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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA YIFAN XING - 2018 ASYNCHRONOUS PROGRAMMING Yifan Xing SCALA.CONCURRENT AND MONIX! @yifan_xing_e

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01 Synchronous vs. Asynchronous Differences Futures & Promises Debugging Async Programs Monix A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA 02 03 04 05 Overview ASYNCHRONOUS PROGRAMMING: SCALA.CONCURRENT AND MONIX! 1

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Concurrency Synchronous Asynchronous Single-threaded Multi-threaded YIFAN XING - 2018 @yifan_xing_e 2

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Synchronous: Single-threaded YIFAN XING - 2018 Task 1 Task 2 Task 3 @yifan_xing_e 3

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Synchronous: Multi-threaded YIFAN XING - 2018 Task 1 Task 2 Task 3 @yifan_xing_e 4

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Asynchronous: Single-threaded YIFAN XING - 2018 Task 1 Task 2 Task 3 @yifan_xing_e 5

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Asynchronous: Multi-threaded YIFAN XING - 2018 Task 1 Task 2 Task 3 @yifan_xing_e 6

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Future Promise ExecutionContext Examples Scala.concurrent

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YIFAN XING - 2018 Scala.concurrent: Future Computation Incomplete: Computation Completed: Future is not completed Future is completed: with a Value => Success Future is completed: with an Exception => Failure An object holding a value which may become available at some point Immutable A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e Future 7

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YIFAN XING - 2018 Example: Callbacks Multiple callbacks may be registered; NO guarantee that they will be executed in a particular order. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 8

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YIFAN XING - 2018 Example: Callbacks Multiple callbacks may be registered; NO guarantee that they will be executed in a particular order. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 8

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YIFAN XING - 2018 Example: Callbacks Multiple callbacks may be registered; NO guarantee that they will be executed in a particular order. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 8

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YIFAN XING - 2018 Example: Callbacks Multiple callbacks may be registered; NO guarantee that they will be executed in a particular order. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 8

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YIFAN XING - 2018 Example: Callbacks Chain callbacks Allow one to enforce callbacks to be executed in a specified order. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 9

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YIFAN XING - 2018 Example: Callbacks Chain callbacks Allow one to enforce callbacks to be executed in a specified order. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 9

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YIFAN XING - 2018 Example: Callbacks A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e Exception in callback: NOT propagated to the subsequent andThen callbacks. 10

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YIFAN XING - 2018 Example: Transformations A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 11

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YIFAN XING - 2018 Example: Transformations A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 11

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YIFAN XING - 2018 Example: Transformations A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 12

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YIFAN XING - 2018 Example: Transformations A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 13

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YIFAN XING - 2018 Example: Transformations More generic & flexible A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 14

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YIFAN XING - 2018 Example: Transformations More generic & flexible A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 14

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YIFAN XING - 2018 Example: Transformations More generic & flexible A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 14

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YIFAN XING - 2018 Example: Transformations More generic & flexible A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 14

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YIFAN XING - 2018 Example: Transformations More generic & flexible A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 14

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YIFAN XING - 2018 Example: Transformations If no match cases or original future contains a valid result: New future will contain the same result as the original one. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e Evaluated only after a Failure 15

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YIFAN XING - 2018 Example: Transformations If no match cases or original future contains a valid result: New future will contain the same result as the original one. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e Evaluated only after a Failure 15

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YIFAN XING - 2018 Example: Transformations If no match cases or original future contains a valid result: New future will contain the same result as the original one. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e Evaluated only after a Failure 15

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YIFAN XING - 2018 Example: Transformations If no match cases or original future contains a valid result: New future will contain the same result as the original one. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e Evaluated only after a Failure 15

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YIFAN XING - 2018 Example: Transformations If both futures failed, the resulting future holds the throwable object of the first future. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 16

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YIFAN XING - 2018 Example: Transformations If both futures failed, the resulting future holds the throwable object of the first future. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 16

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YIFAN XING - 2018 Example: Transformations A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 16 If both futures failed, the resulting future holds the throwable object of the first future.

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YIFAN XING - 2018 Scala.concurrent: Promises A writable, single-assignment container Can create a Future Can complete a Future, only ONCE A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e Promise: 17

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YIFAN XING - 2018 Example: Promises A Promise can be completed at most ONCE. If the promise has already been fulfilled, failed or has timed out, calling this method will throw an IllegalStateException. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 18

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YIFAN XING - 2018 Example: Promises A Promise can be completed at most ONCE. If the promise has already been fulfilled, failed or has timed out, calling this method will throw an IllegalStateException. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 18

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YIFAN XING - 2018 Example: Promises A Promise can be completed at most ONCE. If the promise has already been fulfilled, failed or has timed out, calling this method will throw an IllegalStateException. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 18

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YIFAN XING - 2018 Example: Promises If the promise has already been completed returns false, or true otherwise. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 19

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YIFAN XING - 2018 Example: Promises If the promise has already been completed returns false, or true otherwise. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 19

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YIFAN XING - 2018 Example: Promises If the promise has already been completed returns false, or true otherwise. A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA @yifan_xing_e 19

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YIFAN XING - 2018 A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Building A Client-facing Interface @yifan_xing_e 20

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YIFAN XING - 2018 A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA p.future Problem in A Client-facing Interface @yifan_xing_e 21

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YIFAN XING - 2018 Monix @yifan_xing_e

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA What is Monix? Asynchronous, event-based programs Data type: Task, etc. "Factory" of Future instances Lazy & asynchronous computations YIFAN XING - 2018 @yifan_xing_e 22

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Task YIFAN XING - 2018 Lazily evaluated Evaluated when call runAsync Trigger side effects @yifan_xing_e 23

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Task YIFAN XING - 2018 Lazily evaluated Evaluated when call runAsync Trigger side effects @yifan_xing_e 23

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Task YIFAN XING - 2018 Lazily evaluated Evaluated when call runAsync Trigger side effects @yifan_xing_e 23

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Task Callback YIFAN XING - 2018 Eagerly evaluate task Register callbacks Similar to Future#onComplete @yifan_xing_e 24

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Task Callback YIFAN XING - 2018 Eagerly evaluate task Register callbacks Similar to Future#onComplete @yifan_xing_e 24

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Task Callback YIFAN XING - 2018 Eagerly evaluate task Register callbacks Similar to Future#onComplete @yifan_xing_e 24

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Eager/ Lazy YIFAN XING - 2018 Evaluate eagerly Equivalent to Future#successful Defer eager evaluation Similar to Task#eval @yifan_xing_e 25

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Eager/ Lazy YIFAN XING - 2018 Evaluate eagerly Equivalent to Future#successful Defer eager evaluation Similar to Task#eval @yifan_xing_e 25

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Memoization YIFAN XING - 2018 Evaluated lazily Not memoized, recompute each time the Task is executed. Evaluate lazily Evaluated exactly ONCE Result is memoized @yifan_xing_e 26

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Memoization YIFAN XING - 2018 Evaluated lazily Not memoized, recompute each time the Task is executed. Evaluate lazily Evaluated exactly ONCE Result is memoized @yifan_xing_e 26

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: MemoizeOnSuccess YIFAN XING - 2018 Exceptions are not cached. Only cache the first successful result @yifan_xing_e 27

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: MemoizeOnSuccess YIFAN XING - 2018 Exceptions are not cached. Only cache the first successful result @yifan_xing_e 27

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: MemoizeOnSuccess YIFAN XING - 2018 Exceptions are not cached. Only cache the first successful result @yifan_xing_e 27

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Alternative Thread Pool YIFAN XING - 2018 Overrides default scheduler Overriding the "default" scheduler can only happen ONCE Task is immutable @yifan_xing_e 28

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Alternative Thread Pool YIFAN XING - 2018 Overrides default scheduler Overriding the "default" scheduler can only happen ONCE Task is immutable @yifan_xing_e 28

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: Alternative Thread Pool YIFAN XING - 2018 Overrides default scheduler Overriding the "default" scheduler can only happen ONCE Task is immutable @yifan_xing_e 28

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Monix: CancelableFuture YIFAN XING - 2018 Calling it multiple times has the same side- effect as calling it only once. @yifan_xing_e 29

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- A value - Executed when constructed - Eager evaluation - ExecutionContext needed whenever use operators A function - Execution controllable by user - Lazy evaluation - ExecutionScheduler needed whenever - use runAsync Monix Future Eager/Lazy A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA 30

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- Memoized by default - Evaluated once - Store result Explicitly use memoization operators - Evaluated whenever needed - Referential transparency - Monix Future Memoization A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA 31

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- Sometimes errors are not propagated - Override reportFailure in provided ExecutionContext to control output of unpropagated exceptions Scheduler.reportFailure - Defaults to System.err - Allow customized logging tools - Monix Future ErrorHandling A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA 32

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Future Monix A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA 33

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Future Monix A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA 34

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Debugging BEST PRACTICES In Asynchronous Programs @yifan_xing_e

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA 35

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Writing Async Code 1. Rethink before adding more code 2. Adding more code to fix problems will usually add more bugs D e b u g 1. Test code in isolation 2. Observe what is happening 3. Confirm behavior before moving on T e s t 36

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Using Await & Print YIFAN XING - 2018 @yifan_xing_e TimeoutException if after waiting for the specified time awaitable is still not ready atMost may be: A finite positive duration Negative (no waiting is done) Duration.Inf for unbounded waiting 37

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Using Await & Print YIFAN XING - 2018 @yifan_xing_e TimeoutException if after waiting for the specified time awaitable is still not ready atMost may be: A finite positive duration Negative (no waiting is done) Duration.Inf for unbounded waiting 37

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA ScalaTest: ScalaFutures YIFAN XING - 2018 @yifan_xing_e Default timeout 150ms TestFailedException if not finished after timeout 38

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA ScalaTest: ScalaFutures YIFAN XING - 2018 @yifan_xing_e Default timeout 150ms TestFailedException if not finished after timeout 38

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA ScalaTest: ScalaFutures YIFAN XING - 2018 @yifan_xing_e Default timeout 150ms TestFailedException if not finished after timeout 38

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Resources: Async Debugger & Capture YIFAN XING - 2018 @yifan_xing_e IntelliJ Capture (2017): Iulian Dragos - Async Debugger in Scala IDE IntelliJ IDEA 2017.1 EAP Extends Debugger with Async Stacktraces Developer's Explanation Debugging Tutorial Async Stacktraces Stack Retention Scala IDE Doc Demo: Jamie Allen Rethink the Debugger: Scala Days 2014 39

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA Using Async Debugger / Capture YIFAN XING - 2018 @yifan_xing_e Substituting its parts related to the asynchronous code execution with where it was called Sender: Async code executor Receiver: executed code Config exact signatures of methods of the async code Stores the stack and variables info in a map (1000 stacks), where the key is a parameter with the specified number. 40

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA YIFAN XING - 2018 @yifan_xing_e ( Sorry Alex :P ) 41

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A TOUR OF ASYNCHRONOUS PROGRAMMING IN SCALA YIFAN XING - 2018 @yifan_xing_e 42

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T H A N K Y O U @yifan_xing_e