mutex 相关问题

我需要一些帮助来理解如何在 C 中使用条件变量来解决练习。这是一个小例子： #包括 #包括 #包括我需要一些帮助来理解如何在 C 中使用条件变量来解决练习。这是一个小例子： #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <pthread.h> #include <string.h> #include <errno.h> #include <sys/types.h> #include <sys/mman.h> #include <sys/stat.h> #include <fcntl.h> #define OKTOWRITE "/oktowrite" #define MESSAGE "/message" #define MUTEX "/lock" int main(int argc, char** argv) { pthread_cond_t* condition; pthread_mutex_t *mutex; char* message; int des_cond, des_msg, des_mutex; int mode = S_IRWXU | S_IRWXG; des_mutex = shm_open(MUTEX, O_CREAT | O_RDWR | O_TRUNC, mode); if (des_mutex < 0) { perror("failure on shm_open on des_mutex"); exit(1); } if (ftruncate(des_mutex, sizeof(pthread_mutex_t)) == -1) { perror("Error on ftruncate to sizeof pthread_cond_t\n"); exit(-1); } mutex = (pthread_mutex_t*) mmap(NULL, sizeof(pthread_mutex_t), PROT_READ | PROT_WRITE, MAP_SHARED, des_mutex, 0); if (mutex == MAP_FAILED ) { perror("Error on mmap on mutex\n"); exit(1); } pthread_mutex_init(mutex, NULL ); des_cond = shm_open(OKTOWRITE, O_CREAT | O_RDWR | O_TRUNC, mode); if (des_cond < 0) { perror("failure on shm_open on des_cond"); exit(1); } if (ftruncate(des_cond, sizeof(pthread_cond_t)) == -1) { perror("Error on ftruncate to sizeof pthread_cond_t\n"); exit(-1); } condition = (pthread_cond_t*) mmap(NULL, sizeof(pthread_cond_t), PROT_READ | PROT_WRITE, MAP_SHARED, des_cond, 0); if (condition == MAP_FAILED ) { perror("Error on mmap on condition\n"); exit(1); } pthread_cond_init(condition, NULL ); if (!fork()) { sleep(3); pthread_mutex_lock(mutex); pthread_cond_signal(condition); pthread_mutex_unlock(mutex); printf("son signaled\n"); exit(0); } else { printf("wait on condition\n"); pthread_mutex_lock(mutex); pthread_cond_wait(condition, mutex); pthread_mutex_unlock(mutex); printf("Signaled by son process, wake up\n"); pthread_mutex_destroy(mutex); pthread_cond_destroy(condition); shm_unlink(OKTOWRITE); shm_unlink(MESSAGE); shm_unlink(MUTEX); return 0; } } 问题是进程的父亲继续被锁定，即使在儿子发出信号之后也是如此。一切都在共享内存中（使用shm_open和mmap）所以两个进程的条件应该相同。在调用 wait 或 signal 之前锁定互斥锁可能是我犯了一个错误吗？编辑：感谢所有帮助过我的人。这是标有关键部分的正确代码： #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <pthread.h> #include <string.h> #include <errno.h> #include <sys/types.h> #include <sys/mman.h> #include <sys/stat.h> #include <fcntl.h> #define OKTOWRITE "/condwrite" #define MESSAGE "/msg" #define MUTEX "/mutex_lock" int main(int argc, char** argv) { pthread_cond_t* condition; pthread_mutex_t* mutex; char* message; int des_cond, des_msg, des_mutex; int mode = S_IRWXU | S_IRWXG; des_mutex = shm_open(MUTEX, O_CREAT | O_RDWR | O_TRUNC, mode); if (des_mutex < 0) { perror("failure on shm_open on des_mutex"); exit(1); } if (ftruncate(des_mutex, sizeof(pthread_mutex_t)) == -1) { perror("Error on ftruncate to sizeof pthread_cond_t\n"); exit(-1); } mutex = (pthread_mutex_t*) mmap(NULL, sizeof(pthread_mutex_t), PROT_READ | PROT_WRITE, MAP_SHARED, des_mutex, 0); if (mutex == MAP_FAILED ) { perror("Error on mmap on mutex\n"); exit(1); } des_cond = shm_open(OKTOWRITE, O_CREAT | O_RDWR | O_TRUNC, mode); if (des_cond < 0) { perror("failure on shm_open on des_cond"); exit(1); } if (ftruncate(des_cond, sizeof(pthread_cond_t)) == -1) { perror("Error on ftruncate to sizeof pthread_cond_t\n"); exit(-1); } condition = (pthread_cond_t*) mmap(NULL, sizeof(pthread_cond_t), PROT_READ | PROT_WRITE, MAP_SHARED, des_cond, 0); if (condition == MAP_FAILED ) { perror("Error on mmap on condition\n"); exit(1); } /* HERE WE GO */ /**************************************/ /* set mutex shared between processes */ pthread_mutexattr_t mutexAttr; pthread_mutexattr_setpshared(&mutexAttr, PTHREAD_PROCESS_SHARED); pthread_mutex_init(mutex, &mutexAttr); /* set condition shared between processes */ pthread_condattr_t condAttr; pthread_condattr_setpshared(&condAttr, PTHREAD_PROCESS_SHARED); pthread_cond_init(condition, &condAttr); /*************************************/ if (!fork()) { sleep(10); pthread_mutex_lock(mutex); pthread_cond_signal(condition); printf("son signaled\n"); pthread_mutex_unlock(mutex); exit(0); } else { printf("father waits on condition\n"); pthread_mutex_lock(mutex); pthread_cond_wait(condition, mutex); pthread_mutex_unlock(mutex); printf("Signaled by son process, wake up!!!!!!!!\n"); pthread_condattr_destroy(&condAttr); pthread_mutexattr_destroy(&mutexAttr); pthread_mutex_destroy(mutex); pthread_cond_destroy(condition); shm_unlink(OKTOWRITE); shm_unlink(MESSAGE); shm_unlink(MUTEX); } return 0; } 要在进程之间共享，需要通过正确初始化的属性相应地初始化互斥量：http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_mutexattr_setpshared.html #include <pthread.h> ... pthread_mutex_t * pmutex = NULL; pthread_mutexattr_t attrmutex; /* Initialise attribute to mutex. */ pthread_mutexattr_init(&attrmutex); pthread_mutexattr_setpshared(&attrmutex, PTHREAD_PROCESS_SHARED); /* Allocate memory to pmutex here. */ /* Initialise mutex. */ pthread_mutex_init(pmutex, &attrmutex); /* Use the mutex. */ /* Clean up. */ pthread_mutex_destroy(pmutex); pthread_mutexattr_destroy(&attrmutex); （为了本示例的可读性，省略了错误检查）这同样适用于应该在进程之间共享的条件变量：http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_condattr_setpshared.html #include <pthread.h> ... pthread_cond_t * pcond = NULL; pthread_condattr_t attrcond; /* Initialise attribute to condition. */ pthread_condattr_init(&attrcond); pthread_condattr_setpshared(&attrcond, PTHREAD_PROCESS_SHARED); /* Allocate memory to pcond here. */ /* Initialise condition. */ pthread_cond_init(pcond, &attrcond); /* Use the condition. */ /* Clean up. */ pthread_cond_destroy(pcond); pthread_condattr_destroy(&attrcond); （为了本示例的可读性，省略了错误检查）另请参阅此答案：https://stackoverflow.com/a/2390670/694576 等待一个条件之前应该有一个 while 语句，像这样： pthread_mutex_lock(mutex); while(!conditionSatisfied) pthread_cond_wait(condition, mutex); pthread_mutex_unlock(mutex); while 信号应该通过以下方式完成： pthread_mutex_lock(mutex); conditionSatisfied = true; pthread_cond_signal(condition); pthread_mutex_unlock(mutex); 是的，必须在pthread_cond_wait之前锁定互斥量，但不必为pthread_cond_signal锁定。如果你回头看看你的代码，你会发现互斥量将被解锁两次，这是错误的标志......孩子也有可能在已被父母破坏的互斥量上调用解锁...... 顺便说一下，睡眠并不能保证父进程会先执行。为了确保这一点，您将需要……一个条件变量……

c pthreads ipc mutex condition-variable

回答 3 投票 0

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使用现代 C++ 来拥有一些由一个线程初始化的共享内存的最佳方法是什么，第一个到达这一点，然后由多个线程读取。它需要尽可能轻巧……

c++ mutex c++20 atomic stdatomic

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c multithreading pthreads mutex condition-variable

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