select5.go

// runoutput

// 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.

// Generate test of channel operations and simple selects.
// The output of this program is compiled and run to do the
// actual test.

// Each test does only one real send or receive at a time, but phrased
// in various ways that the compiler may or may not rewrite
// into simpler expressions.

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"text/template"
)

func main() {
	out := bufio.NewWriter(os.Stdout)
	fmt.Fprintln(out, header)
	a := new(arg)

	// Generate each test as a separate function to avoid
	// hitting the gc optimizer with one enormous function.
	// If we name all the functions init we don't have to
	// maintain a list of which ones to run.
	do := func(t *template.Template) {
		for ; next(); a.reset() {
			fmt.Fprintln(out, `func init() {`)
			run(t, a, out)
			fmt.Fprintln(out, `}`)
		}
	}

	do(recv)
	do(send)
	do(recvOrder)
	do(sendOrder)
	do(nonblock)

	fmt.Fprintln(out, "//", a.nreset, "cases")
	out.Flush()
}

func run(t *template.Template, a interface{}, out io.Writer) {
	if err := t.Execute(out, a); err != nil {
		panic(err)
	}
}

type arg struct {
	def    bool
	nreset int
}

func (a *arg) Maybe() bool {
	return maybe()
}

func (a *arg) MaybeDefault() bool {
	if a.def {
		return false
	}
	a.def = maybe()
	return a.def
}

func (a *arg) MustDefault() bool {
	return !a.def
}

func (a *arg) reset() {
	a.def = false
	a.nreset++
}

const header = `// GENERATED BY select5.go; DO NOT EDIT

package main

// channel is buffered so test is single-goroutine.
// we are not interested in the concurrency aspects
// of select, just testing that the right calls happen.
var c = make(chan int, 1)
var nilch chan int
var n = 1
var x int
var i interface{}
var dummy = make(chan int)
var m = make(map[int]int)
var order = 0

func f(p *int) *int {
	return p
}

// check order of operations by ensuring that
// successive calls to checkorder have increasing o values.
func checkorder(o int) {
	if o <= order {
		println("invalid order", o, "after", order)
		panic("order")
	}
	order = o
}

func fc(c chan int, o int) chan int {
	checkorder(o)
	return c
}

func fp(p *int, o int) *int {
	checkorder(o)
	return p
}

func fn(n, o int) int {
	checkorder(o)
	return n
}

func die(x int) {
	println("have", x, "want", n)
	panic("chan")
}

func main() {
	// everything happens in init funcs
}
`

func parse(name, s string) *template.Template {
	t, err := template.New(name).Parse(s)
	if err != nil {
		panic(fmt.Sprintf("%q: %s", name, err))
	}
	return t
}

var recv = parse("recv", `
	{{/*  Send n, receive it one way or another into x, check that they match. */}}
	c <- n
	{{if .Maybe}}
	x = <-c
	{{else}}
	select {
	{{/*  Blocking or non-blocking, before the receive. */}}
	{{/*  The compiler implements two-case select where one is default with custom code, */}}
	{{/*  so test the default branch both before and after the send. */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Receive from c.  Different cases are direct, indirect, :=, interface, and map assignment. */}}
	{{if .Maybe}}
	case x = <-c:
	{{else}}{{if .Maybe}}
	case *f(&x) = <-c:
	{{else}}{{if .Maybe}}
	case y := <-c:
		x = y
	{{else}}{{if .Maybe}}
	case i = <-c:
		x = i.(int)
	{{else}}
	case m[13] = <-c:
		x = m[13]
	{{end}}{{end}}{{end}}{{end}}
	{{/*  Blocking or non-blocking again, after the receive. */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Dummy send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case dummy <- 1:
		panic("dummy send")
	{{end}}
	{{if .Maybe}}
	case <-dummy:
		panic("dummy receive")
	{{end}}
	{{/*  Nil channel send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case nilch <- 1:
		panic("nilch send")
	{{end}}
	{{if .Maybe}}
	case <-nilch:
		panic("nilch recv")
	{{end}}
	}
	{{end}}
	if x != n {
		die(x)
	}
	n++
`)

var recvOrder = parse("recvOrder", `
	{{/*  Send n, receive it one way or another into x, check that they match. */}}
	{{/*  Check order of operations along the way by calling functions that check */}}
	{{/*  that the argument sequence is strictly increasing. */}}
	order = 0
	c <- n
	{{if .Maybe}}
	{{/*  Outside of select, left-to-right rule applies. */}}
	{{/*  (Inside select, assignment waits until case is chosen, */}}
	{{/*  so right hand side happens before anything on left hand side. */}}
	*fp(&x, 1) = <-fc(c, 2)
	{{else}}{{if .Maybe}}
	m[fn(13, 1)] = <-fc(c, 2)
	x = m[13]
	{{else}}
	select {
	{{/*  Blocking or non-blocking, before the receive. */}}
	{{/*  The compiler implements two-case select where one is default with custom code, */}}
	{{/*  so test the default branch both before and after the send. */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Receive from c.  Different cases are direct, indirect, :=, interface, and map assignment. */}}
	{{if .Maybe}}
	case *fp(&x, 100) = <-fc(c, 1):
	{{else}}{{if .Maybe}}
	case y := <-fc(c, 1):
		x = y
	{{else}}{{if .Maybe}}
	case i = <-fc(c, 1):
		x = i.(int)
	{{else}}
	case m[fn(13, 100)] = <-fc(c, 1):
		x = m[13]
	{{end}}{{end}}{{end}}
	{{/*  Blocking or non-blocking again, after the receive. */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Dummy send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case fc(dummy, 2) <- fn(1, 3):
		panic("dummy send")
	{{end}}
	{{if .Maybe}}
	case <-fc(dummy, 4):
		panic("dummy receive")
	{{end}}
	{{/*  Nil channel send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case fc(nilch, 5) <- fn(1, 6):
		panic("nilch send")
	{{end}}
	{{if .Maybe}}
	case <-fc(nilch, 7):
		panic("nilch recv")
	{{end}}
	}
	{{end}}{{end}}
	if x != n {
		die(x)
	}
	n++
`)

var send = parse("send", `
	{{/*  Send n one way or another, receive it into x, check that they match. */}}
	{{if .Maybe}}
	c <- n
	{{else}}
	select {
	{{/*  Blocking or non-blocking, before the receive (same reason as in recv). */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Send c <- n.  No real special cases here, because no values come back */}}
	{{/*  from the send operation. */}}
	case c <- n:
	{{/*  Blocking or non-blocking. */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Dummy send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case dummy <- 1:
		panic("dummy send")
	{{end}}
	{{if .Maybe}}
	case <-dummy:
		panic("dummy receive")
	{{end}}
	{{/*  Nil channel send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case nilch <- 1:
		panic("nilch send")
	{{end}}
	{{if .Maybe}}
	case <-nilch:
		panic("nilch recv")
	{{end}}
	}
	{{end}}
	x = <-c
	if x != n {
		die(x)
	}
	n++
`)

var sendOrder = parse("sendOrder", `
	{{/*  Send n one way or another, receive it into x, check that they match. */}}
	{{/*  Check order of operations along the way by calling functions that check */}}
	{{/*  that the argument sequence is strictly increasing. */}}
	order = 0
	{{if .Maybe}}
	fc(c, 1) <- fn(n, 2)
	{{else}}
	select {
	{{/*  Blocking or non-blocking, before the receive (same reason as in recv). */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Send c <- n.  No real special cases here, because no values come back */}}
	{{/*  from the send operation. */}}
	case fc(c, 1) <- fn(n, 2):
	{{/*  Blocking or non-blocking. */}}
	{{if .MaybeDefault}}
	default:
		panic("nonblock")
	{{end}}
	{{/*  Dummy send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case fc(dummy, 3) <- fn(1, 4):
		panic("dummy send")
	{{end}}
	{{if .Maybe}}
	case <-fc(dummy, 5):
		panic("dummy receive")
	{{end}}
	{{/*  Nil channel send, receive to keep compiler from optimizing select. */}}
	{{if .Maybe}}
	case fc(nilch, 6) <- fn(1, 7):
		panic("nilch send")
	{{end}}
	{{if .Maybe}}
	case <-fc(nilch, 8):
		panic("nilch recv")
	{{end}}
	}
	{{end}}
	x = <-c
	if x != n {
		die(x)
	}
	n++
`)

var nonblock = parse("nonblock", `
	x = n
	{{/*  Test various combinations of non-blocking operations. */}}
	{{/*  Receive assignments must not edit or even attempt to compute the address of the lhs. */}}
	select {
	{{if .MaybeDefault}}
	default:
	{{end}}
	{{if .Maybe}}
	case dummy <- 1:
		panic("dummy <- 1")
	{{end}}
	{{if .Maybe}}
	case nilch <- 1:
		panic("nilch <- 1")
	{{end}}
	{{if .Maybe}}
	case <-dummy:
		panic("<-dummy")
	{{end}}
	{{if .Maybe}}
	case x = <-dummy:
		panic("<-dummy x")
	{{end}}
	{{if .Maybe}}
	case **(**int)(nil) = <-dummy:
		panic("<-dummy (and didn't crash saving result!)")
	{{end}}
	{{if .Maybe}}
	case <-nilch:
		panic("<-nilch")
	{{end}}
	{{if .Maybe}}
	case x = <-nilch:
		panic("<-nilch x")
	{{end}}
	{{if .Maybe}}
	case **(**int)(nil) = <-nilch:
		panic("<-nilch (and didn't crash saving result!)")
	{{end}}
	{{if .MustDefault}}
	default:
	{{end}}
	}
	if x != n {
		die(x)
	}
	n++
`)

// Code for enumerating all possible paths through
// some logic.  The logic should call choose(n) when
// it wants to choose between n possibilities.
// On successive runs through the logic, choose(n)
// will return 0, 1, ..., n-1.  The helper maybe() is
// similar but returns true and then false.
//
// Given a function gen that generates an output
// using choose and maybe, code can generate all
// possible outputs using
//
//	for next() {
//		gen()
//	}

type choice struct {
	i, n int
}

var choices []choice
var cp int = -1

func maybe() bool {
	return choose(2) == 0
}

func choose(n int) int {
	if cp >= len(choices) {
		// never asked this before: start with 0.
		choices = append(choices, choice{0, n})
		cp = len(choices)
		return 0
	}
	// otherwise give recorded answer
	if n != choices[cp].n {
		panic("inconsistent choices")
	}
	i := choices[cp].i
	cp++
	return i
}

func next() bool {
	if cp < 0 {
		// start a new round
		cp = 0
		return true
	}

	// increment last choice sequence
	cp = len(choices) - 1
	for cp >= 0 && choices[cp].i == choices[cp].n-1 {
		cp--
	}
	if cp < 0 {
		choices = choices[:0]
		return false
	}
	choices[cp].i++
	choices = choices[:cp+1]
	cp = 0
	return true
}