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Making CocoaPods Fast with Modern Ruby Tooling Samuel Giddins 1

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@segiddins Mobile Developer Experience @ Square CocoaPods Core Team Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 2

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bundler & rubygems Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 3

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quick aside ➡ how many of you write ruby almost every day? ➡ how many of you write ruby that's deployed to a web server? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 4

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What even is CocoaPods? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 5

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== + Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 6

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CocoaPods combines a definition of libraries (podspecs) with a way to integrate them into a user's application (podfile) Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 7

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RubyGems Bundler CocoaPods Gemspec Podspec Gemfile Podfile Gemfile.lock Podfile.lock rubygems.org index.rubygems.org github.com/CocoaPods/ Specs Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 8

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That little difference: Xcode Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 9

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Xcode ➡ Proprietary toolchain for compiling apps for apple platforms ➡ Uses its own manifest file format ➡ Invokes many compilation tools Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 10

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So, CocoaPods has to do a heck of lot more than RubyGems or Bundler Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 11

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pod install ➡ Updating local specs repositories ➡ Analyzing dependencies ➡ Fetching dependencies ➡ Installing dependencies ➡ Generating Pods project ➡ Integrating client project Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 12

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So, CocoaPods exists! It was slow? So what. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 13

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Why Performance? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 14

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Why Performance? ➡ Optimization is fun! ➡ Rapid iteration == happier & more productive developers ➡ "Scale" ➡ Free performance is hard to find Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 15

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So, I have a slow ruby app. How do I make it faster? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 16

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How do I make it faster? ➡ Is it really slow? ➡What is it doing? ➡How often does it run? ➡Would it being faster make a difference? ➡ Can it do less work? ➡ How can I keep it from getting worse? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 17

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Is it really slow? ➡ How much would I invest to make it 10% faster? 50%? 90%? ➡ How do I know which part of what it's doing is slow? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 18

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➡ ! this feels slow ➡ ⏱ this took 10 seconds ➡ # this segment took 10 seconds ➡ $ this method was called 97645 times, averaging 23ms per call, taking up 48% of total runtime Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 19

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Profiling Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 20

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Profiling The art of putting numbers to the feeling of "this feels slow" Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 21

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What can I profile? ➡ Method calls ➡ Call Stack Sampling ➡ Memory allocations ➡ Disk I/O ➡ Network I/O ➡ Database queries ➡ Garbage collection Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 22

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My work on CocoaPods focused on: Method Call Profiling Call Stack Sampling Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 23

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quick aside: One of our contributors got amazing gains by profiling allocations and memoizing things like #hash & Pathname#join Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 24

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Profilers Just like most tools, it's important to pick the right one for the job at hand Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 25

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Tracing Profilers Tell you how many times something was called, and usually how much time is spent in that call. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 26

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Tracing Profilers ➡ Can distort relative numbers ➡ Can make running a program painfully slow Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 27

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Tracing Profilers If it takes 35 minutes with no profiling, it may never finish under rubyprof. Sorry, I didn't think of that. — CocoaPods/CocoaPods#5180 Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 28

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Allocation Profilers Tracing profilers that count memory allocations instead of method calls. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 29

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Allocation Profilers ➡ Suffer from similiar problems, but even more so since the typical ruby program is incredibly allocation-heavy. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 30

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Sampling Profilers Takes a peek at your program at regular intervals, from the outside. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 31

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Sampling Profilers ➡ (Generally) will not interfere at all with your app's normal execution. ➡ Possible to miss things, it's luck whether a particular stack trace gets sampled at the right time. ➡ Can’t tell you how many times something has been called. ➡ “Here were the stack traces when I looked” ➡What was at the top of the stack at the time? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 32

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Manual Profilers Sometimes, you don't want or need a fancy tool. The easiest output to understand is the one you write yourself. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 33

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Manual Profilers ➡ Wrapping method calls in a call to Benchmark.measure will tell you how long it took. ➡ Can help you focus in on what you already suspect to be hotspots ➡ More likely to tell you if the distribution of calls is not unimodal ➡e.g. calling a memoized method, so only the first call will take a significant amount of time Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 34

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Chronometer A tool I built to automate this sort of low-fidelity tracing. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 35

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Chronometer ➡ Wraps methods with some timing / recording infrastructure ➡ Can output results in a format compatible with chrome://tracing ➡ Happens in-process, so you can write code that uses the timing results Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 36

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Chronofile for_class Pod::Installer do method :install!, context: event_phase_context[:toplevel] methods %i[ prepare resolve_dependencies download_dependencies validate_targets generate_pods_project integrate_user_project perform_post_install_actions run_podfile_post_install_hooks ] end # ... for_class Pod::Resolver do method :resolve end Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 37

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Profilers For me, this meant a mix of ➡ rubyprof ➡Tracing Profiler ➡ rbspy ➡Sampling Profiler ➡ chronometer Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 38

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All 3 are amazing, and I used all of them extensively last year. But knowing which to reach for at each step of the investigation would’ve saved me a bunch of time Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 39

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Chronometer hit the sweet spot for the type of software I was developing, and also solved a couple other problems I had. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 40

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Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 41

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Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 42

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Profiling revealed a fundemental problem with CocoaPods' architecture. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 43

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Graph Traversal Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 44

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Graph Traversal The performance bottleneck that all build systems end up fighting. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 45

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Graph Traversal A / \ B C \ / D Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 46

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Dependency Graph Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 47

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Graph Traversal The base problem we often face is How do you find “all the nodes/vertices that come after A”? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 48

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It's tempting to say: “A is followed by B and C, let’s recurse!” Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 49

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It's tempting to say: “A is followed by B and C, let’s recurse!” But then you end up visiting D twice! This might not sound like a big deal, but imagine 50 more nodes come after D... Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 50

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It's not just CocoaPods that has this issue! Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 51

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Graph traversal like this happens all over build tools. Why? Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 52

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DAGs ➡ Directed Acyclic Graphs ➡describe dependency structure. ➡ Every node (target, library, gem, etc.) has a list of dependencies ➡only rule is “you can’t depend upon something that depends on you” ➡ Most operations rely on what’s called the “transitive closure” of a node ➡“what are all the nodes that come after this one, no matter how far away?” Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 53

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def recursive_predecessors vertices = predecessors vertices += vertices.flat_map(&:recursive_predecessors) vertices.uniq! end to def recursive_predecessors vertices = Set.new visit = ->(vertex) do vertex.incoming_edges.each do |edge| vertex = edge.origin next unless vertices.add?(vertex) visit[vertex] end visit[self] vertices end Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 54

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Memoization Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 55

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Something that comes along with trying to solve graph traversal problems is memoization! Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 56

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From before: A / \ B C \ / D Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 57

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Let’s say some build setting for A depends on a build setting of B, C, D. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 58

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This can get slow. Really slow. Reeeeeeeeeaaaaaaaallllllly slow. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 59

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Memoization Calculate the value for the setting once and then store it Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 60

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➡ This is slightly different from caching ➡There’s no “invalidation” that can happen ➡ We’re just lazily computing a value, and storing it so next time it’s needed, we can return the stored value Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 61

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In ruby, we do this a lot! ever seen something like this: def expensive_to_calculate @expensive_to_calculate ||= ... end Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 62

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This works great! ➡ But imagine if the return value for expensive_to_calculate can be nil, or false. ➡ The ||= short-circuiting won’t kick in. ➡ We’ll need to recompute the value every time. ➡ Not ideal. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 63

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Instead, we need to turn to a more complicated variation on the pattern: def expensive_to_calculate return @expensive_to_calculate if defined?(@expensive_to_calculate) @expensive_to_calculate = ... end Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 64

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In CocoaPods, when I re-wrote the build settings, I added a tiny little DSL to make memoization a bit easier: def self.define_build_settings_method( method_name, build_setting: false, memoized: false, sorted: false, uniqued: false, compacted: false, frozen: true, from_search_paths_aggregate_targets: false, from_pod_targets_to_link: false, &implementation) Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 65

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➡ It uses an ivar hash called @__memoized to store those values, calls #fetch on that hash, returns the value unless the hash doesnt yet contain the key. ➡ One benefit of this is that the memoized state can be easily discarded by clearing that one ivar, instead of needing to keep track of a bunch of ivars, each only used in a single method implementation. ➡ By carefully selecting the key, we’re able to memoize both what a superclass and subclass return separately, so multiple calls to super can also be memoized. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 66

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This DSL (and accompanying refactor) allowed me to fix years-old bugs in build settings generation. Bug fixes which would've slowed installation down by over 5 minutes under the old implementation. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 67

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Design Lessons Learned Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 68

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Design Lessons Learned Even after all this work (and it’s still ongoing!), CocoaPods isn't as fast as I’d like. And it never will be. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 69

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➡ Some of this comes down to language. ➡ Some of this comes down to the fact that the job CocoaPods does is inherently complicated. ➡ Some of it is our own fault, for having a system design from 7 years ago that wasn’t built to scale this far. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 70

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Some particulars Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 71

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Exposing Mutable Objects ➡ Makes memoization hard. ➡ Need to have sidecar objects that hold computed values only when its safe to do so. ➡ (unless you want to get into cache invalidation bugs) Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 72

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Reading & Writing to the File System In-Line ➡ Makes it very hard to parallelize IO. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 73

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Having Consistent CLI Output ➡ Once again, makes parallelization hard. ➡ How do you show: ➡progress ➡underlying command invocations ➡failures Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 74

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Inefficient Data Structures ➡ Particularly the podfile & podspec. ➡ The entire Xcode project model ➡ Built using nested hashes, making change-tracking hard. ➡ Lack of copy-on-write. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 75

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Using Ruby to eval Objects Stored on Disk ➡ Allows state to leak in, makes computing stable hashes complicated because there are multiple valid representations to compute them from. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 76

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Not Storing all Podfile information in the Podfile.lock ➡ Figuring out when its changed based on only the info checked into git is nearly impossible. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 77

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All-or-Nothing Installation Operation ➡ Needing to do the entire installation every time means all invocations are equally slow. ➡ Fixed now, thanks to @sebastianv1! Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 78

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Pathname ➡ Nope. ➡ Just nope. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 79

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Design Lessons Learned Architecture matters just as much as algorithms. Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 80

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Picking your programming language is a tradeoff Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 81

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The Future of CocoaPods Performance Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 82

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Samuel Giddins @segiddins Making CocoaPods Fast – Samuel Giddins @ RubyConf Taiwan 2019 83