Is it possible in some way to use POSIX semaphores between Docker containers or between a container and the host?

I solved the problem using shared memory between Docker containers as explained in this question.

The following code is a modified version of this tutorial.

File server.c

/* To be compiled with -lpthread */#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <sys/ipc.h>#include <sys/shm.h>#include <fcntl.h>#include <semaphore.h>#define SHM_SIZE     1000int main(void) {    int shmid;    key_t key;    char *shm;    sem_t * mySem;    /* We'll name our shared memory segment "5678" */    key = 5678;    /* Create the segment.*/    if ((shmid = shmget(key, SHM_SIZE, IPC_CREAT | IPC_EXCL | 0666)) < 0) {        perror("shmget");        exit(1);    }    /* Now we attach the segment to our data space */    if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {        perror("shmat");        exit(1);    }    /* Create a new semaphore */    mySem = sem_open("sem1", O_CREAT, 0777, 0);    /* Copy the semaphore on the shared memory segment */      memcpy(shm, mySem, sizeof(*mySem));    /* Do stuff ... */    /* REMEMBER TO USE THE SHARED MEMORY SEGMENT */    /* AND NOT THE LOCAL mySem, USE (sem_t*)shm INSTEAD! */    /* Finally, we wait until the other process      * changes the first character of our memory     * to '*', indicating that it has read what      * we put there.     */    while (*shm != '*')        sleep(1);    /* Mark the memory segment to be destroyed */    shmctl(shmid, IPC_RMID, NULL);    /* Detach of the memory segment */    shmdt(&shm);    sem_unlink("sem1");    return 0;}

File client.c

/* To be compiled with -lpthread */#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <sys/ipc.h>#include <sys/shm.h>#include <fcntl.h>#include <semaphore.h>#define SHM_SIZE     1000int main(void) {    int shmid;    key_t key;    char *shm;    int ret, val;    key = 5678;    if ((shmid = shmget(key, SHM_SIZE, 0666)) < 0) {        perror("shmget");        exit(1);    }    if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {        perror("shmat");        exit(1);    }    /* SEMAPHORE IS IN THE SHARED MEMORY SEGMENT */    /* USE (sem_t*)shm TO ACCESS IT */    *shm = '*';    shmdt(&shm);    sem_close("sem1");    return 0;}

The code examples miss lots of controls due to readability purposes.

I run the server on the host machine, the client inside a Docker container and checked that the semaphore was accessible from both processes.