Not knowing how to reduce allocations
API changes
Mistake
Returning a slice is sharing up and causes the slice to escape the stack and get allocated on the heap.
type Reader interface {
Read(n int) (p []byte, err error)
}
Fix
Passing the slice as a parameter is an example of sharing down and the slice is able to be allocated on the stack instead of the heap.
type Reader interface {
Read(p []byte) (n int, err error)
}
Compiler optimizations
In the event we would want to create a map with a []byte key, we would write
the following:
type cache struct {
m map[string]int
}
func (c *cache) get(bytes []byte) (v int, contains bool) {
key := string(bytes)
v, contains := c.m[key]
return
}
However, if we rewrite this to query the map directly, we can avoid the bytes to string conversion entirely using a Go compiler optimization:
func (c *cache) get(bytes []byte) (v int, contains bool) {
v, contains := c.m[string(bytes)] // queries the map directly
return
}
sync.Pool
sync.Pool is a pool for re-using common objects.
func write(w io.Writer) {
b := getResponse() // returns a new []byte on every call
_, _ = w.Write(b)
}
We can reduce these allocations using sync.Pool.
var pool = sync.Pool{
New: func() any {
return make([]byte, 1024)
}
}
func write(w io.Writer) {
buffer := pool.Get().([]byte) // Get or create buffer from pool
buffer = buffer[:0] // reset buffer
defer pool.Put(buffer) // release buffer back to the pool
getResponse(buffer)
_, _ = w.Write(buffer)
}