cancel method of timerCtx of context package

[qinggeer Bao]

In the cancel method of timerCtx type:

func (c *timerCtx) cancel(removeFromParent bool, err error) {

    c.cancelCtx.cancel(false, err)

    if removeFromParent {

        // Remove this timerCtx from its parent cancelCtx's children.

        removeChild(c.cancelCtx.Context, c)

    }

    c.mu.Lock()

    if c.timer != nil {

        c.timer.Stop()

        c.timer = nil

    }

    c.mu.Unlock()

}

why it use the following:

    c.cancelCtx.cancel(false, err)

    if removeFromParent {

        // Remove this timerCtx from its parent cancelCtx's children.

        removeChild(c.cancelCtx.Context, c)

    }

instead, direclty call 

c.cancelCtx.cancel(removeFromParent, err)

Is there any reason? 

[Ian Lance Taylor]

The two calls look the same but they are not the same. The c passed
to removeChild by cancelCtx.cancel is not the same as the c passed to
removeChild by timerCtx.cancel.

Ian