c - 已解决的睡眠方法将程序线程挂在 C pthreads 中(竞争条件,它与睡眠无关)
问题描述
我用 pthreads 创建了一个 C 程序,它运行良好,直到我添加任何类型的睡眠函数,无论是 sleep()、usleep() 还是 nanosleep()。
是的,在你问之前,我知道 usleep() 已被弃用,我已经从另一个 stackoferflow 帖子中复制了 nanosleep() 的正确用法,但即使 sleep() 也不起作用。
代码(关键部分在“clients”线程中,第 99 行):
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdlib.h>
#include <time.h>
#define LIBERA 0
#define OCCUPATA 1
#define TUTTE_SEDIE_OCCUPATE -1
#define OCCUPATA_DA_BARBIERE -2
#define NRCLIENTI 10
#define NRSEDIE 5
pthread_mutex_t poltrona_m, dorme_m, get_sedia_m, occupa_sedia_m;
sem_t sem;
int sedia_taglio = LIBERA, sedia_attesa[NRSEDIE];
void init_attr(void) {
int i;
for (i = 0; i < NRSEDIE; i++)
sedia_attesa[i] = LIBERA;
sem_init(&sem, 0, NRSEDIE);
pthread_mutex_unlock(&poltrona_m);
pthread_mutex_unlock(&dorme_m);
pthread_mutex_unlock(&get_sedia_m);
pthread_mutex_unlock(&occupa_sedia_m);
}
int my_sleep(long millis) {
struct timespec req, rem;
if (millis > 999) {
req.tv_sec = (int) (millis / 1000);
req.tv_nsec = (millis - ((long) req.tv_sec * 1000)) * 1000000;
} else {
req.tv_sec = 0;
req.tv_nsec = millis * 1000000;
}
return nanosleep(&req, &rem);
}
int get_sedia_libera() {
pthread_mutex_lock(&get_sedia_m);
int i;
for (i = 0; i < NRSEDIE; i++)
if (sedia_attesa[i] == LIBERA)
return i;
pthread_mutex_unlock(&get_sedia_m);
return TUTTE_SEDIE_OCCUPATE;
}
int occupa_sedia(int index) {
pthread_mutex_lock(&occupa_sedia_m);
int result;
if(sedia_attesa[index] == LIBERA){
sedia_attesa[index] = OCCUPATA;
result = 1;
}else
result = 0;
pthread_mutex_unlock(&occupa_sedia_m);
return result;
}
void libera_sedia(int index) {
sedia_attesa[index] = LIBERA;
}
void *barbiere(void *arg) {
while (1)
{
if (sedia_taglio == OCCUPATA) {
pthread_mutex_lock(&poltrona_m);
sedia_taglio = LIBERA;
pthread_mutex_unlock(&poltrona_m);
}
if (get_sedia_libera() == 0 && sedia_taglio == LIBERA) {
sedia_taglio = OCCUPATA_DA_BARBIERE;
pthread_mutex_lock(&dorme_m);
printf("[BARBIERE] il barbiere dorme...\n");
}
}
}
void *cliente(void *arg) {
int n;
int *id = (void *)arg;
while (1)
{
if (sedia_taglio == LIBERA || sedia_taglio == OCCUPATA_DA_BARBIERE) {
pthread_mutex_lock(&poltrona_m);
pthread_mutex_unlock(&dorme_m);
sedia_taglio = OCCUPATA;
printf("----[CLIENTE] Cliente \"%d\" si taglia i capelli!\n", *id);
my_sleep(2000);
sedia_taglio = LIBERA;
pthread_mutex_unlock(&poltrona_m);
pthread_exit(0);
} else {
n = get_sedia_libera();
if(n == TUTTE_SEDIE_OCCUPATE) {
fprintf(stderr, "----[CLIENTE] No posti liberi cliente \"%d\" lascia il negozio\n", *id);
pthread_exit((void *)1);
} else {
sem_wait(&sem);
n = get_sedia_libera();
if(occupa_sedia(n) && n != TUTTE_SEDIE_OCCUPATE){
printf("----[CLIENTE] Cliente \"%d\" aspetta su sedia #%d\n", *id, n+1);
while (sedia_taglio != LIBERA);
sem_post(&sem);
libera_sedia(n);
} else {
sem_post(&sem);
fprintf(stderr, "----[CLIENTE] No posti liberi cliente \"%d\" lascia il negozio\n", *id);
pthread_exit(0);
}
}
}
}
}
int main(int argc, char **argv) {
init_attr();
int i, id[NRCLIENTI];
pthread_t barbiere_thread, cliente_thread[NRCLIENTI];
if(pthread_create(&barbiere_thread, NULL, barbiere, NULL ) < 0){
fprintf(stderr, "[MAIN] Error creating \"barber\" thread!\n");
exit(EXIT_FAILURE);
}
printf("[MAIN] thread \"barber\" creato\n\n");
for (i = 0; i < NRCLIENTI; ++i) {
id[i] = i+1;
printf("[MAIN] thread \"client %d\" creato\n", id[i]);
if(pthread_create(&cliente_thread[i], NULL, cliente, &id[i]) < 0){
fprintf(stderr, "[MAIN] Error creating \"client %d\" thread!\n", id[i]);
exit(EXIT_FAILURE);
}
}
for (i = 0; i < NRCLIENTI; i++){
pthread_join(cliente_thread[i], NULL);
printf("[MAIN]Joined client \"%d\"\n", i+1);
}
//il programma non finira mai se sta ad aspettare un thread con un ciclo while(1) al suo interno
//senza condizioni di break!!!
pthread_join(barbiere_thread, NULL);
return 0;
}
正常执行(这是程序应该如何工作):
[MAIN] thread "client 1" creato
[BARBIERE] il barbiere dorme...
hey
[MAIN] thread "client 2" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "1" si taglia i capelli!
[MAIN] thread "client 3" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "2" si taglia i capelli!
[MAIN] thread "client 4" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "3" si taglia i capelli!
[MAIN] thread "client 5" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "4" si taglia i capelli!
[MAIN] thread "client 6" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "5" si taglia i capelli!
[MAIN] thread "client 7" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "6" si taglia i capelli!
[MAIN] thread "client 8" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "7" si taglia i capelli!
[MAIN] thread "client 9" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "8" si taglia i capelli!
[MAIN] thread "client 10" creato
----<<<<<<<<<<<<[CLIENTE] Cliente "9" si taglia i capelli!
----<<<<<<<<<<<<[CLIENTE] Cliente "10" si taglia i capelli!
[MAIN]Joined client "1"
[MAIN]Joined client "2"
[MAIN]Joined client "3"
[MAIN]Joined client "4"
[MAIN]Joined client "5"
[MAIN]Joined client "6"
[MAIN]Joined client "7"
[MAIN]Joined client "8"
[MAIN]Joined client "9"
[MAIN]Joined client "10"
使用任何睡眠方法执行,sleep(1),nanosleep() 1 秒或 100k 微秒 usleep() 但我不考虑 usleep() 因为a) * 它已弃用和 * b)你不能放更多或等于超过 100 万微秒;usleep(1000000) 无效
[MAIN] thread "client 1" creato
[BARBIERE] il barbiere dorme...
[MAIN] thread "client 2" creato
----[CLIENTE] Cliente "1" si taglia i capelli!
[MAIN] thread "client 3" creato
[MAIN] thread "client 4" creato
[MAIN] thread "client 5" creato
[MAIN] thread "client 6" creato
[MAIN] thread "client 7" creato
[MAIN] thread "client 8" creato
[MAIN] thread "client 9" creato
[MAIN] thread "client 10" creato
[MAIN]Joined client "1"
正如你所看到的,线程只是......停滞不前。我在终端打开的情况下等了 5 分钟,但仍然没有任何改变。 最奇怪的是,如果我使用 MinGW 在 Windows IntelliJ Clion 中运行它,sleep() 函数似乎完全被忽略了(程序在几分之一秒内自行执行)!
感谢您阅读所有这些内容,我希望我们能找到解决方案,如果我得到任何帮助,我将不胜感激!
解决方案
您会创建死锁,因为您在线程之间存在竞争条件。
pthread_mutex_t poltrona_m, dorme_m, get_sedia_m, occupa_sedia_m;
在全局范围内移动,添加这些详细函数:
const char * whoIam()
{
if (pthread_self() == barbiere_thread)
return "barbiere";
for (int i = 0; i != NRCLIENTI; ++i) {
if (pthread_self() == cliente_thread[i]) {
static char str[NRCLIENTI][64];
sprintf(str[i], "cliente %d", i+1); /* done several times but whatever */
return str[i];
}
}
return "unknown-thread";
}
const char * whoIsMutex(pthread_mutex_t * m)
{
if (m == &poltrona_m)
return "poltrona";
if (m == &dorme_m)
return "dorme";
if (m == &get_sedia_m)
return "sedia";
if (m == &occupa_sedia_m)
return "occupa_sedia";
return "unknown-mutex";
}
void my_pthread_mutex_unlock(pthread_mutex_t * m)
{
printf("%s unlock %s\n", whoIam(), whoIsMutex(m));
pthread_mutex_unlock(m);
}
void my_pthread_mutex_lock(pthread_mutex_t * m)
{
printf("%s want to lock %s\n", whoIam(), whoIsMutex(m));
pthread_mutex_lock(m);
printf("%s locked %s\n", whoIam(), whoIsMutex(m));
}
并且使用my_pthread_mutex_lock
和my_pthread_mutex_unlock
退出init_attr
执行可以是:
[MAIN] thread "barber" creato
[MAIN] thread "client 1" creato
barbiere want to lock sedia
barbiere locked sedia
barbiere want to lock dorme
barbiere locked dorme
cliente 1 want to lock poltrona
cliente 1 locked poltrona
cliente 1 unlock dorme <<< does nothing because does not have it
----[CLIENTE] Cliente "1" si taglia i capelli!
[BARBIERE] il barbiere dorme...
barbiere want to lock poltrona <<< wait while get by client 1
[MAIN] thread "client 2" creato
[MAIN] thread "client 3" creato
[MAIN] thread "client 4" creato
cliente 2 want to lock sedia
[MAIN] thread "client 5" creato
cliente 4 want to lock sedia
[MAIN] thread "client 6" creato
cliente 3 want to lock sedia
[MAIN] thread "client 7" creato
cliente 6 want to lock sedia
cliente 5 want to lock sedia
[MAIN] thread "client 8" creato
cliente 7 want to lock sedia
[MAIN] thread "client 9" creato
cliente 8 want to lock sedia
[MAIN] thread "client 10" creato
cliente 9 want to lock sedia
cliente 10 want to lock sedia
cliente 1 unlock poltrona <<< finally unlock poltrona
barbiere locked poltrona <<< wake up
barbiere unlock poltrona
barbiere want to lock sedia <<< dead because get by itself
[MAIN]Joined client "1"
在cliente中添加my_sleep(1000);
before有助于避免竞争条件:sedia_taglio = occupata;
bruno@bruno-XPS-8300:/tmp$ gcc -Wall t.c -lpthread
bruno@bruno-XPS-8300:/tmp$ ./a.out
[MAIN] thread "barber" creato
[MAIN] thread "client 1" creato
[BARBIERE] il barbiere dorme...
[MAIN] thread "client 2" creato
[MAIN] thread "client 3" creato
[MAIN] thread "client 4" creato
[MAIN] thread "client 5" creato
[MAIN] thread "client 6" creato
[MAIN] thread "client 7" creato
[MAIN] thread "client 8" creato
[MAIN] thread "client 9" creato
[MAIN] thread "client 10" creato
----[CLIENTE] Cliente "1" si taglia i capelli!
[MAIN]Joined client "1"
----[CLIENTE] Cliente "3" si taglia i capelli!
----[CLIENTE] Cliente "2" si taglia i capelli!
[MAIN]Joined client "2"
[MAIN]Joined client "3"
----[CLIENTE] Cliente "4" si taglia i capelli!
[MAIN]Joined client "4"
----[CLIENTE] Cliente "5" si taglia i capelli!
[MAIN]Joined client "5"
----[CLIENTE] Cliente "6" si taglia i capelli!
[MAIN]Joined client "6"
----[CLIENTE] Cliente "7" si taglia i capelli!
[MAIN]Joined client "7"
----[CLIENTE] Cliente "8" si taglia i capelli!
[MAIN]Joined client "8"
----[CLIENTE] Cliente "9" si taglia i capelli!
[MAIN]Joined client "9"
----[CLIENTE] Cliente "10" si taglia i capelli!
[MAIN]Joined client "10"
其中,关于sleep的方式,函数sleep会阻止所有进程,与usleep和nanosleep相反。
这里是一个没有竞争条件的提案,也没有对互斥锁实现做出假设(没有未定义的行为)。
只有一个互斥锁来保护数据的一致性,对于条件,我也用它来保护打印。
有座位等着,还有一个用来剪头发。为了按到达顺序管理客户,他们会得到一张有编号的票,当根本没有空闲座位时,客户将无法获得票,稍后将重试。CurrentTicket给出了客户剪头发的票号(作为屏幕客户端读取),并产生信号NextClient(作为哔声)以允许客户检查是否轮到他们。分配器中的票号由LastTicket管理。当客户到达理发师并可能唤醒他时,HelloBarber信号由客户发送。理发师在没有客户的时候睡觉。
我使用限制为 5 秒的随机时间来让客户(重新)尝试获得一个位置,而理发师在限制为 3 秒的随机时间内为客户剪头发。
#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <time.h>
#define NCLIENT 10
#define NSEAT 5 /* seats to wait */
unsigned int Seed;
int Nseat = NSEAT + 1; /* add 1 to have seat to cut hairs */
int CurrentTicket = 0;
int LastTicket = 0;
pthread_mutex_t Mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t NextClient = PTHREAD_COND_INITIALIZER;
pthread_cond_t HelloBarber = PTHREAD_COND_INITIALIZER;
/* return -1 is no seat, else ticket number */
int getTicket()
{
int result;
pthread_mutex_lock(&Mutex);
if (Nseat == 0)
result = -1;
else {
Nseat -= 1;
result = ++LastTicket;
}
pthread_mutex_unlock(&Mutex);
return result;
}
void randomSleep(int max)
{
int millis = rand_r(&Seed) % (max * 1000);
struct timespec req, rem;
if (millis > 999) {
req.tv_sec = (int) (millis / 1000);
req.tv_nsec = (millis - ((long) req.tv_sec * 1000)) * 1000000;
} else {
req.tv_sec = 0;
req.tv_nsec = millis * 1000000;
}
nanosleep(&req, &rem);
}
void * client(void * arg)
{
int id = *((int *) arg);
int ticket;
int justArrived = 1;
while (randomSleep(5), ((ticket = getTicket()) == -1)) {
pthread_mutex_lock(&Mutex);
printf("----[CLIENT] Client \"%d\" no place, will try again later\n", id);
pthread_mutex_unlock(&Mutex);
}
pthread_mutex_lock(&Mutex);
printf("----[CLIENT] Client \"%d\" got ticket number %d\n", id, ticket);
while (ticket != CurrentTicket) {
printf("----[CLIENT] Client \"%d\" not my turn\n", id);
if (justArrived) {
justArrived = 0;
printf("----[CLIENT] Client \"%d\" seat to wait\n", id);
}
pthread_cond_wait(&NextClient, &Mutex);
}
printf("----[CLIENT] Client \"%d\" my turn\n", id);
if (justArrived)
printf("----[CLIENT] Client \"%d\" do not need to seat to wait\n", id);
pthread_cond_signal(&HelloBarber);
pthread_cond_wait(&NextClient, &Mutex);
printf("----[CLIENT] Client \"%d\" done for me\n", id);
pthread_mutex_unlock(&Mutex);
return NULL;
}
void * barber(void * dummy)
{
pthread_mutex_lock(&Mutex);
puts("[BARBER] ready");
CurrentTicket = 1;
pthread_cond_signal(&NextClient);
for (;;) {
printf("[BARBER] screen indicates ticket %d\n", CurrentTicket);
int sleep = (Nseat == NSEAT + 1);
if (sleep)
puts("[BARBER] no client, time to sleep");
pthread_cond_wait(&HelloBarber, &Mutex); /* in all cases to be sure next client had time to see his turn */
if (sleep)
puts("[BARBER] woken up by a client");
puts("[BARBER] cutting hairs");
pthread_mutex_unlock(&Mutex);
randomSleep(3); /* time to cut hairs of current client */
pthread_mutex_lock(&Mutex);
puts("[BARBER] haircut done");
Nseat += 1;
CurrentTicket += 1;
pthread_cond_broadcast(&NextClient);
}
}
int main()
{
pthread_t barber_thread, client_thread[NCLIENT];
int i, id[NCLIENT];
Seed = time(NULL);
if (pthread_create(&barber_thread, NULL, barber, NULL ) < 0){
fprintf(stderr, "[MAIN] Error creating \"barber\" thread!\n");
exit(EXIT_FAILURE);
}
pthread_mutex_lock(&Mutex);
if (CurrentTicket == 0) {
/* wait barber ready */
pthread_cond_wait(&NextClient, &Mutex);
}
pthread_mutex_unlock(&Mutex);
for (i = 0; i < NCLIENT; ++i) {
id[i] = i+1;
if (pthread_create(&client_thread[i], NULL, client, &id[i]) < 0) {
fprintf(stderr, "[MAIN] Error creating \"client %d\" thread!\n", id[i]);
exit(EXIT_FAILURE);
}
}
for (i = 0; i < NCLIENT; i++) {
pthread_join(client_thread[i], NULL);
pthread_mutex_lock(&Mutex);
printf("[MAIN] Joined client \"%d\"\n", i+1);
pthread_mutex_unlock(&Mutex);
}
return 0;
}
编译和执行示例:
pi@raspberrypi:~ $ gcc -Wall barber.c -lpthread
pi@raspberrypi:~ $ ./a.out
[BARBER] ready
[BARBER] screen indicates ticket 1
[BARBER] no client, time to sleep
----[CLIENT] Client "7" got ticket number 1
----[CLIENT] Client "7" my turn
----[CLIENT] Client "7" do not need to seat to wait
[BARBER] woken up by a client
[BARBER] cutting hairs
----[CLIENT] Client "6" got ticket number 2
----[CLIENT] Client "6" not my turn
----[CLIENT] Client "6" seat to wait
----[CLIENT] Client "5" got ticket number 3
----[CLIENT] Client "5" not my turn
----[CLIENT] Client "5" seat to wait
----[CLIENT] Client "1" got ticket number 4
----[CLIENT] Client "1" not my turn
----[CLIENT] Client "1" seat to wait
----[CLIENT] Client "3" got ticket number 5
----[CLIENT] Client "3" not my turn
----[CLIENT] Client "3" seat to wait
[BARBER] haircut done
[BARBER] screen indicates ticket 2
----[CLIENT] Client "7" done for me
----[CLIENT] Client "3" not my turn
----[CLIENT] Client "1" not my turn
----[CLIENT] Client "6" my turn
----[CLIENT] Client "5" not my turn
[BARBER] cutting hairs
----[CLIENT] Client "9" got ticket number 6
----[CLIENT] Client "9" not my turn
----[CLIENT] Client "9" seat to wait
----[CLIENT] Client "8" got ticket number 7
----[CLIENT] Client "8" not my turn
----[CLIENT] Client "8" seat to wait
----[CLIENT] Client "4" no place, will try again later
----[CLIENT] Client "2" no place, will try again later
----[CLIENT] Client "10" no place, will try again later
[BARBER] haircut done
[BARBER] screen indicates ticket 3
----[CLIENT] Client "8" not my turn
----[CLIENT] Client "5" my turn
----[CLIENT] Client "9" not my turn
----[CLIENT] Client "1" not my turn
----[CLIENT] Client "6" done for me
[BARBER] cutting hairs
----[CLIENT] Client "3" not my turn
[BARBER] haircut done
[BARBER] screen indicates ticket 4
----[CLIENT] Client "9" not my turn
----[CLIENT] Client "1" my turn
----[CLIENT] Client "3" not my turn
----[CLIENT] Client "5" done for me
----[CLIENT] Client "8" not my turn
[BARBER] cutting hairs
[BARBER] haircut done
[BARBER] screen indicates ticket 5
----[CLIENT] Client "8" not my turn
----[CLIENT] Client "1" done for me
[MAIN] Joined client "1"
----[CLIENT] Client "9" not my turn
----[CLIENT] Client "3" my turn
[BARBER] cutting hairs
----[CLIENT] Client "10" got ticket number 8
----[CLIENT] Client "10" not my turn
----[CLIENT] Client "10" seat to wait
----[CLIENT] Client "2" got ticket number 9
----[CLIENT] Client "2" not my turn
----[CLIENT] Client "2" seat to wait
----[CLIENT] Client "4" got ticket number 10
----[CLIENT] Client "4" not my turn
----[CLIENT] Client "4" seat to wait
[BARBER] haircut done
[BARBER] screen indicates ticket 6
----[CLIENT] Client "2" not my turn
----[CLIENT] Client "3" done for me
----[CLIENT] Client "4" not my turn
----[CLIENT] Client "8" not my turn
----[CLIENT] Client "9" my turn
----[CLIENT] Client "10" not my turn
[BARBER] cutting hairs
[BARBER] haircut done
[BARBER] screen indicates ticket 7
----[CLIENT] Client "2" not my turn
----[CLIENT] Client "9" done for me
----[CLIENT] Client "4" not my turn
----[CLIENT] Client "8" my turn
[BARBER] cutting hairs
----[CLIENT] Client "10" not my turn
[BARBER] haircut done
[BARBER] screen indicates ticket 8
----[CLIENT] Client "10" my turn
[BARBER] cutting hairs
----[CLIENT] Client "2" not my turn
----[CLIENT] Client "8" done for me
----[CLIENT] Client "4" not my turn
[BARBER] haircut done
[BARBER] screen indicates ticket 9
----[CLIENT] Client "10" done for me
----[CLIENT] Client "2" my turn
----[CLIENT] Client "4" not my turn
[BARBER] cutting hairs
[BARBER] haircut done
[BARBER] screen indicates ticket 10
----[CLIENT] Client "2" done for me
----[CLIENT] Client "4" my turn
[BARBER] cutting hairs
[MAIN] Joined client "2"
[MAIN] Joined client "3"
[BARBER] haircut done
[BARBER] screen indicates ticket 11
[BARBER] no client, time to sleep
----[CLIENT] Client "4" done for me
[MAIN] Joined client "4"
[MAIN] Joined client "5"
[MAIN] Joined client "6"
[MAIN] Joined client "7"
[MAIN] Joined client "8"
[MAIN] Joined client "9"
[MAIN] Joined client "10"
pi@raspberrypi:~ $
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