What is the recommended approach to replacing a `synchronize

Question

What is the recommended approach to replacing a `synchronized` block since its now deprecated in Kotlin

gildor · Answer

I would say that especially in context of Android where you don t want too block UI even because of locks usually use <https kotlinlang org api kotlinx coroutines kotlinx coroutines core kotlinx coroutines sync mutex |coroutines Mutex> because anyway most of our business logic is suspend function based

gildor · Answer

But nothing wrong with usage of Java s concurrency primitives like ReentrantLock

lawlorslaw · Answer

Yeah so I was thinking about a reentrantlock but how do I guarantee only one instance of that object is created

gildor · Answer

If you looking for replacement for synchronized block I don t see a problem

gildor · Answer

synchronized already works only on object level so it s exactly the same as creating ReentrantLock as class level property

lawlorslaw · Answer

so this is the code i m trying to refactor which results in this logic potentially being executed in parallel ```val lockObject = StarPrinterManager manager Object synchronized lockObject code to be executed inside the lock to prevent multiple resources from calling this code ``` and as it stands now if the `StarPrinterManager manager` there will be a new object instance created everytime it hits that condition

gildor · Answer

so lockObject just becomes ReentrantLock

gildor · Answer

Honestly I m not that understand code snippet which you showed if it a part of the same function it doesn t look that synchronization is correct

gildor · Answer

Usually you init lock on the class creation level to sync operation inside of your class f you want global lock just make declare it on top level not as part of your class so it will be a single lock per process of your application

lawlorslaw · Answer

Yes this code snippet is all inside a single function

gildor · Answer

Then it not syncronized correctly

gildor · Answer

Multiple threads may execute code to be executed inside the lock simultaneusly if StarPrinterManager manager is null

lawlorslaw · Answer

So that s what I need to figure out how do I declare it on the top level so it s a single lock per application

gildor · Answer

single lock per application is just val myResourceLock = ReentrantLock

lawlorslaw · Answer

But do I need to use dependency injection

gildor · Answer

It s up to you

lawlorslaw · Answer

Which class do I declare the reentrantlock instance

gildor · Answer

If you use DI which supports Singleton correctly sure

gildor · Answer

Usually you do not declare lock public and instead you create a class some repository for your resource make this class Singleton using DI or just kotlin object And expose functions to work with this resource which under the hood use lock

lawlorslaw · Answer

Okay I ll look into something like that

lawlorslaw · Answer

Was hoping to find some open source examples of this

gildor · Answer

Of what exactly

lawlorslaw · Answer

Just that singleton pattern

gildor · Answer

Do you use DI library If so it probably should already support it If not use Kotlin object declaration

Petr Laštovička · Answer

You can also try Kotlin Atomicfu

gildor · Answer

I wouldn t recommend atomicfu until you really know what you are doing it s very low level and exists as building block for multiplatform synchronization