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69 lines
1.5 KiB
C
69 lines
1.5 KiB
C
#include <stdlib.h>
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#include <stdio.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <string.h>
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#include <semaphore.h>
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#define SHARED_MEM "/SHARED_MEM"
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#define NUM_CALLS 5
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struct shared_str {
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sem_t sem;
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size_t len;
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char buf[256];
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};
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void errExit(char* msg){
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perror(msg);
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exit(EXIT_FAILURE);
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}
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int main(){
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int fd = shm_open(SHARED_MEM, O_CREAT | O_RDWR, S_IRUSR);
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if (fd < 0){
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errExit("failed to open shared memory object");
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}
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if (ftruncate(fd, sizeof(struct shared_str))){
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errExit("failed to truncate");
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}
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struct shared_str *sstr = mmap(NULL, sizeof(struct shared_str),
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PROT_READ | PROT_WRITE,
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MAP_SHARED, fd, 0);
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if (sstr == MAP_FAILED)
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errExit("mmap");
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if (sem_init(&sstr->sem, 1, 0) == -1)
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errExit("sem_init-sem1");
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pid_t pid;
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if ((pid = fork()) < 0) {
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errExit("failed to fork");
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}
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if ( pid == 0 ){
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printf("child is running...\n");
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for (int i =0 ; i <NUM_CALLS ; i++) {
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sleep(1);
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sstr -> len = snprintf((char*)&sstr->buf,256,"hallo no. %d",i);
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if (sem_post(&sstr->sem) == -1)
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errExit("sem_post");
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}
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close(fd);
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exit(EXIT_SUCCESS);
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}
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for (int i =0 ; i<NUM_CALLS ; i++) {
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if (sem_wait(&sstr->sem) == -1)
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errExit("sem_wait");
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pread(fd,sstr, sizeof(struct shared_str),0);
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printf("text in shared buffer: %s\n",sstr -> buf);
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}
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int status;
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pid = wait(&status);
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printf("child process %d terminated with status %d\n", pid, WEXITSTATUS(status));
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shm_unlink(SHARED_MEM);
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exit(EXIT_SUCCESS);
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}
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