Multithreading using NSOperation - 2

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Multi - Threading using NSOperation by zeeshan 1 Using Blocks & GCD and Using Asynchronous APIs

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• Please point out, if anything is wrong. • Please stop me & raise your voice, for: • Going too fast... • Not getting anything... • Any doubts... • Any inclusion from your side. 2

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Central Processing Unit 3

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• Why CPU is in the ﬁrst slide? • How early days of computing works? • What do we understand by cores? • How does these came into existence? • How does it effect our system? 4 CPU

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nothing is limitless & every problem has a solution Clock Speed A time unit 5

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Clock Speed • What is Clock Speed? • Any problem with it? • Any solution for that? • How to use these cores? How to take advantage of extra cores? 6

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Thread ‘Kernel-level’ + ‘Application-level’ Data Structures An application can use multiple cores by creating multiple threads. 7 Parallel Computation Asynchronous Solution

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Threads • What is Thread? • What are the problems it solves? (Advantages?) • Does anyone can create thread APIs or any standard follows? • What does Objective C do about thread? 8

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Key Terms • Process • Thread • Task (Any diagram?) • Concurrent / Non-Concurrent • Thread Safe / Thread Un-Safe (Any diagram?) X

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NSThread POSIX (Mavericks is 100% POSIX conferment) 9 Life Cycle

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NSThread • In which framework is it written? • What is the lifecycle? • What is it based on? • How can we use it? (Any code?) 10

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Is Thread a Problem • It is a right solution? • What are the cost of using it? • When does problem arise? and Why? • Who gets the burden of it? • How does Thread is different from Process and Task? (Any visual show?) 11

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Hazard of Threaded Programming • UIKit access • Database access • Stale result • Cancellation • De-allocation 12

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Solutions • Operations (Current Session) • GCD (Next Session) • Notiﬁcation Queue • Asynchronous (Hopefully Next to Next Session) • Timers 13

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NS Operation to the rescue 14

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NS Operation • When does it introduced? • What is it actually and how it does? • How to use it? • How many times I can use one operation? • What are the features? 15

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NS Operation II • Manage all threaded code • Model asynchronous operations • KVO Support (Any APIs) • Dependencies (Any APIs) • Priorities (Any APIs) 16

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NS Operation III • Thread Conﬁnement • Completion Block (Any APIs?) • Cancellation • Concurrent vs Non-Concurrent • Some Caveats... 17

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NS Operation Queue • Simpler, Name it • Add, Ready & Execute, Cancel | Finish • Pending Operations (Operations vs OperationCounts) • Multiple Queues • Threads & Queues (How many threads?) 18

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NS Operations Queue II • Queue Width (Any APIs?) • Pause (Suspended) Queues • Cancellation • KVC Compliant (APIs?) • Add Operation with Blocks 19

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NS Operations - Use • Blocks • Concrete sub classes • Selector • Block • User deﬁned sub classes 20

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References: • Multithreading Using NSOperation (http:// izeeshan.wordpress.com/2014/08/17/multi-threading- using-nsoperation/) • Threading Programming Guide • Concurrency Programming Guide • API References (NSOperation and NSOperationQueue) 21

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Lets Revise 22 • CPU / Clock Speed • Thread Solutions and Problems • Process, Thread, Task, Concurrency, • Safe, Un-Safe, Parallel • Operation, Queue,