hi, is there an alternative of @synchronized in kmm?

# multiplatform

[nikhil kumar]

hi, is there an alternative of @synchronized in kmm?

[magnumrocha]

https://kotlinlang.org/docs/shared-mutable-state-and-concurrency.html#mutual-exclusion

[magnumrocha]

“Mutual exclusion solution to the problem is to protect all modifications of the shared state with a critical section that is never executed concurrently. In a blocking world you’d typically use synchronized or ReentrantLock for that. Coroutine’s alternative is called Mutex. It has lock and unlock functions to delimit a critical section. The key difference is that Mutex.lock() is a suspending function. It does not block a thread.”

[kpgalligan]

There’s no language-level equivalent. Locks are the way to go. Atomic-fu (https://github.com/Kotlin/kotlinx.atomicfu) or Stately (https://github.com/touchlab/Stately, disclaimer, it’s ours) are libraries you could use for locks.

[kpgalligan]

Doing an interesting thing in Koin now for the new memory model. Define an expect function fun <R> synchronized(lock: Lockable, block: () -> R): R. Lockable is an expect class expect open class Lockable(). See source: https://github.com/InsertKoinIO/koin/blob/3.2.x/core/koin-core/src/commonMain/kotlin/org/koin/mp/KoinPlatformTools.kt

[kpgalligan]

On the JVM, Lockable is typealiased to Any, because any class in the JVM can be use for synchronize. actual typealias Lockable = Any. Source: https://github.com/InsertKoinIO/koin/blob/3.2.x/core/koin-core/src/jvmMain/kotlin/org/koin/mp/PlatformToolsJVM.kt

[kpgalligan]

On native, Lockable is a class you need to extend, but it has a lock internally which you can use like synchronize on the JVM.

actual open class Lockable {
    internal val lock = Lock()
}

[kpgalligan]

https://github.com/InsertKoinIO/koin/blob/3.2.x/core/koin-core/src/nativeMain/kotlin/org/koin/mp/PlatformToolsNative.kt

[kpgalligan]

Anyway, blog post overdue. This is all for the new memory model, btw. Old model is a whole different discussion.

[Tijl]

for the old memory model I can endorse stately (as a non-author)