Concurrency in iOS: #iOScon 2016

What is concurrency? Why use it? Why is so bloody hard?

Learn about using concurrency on Apple's platforms, and how you can improve your app by taking full advantage of the device.

Presented at #iOScon 2016.

Transcript

1. Concurrency on iOS Sam Davies @iwantmyrealname _ github.com/sammyd/iOSConcurrency
3. concurrency is hard
4. what is concurrency?
5. why use concurrency?
6. common concurrency problems
7. race condition
8. Race Condition time Value 1 Thread 1 Thread 2 inc
9. Race Condition time Value 1 1 Thread 1 Thread 2 inc r1
10. Race Condition time Value 1 1 1 Thread 1 Thread 2 inc r1 +1
11. Race Condition time Value 1 1 1 2 Thread 1 Thread 2 inc r1 w2 +1
12. Race Condition time Value 1 1 1 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc
13. Race Condition time Value 1 1 1 2 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc r2
14. Race Condition time Value 1 1 1 2 2 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc r2 +1
15. Race Condition time Value 1 1 1 2 2 2 2 3 Thread 1 Thread 2 inc r1 w2 +1 inc r2 w3 +1
16. Race Condition time Value 1 Thread 1 Thread 2 inc
17. Race Condition time Value 1 1 Thread 1 Thread 2 inc r1 inc
18. Race Condition time Value 1 1 1 Thread 1 Thread 2 inc r1 inc r1
19. Race Condition time Value 1 1 1 1 Thread 1 Thread 2 inc r1 inc r1 +1
20. Race Condition time Value 1 1 1 2 1 Thread 1 Thread 2 inc r1 inc r1 w2 +1
21. Race Condition time Value 1 1 1 2 1 2 Thread 1 Thread 2 inc r1 +1 inc r1 w2 +1
22. Race Condition time Value 1 1 1 2 1 2 2 Thread 1 Thread 2 inc r1 w2 +1 inc r1 w2 +1
23. priority inversion
24. Priority Inversion time low priority resource
25. Priority Inversion time low priority resource
26. Priority Inversion time low medium 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. Priority Inversion time low medium high priority resource
31. deadlock
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. Deadlock time resource1 resource2 Thread 1 Thread 2
40. $&'( queueueueueue paradigm
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. Tasks & Queues Thread 1 Thread 2 Queue
48. feeling brave?
49. a touch more theory
50. Thread Safety time Value 1111 Thread 1 Thread 2 Thread 3
51. Thread Safety time Value 1111 Thread 1 Thread 2 r1111 Thread 3
52. Thread Safety time Value 1111 1112 Thread 1 Thread 2 r1111 w2222 Thread 3
53. Thread Safety time Value 1111 1112 1122 Thread 1 Thread 2 r1111 w2222 r1122 Thread 3
54. Thread Safety time Value 1111 1112 1122 1223 Thread 1 Thread 2 r1111 w2222 r1122 w3333 Thread 3 r1223
55. Thread Safety time Value 1111 1112 1122 1223 2233 Thread 1 Thread 2 r1111 w2222 r1122 w3333 Thread 3 r1223
56. Thread Safety time Value 1111 1112 1122 1223 2233 2333 Thread 1 Thread 2 r1111 w2222 r1122 r2333 w3333 Thread 3 r1223
57. Thread Safety time Value 1111 1112 1122 1223 2233 2333 3333 Thread 1 Thread 2 r1111 w2222 r1122 r2333 w3333 Thread 3 r1223
58. 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
59. Dispatch Barrier time task task task task task barrier task task task task task task task task
60. Dispatch Barrier time read read read read read read write read read read read read read
61. alternatives to 
62. promises networkRequest(url, callback: { data in decompressor(data, callback: { image in imageResizer(image, callback: { small in filterImage(small, callback: { filtered in displayImage(filtered) }) }) }) })
63. promises promise<int> int error
64. promises str
65. promises promise<img> str f
66. promises promise<img> str error f img
67. promises promise<img> str error f img error handler
68. promises promise<img> str error f img g promise<img> error handler
69. promises promise<img> str error f img g promise<img> error error handler img
70. promises promise<img> str error f img g promise<img> error error handler img
71. promises networkRequest(url) .then(decompressor) .then(imageResizer) .then({ (image) in return filterImage(image) }).then(displayImage) .catch({ (error) in print(error) })
72. imagine the “promise pipeline” accepted a sequence of values…
73. that’s reactive programming
74. testing
75. don’t do it
76. test core, synchronous logic
77. let libraries handle concurrency
78. conclusion
79. concurrency is hard
80. you will get it wrong
81. • raywenderlich.com/videos • github.com/sammyd/iOSConcurrency • @iwantmyrealname