Sleeping by Embedded MzScheme

When all MzScheme threads are blocked, MzScheme must ``sleep'' for a certain number of seconds or until external input appears on some file descriptor. Generally, sleeping should block the main event loop of the entire application. However, the way in which sleeping is performed may depend on the embedding application. The global function pointer scheme_sleep can be set by an embedding application to implement a blocking sleep, although MzScheme implements this function for you.

A scheme_sleep function takes two arguments: a float and a void *. The latter is really points to an array of three ``fd_set'' records (one for read, one for write, and one for exceptions); these records are described further below. If the float argument is non-zero, then the scheme_sleep function blocks for the specified number of seconds, at most. The scheme_sleep function should block until there is input one of the file descriptors specified in the ``fd_set,'' indefinitely if the float argument is zero.

The second argument to scheme_sleep is conceptually an array of three fd_set records, but always use scheme_get_fdset to get anything other than the zeroth element of this array, and manipulate each ``fd_set'' with MZ_FD_XXX instead of FD_XXX.

The following function mzsleep is an appropriate scheme_sleep function for most any Unix or Windows application. (This is approximately the built-in sleep used by MzScheme.)

void mzsleep(float v, void *fds)
{
  if (v) {
    sleep(v);
  } else {
    int limit;
    fd_set *rd, *wr, *ex;
    
# ifdef WIN32
    limit = 0;
# else
    limit = getdtablesize();
# endif

    rd = (fd_set *)fds;
    wr = (fd_set *)scheme_get_fdset(fds, 1);
    ex = (fd_set *)scheme_get_fdset(fds, 2);

    select(limit, rd, wr, ex, NULL);
  }
}