我尝试使用共享内存进行首次运行并命名信号量来同步对它的访问。
我的程序有3个进程 - 父进程和两个进程，都必须使用相同的进程 共享内存。为了在它们之间进行同步，我使用了名为sempahore。 当 array [0] - 退出标志位置时，它们共享的资源是3个整数数组，子进程在运行之前读取这些数据以确定父进程是否要退出。 array [1]，array [2] - 用于与父进程通信，每个进程在自己的数组单元中放置一条消息，父进程读取它，并放置一个 ACK 消息已反映。
我试图获得我的代码的基本工作流程 - 制作所有必要的资源，使父级睡眠3秒钟，然后启动exit_procedure。
我的问题是，当进入 exit_procedure 时，主进程会永远阻塞 sem_wait（）操作 - 显然是死锁。 我试图找出问题并且似乎无法确定问题。 我是处理同步的新手 - 直到此代码我只同步了线程。
更新： 我已经使用POSIX内存映射切换，现在我遇到了同样的死锁问题。 process_api.h中的相关方法无法获得锁定，它们只是永久阻止。我不知道自己做错了什么。 有人可以帮忙吗？
我的代码：
主文件：
int *shmem_p; //!< Shared variable to be used across different proccesses
int shmem_fd; //!< Shared memory id
sem_t *sem_p; //!< Sempahore for syncronizing access to shared memory
volatile sig_atomic_t done; //!< An atomic flag to signal this process threads they are done
volatile sig_atomic_t signal_rcvd; //!< Indication to exit procedure if a signal caused termination
/**
* @brief Exit procedure to be called when program is done
*/
static void exit_procedure()
{
block_all_signals(); /* Block all signals - we're already existing */
if(signal_rcvd == SIGTERM) { /* SIGTERM is manually raised by us when a thread terminates, thus not handled in signal handler */
write(STDERR_FILENO, "Error occured - thread terminated\n", 33);
}
if( !signal_rcvd ) { /* We got here normally, or by thread termination - set done flag */
done = true;
}
/* Free all relevant resources */
sem_unlink("/shmemory");
sem_close(sem_p);
munmap(shmem_p, TOTAL_PROC_NUM*sizeof(int));
shm_unlink("/shmemory");
sem_p = NULL;
shmem_p = NULL;
}
static void signal_handler(int sig_num) {
switch(sig_num) {
case SIGCHLD:
write(STDERR_FILENO, "Error occured - Child process terminated\n", 43);
break;
case SIGALRM:
write(STDOUT_FILENO, "Successfully finished sim\n", 28);
break;
default:
fprintf(stderr, "Error - Signal %s has been raised", strsignal(sig_num));
fflush(stderr);
break;
}
done = true;
signal_rcvd = true;
}
static status_t init_procedure()
{
done = false;
signal_rcvd = false;
size_t size = TOTAL_PROC_NUM*sizeof(int);
/* Initialize shared memory to be used as an exit flag to be used by all processes */
shmem_fd = shm_open("/shmemory", O_CREAT | O_TRUNC | O_RDWR, 0644);
if(shmem_fd < 0) {
error_and_exit("shm_open() failed, err = ", errno);
}
if(ftruncate(shmem_fd, size)) {
shm_unlink("/shmemory");
error_and_exit("ftruncate() failed, err = ", errno);
}
shmem_p = (int *)mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, shmem_fd, 0);
if(shmem_p == MAP_FAILED) {
shm_unlink("/shmemory");
error_and_exit("mmap() failed, err = ", errno);
}
close(shmem_fd); /* No longer needed */
memset(shmem_p, 0, size);
/* Initialize a named sempahore for the procceses shared memory */
sem_p = sem_open("/shsemaphore", O_CREAT | O_RDWR, 0644, 1);
if(SEM_FAILED == sem_p) {
error("sem_open() failed, err = ", errno);
munmap(shmem_p, size);
shm_unlink("/shmemory");
}
/* Initialize memory access invokers processes */
if(processes_init() != SUCCESS) {
error("init_processes() failed\n", ERR);
munmap(shmem_p, size);
shm_unlink("/shmemory");
sem_close(sem_p);
return FAILURE;
}
/* Handle Signals - Ignore SIGINT, SIGQUIT, handle SIGCHLD & SIGALRM */
struct sigaction sig_handler;
sig_handler.sa_flags = 0;
if(sigfillset(&sig_handler.sa_mask)) { /* Mask all other signals inside the handler */
error("sigemptyset() failed, err = ", errno);
exit_procedure();
return FAILURE;
}
sig_handler.sa_handler = signal_handler;
if(sigaction(SIGCHLD, &sig_handler, NULL) || sigaction(SIGALRM, &sig_handler, NULL)) { /* Set the signal handler for SIGCHLD & SIGALRM */
error("sigaction() failed, err = ", errno);
exit_procedure();
return FAILURE;
}
sig_handler.sa_handler = SIG_IGN;
if(sigaction(SIGINT, &sig_handler, NULL) || sigaction(SIGQUIT, &sig_handler, NULL)) { /* Ignore ctrl+c and ctrl+z */
error("sigaction() failed, err = ", errno);
exit_procedure();
return FAILURE;
}
return SUCCESS;
}
int main(int argc, char *argv[])
{
if(argc != 1) {
fprintf(stderr, "usage: %s (no arguments allowed)\n", argv[0]);
exit(EXIT_FAILURE);
}
if(SUCCESS != init_procedure()) {
error_and_exit("init_procedure() failed\n", ERR);
}
sleep(5);
exit_procedure();
return EXIT_SUCCESS;
}
流程处理程序：
#define WR_RATE (0.8) //!< Writing probabilty when invoking memory access
#define WR_RATE_INT (WR_RATE*10) //!< WR_RATE as an int value between 1 and 10
#define INTER_MEM_ACCS_T (100000) //!< Waiting time between memory accesses
static pid_t child_pids[CHILD_PROC_NUM];
int process_cnt; //!< Determines the index of the process, for child processes
extern sem_t *sem_p;
static bool is_ack_received(int *mem_p, off_t size)
{
bool ack;
/*********************************************************/
/** Critical Section start **/
if((sem_wait(sem_p) != 0) && (errno != EINTR)) {
munmap(mem_p, size);
shm_unlink("/shmemory");
error_and_Exit("sem_wait() failed, err = ", errno);
}
ack = (mem_p[process_cnt] == MSG_ACK);
if(ack) {// TODO - Remove
fprintf(stdout, "Process %d received ACK\n", process_cnt);
fflush(stdout);
}
if((sem_post(sem_p) != 0) && (errno != EINTR)) {
munmap(mem_p, size);
shm_unlink("/shmemory");
error_and_Exit("sem_post() failed, err = ", errno);
}
/** Critical Section end **/
/*********************************************************/
return ack;
}
static void invoke_memory_access(int *mem_p, off_t size)
{
msg_e send_msg = MSG_READ;
if(rand_range(1, 10) <= WR_RATE_INT) { /* Write Memory */
send_msg = MSG_WRITE;
}
/*********************************************************/
/** Critical Section start **/
if((sem_wait(sem_p) != 0) && (errno != EINTR)) {
munmap(mem_p, size);
shm_unlink("/shmemory");
error_and_Exit("sem_wait() failed, err = ", errno);
}
mem_p[process_cnt] = send_msg;
fprintf(stdout, "Process %d sent MSG_%d in mem_address: %p\n", process_cnt, send_msg, &mem_p[process_cnt]); // TODO - Remove
fflush(stdout);
if((sem_post(sem_p) != 0) && (errno != EINTR)) {
munmap(mem_p, size);
shm_unlink("/shmemory");
error_and_Exit("sem_post() failed, err = ", errno);
}
/** Critical Section end **/
/*********************************************************/
}
static void main_loop()
{
int shmem_fd = shm_open("/shmemory", O_RDWR, 0);
if(shmem_fd < 0) {
error_and_Exit("shm_open() failed, err = ", errno);
}
struct stat mem_stat;
fstat(shmem_fd, &mem_stat);
int *child_memory_p = (int *)mmap(NULL, mem_stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, shmem_fd, 0);
if(child_memory_p == MAP_FAILED) {
shm_unlink("/shmemory");
error_and_Exit("mmap() failed, err = ", errno);
}
close(shmem_fd); /* No longer needed */
bool first_run = true;
bool ack = false;
const struct timespec ns_wait = {.tv_sec = 0, .tv_nsec = INTER_MEM_ACCS_T};
while(child_memory_p[0] != MSG_EXIT) {
if( !first_run ) { /* Not the first run, check for ack */
ack = is_ack_received(child_memory_p, mem_stat.st_size);
}
nanosleep(&ns_wait, NULL);
if( !first_run && !ack ) { /* No ack received for latest call, nothing to be done */
continue;
}
invoke_memory_access(child_memory_p, mem_stat.st_size);
if(first_run) { /* First run is over.. */
first_run = false;
}
}
fprintf(stdout, "PROCCESS %d EXIT!\n", process_cnt); // TODO Remove this
fflush(stdout);
munmap(child_memory_p, mem_stat.st_size);
shm_unlink("/shmemory");
child_memory_p = NULL;
_Exit(EXIT_SUCCESS);
}
status_t processes_init()
{
pid_t pid;
process_cnt = 1; /* Will be used for child processes to determine their order creation */
int i;
for(i = 0; i < CHILD_PROC_NUM; ++i) {
pid = fork();
if(ERR == pid) {
error("fork() failed, err = ", errno);
return FAILURE;
} else if(pid != 0) { /* Parent process */
child_pids[i] = pid;
process_cnt++;
} else { /* Child process */
block_all_signals(); /* Only main process responsible for indicate exit to its child*/
main_loop();
}
}
return SUCCESS;
}
void processes_deinit(int **mem_p)
{
(*mem_p)[0] = MSG_EXIT;
fprintf(stdout, "EXIT wrriten to address %p\n", *mem_p);
/* Wait for all child processes to terminate */
int i;
write(STDOUT_FILENO, "Waiting for children to exit\n", 29); // TODO Remove this
for(i = 0; i < CHILD_PROC_NUM; ++i) {
if((ERR == waitpid(child_pids[i], NULL, 0)) && (ECHILD != errno)) {
error("waitpid() failed, err = ", errno);
}
}
fprintf(stdout, "PROCCESS DEINIT DONE!\n"); // TODO Remove this
fflush(stdout);
}
有人可以解释一下我做错了什么吗？
我尝试过：
将sem_t指针从主进程传递为* sem_t ** semaphore_p *到 processes_init 方法，并让每个子进程使用指向信号量的真实指针（即使子进程也会复制指针） COW mecanishm，他仍然会使用实际的地址 感谢
在进程处理程序中将sem_t指针声明为extern
打开每个子进程（在 main_loop 方法中）a＆＃34; copy＆＃34;使用 sem_open（＆＃34; / shsemaphore＆＃34;，O_RDWR）命名的信号量
这些都没有奏效。我对这些家伙发疯了，请帮助我:(
答案 0 :(得分：2)
在打开信号量后的函数init_procedure（）中，有一个函数调用
sem_unlink(shared_sem_name);
始终执行，在创建后立即销毁信号量。您希望在错误处理块中使用此行。
答案 1 :(得分：1)
找到解决方案：
在主文件中创建命名信号量时，权限设置为0644， 这给了进程组只读权限。
更改为以下内容后：
sem_open(semaphore_name, O_CREAT, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP, 1)
问题似乎已经解决了！ 显然，如果调用sem_wait而没有对信号量具有读/写权限（在子进程中发生 - 它们仅使用具有READ权限的信号量），则行为未定义