How to share semaphores between processes using shared memory

by

It’s easy to share named POSIX semaphores

  • Choose a name for your semaphore

    #define SNAME "/mysem"

  • Use sem_open with O_CREAT in the process that creates them

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

  • Open semaphores in the other processes

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

If you insist on using shared memory, it’s certainly possible.

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);

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

More Related Contents:

  1. sem_init on OS X
  2. How to use POSIX semaphores on forked processes in C?
  3. Is changing a pointer considered an atomic action in C?
  4. Do forked child processes use the same semaphore?
  5. close() is not closing socket properly
  6. ReleaseSemaphore does not release the semaphore
  7. WaitForSingleObject and WaitForMultipleObjects equivalent in Linux?
  8. What’s the difference between a null pointer and a void pointer?
  9. When should I pass or return a struct by value?
  10. How to do encryption using AES in Openssl
  11. Can a pointer ever point to itself?
  12. How can a C program produce a core dump of itself without terminating?
  13. How to return a 2D array from a function in C?
  14. Creating your own syntax highlighting in GEdit?
  15. Synchronizing 2 processes using interprocess synchronizations objects – Mutex or AutoResetEvent
  16. How to make a linux shared object (library) runnable on its own?
  17. Can the following code be true for pointers to different things
  18. getrandom syscall in C not found
  19. Why is “typedef struct foo foo;” considered harmful?
  20. Sharing same variable between more than one independent programs in Linux [closed]
  21. Automated field re-ordering in C structs to avoid padding
  22. Is it possible to declare multiple static variables with same name in a single C file?
  23. Tried and true simple file copying code in C?
  24. argv: Sanitizing wildcards
  25. Is null character included while allocating using malloc
  26. C prototype functions
  27. Want to know the ESSID of wireless network via C++ in UBUNTU
  28. Need for prefixing a function with (void)
  29. Declaring 64-bit variables in C
  30. How to change the stack size using ulimit or per process on Mac OS X for a C or Ruby program?

Leave a Comment