docs: function(fiberId) {
      var ret = undefined
      try {
        ret = f()
        if (next) {
          return next(ret)
        } else {
          // drop it
        }
      } catch (e) {
        (logger || debug)(e.stack)
        if (error) {
          // if there's an error callback then throw it that way
          return error(e)
        } else {
          throw e
        }
      } finally {
        // clean up
        var fiber_ = _spawnBookkeeping._fibers[fiberId]
        if (typeof fiber_ === 'undefined') {
          throw new Error('Failed to find current fiber in spawn.fibers')
        }
        // remove our handle on this fiber so that it will get garbage collected
        delete _spawnBookkeeping._fibers[fiberId]
        --_spawnBookkeeping._fibers._length
      }
    }