在操作队列中打印 1 到 10 不打印整数

Question

我正在学习Combine Scheduler，我有Raywenderlich的书中的示例代码

let queue = OperationQueue()
let subscription = (1...10).publisher
.receive(on: queue)
.sink { value in
print("Received (value) on thread (Thread.current.number)")
}

这本书解释了OperationQueue使用所有可用的线程，因此打印顺序和线程可以是随机的。我理解这一部分，但当我在操场上运行这段代码时，我只看到10个数字中的5个。

Received 1 on thread 7
Received 2 on thread 6
Received 3 on thread 5
Received 7 on thread 9
Received 6 on thread 4

为什么那个代码没有显示全部10个数字？？

Answer 1

您需要导入PlaygroundSupport并在文件顶部设置PlaygroundPage.current.needsIndefiniteExecution = true。

如果您使用另一个sink方法，也就是您获得完成处理程序块的方法，那么在该完成处理程序中，您应该调用PlaygroundPage.current.finishExecution()

编辑：在队列的屏障块中调用PlaygroundPage.current.finishExecution()，否则它会在打印语句全部执行之前被调用。

这是我的测试代码：

PlaygroundPage.current.needsIndefiniteExecution = true
let queue = OperationQueue()
let subscription = (1...10).publisher
.receive(on: queue)
.sink(receiveCompletion: { _ in
queue.addBarrierBlock {
print("Finished")
PlaygroundPage.current.finishExecution()
}
}, receiveValue: { value in
print("Received (value) on thread (Thread.current)")
})

输出：

Received 1 on thread <NSThread: 0x7fd86f204080>{number = 2, name = (null)}
Received 2 on thread <NSThread: 0x7fd86f404340>{number = 3, name = (null)}
Received 3 on thread <NSThread: 0x7fd86f404430>{number = 4, name = (null)}
Received 7 on thread <NSThread: 0x7fd86f405240>{number = 5, name = (null)}
Received 6 on thread <NSThread: 0x7fd86f205c50>{number = 6, name = (null)}
Received 10 on thread <NSThread: 0x7fd86ce487f0>{number = 7, name = (null)}
Received 5 on thread <NSThread: 0x7fd86cf048a0>{number = 10, name = (null)}
Received 9 on thread <NSThread: 0x7fd86ce49b20>{number = 11, name = (null)}
Received 4 on thread <NSThread: 0x7fd86cf2a4c0>{number = 12, name = (null)}
Received 8 on thread <NSThread: 0x7fd86ce4ad60>{number = 13, name = (null)}
Finished