如何使用共享内存进程之间共享信号灯 [英] How to share semaphores between processes using shared memory

问题描述

我要一台服务器同步ñ客户端进程。这些过程由我宣布3信号灯main函数叉。我决定使用POSIX信号，但我不知道如何把这些进程间共享。我以为共享内存应能正常工作，但我有一些问题：

I have to synchronize N client processes with one server. These processes are forked by a main function in which I declared 3 semaphores. I decided to use POSIX semaphores but I don't know how to share them between these processes. I thought that shared memory should work correctly, but I have some questions:

• 如何分配的内存在我段各空间？


• 我可以使用的sizeof（sem_t）在为size_t 的字段 shmget的为了准确地分配给我所需要的空间？


• 有没有人有类似于这种情况的例子吗？

• How can I allocate the right space of memory in my segment?
• Can I use sizeof(sem_t) in size_t field of shmget in order to allocate exactly the space I need?
• Does anyone have some examples similar to this situation?

推荐答案

这很容易共享名为 POSIX 信号灯

It's easy to share named POSIX semaphores

• 选择一个名称为您的信号灯

• Choose a name for your semaphore

#define SNAME "/mysem"

使用 sem_open 与 O_CREAT 在创建它们的进程

sem_t *sem = sem_open(SNAME, O_CREAT, 0644, 3); /* Initial value is 3. */

在其他进程打开信号灯

Open semaphores in the other processes

sem_t *sem = sem_open(SEM_NAME, 0); /* Open a preexisting semaphore. */

如果您坚持使用共享内存，这是可能的。

int fd = shm_open("shmname", O_CREAT, O_RDWR);
ftruncate(fd, sizeof(sem_t));
sem_t *sem = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE,
    MAP_SHARED, fd, 0);

sem_init(sem, 1, 1);

我没有测试上述所以它可能是完全疯狂。

I haven't tested the above so it could be completely bonkers.

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