// Copyright 2020 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.

// +build !plan9,!windows

package main

// This is for issue #42207.
// During a call to needm we could get a SIGCHLD signal
// which would itself call needm, causing a deadlock.

/*
#include <signal.h>
#include <pthread.h>
#include <sched.h>
#include <unistd.h>

extern void GoNeedM();

#define SIGNALERS 10

static void* needmSignalThread(void* p) {
	pthread_t* pt = (pthread_t*)(p);
	int i;

	for (i = 0; i < 100; i++) {
		if (pthread_kill(*pt, SIGCHLD) < 0) {
			return NULL;
		}
		usleep(1);
	}
	return NULL;
}

// We don't need many calls, as the deadlock is only likely
// to occur the first couple of times that needm is called.
// After that there will likely be an extra M available.
#define CALLS 10

static void* needmCallbackThread(void* p) {
	int i;

	for (i = 0; i < SIGNALERS; i++) {
		sched_yield(); // Help the signal threads get started.
	}
	for (i = 0; i < CALLS; i++) {
		GoNeedM();
	}
	return NULL;
}

static void runNeedmSignalThread() {
	int i;
	pthread_t caller;
	pthread_t s[SIGNALERS];

	pthread_create(&caller, NULL, needmCallbackThread, NULL);
	for (i = 0; i < SIGNALERS; i++) {
		pthread_create(&s[i], NULL, needmSignalThread, &caller);
	}
	for (i = 0; i < SIGNALERS; i++) {
		pthread_join(s[i], NULL);
	}
	pthread_join(caller, NULL);
}
*/
import "C"

import (
	"fmt"
	"os"
	"time"
)

func init() {
	register("NeedmDeadlock", NeedmDeadlock)
}

//export GoNeedM
func GoNeedM() {
}

func NeedmDeadlock() {
	// The failure symptom is that the program hangs because of a
	// deadlock in needm, so set an alarm.
	go func() {
		time.Sleep(5 * time.Second)
		fmt.Println("Hung for 5 seconds")
		os.Exit(1)
	}()

	C.runNeedmSignalThread()
	fmt.Println("OK")
}