand at the end, no need to reorder

				gnuArg(&inst, 2, inst.Args[2], PC))
			buf.WriteString(asm)
			startArg = 4
		}

	case "sync":
		lsc := inst.Args[0].(Imm)<<4 | inst.Args[1].(Imm)
		switch lsc {
		case 0x00:
			buf.WriteString("hwsync")
			startArg = 2
		case 0x10:
			buf.WriteString("lwsync")
			startArg = 2
		default:
			buf.WriteString(opName)
		}

	case "lbarx", "lharx", "lwarx", "ldarx":

		// atomic exchange32, 64
		// LWSYNC
		// LDAR         (Rarg0), Rout
		// STDCCC       Rarg1, (Rarg0)
		// BNE          -2(PC)
		// ISYNC
		// return old val
		{name: "LoweredAtomicExchange32", argLength: 3, reg: gpxchg, resultNotInArgs: true, clobberFlags: true, faultOnNilArg0: true, hasSideEffects: true},

	STSW R3, (R4)                   // 7c60252a

	SYNC                            // 7c0004ac
	ISYNC                           // 4c00012c
	LWSYNC                          // 7c2004ac
	EIEIO                           // 7c0006ac
	PTESYNC                         // 7c4004ac
	TLBIE R3                        // 7c001a64
	TLBIEL R3                       // 7c001a24
	TLBSYNC                         // 7c00046c

// 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 mysync

import "runtime"

type WaitGroup struct {
	Callers []uintptr
}

func (wg *WaitGroup) Add(x int) {
	wg.Callers = make([]uintptr, 32)
	n := runtime.Callers(1, wg.Callers)
	wg.Callers = wg.Callers[:n]
}

func (wg *WaitGroup) Done() {
	wg.Add(-1)

```Python hl_lines="2-3"
@app.get('/burgers')
async def read_burgers():
    burgers = await get_burgers(2)
    return burgers
```

### More technical details

You might have noticed that `await` can only be used inside of functions defined with `async def`.