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Go: a simple programming environment
Andrew Gerrand
Google
@enneff
adg@golang.org
http://golang.org
* Why Go?
* Software should be simple
* Software can be simple
* What I mean by "simple"
- Small
- Readable
- Consistent
- Orthogonal
- Predictable
- Robust
- Useful by default
* Go at a glance
- Compiled
- Statically typed
- Clean syntax
- Simple type system
- Concurrency primitives
- Rich standard library
- Great tools
- Open source
This talk is just a taste.
* The Gopher
.image support/gopher.jpg
* Go at Google
Go was created at Google to solve Google's problems:
- Network servers that do a lot of stuff concurrently
- Run on huge clusters of networked machines
- Maintained by large teams of programmers
Currently used by/for:
- YouTube (see the [[https://code.google.com/p/vitess/][vitess project]])
- [[http://talks.golang.org/2013/oscon-dl.slide][dl.google.com]]
- Logs Analysis teams
- Site Reliability and Operations teams
- Many others (the details are confidential, sorry!)
* Go beyond Google (two short lists)
Companies:
- Canonical
- CloudFlare
- Heroku
- Mozilla
- ngmoco:)
- Soundcloud
- Zynga
Open source projects:
- Camlistore
- Docker
* Hello, Go
.play support/hello.go
* go
Goroutines are lightweight threads that are managed by the Go runtime.
To run a function in a new goroutine, just put `"go"` before the function call.
.play support/goroutines.go
* chan
Channels are typed conduits for sychronization and communication between goroutines.
They're a versatile and expressive means of modelling concurrent processes.
But we're not going to look at them today. (There's no time!)
* sync
Channels are great, but sometimes other concurrency mechanisms are a better fit.
The `sync` package provides mutexes, condition variables, and more useful primitives.
.play support/sync.go /func main/,$
* net/http (1/2)
The `net/http` package provides an HTTP client.
.play support/http-client.go /func main/,$
The client handles HTTP `Keep-Alive` using a pool of connections, by default.
(This is configurable, of course.)
* net/http (2/2)
The `net/http` package also provides an HTTP server.
.play support/http-server.go /func main/,$
This is a high-performance, DoS-hardened, production-ready web server.
It serves `dl.google.com`.
* html/template
The `html/template` package provides an HTML templating system that automatically escapes content depending on its context.
.play support/template.go /const/,$
* flag
The `flag` package provides a simple API for parsing command-line flags.
.play support/flag.go /var/,$
Example invocation (a little different than GNU getopt):
$ flag -message 'Hold on...' -delay 5m
* An example
.link http://isgo1point1outyet.com
.image support/screenshot.png
* Structure
The program has two parts that execute concurrently:
- a poller that continuously checks whether Go 1.2 has been tagged, and
- an HTTP server that provides the user interface.
Go 1.2 can be considered "tagged" when this URL returns a `"200`OK"` response:
https://code.google.com/p/go/source/detail?r=go1.2
* The Server type
The `Server` struct contains the server state:
- the poll URL and period, and
- a boolean value ("Is Go 1.2 out yet?") and a mutex to protect it.
.code support/main-orig.go /type Server/,/^}/
* Sharing state
We must share state ("Is Go 1.2 out?") between the repo poller and the user interface.
To read from a `Server` value `s`, take the read lock (multiple goroutines can do this simultaneously):
s.mu.RLock()
yes := s.yes
s.mu.RUnlock()
To write, take the write lock (only one goroutine can do this at a time):
s.mu.Lock()
s.yes = true
s.mu.Unlock()
* Polling (1/2)
The `isTagged` function returns `true` if the given URL returns `"200`OK"`:
.code support/main-orig.go /func isTagged/,/^}/
* Polling (2/2)
The `poll` method loops until `isTagged` returns `true`.
Then it updates the state ("Go 1.2 is out!") and returns.
.code support/main-orig.go /func .+ poll/,/^}/
* Constructing a Server
The `NewServer` function constructs a new `Server`, starts the polling goroutine, and returns a `*Server` value.
.code support/main-orig.go /func NewServer/,/^}/
* Serving the user interface
The `ServeHTTP` method serves an HTTP request.
It puts the `s.yes` and `s.url` values into a struct,
and uses the struct to render the template as the HTTP response.
.code support/main-orig.go /func .+ ServeHTTP/,/^}/
This is an implementation of the `http.Handler` interface.
* The HTML user interface
The `tmpl` variable is a template that provides the HTML user inteface.
It is a global variable, so the template is parsed just once at init time.
.code support/main-orig.go /var tmpl/,/^`/
* Putting it all together
The `main` function creates a new `Server` and sets up the web server.
Some command-line flags enable run time configuration.
.code support/main-orig.go /const default/,/^}/
The whole program is just 87 lines of code.
* Demo
* Testing: writing tests
The `testing` package provides a lightweight test framework.
.code support/string_test.go /func TestIndex/,/^}/
* Testing: running tests
The go tool runs tests.
$ go test
PASS
ok strings 0.682s
$ go test -v
=== RUN TestIndex
--- PASS: TestIndex (0.00 seconds)
=== RUN TestReplace
--- PASS: TestReplace (0.00 seconds)
=== RUN TestContains
--- PASS: TestContains (0.00 seconds)
... many lines omitted ...
PASS
ok strings 0.659s
* Testing: coverage statistics
New in Go 1.2: the `go` tool can report test coverage statistics.
$ go test -cover
PASS
coverage: 96.4% of statements
ok strings 0.692s
The `go` tool can generate coverage profiles that may be intepreted by the `cover` tool.
$ go test -coverprofile=cover.out
$ go tool cover -func=cover.out
strings/reader.go: Len 66.7%
strings/strings.go: TrimSuffix 100.0%
... many lines omitted ...
strings/strings.go: Replace 100.0%
strings/strings.go: EqualFold 100.0%
total: (statements) 96.4%
* Testing: coverage visualization
$ go tool cover -html=cover.out
.image support/cover.png
* Testing: isTagged
To test the `isTagged` function we'll use the `net/http/httptest` package.
.code main_test.go /func TestIsTagged/,/^}/
The `StatusHandler` type is an `http.Handler` that sends an HTTP status of itself.
.code main_test.go /type StatusHandler/,/^}/
* Testing: an integration test (1/2)
.code main_test.go /func TestIntegration/,/^}/
* One more thing
* expvar (1/2)
The `expvar` package allows you to export variables via an HTTP handler
registered at [[http://localhost:8080/debug/vars][`/debug/vars`]].
.play support/expvar.go
* expvar (2/2)
.code main.go /Exported variables/,/^\)/
.code main.go /func isTagged/,/^}/
.code main.go /func .+ ServeHTTP/,/hitCount/
* Demo
* Conclusion
Simplicity revisited:
- Small
- Readable
- Consistent
- Orthogonal
- Predictable
- Robust
- Useful by default
* Stuff I didn't talk about
- Types and interfaces
- Concurrency in depth
- Packages and the build system
- Code formatting
- Benchmarking
- Debugging
- Documentation
* Learn more about Go
The Go web site
- [[http://golang.org][golang.org]]
The Go blog
- [[http://blog.golang.org][blog.golang.org]]
Go talks
- [[http://talks.golang.org][talks.golang.org]]
A Tour of Go
- [[http://tour.golang.org][tour.golang.org]]