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線程同步的方法有哪些?Linux下實現線程同步的三種方法

時間:2017-10-26 來源:系統之家 作者:chunhua

  線程同步的方法有哪些?在linux下,系統提供了很多種方式來實現線程同步,其中最常用的便是互斥鎖、條件變量和信號量這三種方式,可能還有很多伙伴對于這三種方法都不熟悉,下面就給大家詳細介紹下。

線程同步的方法有哪些?Linux下實現線程同步的三種方法

  Linux下實現線程同步的三種方法:

  一、互斥鎖(mutex)

  通過鎖機制實現線程間的同步。

  1、初始化鎖。在Linux下,線程的互斥量數據類型是pthread_mutex_t。在使用前,要對它進行初始化。

  靜態分配:pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

  動態分配:int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutex_attr_t *mutexattr);

  2、加鎖。對共享資源的訪問,要對互斥量進行加鎖,如果互斥量已經上了鎖,調用線程會阻塞,直到互斥量被解鎖。

  int pthread_mutex_lock(pthread_mutex *mutex);

  int pthread_mutex_trylock(pthread_mutex_t *mutex);

  3、解鎖。在完成了對共享資源的訪問后,要對互斥量進行解鎖。

  int pthread_mutex_unlock(pthread_mutex_t *mutex);

  4、銷毀鎖。鎖在是使用完成后,需要進行銷毀以釋放資源。

  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//編譯:g++ -o thread testthread.cpp -lpthread
復制代碼
#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; } //編譯:g++ -o thread testthread.cpp -lpthread

  二、條件變量(cond)

  與互斥鎖不同,條件變量是用來等待而不是用來上鎖的。條件變量用來自動阻塞一個線程,直到某特殊情況發生為止。通常條件變量和互斥鎖同時使用。條件變量分為兩部分: 條件和變量。條件本身是由互斥量保護的。線程在改變條件狀態前先要鎖住互斥量。條件變量使我們可以睡眠等待某種條件出現。條件變量是利用線程間共享的全局變量進行同步的一種機制,主要包括兩個動作:一個線程等待“條件變量的條件成立”而掛起;另一個線程使“條件成立”(給出條件成立信號)。條件的檢測是在互斥鎖的保護下進行的。如果一個條件為假,一個線程自動阻塞,并釋放等待狀態改變的互斥鎖。如果另一個線程改變了條件,它發信號給關聯的條件變量,喚醒一個或多個等待它的線程,重新獲得互斥鎖,重新評價條件。如果兩進程共享可讀寫的內存,條件變量可以被用來實現這兩進程間的線程同步。

  1、初始化條件變量。

  靜態態初始化,pthread_cond_t cond = PTHREAD_COND_INITIALIER;

  動態初始化,int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);

  2、等待條件成立。釋放鎖,同時阻塞等待條件變量為真才行。timewait()設置等待時間,仍未signal,返回ETIMEOUT(加鎖保證只有一個線程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、激活條件變量。pthread_cond_signal,pthread_cond_broadcast(激活所有等待線程)

  int pthread_cond_signal(pthread_cond_t *cond);

  int pthread_cond_broadcast(pthread_cond_t *cond); //解除所有線程的阻塞

  5、清除條件變量。無線程等待,否則返回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}
復制代碼
[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//這個mutex主要是用來保證pthread_cond_wait的并發性
  25. 25pthread_mutex_lock(&mtx);
  26. 26while (head == NULL)
  27. 27{
  28. 28//這個while要特別說明一下,單個pthread_cond_wait功能很完善,為何
  29. 29//這里要有一個while (head == NULL)呢?因為pthread_cond_wait里的線
  30. 30//程可能會被意外喚醒,如果這個時候head != NULL,則不是我們想要的情況。
  31. 31//這個時候,應該讓線程繼續進入pthread_cond_wait
  32. 32// pthread_cond_wait會先解除之前的pthread_mutex_lock鎖定的mtx,
  33. 33//然后阻塞在等待對列里休眠,直到再次被喚醒(大多數情況下是等待的條件成立
  34. 34//而被喚醒,喚醒后,該進程會先鎖定先pthread_mutex_lock(&mtx);,再讀取資源
  35. 35//用這個流程是比較清楚的
  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); //臨界區數據操作完畢,釋放互斥鎖
  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//子線程會一直等待資源,類似生產者和消費者,但是這里的消費者可以是多個消費者,而
  53. 53//不僅僅支持普通的單個消費者,這個模型雖然簡單,但是很強大
  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這個臨界資源,先加鎖,
  61. 61p->n_next = head;
  62. 62head = p;
  63. 63pthread_cond_signal(&cond);
  64. 64pthread_mutex_unlock(&mtx); //解鎖
  65. 65sleep(1);
  66. 66}
  67. 67printf("thread 1 wanna end the line.So cancel thread 2./n");
  68. 68//關于pthread_cancel,有一點額外的說明,它是從外部終止子線程,子線程會在最近的取消點,退出
  69. 69//線程,而在我們的代碼里,最近的取消點肯定就是pthread_cond_wait()了。
  70. 70pthread_cancel(tid);
  71. 71pthread_join(tid, NULL);
  72. 72printf("All done -- exiting/n");
  73. 73return 0;
  74. 74}
復制代碼
#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) { //這個mutex主要是用來保證pthread_cond_wait的并發性 pthread_mutex_lock(&mtx); while (head == NULL) { //這個while要特別說明一下,單個pthread_cond_wait功能很完善,為何 //這里要有一個while (head == NULL)呢?因為pthread_cond_wait里的線 //程可能會被意外喚醒,如果這個時候head != NULL,則不是我們想要的情況。 //這個時候,應該讓線程繼續進入pthread_cond_wait // pthread_cond_wait會先解除之前的pthread_mutex_lock鎖定的mtx, //然后阻塞在等待對列里休眠,直到再次被喚醒(大多數情況下是等待的條件成立 //而被喚醒,喚醒后,該進程會先鎖定先pthread_mutex_lock(&mtx);,再讀取資源 //用這個流程是比較清楚的 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); //臨界區數據操作完畢,釋放互斥鎖 } pthread_cleanup_pop(0); return 0; } int main(void) { pthread_t tid; int i; struct node *p; //子線程會一直等待資源,類似生產者和消費者,但是這里的消費者可以是多個消費者,而 //不僅僅支持普通的單個消費者,這個模型雖然簡單,但是很強大 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這個臨界資源,先加鎖, p->n_next = head; head = p; pthread_cond_signal(&cond); pthread_mutex_unlock(&mtx); //解鎖 sleep(1); } printf("thread 1 wanna end the line.So cancel thread 2./n"); //關于pthread_cancel,有一點額外的說明,它是從外部終止子線程,子線程會在最近的取消點,退出 //線程,而在我們的代碼里,最近的取消點肯定就是pthread_cond_wait()了。 pthread_cancel(tid); pthread_join(tid, NULL); printf("All done -- exiting/n"); return 0; }

  三、信號量(sem)

  如同進程一樣,線程也可以通過信號量來實現通信,雖然是輕量級的。信號量函數的名字都以“sem_”打頭。線程使用的基本信號量函數有四個。

  1、信號量初始化。

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

  這是對由sem指定的信號量進行初始化,設置好它的共享選項(linux 只支持為0,即表示它是當前進程的局部信號量),然后給它一個初始值VALUE。

  2、等待信號量。給信號量減1,然后等待直到信號量的值大于0。

  int sem_wait(sem_t *sem);

  3、釋放信號量。信號量值加1。并通知其他等待線程。

  int sem_post(sem_t *sem);

  4、銷毀信號量。我們用完信號量后都它進行清理。歸還占有的一切資源。

  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}
復制代碼
#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下實現線程同步常用的三種方法,大家都知道,線程的最大的亮點便是資源共享性,而資源共享中的線程同步問題卻是一大難點,希望小編的歸納能夠對大家有所幫助!

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