code: function _reseed(callback) {
      if(ctx.pools[0].messageLength >= 32) {
        _seed();
        return callback();
      }
      // not enough seed data...
      var needed = (32 - ctx.pools[0].messageLength) << 5;
      ctx.seedFile(needed, function(err, bytes) {
        if(err) {
          return callback(err);
        }
        ctx.collect(bytes);
        _seed();
        callback();
      });
    }
docs: Private function that asynchronously reseeds a generator.
  
  @param callback(err) called once the operation completes.