You could add them as methods. But as I said, I don't think they are good
APIs.
I think the `Do` I described is the most reasonable compromise, if you
really want a one-size-fits-all generic solution.
Otherwise, use fine-grained locking or sync/atomic specific to your
use-case.
On Mon, May 23, 2022 at 10:56 AM Zhaoxun Yan <yan.zhao...@gmail.com> wrote:
>
> type Locked[T any] struct {
> mu sync.Mutex
> val T
> }
>
> func (l *Locked[T]) Do(f func(T) T) {
> l.mu.Lock()
> defer l.mu.Unlock()
> l.val = f(l.val)
> }
>
> Could you elaborate how 'Save/Store' , 'Load' and 'Tick / Increase ' get
> applied to the code above?
>
> Thanks.
>
> On Mon, May 23, 2022 at 3:24 PM 'Axel Wagner' via golang-nuts <
> golang-nuts@googlegroups.com> wrote:
>
>> FWIW a compromise is to have
>>
>> type Locked[T any] struct {
>> mu sync.Mutex
>> val T
>> }
>>
>> func (l *Locked[T]) Do(f func(T) T) {
>> l.mu.Lock()
>> defer l.mu.Unlock()
>> l.val = f(l.val)
>> }
>>
>> This forces modifications to be under the protection of a mutex while
>> also allowing those modifications to do arbitrary things.
>>
>> The downside is that this might do more locking than is strictly needed.
>> So, under contention, it might perform significantly worse than "manually"
>> managing the critical section.
>>
>> On Mon, May 23, 2022 at 9:11 AM Brian Candler <b.cand...@pobox.com>
>> wrote:
>>
>>> > It's best to be intentional about it and explicitly acquire and
>>> release a mutex around the critical sections of your code - because
>>> ultimately, only your code knows which sections are critical.
>>>
>>> That's really essential. For example, using your library, the following
>>> code is most definitely *not* race-free:
>>>
>>> tmp := v.Load()
>>> tmp = tmp + 1
>>> v.Save(tmp)
>>>
>>> The mutex has to protect the entire sequence, not the individual load
>>> and save operations.
>>>
>>> On Monday, 23 May 2022 at 07:57:02 UTC+1 axel.wa...@googlemail.com
>>> wrote:
>>>
>>>> Just to be clear, are you aware of the sync/atomic package?
>>>> https://pkg.go.dev/sync/atomic
>>>> There are also some changes in there for Go 1.18, specifically the
>>>> addition of some types, so that only atomic operations can be done:
>>>> https://pkg.go.dev/sync/atomic@master
>>>> I mention this because atomic.Value and atomic.Pointer[T] are
>>>> essentially what you are suggesting here.
>>>>
>>>> On Mon, May 23, 2022 at 8:04 AM Zhaoxun Yan <yan.z...@gmail.com> wrote:
>>>>
>>>>> However, as I want to narrow the scope of this type down to generate
>>>>> integer types (as in the commented code), it encountered two obstacles:
>>>>>
>>>>> 1) It is not legal to embed a generic inside a struct, nor can it make
>>>>> generalized computation =+1
>>>>>
>>>>> 2) Inheritance is not available in golang, so type "Counter" cannot
>>>>> inherit type "Global" and get its methods automatically. I need to repeat
>>>>> Save and Load methods to "Counter".
>>>>>
>>>>> Am I correct? Or can you improve it?
>>>>>
>>>>
>>>> You are correct that there is no way in Go to write a type which gets
>>>> all methods from an embedded field using generics. However, that is a good
>>>> thing. For example, say you could write
>>>>
>>>> type Locked[T any] struct {
>>>> sync.Mutex
>>>> T
>>>> }
>>>>
>>>> And this would get the methods of T and the methods of sync.Mutex. Then
>>>> a user could do
>>>>
>>>> type Counter int64
>>>> func (c *Counter) Increment() { *c += 1 }
>>>>
>>>> func main() {
>>>> var c Locked[Counter]
>>>> go c.Increment()
>>>> go c.Increment()
>>>> }
>>>>
>>>> And get a data race. That is, a method can modify a value in a way that
>>>> is incompatible with what your wrapper type is trying to do.
>>>>
>>>> That's really the crux of both of the obstacles you mention. You can't
>>>> run arbitrary computations and you can't promote methods, because *not all
>>>> computation and not all methods can be made concurrency safe this way*.
>>>>
>>>> It's best to be intentional about it and explicitly acquire and release
>>>> a mutex around the critical sections of your code - because ultimately,
>>>> only your code knows which sections are critical.
>>>>
>>>>
>>>>>
>>>> --
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>>>>>
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