Inter-Process Communication using Shared Memory

shm_com.c

#define SIZE 2048 struct shared_mem_st { int written_by; char text[SIZE]; };

shm1.c

#include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/shm.h> #include "shm_com.h" int main() { int running = 1; void *shared_memory = (void *) 0; struct shared_mem_st *shared_stuff; int shmid; srand((unsigned int) getpid()); shmid = shmget((key_t) 1234, sizeof(struct shared_mem_st), 0666 | IPC_CREAT); if (shmid == -1) { fprintf(stderr, "shmget failed\n"); exit(EXIT_FAILURE); } shared_memory = shmat(shmid, (void *) 0, 0); if (shared_memory == (void *) -1) { fprintf(stderr, "shmat failed\n"); exit(EXIT_FAILURE); } printf("Memory attached at %X\n", (int)shared_memory); shared_stuff = (struct shared_mem_st *) shared_memory; shared_stuff->written_by = 0; while (running) { if (shared_stuff->written_by) { printf("You wrote: %s", shared_stuff->text); sleep(rand() % 4); /* make the other process wait for us ! */ shared_stuff->written_by = 0; if (strncmp(shared_stuff->text, "end", 3) == 0) { running = 0; } } } if (shmdt(shared_memory) == -1) { fprintf(stderr, "shmdt failed\n"); exit(EXIT_FAILURE); } if (shmctl(shmid, IPC_RMID, 0) == -1) { fprintf(stderr, "shmctl(IPC_RMID) failed\n"); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); }

shm2.c

#include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/shm.h> #include "shm_com.h" int main() { int running = 1; void *shared_memory = (void *) 0; struct shared_mem_st *shared_stuff; char buffer[BUFSIZ]; int shmid; shmid = shmget((key_t) 1234, sizeof(struct shared_mem_st), 0666 | IPC_CREAT); if (shmid == -1) { fprintf(stderr, "shmget failed\n"); exit(EXIT_FAILURE); } shared_memory = shmat(shmid, (void *) 0, 0); if (shared_memory == (void *) -1) { fprintf(stderr, "shmat failed\n"); exit(EXIT_FAILURE); } printf("Memory attached at %X\n", (int)shared_memory); shared_stuff = (struct shared_mem_st *) shared_memory; while (running) { while (shared_stuff->written_by == 1) { sleep(1); printf("waiting for client...\n"); } printf("Enter some text: "); fgets(buffer, BUFSIZ, stdin); strncpy(shared_stuff->text, buffer, SIZE); shared_stuff->written_by = 1; if (strncmp(buffer, "end", 3) == 0) { running = 0; } } if (shmdt(shared_memory) == -1) { fprintf(stderr, "shmdt failed\n"); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); }

Happy Exploring!