The abstract data buffer allocates the memory blocks when and only when the actual data becomes available.

抽象数据缓冲区仅在实际数据变得可用时才分配内存。

youdao

And this is what logistics is chiefly concerned with. Products are of any value when and only when they are moved to the right place where it is available to the customer.

而这也正是物流所关心的，产品只有在被运送到能被消费者买到的场所时才体现出价值。

youdao

When, and only when, these behaviors occur does an authority relationship exist between the superior and subordinate.

当且仅当这些行为发生时，在上级和下级之间才存在一种权威关系。

youdao

This is when a bone is bent and breaks along only one side, like a young stick of wood.

VOA: special.2009.02.04

And only when one has accepted that, is there any possibility of scoring a bull's eye.

只有当一个人意识到这一点，才能够射中靶心。

普林斯顿公开课 - 人性课程节选

So that's the only change we need to make there and watch what happens when we actually run this.

那就是我们需要改变的,并且当我们运行它，会发生什么事情。

哈佛公开课 - 计算机科学课程节选

Sad as it may be the trade is bullish but when and only when the Federal Reserve moves forward with another round of liquidity.

FORBES: How to Trade QE3

They returned fire with 50-caliber machine guns, they also returned fire with their M-16's -- Marines pointing out of the top firing, but not indiscriminantly, that is something the Marines point out -- only when they were fired upon and only when they could see the flashes, did they fire back.

CNN: Martin Savidge: 'Pitched battle that went on and on'

She said there were lots of pieces of evidence that when put together, could look different from when they were considered separately and it was only when the investigation was completed that they could look at all the pieces of evidence together.

BBC: NEWS | UK | UK Politics | Key points: Cash-for-honours hearing