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线程同步的方法有哪些?Linux下实现线程同步的三种方法

  线程同步的方法有哪些?在linux下,系统提供了很多种方式来实现线程同步,其中最常用的便是互斥锁、条件变量和信号量这三种方式,可能还有很多伙伴对于这三种方法都不熟悉,下面就给大家详细介绍下。

线程同步的方法有哪些?Linux下实现线程同步的三种方法

  Linux下实现线程同步的三种方法:

  一、互斥锁(mutex)

  通过锁机制实现线程间的同步。

  1、初始化锁。在Linux下,线程的互斥量数据类型是pthread_mutex_t。在使用前,要对它进行初始化。

  静态分配:pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

  动态分配:int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutex_attr_t *mutexattr);

  2、加锁。对共享资源的访问,要对互斥量进行加锁,如果互斥量已经上了锁,调用线程会阻塞,直到互斥量被解锁。

  int pthread_mutex_lock(pthread_mutex *mutex);

  int pthread_mutex_trylock(pthread_mutex_t *mutex);

  3、解锁。在完成了对共享资源的访问后,要对互斥量进行解锁。

  int pthread_mutex_unlock(pthread_mutex_t *mutex);

  4、销毁锁。锁在是使用完成后,需要进行销毁以释放资源。

  int pthread_mutex_destroy(pthread_mutex *mutex);

  1. 01#include <cstdio>
  2. 02#include <cstdlib>
  3. 03#include <unistd.h>
  4. 04#include <pthread.h>
  5. 05#include "iostream"
  6. 06using namespace std;
  7. 07pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
  8. 08int tmp;
  9. 09void* thread(void *arg)
  10. 10{
  11. 11cout << "thread id is " << pthread_self() << endl;
  12. 12pthread_mutex_lock(&mutex);
  13. 13tmp = 12;
  14. 14cout << "Now a is " << tmp << endl;
  15. 15pthread_mutex_unlock(&mutex);
  16. 16return NULL;
  17. 17}
  18. 18int main()
  19. 19{
  20. 20pthread_t id;
  21. 21cout << "main thread id is " << pthread_self() << endl;
  22. 22tmp = 3;
  23. 23cout << "In main func tmp = " << tmp << endl;
  24. 24if (!pthread_create(&id, NULL, thread, NULL))
  25. 25{
  26. 26cout << "Create thread success!" << endl;
  27. 27}
  28. 28else
  29. 29{
  30. 30cout << "Create thread failed!" << endl;
  31. 31}
  32. 32pthread_join(id, NULL);
  33. 33pthread_mutex_destroy(&mutex);
  34. 34return 0;
  35. 35}
  36. 36//编译:g++ -o thread testthread.cpp -lpthread

复制代码

#include <cstdio>
#include <cstdlib>
#include <unistd.h>
#include <pthread.h>
#include "iostream"
using namespace std;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int tmp;
void* thread(void *arg)
{
cout << "thread id is " << pthread_self() << endl;
pthread_mutex_lock(&mutex);
tmp = 12;
cout << "Now a is " << tmp << endl;
pthread_mutex_unlock(&mutex);
return NULL;
}
int main()
{
pthread_t id;
cout << "main thread id is " << pthread_self() << endl;
tmp = 3;
cout << "In main func tmp = " << tmp << endl;
if (!pthread_create(&id, NULL, thread, NULL))
{
cout << "Create thread success!" << endl;
}
else
{
cout << "Create thread failed!" << endl;
}
pthread_join(id, NULL);
pthread_mutex_destroy(&mutex);
return 0;
}
//编译:g++ -o thread testthread.cpp -lpthread

  二、条件变量(cond)

  与互斥锁不同,条件变量是用来等待而不是用来上锁的。条件变量用来自动阻塞一个线程,直到某特殊情况发生为止。通常条件变量和互斥锁同时使用。条件变量分为两部分: 条件和变量。条件本身是由互斥量保护的。线程在改变条件状态前先要锁住互斥量。条件变量使我们可以睡眠等待某种条件出现。条件变量是利用线程间共享的全局变量进行同步的一种机制,主要包括两个动作:一个线程等待“条件变量的条件成立”而挂起;另一个线程使“条件成立”(给出条件成立信号)。条件的检测是在互斥锁的保护下进行的。如果一个条件为假,一个线程自动阻塞,并释放等待状态改变的互斥锁。如果另一个线程改变了条件,它发信号给关联的条件变量,唤醒一个或多个等待它的线程,重新获得互斥锁,重新评价条件。如果两进程共享可读写的内存,条件变量可以被用来实现这两进程间的线程同步。

  1、初始化条件变量。

  静态态初始化,pthread_cond_t cond = PTHREAD_COND_INITIALIER;

  动态初始化,int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);

  2、等待条件成立。释放锁,同时阻塞等待条件变量为真才行。timewait()设置等待时间,仍未signal,返回ETIMEOUT(加锁保证只有一个线程wait)

  int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

  int pthread_cond_timewait(pthread_cond_t *cond,pthread_mutex *mutex,const timespec *abstime);

  4、激活条件变量。pthread_cond_signal,pthread_cond_broadcast(激活所有等待线程)

  int pthread_cond_signal(pthread_cond_t *cond);

  int pthread_cond_broadcast(pthread_cond_t *cond); //解除所有线程的阻塞

  5、清除条件变量。无线程等待,否则返回EBUSY

  int pthread_cond_destroy(pthread_cond_t *cond);

  1. 01[cpp] view plain copy
  2. 02#include <stdio.h>
  3. 03#include <pthread.h>
  4. 04#include "stdlib.h"
  5. 05#include "unistd.h"
  6. 06pthread_mutex_t mutex;
  7. 07pthread_cond_t cond;
  8. 08void hander(void *arg)
  9. 09{
  10. 10free(arg);
  11. 11(void)pthread_mutex_unlock(&mutex);
  12. 12}
  13. 13void *thread1(void *arg)
  14. 14{
  15. 15pthread_cleanup_push(hander, &mutex);
  16. 16while(1)
  17. 17{
  18. 18printf("thread1 is running\n");
  19. 19pthread_mutex_lock(&mutex);
  20. 20pthread_cond_wait(&cond, &mutex);
  21. 21printf("thread1 applied the condition\n");
  22. 22pthread_mutex_unlock(&mutex);
  23. 23sleep(4);
  24. 24}
  25. 25pthread_cleanup_pop(0);
  26. 26}
  27. 27void *thread2(void *arg)
  28. 28{
  29. 29while(1)
  30. 30{
  31. 31printf("thread2 is running\n");
  32. 32pthread_mutex_lock(&mutex);
  33. 33pthread_cond_wait(&cond, &mutex);
  34. 34printf("thread2 applied the condition\n");
  35. 35pthread_mutex_unlock(&mutex);
  36. 36sleep(1);
  37. 37}
  38. 38}
  39. 39int main()
  40. 40{
  41. 41pthread_t thid1,thid2;
  42. 42printf("condition variable study!\n");
  43. 43pthread_mutex_init(&mutex, NULL);
  44. 44pthread_cond_init(&cond, NULL);
  45. 45pthread_create(&thid1, NULL, thread1, NULL);
  46. 46pthread_create(&thid2, NULL, thread2, NULL);
  47. 47sleep(1);
  48. 48do
  49. 49{
  50. 50pthread_cond_signal(&cond);
  51. 51}while(1);
  52. 52sleep(20);
  53. 53pthread_exit(0);
  54. 54return 0;
  55. 55}

复制代码

[cpp] view plain copy
#include <stdio.h>
#include <pthread.h>
#include "stdlib.h"
#include "unistd.h"
pthread_mutex_t mutex;
pthread_cond_t cond;
void hander(void *arg)
{
free(arg);
(void)pthread_mutex_unlock(&mutex);
}
void *thread1(void *arg)
{
pthread_cleanup_push(hander, &mutex);
while(1)
{
printf("thread1 is running\n");
pthread_mutex_lock(&mutex);
pthread_cond_wait(&cond, &mutex);
printf("thread1 applied the condition\n");
pthread_mutex_unlock(&mutex);
sleep(4);
}
pthread_cleanup_pop(0);
}
void *thread2(void *arg)
{
while(1)
{
printf("thread2 is running\n");
pthread_mutex_lock(&mutex);
pthread_cond_wait(&cond, &mutex);
printf("thread2 applied the condition\n");
pthread_mutex_unlock(&mutex);
sleep(1);
}
}
int main()
{
pthread_t thid1,thid2;
printf("condition variable study!\n");
pthread_mutex_init(&mutex, NULL);
pthread_cond_init(&cond, NULL);
pthread_create(&thid1, NULL, thread1, NULL);
pthread_create(&thid2, NULL, thread2, NULL);
sleep(1);
do
{
pthread_cond_signal(&cond);
}while(1);
sleep(20);
pthread_exit(0);
return 0;
}

  1. 01#include <pthread.h>
  2. 02#include <unistd.h>
  3. 03#include "stdio.h"
  4. 04#include "stdlib.h"
  5. 05static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
  6. 06static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
  7. 07struct node
  8. 08{
  9. 09int n_number;
  10. 10struct node *n_next;
  11. 11}*head = NULL;
  12. 12static void cleanup_handler(void *arg)
  13. 13{
  14. 14printf("Cleanup handler of second thread./n");
  15. 15free(arg);
  16. 16(void)pthread_mutex_unlock(&mtx);
  17. 17}
  18. 18static void *thread_func(void *arg)
  19. 19{
  20. 20struct node *p = NULL;
  21. 21pthread_cleanup_push(cleanup_handler, p);
  22. 22while (1)
  23. 23{
  24. 24//这个mutex主要是用来保证pthread_cond_wait的并发性
  25. 25pthread_mutex_lock(&mtx);
  26. 26while (head == NULL)
  27. 27{
  28. 28//这个while要特别说明一下,单个pthread_cond_wait功能很完善,为何
  29. 29//这里要有一个while (head == NULL)呢?因为pthread_cond_wait里的线
  30. 30//程可能会被意外唤醒,如果这个时候head != NULL,则不是我们想要的情况。
  31. 31//这个时候,应该让线程继续进入pthread_cond_wait
  32. 32// pthread_cond_wait会先解除之前的pthread_mutex_lock锁定的mtx,
  33. 33//然后阻塞在等待对列里休眠,直到再次被唤醒(大多数情况下是等待的条件成立
  34. 34//而被唤醒,唤醒后,该进程会先锁定先pthread_mutex_lock(&mtx);,再读取资源
  35. 35//用这个流程是比较清楚的
  36. 36pthread_cond_wait(&cond, &mtx);
  37. 37p = head;
  38. 38head = head->n_next;
  39. 39printf("Got %d from front of queue/n", p->n_number);
  40. 40free(p);
  41. 41}
  42. 42pthread_mutex_unlock(&mtx); //临界区数据操作完毕,释放互斥锁
  43. 43}
  44. 44pthread_cleanup_pop(0);
  45. 45return 0;
  46. 46}
  47. 47int main(void)
  48. 48{
  49. 49pthread_t tid;
  50. 50int i;
  51. 51struct node *p;
  52. 52//子线程会一直等待资源,类似生产者和消费者,但是这里的消费者可以是多个消费者,而
  53. 53//不仅仅支持普通的单个消费者,这个模型虽然简单,但是很强大
  54. 54pthread_create(&tid, NULL, thread_func, NULL);
  55. 55sleep(1);
  56. 56for (i = 0; i < 10; i++)
  57. 57{
  58. 58p = (struct node*)malloc(sizeof(struct node));
  59. 59p->n_number = i;
  60. 60pthread_mutex_lock(&mtx); //需要操作head这个临界资源,先加锁,
  61. 61p->n_next = head;
  62. 62head = p;
  63. 63pthread_cond_signal(&cond);
  64. 64pthread_mutex_unlock(&mtx); //解锁
  65. 65sleep(1);
  66. 66}
  67. 67printf("thread 1 wanna end the line.So cancel thread 2./n");
  68. 68//关于pthread_cancel,有一点额外的说明,它是从外部终止子线程,子线程会在最近的取消点,退出
  69. 69//线程,而在我们的代码里,最近的取消点肯定就是pthread_cond_wait()了。
  70. 70pthread_cancel(tid);
  71. 71pthread_join(tid, NULL);
  72. 72printf("All done — exiting/n");
  73. 73return 0;
  74. 74}

复制代码

#include <pthread.h>
#include <unistd.h>
#include "stdio.h"
#include "stdlib.h"
static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
struct node
{
int n_number;
struct node *n_next;
}*head = NULL;
static void cleanup_handler(void *arg)
{
printf("Cleanup handler of second thread./n");
free(arg);
(void)pthread_mutex_unlock(&mtx);
}
static void *thread_func(void *arg)
{
struct node *p = NULL;
pthread_cleanup_push(cleanup_handler, p);
while (1)
{
//这个mutex主要是用来保证pthread_cond_wait的并发性
pthread_mutex_lock(&mtx);
while (head == NULL)
{
//这个while要特别说明一下,单个pthread_cond_wait功能很完善,为何
//这里要有一个while (head == NULL)呢?因为pthread_cond_wait里的线
//程可能会被意外唤醒,如果这个时候head != NULL,则不是我们想要的情况。
//这个时候,应该让线程继续进入pthread_cond_wait
// pthread_cond_wait会先解除之前的pthread_mutex_lock锁定的mtx,
//然后阻塞在等待对列里休眠,直到再次被唤醒(大多数情况下是等待的条件成立
//而被唤醒,唤醒后,该进程会先锁定先pthread_mutex_lock(&mtx);,再读取资源
//用这个流程是比较清楚的
pthread_cond_wait(&cond, &mtx);
p = head;
head = head->n_next;
printf("Got %d from front of queue/n", p->n_number);
free(p);
}
pthread_mutex_unlock(&mtx); //临界区数据操作完毕,释放互斥锁
}
pthread_cleanup_pop(0);
return 0;
}
int main(void)
{
pthread_t tid;
int i;
struct node *p;
//子线程会一直等待资源,类似生产者和消费者,但是这里的消费者可以是多个消费者,而
//不仅仅支持普通的单个消费者,这个模型虽然简单,但是很强大
pthread_create(&tid, NULL, thread_func, NULL);
sleep(1);
for (i = 0; i < 10; i++)
{
p = (struct node*)malloc(sizeof(struct node));
p->n_number = i;
pthread_mutex_lock(&mtx); //需要操作head这个临界资源,先加锁,
p->n_next = head;
head = p;
pthread_cond_signal(&cond);
pthread_mutex_unlock(&mtx); //解锁
sleep(1);
}
printf("thread 1 wanna end the line.So cancel thread 2./n");
//关于pthread_cancel,有一点额外的说明,它是从外部终止子线程,子线程会在最近的取消点,退出
//线程,而在我们的代码里,最近的取消点肯定就是pthread_cond_wait()了。
pthread_cancel(tid);
pthread_join(tid, NULL);
printf("All done — exiting/n");
return 0;
}

  三、信号量(sem)

  如同进程一样,线程也可以通过信号量来实现通信,虽然是轻量级的。信号量函数的名字都以“sem_”打头。线程使用的基本信号量函数有四个。

  1、信号量初始化。

  int sem_init (sem_t *sem , int pshared, unsigned int value);

  这是对由sem指定的信号量进行初始化,设置好它的共享选项(linux 只支持为0,即表示它是当前进程的局部信号量),然后给它一个初始值VALUE。

  2、等待信号量。给信号量减1,然后等待直到信号量的值大于0。

  int sem_wait(sem_t *sem);

  3、释放信号量。信号量值加1。并通知其他等待线程。

  int sem_post(sem_t *sem);

  4、销毁信号量。我们用完信号量后都它进行清理。归还占有的一切资源。

  int sem_destroy(sem_t *sem);

  1. 01#include <stdlib.h>
  2. 02#include <stdio.h>
  3. 03#include <unistd.h>
  4. 04#include <pthread.h>
  5. 05#include <semaphore.h>
  6. 06#include <errno.h>
  7. 07#define return_if_fail(p) if((p) == 0){printf ("[%s]:func error!/n", __func__);return;}
  8. 08typedef struct _PrivInfo
  9. 09{
  10. 10sem_t s1;
  11. 11sem_t s2;
  12. 12time_t end_time;
  13. 13}PrivInfo;
  14. 14static void info_init (PrivInfo* thiz);
  15. 15static void info_destroy (PrivInfo* thiz);
  16. 16static void* pthread_func_1 (PrivInfo* thiz);
  17. 17static void* pthread_func_2 (PrivInfo* thiz);
  18. 18int main (int argc, char** argv)
  19. 19{
  20. 20pthread_t pt_1 = 0;
  21. 21pthread_t pt_2 = 0;
  22. 22int ret = 0;
  23. 23PrivInfo* thiz = NULL;
  24. 24thiz = (PrivInfo* )malloc (sizeof (PrivInfo));
  25. 25if (thiz == NULL)
  26. 26{
  27. 27printf ("[%s]: Failed to malloc priv./n");
  28. 28return -1;
  29. 29}
  30. 30info_init (thiz);
  31. 31ret = pthread_create (&pt_1, NULL, (void*)pthread_func_1, thiz);
  32. 32if (ret != 0)
  33. 33{
  34. 34perror ("pthread_1_create:");
  35. 35}
  36. 36ret = pthread_create (&pt_2, NULL, (void*)pthread_func_2, thiz);
  37. 37if (ret != 0)
  38. 38{
  39. 39perror ("pthread_2_create:");
  40. 40}
  41. 41pthread_join (pt_1, NULL);
  42. 42pthread_join (pt_2, NULL);
  43. 43info_destroy (thiz);
  44. 44return 0;
  45. 45}
  46. 46static void info_init (PrivInfo* thiz)
  47. 47{
  48. 48return_if_fail (thiz != NULL);
  49. 49thiz->end_time = time(NULL) + 10;
  50. 50sem_init (&thiz->s1, 0, 1);
  51. 51sem_init (&thiz->s2, 0, 0);
  52. 52return;
  53. 53}
  54. 54static void info_destroy (PrivInfo* thiz)
  55. 55{
  56. 56return_if_fail (thiz != NULL);
  57. 57sem_destroy (&thiz->s1);
  58. 58sem_destroy (&thiz->s2);
  59. 59free (thiz);
  60. 60thiz = NULL;
  61. 61return;
  62. 62}
  63. 63static void* pthread_func_1 (PrivInfo* thiz)
  64. 64{
  65. 65return_if_fail(thiz != NULL);
  66. 66while (time(NULL) < thiz->end_time)
  67. 67{
  68. 68sem_wait (&thiz->s2);
  69. 69printf ("pthread1: pthread1 get the lock./n");
  70. 70sem_post (&thiz->s1);
  71. 71printf ("pthread1: pthread1 unlock/n");
  72. 72sleep (1);
  73. 73}
  74. 74return;
  75. 75}
  76. 76static void* pthread_func_2 (PrivInfo* thiz)
  77. 77{
  78. 78return_if_fail (thiz != NULL);
  79. 79while (time (NULL) < thiz->end_time)
  80. 80{
  81. 81sem_wait (&thiz->s1);
  82. 82printf ("pthread2: pthread2 get the unlock./n");
  83. 83sem_post (&thiz->s2);
  84. 84printf ("pthread2: pthread2 unlock./n");
  85. 85sleep (1);
  86. 86}
  87. 87return;
  88. 88}

复制代码

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <errno.h>
#define return_if_fail(p) if((p) == 0){printf ("[%s]:func error!/n", __func__);return;}
typedef struct _PrivInfo
{
sem_t s1;
sem_t s2;
time_t end_time;
}PrivInfo;
static void info_init (PrivInfo* thiz);
static void info_destroy (PrivInfo* thiz);
static void* pthread_func_1 (PrivInfo* thiz);
static void* pthread_func_2 (PrivInfo* thiz);
int main (int argc, char** argv)
{
pthread_t pt_1 = 0;
pthread_t pt_2 = 0;
int ret = 0;
PrivInfo* thiz = NULL;
thiz = (PrivInfo* )malloc (sizeof (PrivInfo));
if (thiz == NULL)
{
printf ("[%s]: Failed to malloc priv./n");
return -1;
}
info_init (thiz);
ret = pthread_create (&pt_1, NULL, (void*)pthread_func_1, thiz);
if (ret != 0)
{
perror ("pthread_1_create:");
}
ret = pthread_create (&pt_2, NULL, (void*)pthread_func_2, thiz);
if (ret != 0)
{
perror ("pthread_2_create:");
}
pthread_join (pt_1, NULL);
pthread_join (pt_2, NULL);
info_destroy (thiz);
return 0;
}
static void info_init (PrivInfo* thiz)
{
return_if_fail (thiz != NULL);
thiz->end_time = time(NULL) + 10;
sem_init (&thiz->s1, 0, 1);
sem_init (&thiz->s2, 0, 0);
return;
}
static void info_destroy (PrivInfo* thiz)
{
return_if_fail (thiz != NULL);
sem_destroy (&thiz->s1);
sem_destroy (&thiz->s2);
free (thiz);
thiz = NULL;
return;
}
static void* pthread_func_1 (PrivInfo* thiz)
{
return_if_fail(thiz != NULL);
while (time(NULL) < thiz->end_time)
{
sem_wait (&thiz->s2);
printf ("pthread1: pthread1 get the lock./n");
sem_post (&thiz->s1);
printf ("pthread1: pthread1 unlock/n");
sleep (1);
}
return;
}
static void* pthread_func_2 (PrivInfo* thiz)
{
return_if_fail (thiz != NULL);
while (time (NULL) < thiz->end_time)
{
sem_wait (&thiz->s1);
printf ("pthread2: pthread2 get the unlock./n");
sem_post (&thiz->s2);
printf ("pthread2: pthread2 unlock./n");
sleep (1);
}
return;
}

  以上便是Linux下实现线程同步常用的三种方法,大家都知道,线程的最大的亮点便是资源共享性,而资源共享中的线程同步问题却是一大难点,希望小编的归纳能够对大家有所帮助!

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文章名称:《线程同步的方法有哪些?Linux下实现线程同步的三种方法》
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