Tips, Tricks and Gotchas

Ensure Concurrency

TinyGo code runs on a single core, in a single thread (think GOMAXPROCS=1). Since scheduling in TinyGo is cooperative, a goroutine that never does IO or other blocking calls (f.ex. time.Sleep()) will lock the single available thread only for itself and never allow other goroutines to execute. In such cases, you can use runtime.Gosched() as a workaround.

package main

import (
    "fmt"
    "time"
    "sync/atomic"
    "runtime"
)

func main() {

    var ops uint64 = 0
    for i := 0; i < 50; i++ {
        go func() {
            for {
                atomic.AddUint64(&ops, 1)
                runtime.Gosched()
            }
        }()
    }

    time.Sleep(time.Second)

    opsFinal := atomic.LoadUint64(&ops)
    fmt.Println("ops:", opsFinal)
}

Save Memory

Use the fact slices are descriptors of array segments to save memory and avoid unnecessary allocations. Allocate once an array of maximum size you ever need and slice it in your methods to the required sizes as you go.

type MyType struct {
    // ...other fields
    buf [6]byte
}

func (t *MyType) SomeMethod() {
    tmpBuf := t.buf[:2] // this method needs a buffer of size 2
    // ... use the buffer
}

You may even find yourself having two or more slices pointing at diferent regions of the same array simultaneously, if you are careful.

buf1 := t.buf[:2]
buf2 := t.buf[2:6]

For more recipes on how to avoid or minimize allocations while working with slices, please see additional tricks section of slice tricks page.

Familiarize yourself with heap allocation concept and use it to your advantage.

How to set build-time variables

You might have some specific value that you want to set for a variable at build-time. For example, you might want to preset a serial number, or set the WiFi access point SSID that you want your device to connect to, or set the version of the code being built.

This can be done using the tinygo build command -ldflags flag like this:

tinygo build -ldflags="-X 'main.version=1.0.0'" -target pyportal .

In your TinyGo program, the variable of the same package name/variable name will have its value set using the value passed in the -ldflags flag. Most commonly this will use the scope of the main package.

package main

var version string

func main() {
	println("the version is", version)
}

One important thing to note is that you cannot use a default value in your code if you want to be able to set that value using -ldflags. If you set the variable to a default value, then the value you pass using ldflags will be ignored. The value of the version variable in this code excerpt would not be changed by for this reason:

// will not be changed by using ldflags
var version = "default value"

Another important thing to note is that the values passed in could end up cached on the machine used to build the binary, for example in ~/.cache/tinygo/thinlto/. Because this feature is often used to pass in secrets, you will want to clear this cache as needed based on the security needs of your application.