The recipient can ask the Future to block until a result is ready, poll to see whether it's complete, cancel the computation, or check whether another thread has canceled it.

接收者可以要求Future阻止线程，直至一个结果就绪，检测查看它是否完成并取消计算指令，或检查是否有其他进程取消了它。

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But amid Pentagon budget pressures, the Air Force moved to cancel a version of the drone known as the "Block 30, " saying that the U-2 would be less expensive to operate.

WSJ: Cold War U-2 Pilot Francis Gary Powers to Receive Silver Star