6.程序同步:互斥量
阿新 • • 發佈:2018-12-18
互斥量mutex
程序間也可以使用互斥鎖,來達到同步的目的。但應在pthread_mutex_init初始化之前,修改其屬性為程序間共享。mutex的屬性修改函式主要有以下幾個。
互斥鎖API
pthread_mutexattr_t mattr 型別 //用於定義mutex鎖的【屬性】
int pthread_mutexattr_init(pthread_mutexattr_tattr); //初始化一個mutex屬性物件 int pthread_mutexattr_destroy(pthread_mutexattr_tattr); //銷燬mutex屬性物件 (而非銷燬鎖)
intpthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared); //修改mutex屬性
- 參2:pshared取值
- 執行緒鎖:PTHREAD_PROCESS_PRIVATE(mutex的預設屬性即為執行緒鎖,程序間私有)
- 程序鎖:PTHREAD_PROCESS_SHARED
示例程式碼
#include <fcntl.h> #include <pthread.h> #include <sys/mman.h> #include <sys/wait.h> struct mt { int num; pthread_mutex_t mutex; pthread_mutexattr_t mutexattr; }; int main(void) { int fd, i; struct mt *mm; pid_t pid; fd = open("mt_test", O_CREAT | O_RDWR, 0777); ftruncate(fd, sizeof(*mm)); mm = mmap(NULL, sizeof(*mm), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); close(fd); unlink("mt_test"); //mm = mmap(NULL, sizeof(*mm), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANON, -1, 0); memset(mm, 0, sizeof(*mm)); pthread_mutexattr_init(&mm->mutexattr); //初始化mutex屬性物件 pthread_mutexattr_setpshared(&mm->mutexattr, PTHREAD_PROCESS_SHARED); //修改屬性為程序間共享 pthread_mutex_init(&mm->mutex, &mm->mutexattr); //初始化一把mutex瑣 pid = fork(); if (pid == 0) { for (i = 0; i < 10; i++) { pthread_mutex_lock(&mm->mutex); (mm->num)++; printf("-child----num++ %d\n", mm->num); pthread_mutex_unlock(&mm->mutex); sleep(1); } } else if (pid > 0) { for ( i = 0; i < 10; i++) { sleep(1); pthread_mutex_lock(&mm->mutex); mm->num += 2; printf("-parent---num+=2 %d\n", mm->num); pthread_mutex_unlock(&mm->mutex); } wait(NULL); } pthread_mutexattr_destroy(&mm->mutexattr); //銷燬mutex屬性物件 pthread_mutex_destroy(&mm->mutex); //銷燬mutex munmap(mm,sizeof(*mm)); //釋放對映區 return 0; }