SwiftConf 2016: Concurrency on iOS

...queueing for the futures

Some slides that accompany a talk presented at SwiftConf 2016. You should check out the Xcode Playground to get a better understanding of what the hell is going on

Transcript

1. Concurrency on iOS Sam Davies @iwantmyrealname _ github.com/sammyd
 git.io/vicO3
2. concurrency is hard
3. what is concurrency?
4. why use concurrency?
5. common concurrency problems
6. race condition
7. Race Condition time Value 1 Thread 1 Thread 2 inc
8. Race Condition time Value 1 1 Thread 1 Thread 2 inc r1
9. Race Condition time Value 1 1 1 Thread 1 Thread 2 inc r1 +1
10. Race Condition time Value 1 1 1 2 Thread 1 Thread 2 inc r1 w2 +1
11. Race Condition time Value 1 1 1 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc
12. Race Condition time Value 1 1 1 2 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc r2
13. Race Condition time Value 1 1 1 2 2 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc r2 +1
14. Race Condition time Value 1 1 1 2 2 2 2 3 Thread 1 Thread 2 inc r1 w2 +1 inc r2 w3 +1
15. Race Condition time Value 1 Thread 1 Thread 2 inc
16. Race Condition time Value 1 1 Thread 1 Thread 2 inc r1 inc
17. Race Condition time Value 1 1 1 Thread 1 Thread 2 inc r1 inc r1
18. Race Condition time Value 1 1 1 1 Thread 1 Thread 2 inc r1 inc r1 +1
19. Race Condition time Value 1 1 1 2 1 Thread 1 Thread 2 inc r1 inc r1 w2 +1
20. Race Condition time Value 1 1 1 2 1 2 Thread 1 Thread 2 inc r1 +1 inc r1 w2 +1
21. Race Condition time Value 1 1 1 2 1 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc r1 w2 +1
22. priority inversion
23. Priority Inversion time low priority resource
24. Priority Inversion time low priority resource
25. Priority Inversion time low medium priority resource
26. Priority Inversion time low medium high priority resource
27. Priority Inversion time low medium high priority resource
28. Priority Inversion time low medium high priority resource
29. Priority Inversion time low medium high priority resource
30. deadlock
31. Deadlock time resource1 resource2 Thread 1 Thread 2
32. Deadlock time resource1 resource2 Thread 1 Thread 2
33. Deadlock time resource1 resource2 Thread 1 Thread 2
34. Deadlock time resource1 resource2 Thread 1 Thread 2
35. Deadlock time resource1 resource2 Thread 1 Thread 2
36. Deadlock time resource1 resource2 Thread 1 Thread 2
37. Deadlock time resource1 resource2 Thread 1 Thread 2
38. Deadlock time resource1 resource2 Thread 1 Thread 2
39. $&'( queueueueueue paradigm
40. Tasks & Queues Thread 1 Thread 2 Queue
41. Tasks & Queues Thread 1 Thread 2 Queue
42. Tasks & Queues Thread 1 Thread 2 Queue
43. Tasks & Queues Thread 1 Thread 2 Queue
44. Tasks & Queues Thread 1 Thread 2 Queue
45. Tasks & Queues Thread 1 Thread 2 Queue
46. Tasks & Queues Thread 1 Thread 2 Queue
47. feeling brave?
48. a touch more theory
49. Thread Safety time Value 1111 Thread 1 Thread 2 Thread 3
50. Thread Safety time Value 1111 Thread 1 Thread 2 r1111 Thread 3
51. Thread Safety time Value 1111 1112 Thread 1 Thread 2 r1111 w2222 Thread 3
52. Thread Safety time Value 1111 1112 1122 Thread 1 Thread 2 r1111 w2222 r1122 Thread 3
53. Thread Safety time Value 1111 1112 1122 1223 Thread 1 Thread 2 r1111 w2222 r1122 w3333 Thread 3 r1223
54. Thread Safety time Value 1111 1112 1122 1223 2233 Thread 1 Thread 2 r1111 w2222 r1122 w3333 Thread 3 r1223
55. Thread Safety time Value 1111 1112 1122 1223 2233 2333 Thread 1 Thread 2 r1111 w2222 r1122 r2333 w3333 Thread 3 r1223
56. Thread Safety time Value 1111 1112 1122 1223 2233 2333 3333 Thread 1 Thread 2 r1111 w2222 r1122 r2333 w3333 Thread 3 r1223
57. Thread Safety time Value 1111 1112 1122 1223 2233 2333 3333 3333 3333 Thread 1 Thread 2 r1111 w2222 r1122 r2333 w3333 Thread 3 r1223 r3333 r3333
58. Dispatch Barrier time task task task task task barrier task task task task task task task task
59. Dispatch Barrier time read read read read read read write read read read read read read
60. alternatives to 
61. promises networkRequest(url, callback: { data in decompressor(data, callback: { image in imageResizer(image, callback: { small in filterImage(small, callback: { filtered in displayImage(filtered) }) }) }) })
62. promises promise<int> int error
63. promises str
64. promises promise<img> str f
65. promises promise<img> str error f img
66. promises promise<img> str error f img error handler
67. promises promise<img> str error f img g promise<img> error handler
68. promises promise<img> str error f img g promise<img> error error handler img
69. promises promise<img> str error f img g promise<img> error error handler img
70. promises networkRequest(url) .then(decompressor) .then(imageResizer) .then({ (image) in return filterImage(image) }).then(displayImage) .catch({ (error) in print(error) })
71. imagine the “promise pipeline” accepted a sequence of values…
72. that’s reactive programming
73. conclusion
74. concurrency is hard
75. you will get it wrong
76. • videos.raywenderlich.com • git.io/vicO3 • @iwantmyrealname