systemV shareMemory limit

目录

#include "unpipc.h"

#define MAX_NIDS 4096

int main(int argc, char **argv)
/* $$.bp$$ */
{
  int i, j, shmid[MAX_NIDS];
  void *addr[MAX_NIDS];
  unsigned long size;
  int maxShmget = 0;

  /* 4see how many identifiers we can "open" */
  for (i = 0; i < MAX_NIDS; i++) {
    shmid[i] = shmget(IPC_PRIVATE, 10, SVSHM_MODE | IPC_CREAT);
    if (shmid[i] == -1) {
      maxShmget = i;
      printf("%d identifiers open at once\n", i);
      break;
    }
  }
  for (j = 0; j < maxShmget; j++) {
    int ret = shmctl(shmid[j], IPC_RMID, NULL);
    (void)ret;
  }
  /* 4now see how many we can "attach" */
  for (i = 0; i < MAX_NIDS && i < maxShmget; i++) {
    shmid[i] = shmget(IPC_PRIVATE, 1024, SVSHM_MODE | IPC_CREAT);
    // printf("shmid num:index%d, id:%d\n", i, shmid[i]);
    addr[i] = shmat(shmid[i], NULL, 0);
    if (addr[i] == (void *)-1) {
      printf("%d shared memory segments attached at once\n", i);
      Shmctl(shmid[i], IPC_RMID, NULL); /* the one that failed */
      break;
    }
  }

  for (j = 0; j < i; j++) {
    Shmdt(addr[j]);
    Shmctl(shmid[j], IPC_RMID, NULL);
  }

  /* 4see how small a shared memory segment we can create */
  for (size = 1;; size++) {
    shmid[0] = shmget(IPC_PRIVATE, size, SVSHM_MODE | IPC_CREAT);
    if (shmid[0] != -1) { /* stop on first success */
      printf("minimum size of shared memory segment = %lu\n", size);
      Shmctl(shmid[0], IPC_RMID, NULL);
      break;
    }
  }

  /* 4see how large a shared memory segment we can create */
  for (size = 65536;; size += 4096) {
    shmid[0] = shmget(IPC_PRIVATE, size, SVSHM_MODE | IPC_CREAT);
    if (shmid[0] == -1) { /* stop on first failure */
      printf("maximum size of shared memory segment = %lu\n", size - 4096);
      break;
    }
    Shmctl(shmid[0], IPC_RMID, NULL);
  }

  exit(0);
}