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Asynchronous programming intro
1. Asynchronous programming allows programs to run tasks concurrently without blocking by using callbacks, tasks, futures/promises, async/await, coroutines, and event loops. This avoids idle waiting time compared to synchronous programs. 2. An event loop handles asynchronous requests by using non-blocking I/O and callbacks to queue tasks. When one task is waiting, like for a network response, the event loop can process other tasks. 3. Async/await and coroutines allow asynchronous code to be written synchronously by yielding control flow between tasks. This makes asynchronous code appear synchronous and easier to read than callbacks or callbacks.
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Asynchronous programming intro
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- 2. Asynchronous Flow • Callbacks •Task (threading) • Future/Promise • AsyncIO • Coroutines • async/await • ...
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- 5. Why we needto run program asynchronously • Some piece of program are slow • Disk IO and Network IO • CPU-intensive jobs
- 6. Synchronous function • Callerneeds to wait for return • Can’t do anything else in-between • Idle time
- 7. How network I/Oworks in Linux system
- 8. Terminology • Blocking I/O •Non-Blocking I/O • Synchronous • Asynchronous Can you tell me what’s the difference? 8
- 9. Before the explanation Inunix world, we need to consider about User space(thread or process) & Kernel space e.g when we invoke a read operator 1. Waiting for data to be ready 2. Copying the data from kernel to the process 9
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- 14. Answer Blocking IO &Non-Blocking IO are determined by function call 1. A synchronous I/O operation causes the requesting process to be blocked until that I/O operation completes; 2. An asynchronous I/O operation does not cause the requesting process to be blocked; 14
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- 16. Concurrency vs Parallelism? Asynchronous vs Synchronous ?
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- 18. Synchronous Model Single Thread MultiThread 18 A B C Thread A B C Thread 1 Thread 2 Thread 3
- 19. Asynchronous Model Single Thread MultiThread 19 T1 T2 T1 Thread T3 T2 T3 T2 T1 Thread1 T1 T3T1 T3 T6 T5 Thread2 T4 T2T4 T5 T10 T11 Thread3 T11 T9T9 T10
- 20. 4 Scenarios 1. SynchronousSingle Thread 2. Synchronous Multi Thread 3. Asynchronous Single Thread 4. Asynchronous Multi Thread 20
- 21. Concurrency In simple terms,concurrency means processing multiple requests at a time. e.g chef can finish multiple tasks at a time. - chopping - prepare sauces - cooking main dishes ... 21
- 22. Concurrency 1. Synchronous SingleThread 2. Synchronous Multi Thread 3. Asynchronous Single Thread 4. Asynchronous Multi Thread 22
- 23. Concurrency 1. Synchronous SingleThread 2. Synchronous Multi Thread 3. Asynchronous Single Thread 4. Asynchronous Multi Thread 23
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- 26. Event loop Port binding,add FD to watch list FD0 FD1 FD2 FD3 Select watch list Wait for activity in the watch list by using Select Client connects, add to watch list Check all FD for available data Client disconnects, remove from watch list Execute handler to deal with fd https://blog.logentries.com/2016/07/what-exactly-is-an-event-loop/
- 27. Event loop 1. Takeadvantage of IO multiplexing a. select O(n) b. epoll O(1) 2. Eliminate idle time 27
- 28. Event Loop injavascript
- 29. Client Client Client Client Event loop (Single Thread, non-blocking) Thread Thread Thread Thread Longrunning task Blocking IO task Callback
- 30. Event loop console.log(‘hi’) setTimeout(function() { console.log(‘there’) },5000) console.log(‘umbocv’) Stack Main Task queue console webapi
- 31. Event loop console.log(‘hi’) setTimeout(function() { console.log(‘there’) },5000) console.log(‘umbocv’) Stack Main Task queue Console hi webapi setTimeout cbAsync func With callback
- 32. Event loop console.log(‘hi’) setTimeout(function() { console.log(‘there’) },5000) console.log(‘umbocv’) Stack Main Task queue Console hi webapi Timer(5000) cb
- 33. Event loop console.log(‘hi’) setTimeout(function() { console.log(‘there’) },5000) console.log(‘umbocv’) Stack Main Task queue Console hi umbocv webapi Timer(5000) cb
- 34. Event loop console.log(‘hi’) setTimeout(function() { console.log(‘there’) },5000) console.log(‘umbocv’) Stack Main Task queue Console hi umbocv webapi cb
- 35. console.log(‘hi’) setTimeout(function() { console.log(‘there’) }, 5000) console.log(‘umbocv’) Stack Taskqueue Console hi umbocv webapi cb Event loop
- 36. Event loop console.log(‘hi’) setTimeout(function() { console.log(‘there’) },5000) console.log(‘umbocv’) Stack Task queue Console hi umbocv there webapi
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- 38. Coroutine Couroutine are computerprogram components that generalize subroutines to allow multiple entry points for suspending and resuming execution at certain locations https://en.wikipedia.org/wiki/Coroutine
- 39. Coroutine function *test() { console.log(‘there’); varx = yield; console.log(‘hi’ + x); var y = yield; console.log(‘hi + y); } var tester = test() tester.next() // there tester.next(‘joe’) // hi joe tester.next(‘daniel’) // hi daniel Main Coroutine1 yield yield spawn switch
- 40. Coroutine function *request() { varresp = yield* getUrlAsync(‘www.umbocv.com’) return resp } var resp_json = request().next().value When you run asynchronous function, Use yield pass control to other coroutine
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- 42. async/await async function getUrlAsync(){ .... } async function request() { const resp = await getUrlAsync(‘www.umbocv.com’) return resp } var resp_json = request() Use await to invoke asynchronous function and pass control to another function.
- 43. Reference • https://codewala.net/2015/07/29/concurrency-vs-multi-threading-vs-asynchronou s-programming-explained/ • https://x.st/javascript-coroutines/ •Javascript eventloop detailed explanation • https://docs.microsoft.com/en-us/dotnet/csharp/async
- 44. Homework 1. Figure outwhat’s the benefit of using select & epoll (e.g c10 problem) 2. Libuv (nodejs, gevent) 3. What is green thread and what’s the relationship with coroutine