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# GoUK '17 Notes from [@gonzaloserrano](https://twitter.com/gonzaloserrano). Last year's Ultimate Go workshop notes https://hackmd.io/s/ByS4NKjc Last year's talks notes https://hackmd.io/s/B1CAXxXq ## Workshop Mark Bates - [@markbates](https://twitter.com/markbates) author of https://github.com/gobuffalo/buffalo slides: http://golanguk.ngrok.io files: https://www.dropbox.com/s/c5aecqoivhb5g2n/2017-golanguk-workshop.zip?dl=0 - general review of `error`, `panic()`, `defer`, `recover()`. - errors: - sentinel errors let us know what's happening in our app, e.g `io.EOF` or `sql.ErrNoRows`. They are interesting for control flow. The speaker uses the stdlib ones but does not create them in his code. Does not say the cons. - https://github.com/pkg/errors to wrap errors and see tracing data. - concurrency: - `WaitGroup`: don't do `wg.Add(1)` inside the goroutine its doing the `Done()`. - example of https://github.com/golang/go/wiki/CommonMistakes#using-goroutines-on-loop-iterator-variables - buffered channels: - they can hide a design mistake, so be really careful with them. - what size do you use? Why? - why you don't want to block the sender? - what about backpressure (more writes in than writes out)? You can avoid memory overflow, but what limit you put? Why that limit? - they can hide a message loss problem. - `select`: be careful of ranging with a `select` with an empty `default` branch, the CPU will suffer. - testing: - https://github.com/smartystreets/goconvey is a cool tool. (Note: I knew about its BDD testing lib which I don't like, but the _reactive_ testing tool is cool). - dependency management: dep - context: API, cancelation propagation, trees - build tools, ldflags - protobufs & gRPC ## Keynote Steve Francia - [@spf13](https://twitter.com/spf13) slides: http://spf13.com/presentation/stateofthegophernation-aug17/ - contributing to go is easier, see https://blog.golang.org/contributor-workshop ## Writing beautiful packages Mat Ryer - [@matryer](https://twitter.com/matryer) - single interface method interfaces allow functions to implement the interface - e.g `http.Handler` and `http.HandlerFunc` - https://rakyll.org/style-packages - for libs, leave concurrency to the user - learn from the stdlib - the pkg name is part of the API, and naming is hard - take advantadge of zero values and avoid constructors *if you can* - e.g if you have not many fields - allow injecting `http.Client` - avoid global state and `init` ## Can you write an OS Kernel in Go? Achilleas Anagnostopoulos - [@achilleasa](https://github.com/achilleasa) slides: https://speakerdeck.com/achilleasa/bare-metal-gophers-can-you-write-an-os-kernel-in-go demo code: https://github.com/achilleasa/bare-metal-gophers Note: Achilleas wrote https://medium.com/geckoboard-under-the-hood/introducing-prism-9c08e9926755, looks like a great profiling tool with performance diff between changes. - unikernels and ring 0: avoid kernel / hypervisor overhead - is Go OK? - is GC'ed, but its fast enough for soft RT - awesome demo: text in framebuffer, image as text, then animation, then a 3D renderer ## Concurrency patterns Arne Claus from Trivago - [@arnecls](https://twitter.com/arnecls) slides: https://speakerdeck.com/arnecls/concurrency-patterns-in-go - blocking channels - channel blocks when no data: - no receiver, for unbuffered buffers - no sender, for all channels - blocking channels are good for synchronizing goroutines - blocking can lead to - deadlocks - scaling problems: adding more blocking goroutines can lead to worse performance - closing channels - closing a channel sends a special _closed_ message to all the readers - send after close panics - closing twice panics - _closed_ makes the reader receive two things: the zero value of the type of the channel, and _false_. - the receiver always knows if the channel is closed, the sender does not. - corolary: **always close the channel from the receiving side, not from the sending side!** - `select` - order of cases does not matter - a _default_ case exists that's executed if the other cases are blocked - to make channels nonblocking, use `time.After` in `select` or `default` - channels are streams of data; combining streams is powerful. Depending on the _shape_ of the combination there are different patterns: - fan-out (1:N): `select` with **writes** to several channels sends to the first non-blocking channel - turn-out (N:M): `select` with multiple reads, to `select` with multiple writes. - quit channel for cancelation - channel failures - deadlocks - memory copying and performance - pasing pointers and race conditions - caches are about sharing, a cache with channels is not a good idea, use mutex instead? - RWLocks can reduce the problem - multiple mutexes _will_ cause deadlocks - three shades of code - blocking: the program can be locked - lock free: at least one part of the program makes progress - wait free: all parts of the program make progress - `sync.Atomic` ops are thread-safe because they are based on CPU instructions - Spin Lock or Spinning CAS: Compare and Swap in a loop. That's how mutex are implemented (?) ## go-swagger Myles McDonnell - [@mylesmcdonnell](https://twitter.com/mylesmcdonnell) slides https://prezi.com/view/wuB2jT1XtDb4IT65S4DS/ - https://swagger.io - https://goswagger.io - https://github.com/go-swagger/go-swagger - define RESTful APIs - goswagger codegen - go-kit does not support it yet https://github.com/go-kit/kit/issues/185 ## embedding Sean Kelly - [@stabbycutyou](https://twitter.com/stabbycutyou) https://github.com/stabbycutyou/embeddingtalk - inheritance does not exist in Go - > embedding is not _better_ than inheritance, is something different to resolve a different problem - embedding is for composing interfaces and structs - behaviour over lineage - no base class - super class relationship - "is-a" vs "has-a" - method dispatching has some edge cases - what the spec says: - https://golang.org/ref/spec#Struct_types - > A field declared with a type but no explicit field name is an anonymous field (colloquially called an embedded field). Such a field type must be specified as a type name T or as a pointer to a non-interface type name \*T, and T itself may not be a pointer type. The unqualified type name acts as the field name. - https://golang.org/ref/spec#Interface_types - > An interface T may use a (possibly qualified) interface type name E in place of a method specification. This is called embedding interface E in T; it adds all (exported and non-exported) methods of E to the interface T. - selectors: https://golang.org/ref/spec#Selectors - shallowest depth concept - promoted fields: https://golang.org/ref/spec#Struct_types - examples: - emdedding a struct with another with the same field name - the field promoted is the one from the embedding not from the embedded struct - if you want to access the embedded one you need to do something like `embedding.embedded.field` - embedding multiple structs - nest embeddings - you cannot embed twice the same thing - same method and field example https://github.com/StabbyCutyou/embeddingtalk/blob/master/5.multiple/main.go - embed interfaces in structs - abstract behaviours instead of concrete behaviours - he does not say it but it's greate for test doubles where one just use/overwrite some of the methods of the interface - warning: explodes at runtime - viewmodels to avoid marshaling some model fields https://github.com/StabbyCutyou/embeddingtalk/blob/master/7.marshalling/1.viewmodel/main.go - extending generated code - embedding generating code makes easy to extend it without modifying the generated code so it can be generated over and over again. - promoted methods are only called in the original receiver **[warning]** ## fighting latency & profiling Filippo Valsorda - [@FiloSottile](https://twitter.com/FiloSottile) slides: https://speakerdeck.com/filosottile/you-latency-and-profiling-at-golanguk-2017 # - definition of fast - regex: MBs of data per second - API: many clients, _OR_ response time - so fast is **throughput** AND **latency** - go GC: better latency with every release, probably less throughput too. - CPU profiling - SIGPROF signal + `signal/runtime.go` - example of pprof for CPU - write tmp files to disk - profile before optimize! - optimizing CPU does not help much (maybe ~15%) - CPU profiling is for **throughput** - the tracer (new tool) is for **latency** - gathers discrete events, vs samples from the profiler, so its better - ways to use: import and pprof - has a web UI - go tool trace -pprof=TYPE trace.out - TYPE = {net, syscall, cpu, mem} - syscall for IO wait - tracing events can be analyzed and new tools can be created to for e.g filter them, like https://github.com/FiloSottile/tracetools/tree/master/cmd/tracefocus - would be great to have more tools! ## contributing to Go Audrey Lim - real-life example - look for `help-wanted` issues in GitHub ## how we built gopherize.me Mat Ryer - [@matryer](https://twitter.com/matryer) Ashley McNamara - [@ashleymcnamara](https://twitter.com/ashleymcnamara) - looks like a fun project - here you are mine https://gopherize.me/gopher/f242f064bb638bb1ef52f7d88e6fe97666f79003 ## goroutines optimitzation Guido Patanella - goroutines are multiplexed into OS threads - how a goroutine ends up in a CPU processor? ![](https://i.imgur.com/knmeePb.jpg =500x) - `ps -T | grep <binary-name>` - to see how many threads (SPIDs) are run by your go program - multiple workers example - tasks to do VS completed tasks - lets put more goroutines: 100, 1000... - there is a point where there is no benefit - context switching cost - map of executions to threads cost - vertical application scalability - requires - scheduler - orchestation - not necessary faster due to overhead - the go runtime gives you that for free - native - lightweight - after benchmarking you find the sweet spot of goroutines - to scale horizontally you need a cluster of servers - cluster scheduler - workers in each server + handshaking - other resources - presents a way to limit resources: files, CPU limit (didn't pay much attention on how he tried to do it) ## static analysis Takuya Ueda - [@tenntenn](https://twitter.com/tenntenn) slides: https://www.slideshare.net/takuyaueda967/static-analysis-in-go - reflection to analyze code - tools (used all of them :-) - gofmt / goimports - go vet / golint - guru - gocode - errcheck - gorename / gomvpkg - there are many go subpkgs in the stdlib to do static analysis: ast, build, parser, scanner, token... - go is very easy to analyze because the language is simple - flow + steps breakdown ![](https://i.imgur.com/30nLNIY.png =400x) - examples of all the steps - interested content in the slides but too low level for a talk or take notes ## deep learning with go Chris Benson - [@chrisbenson](https://twitter.com/chrisbenson) ![](https://i.imgur.com/VcJl0r3.jpg =500x) - deep neural networks to achieven machine learning - learn from data, not algorithms - use cases - anomaly detection - recommenders - computer vision, recognition - health diagnosis - financial analysis - ... - there are applications for ALL industries - super growth because of larger datasets and more powerful computers - neural networks are universal because they approximate to a programming function with at the same time is a universal unit of computation - that's why deep learning is so versatile - Google CEO: next 10 years are about AI - use AI to solve users problems - AI/ML is not just for data scinetists, putting it to production requires devs - you don't need to be an expert to go into the AI/ML space (as before did) - definitions: - gather knowledge from experience, experience to graph of concepts, that are simplified. - we like the one from https://mitpress.mit.edu/books/deep-learning - training a network: generalize predictions using correct results - is not memoritzation for results - how it works: back propagation (the grandfather of all the architectures) - data flows through layers of the network![](https://i.imgur.com/kum1Fqh.jpg =450x) - network architectures: - feed-forward: like the original. - convolutional: for vision recognition - recurrent: speech/writing recognition - generative adversarial (brand new): extends the dataset as you go, you don't need a big dataset - tensorflow - works for go but just for trained networks - you have to do the training in python - go alternative: https://github.com/sjwhitworth/golearn - the tensorflow team needs help in the go side - more links (not necessary from the talk) - machinebox.io - https://keras.io/ - HNews search https://hn.algolia.com/?query=tensorflow&sort=byPopularity&prefix&page=0&dateRange=all&type=story - https://github.com/vahidk/EffectiveTensorflow? - https://github.com/astorfi/TensorFlow-World - https://blog.chewxy.com/2016/09/19/gorgonia/ - http://www.deeplearningbook.org/ ## How to build SDKs (Dropbox experience) Diwaker Gupta - [@diwakergupta](https://twitter.com/diwakergupta) - Dropbox backend infra has been rewritten from Python to Go - talk in GopherCon https://www.youtube.com/watch?v=5doOcaMXx08 - https://github.com/dropbox?utf8=%E2%9C%93&q=&type=source&language=go - how to build SDKs: - coge generation: JSONSpec, IDLs+generators, OpenAPI/Swagger - principle of less surprise: no external or vendored deps - make config simple: - go flags are too limited, avoid them - env vars: they are global state and difficult to test (???) - use a plain struct - don't use persistence or I/O, let that to the consumer - add verbosity levels / logging - how to: - json unions of different types - marhsaling: use `omitempty` tag - unmarshaling: use `json.RawMessage` and implement `json.Unmarshal` and then choose the correct type - inherited types - marshaling: use a dummy interface that returns a bool to assert if its a certain type or the other - unmarshaling: similar, struct embedding of the union and then implement `json.Unmarshal`, inside it another unmarshal to each union'ed type to see if has contents: :rainbow: ![](https://i.imgur.com/8dI1F6Z.jpg =500x) - do not auth - autogenerate tests, like aws-sdk-go which uses json to define them - do idiomatic error handling, pkg/errors is nice. - download https://github.com/dropbox/dbxcli :smiley: ## WebSockets Konrad Reiche - [@konradreiche](https://twitter.com/konradreiche) - WS. 2008. Towards real time. REST is 20 years. - REST maps HTTP verbs to Resources? Not just that. - defined in [Architectural Styles and the Design of Network-based Software Architectures](https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation_2up.pdf) - gorilla/websocket is better than the stdlib one - gorilla's one reads full messages even they are in different frames. The stdlib one not, but they cannot change it. - I think he does not know about https://github.com/gobwas/ws cause its brand new - example code using gorilla's, not many notes because I've already done that in Social Point 3 years ago: http://go-sp.gonzaloserrano.io/#/27 ## syscalls Liz Rice - [@lizrice](https://twitter.com/lizrice) - syscalls are used for: files / devices / processes / network / time-date - you can see them with strace - package `syscall` - OS-specific files - autogenerated files - writing a strace-like tool in go