basics2.slide

Go Basics 2
Tags: golang, workshop, avocode

Daniel Hodan
Avocode
danielhodan@avocode.com
http://avocode.com/

* 

.image images/light-logo.svg
.image images/gopher.png

* Testing

Lightweight test framework included in package `testing`.

File with a name ending in `_test.go` 

    > ls github.com/czertbytes/mypkg
    mypkg.go    mypkg_test.go

That contains functions named `TestXXX` with signature func `(t` `*testing.T)`.

    func TestMyFunc(t *testing.T) {
        ...
    }

Run tests with `go` `test`.

    > go test github.com/czertbytes/mypkg
    ok  	github.com/czertbytes/mypkg 0.085s

* Testing example

.code -edit test/mypkg_test.go /START OMIT/,/END OMIT/

* Benchmarking

Lightweight test framework included in package `testing`.

File with a name ending in `_test.go` 

    > ls github.com/czertbytes/mypkg
    mypkg.go    mypkg_test.go

That contains functions named `BenchmarkXXX` with signature func `(b` `*testing.B)`.

    func BenchmarkMyFunc(b *testing.B) {
        ...
    }

Run tests with `go` `test` `-bench`

    > go test -bench github.com/czertbytes/mypkg
    BenchmarkSHA512Hex-4   	   30000	     41735 ns/op
    PASS
    ok  	github.com/czertbytes/mypkg	1.669s

* Benchmarking example

.code -edit benchmark/mypkg_test.go /START OMIT/,/END OMIT/

* Remote packages

If you need more than standard library use `go` `get`

    > go get github.com/czertbytes/mypkg

- Download package in $GOPATH/src
- Compile in $GOPATH/pkg
- Install binary in $GOPATH/bin

Import as any other package in you $GOPATH

    import "github.com/czertbytes/mypkg"

* Remote packages

What if I have need more versions of given package in one $GOPATH?

- Multiple $GOPATH's
- Package versioning in URL
- Vendor package locally in `vendor`

* Remote packages

Vendoring with `vendor` folder - import path is the same.

    import "github.com/czertbytes/mypkg"

Import order: `vendor`, $GOPATH, $GOROOT

    > tree
    .
    ├── foo.go
    ├── foo_test.go
    └── vendor
        └── github.com
            └── czertbytes
                └── mypkg
                    ├── mypkg.go
                    └── mypkg_test.go
    4 directories, 4 files    

* Concurrency patterns

* WaitGroup

A `WaitGroup` waits for a collection of goroutines to finish.

    var wg sync.WaitGroup

Increase internal counter.

    wg.Add(1)

Decrease internal counter.

    wg.Done()

Wait blocks until counter is 0.

    wg.Wait()

* WaitGroup example

.play waitgroup/waitgroup.go

* Generator

A Generator is function that returns the next value in a sequence each time the function is called.

    for next := range generator() {
        fmt.Println(next)
    }

* Generator example

.play -edit generator/generator.go /START OMIT/,/END OMIT/

* Fan-in

A function can read from multiple inputs and proceed until all are closed by multiplexing the input channels onto a single channel that's closed when all the inputs are closed

.image images/gophermegaphones.jpg

* Fan-in example

.play fanin/fanin.go /START OMIT/,/END OMIT/

* Fan-out

Multiple functions can read from the same channel until that channel is closed.

* Fan-out example

.play fanout/fanout.go /START OMIT/,/END OMIT/

* Context

Context allows passing request scoped values, cancelation signals, and deadlines across API boundaries to all the goroutines involved in handling a request.

With value

    ctx := context.WithValue(context.Background(), "key", "value")

With cancel

    ctx, cancel := context.WithCancel(context.Background())
    defer cancel()

With deadline

    ctx, cancel := context.WithDeadline(context.Background(), deadlineTime)
    defer cancel()

    ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
    defer cancel()

* Context example

.play -edit context/context.go /START OMIT/,/END OMIT/

* Live coding

* Summary