Cancel All My Appointments!

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Cancel All My Appointments! Kyle Simpson @getify

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HAPPENS Failure @getify

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HAPPENS Cancellation @getify

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Cancel Abort Call-Off Abandon Stop Kill Revoke Quit Pause? Terminate Undo? @getify

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Cancel Abort Call-Off Abandon Stop Kill Revoke Quit Pause? Terminate Undo? Final } { Recover  Rollback Event? State @getify

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Events are unexpected. States are expected. Cancellation should never be an unexpected exception. Cancellation should be a predictable state. @getify

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? @getify

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¯\_(ϑ)_/¯  UNCERTAINTY @getify

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ing Problem @getify

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How? @getify

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Approximate! @getify

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Timeouts @getify

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Schrödinger's Cat Quantum Superposition @getify

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@getify

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Schrödinger's Asynchrony @getify

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@getify

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Cancel...a Cancellation? @getify

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@getify

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Cancelable Promise? @getify

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Wrong Level of Abstraction @getify

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Schrödinger's Cancellation @getify

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@getify

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Cancelable Promise: "Action At A Distance" Unpredictable State Just Say No. @getify

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Complexity Randomness ~ ~ @getify

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UNCERTAINTY @getify

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Cancel what? @getify

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I FIGHT FOR THE  USERS . . . . . . AND THEY WANT CANCELLATION! @getify

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@getify

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@getify

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@getify

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@getify

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@getify

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@getify

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@getify

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Cancellation Must Be  A First Class Citizen @getify

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Developers, Developers, Developers? @getify

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Timers @getify

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Ajax Calls @getify

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User Events @getify

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What about...? @getify

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File System Operations @getify

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Stream Operations @getify

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Network I/O @getify

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Database Queries @getify

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Child Processes @getify

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Yadda, Yadda, Yadda... @getify

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@getify

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@getify

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Debounce: Spinner @getify

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Debounce: Spinner @getify

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Un-observable-ation Implied Cancellation @getify

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Starvation @getify

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@getify

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https://vorpus.org/blog/timeouts-and- cancellation-for-humans/ @getify

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Edge-Triggered vs Level-Triggered Event vs State @getify

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@getify

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Events can be missed. State isn't. @getify

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Event composition can be complex. State transition isn't. @getify

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Timeouts vs Deadlines @getify

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Timeouts vs Deadlines @getify

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Cancellation:  Serial vs Concurrent @getify

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@getify

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@getify

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...oops, only Shallow Cancellation @getify

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Deep(er) Cancellation @getify

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Race: A xor B @getify

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@getify

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Promises are a bit awkward here @getify

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Cancellation Tokens @getify

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@getify

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cancelable fetch! @getify

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Async Functions:  not (externally) cancelable @getify

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@getify

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@getify

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CAF (Cancelable Async Flows) https://github.com/getify/CAF @getify

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@getify

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still cancelable fetch! @getify

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Tedious? @getify

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Idea*:  Cancellation Zones (*still very rough idea) @getify

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@getify

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What's missing: atomicity Not just convenience. DB transactions are "easy".  Atomic cancellation as state is hard. @getify

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Cancellation: Abstraction Levels Exception (Uncertainty) Event State Collection of States @getify

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If it's async, it's gonna get  canceled ﬁnally { ...whether you handle that state or not. cancellation shouldn't be an unexpected exception. @getify

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unexpected cancellation states feed uncertainty. } uncertainty spreads unnecessary complexity. complexity cancels out software quality and momentum. @getify