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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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