1// Copyright 2023 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5//go:build !plan9 && !windows
6
7// Test that callbacks from C to Go in the same C-thread always get the same m.
8// Make sure the extra M bind to the C-thread.
9
10package main
11
12/*
13extern void CheckBindM();
14*/
15import "C"
16
17import (
18	"fmt"
19	"os"
20	"runtime"
21	"sync"
22	"sync/atomic"
23)
24
25var (
26	mutex      = sync.Mutex{}
27	cThreadToM = map[uintptr]uintptr{}
28	started    = atomic.Uint32{}
29)
30
31// same as CTHREADS in C, make sure all the C threads are actually started.
32const cThreadNum = 2
33
34func init() {
35	register("EnsureBindM", EnsureBindM)
36}
37
38//export GoCheckBindM
39func GoCheckBindM(thread uintptr) {
40	// Wait all threads start
41	if started.Load() != cThreadNum {
42		// Only once for each thread, since it will wait all threads start.
43		started.Add(1)
44		for started.Load() < cThreadNum {
45			runtime.Gosched()
46		}
47	}
48	m := runtime_getm_for_test()
49	mutex.Lock()
50	defer mutex.Unlock()
51	if savedM, ok := cThreadToM[thread]; ok && savedM != m {
52		fmt.Printf("m == %x want %x\n", m, savedM)
53		os.Exit(1)
54	}
55	cThreadToM[thread] = m
56}
57
58func EnsureBindM() {
59	C.CheckBindM()
60	fmt.Println("OK")
61}
62