我正在研究Combine Scheduler,我从Raywenderlich的书中获得了示例代码
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使用所有可用线程,因此打印顺序和线程可能是随机的。我理解这部分,但是当我在操场上运行此代码时,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
为什么该代码不能显示全部10个数字?
您需要导入PlaygroundSupport
并PlaygroundPage.current.needsIndefiniteExecution = true
在文件顶部设置。
如果您使用另一个接收器方法,也将获得一个完成处理程序块的接收器方法,则在该完成处理程序中,您应调用 PlaygroundPage.current.finishExecution()
编辑:调用PlaygroundPage.current.finishExecution()
队列上的障碍块,否则在您的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)")
})
并输出:
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
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