【发布时间】：2016-05-28 16:37:46
【问题描述】：
我在跨文件使用条件变量和互斥体时遇到了共享内存问题。
我的研究把我带到了这里Share condition variable & mutex between processes: does mutex have to locked before? 如果您运行两个完全独立的可执行文件，则 OP 发布的解决方案将不起作用。我尝试了他的方法来解决我自己的问题，两个单独的进程只是不会互相发出信号。因此，为了确认 OPs 代码确实有效，如下所示，我复制了他的代码并在中途添加了一个#define，以便您可以编译并作为父亲启动，更改定义并作为儿子启动。 如果您像 OP 一样只用一个 fork 运行代码，它就可以工作。如果你作为两个单独的可执行文件运行，它就不起作用...... 有人有什么想法吗？
背景问题 这开始于我之前的问题POSIX Shared Memory Sync Across Processes C++/C++11
测试代码
#include <QCoreApplication>
#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[])
{
QCoreApplication a(argc, 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);
}
//#define father
#ifdef father
/* HERE WE GO */
/**************************************/
/* set mutex shared between processes */
pthread_mutexattr_t mutexAttr;
pthread_mutexattr_init(&mutexAttr);
pthread_mutexattr_setpshared(&mutexAttr, PTHREAD_PROCESS_SHARED);
pthread_mutex_init(mutex, &mutexAttr);
/* set condition shared between processes */
pthread_condattr_t condAttr;
pthread_condattr_init(&condAttr);
pthread_condattr_setpshared(&condAttr, PTHREAD_PROCESS_SHARED);
pthread_cond_init(condition, &condAttr);
/*************************************/
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);
#else
// if (!fork()) {
// sleep(3);
pthread_mutex_lock(mutex);
pthread_cond_signal(condition);
printf("son signaled\n");
pthread_mutex_unlock(mutex);
exit(0);
// }
// else {
#endif
// }
exit(0);
return a.exec();
}
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