void memfd_init()

in source/hack_parallel/hack_parallel/heap/hh_shared.c [638:695]

• 46 lines of code
• 10 McCabe index (conditional complexity)

void memfd_init(
    const char* shm_dir,
    size_t shared_mem_size,
    uint64_t minimum_avail) {
  if (shm_dir == NULL) {
    // This means that we should try to use the anonymous-y system calls
#if defined(MEMFD_CREATE)
    memfd = memfd_create("fb_heap", 0);
#endif
#if defined(__APPLE__)
    if (memfd < 0) {
      char memname[255];
      snprintf(memname, sizeof(memname), "/fb_heap.%d", getpid());
      // the ftruncate below will fail with errno EINVAL if you try to
      // ftruncate the same sharedmem fd more than once. We're seeing this in
      // some tests, which might imply that two flow processes with the same
      // pid are starting up. This shm_unlink should prevent that from
      // happening. Here's a stackoverflow about it
      // http://stackoverflow.com/questions/25502229/ftruncate-not-working-on-posix-shared-memory-in-mac-os-x
      shm_unlink(memname);
      memfd = shm_open(memname, O_CREAT | O_RDWR, 0666);
      if (memfd < 0) {
        uerror("shm_open", Nothing);
      }

      // shm_open sets FD_CLOEXEC automatically. This is undesirable, because
      // we want this fd to be open for other processes, so that they can
      // reconnect to the shared memory.
      int fcntl_flags = fcntl(memfd, F_GETFD);
      if (fcntl_flags == -1) {
        printf("Error with fcntl(memfd): %s\n", strerror(errno));
        uerror("fcntl", Nothing);
      }
      // Unset close-on-exec
      fcntl(memfd, F_SETFD, fcntl_flags & ~FD_CLOEXEC);
    }
#endif
    if (memfd < 0) {
      raise_failed_anonymous_memfd_init();
    }
  } else {
    assert_avail_exceeds_minimum(shm_dir, minimum_avail);
    if (memfd < 0) {
      char template[1024];
      if (!snprintf(template, 1024, "%s/fb_heap-XXXXXX", shm_dir)) {
        uerror("snprintf", Nothing);
      };
      memfd = mkstemp(template);
      if (memfd < 0) {
        uerror("mkstemp", caml_copy_string(template));
      }
      unlink(template);
    }
  }
  if (ftruncate(memfd, shared_mem_size) == -1) {
    uerror("ftruncate", Nothing);
  }
}