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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

      时间:2017-10-26 来源:系统之家 作者:chunhua

        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;さ。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;は陆械。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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