Using a pointer receiver in a goroutine

Question

I have a method with a pointer receiver, I was wondering if using this pointer receiver is safe to use inside a goroutine within this method? or should I pass this pointer receiver as a parameter?

for example:

func (m *dummyStruct) doSomething {
    /* do a bunch of stuff */
    go func() {
        m.a = x
        m.doSomethingElse()
    }()
    return y
}

I know that I can not go wrong by passing m as a parameter to the goroutine but I was wondering if it is extremely necessary

Answer 1

If you are modifying state of m, you'll need a mutex lock and careful locking patterns.

Other than that, this will increase context switching across your thread boundries under most circumstances.

This is why we have the Go idiom:

Do not communicate by sharing memory; instead, share memory by communicating.

https://blog.golang.org/share-memory-by-communicating

Answer 2

I'd seen the link @eduncan911 posted but never tried to apply it. Hopefully this example helps:

package main

import (
    "fmt"
    "time"
)

type dummyStruct struct {
    a int
}

func (m *dummyStruct) doSomethingElse() {
    fmt.Println(m.a)
}

func doSomething(c chan int) {
    for i := 0; i < 5; i++ {
        go func() {
            x := time.Now().Unix()
            c <- int(x)
        }()
        time.Sleep(time.Second)
    }
}

func main() {
    outputs := make(chan int)
    m := &dummyStruct{}
    doSomething(outputs)
    for {
        //block until we can read from channel:
        x := <-outputs
        m.a = x
        m.doSomethingElse()
    }
}

//Output:
go run main.go
1474052448
1474052449
1474052450
1474052451
1474052452
fatal error: all goroutines are asleep - deadlock!

Answer 3

I think Pointer is not the right way to share data with respect to goroutines, as it will decrease the performance. The best option is channels.