[optimization] Avoid unnecessary locking in single and scoped instances #1990
Description
ScopedInstanceFactory and SingleInstanceFactory both lock on every call to get. This adds unnecessary overhead since locking is only required during the first initialization of an object.
Koin should add double-checked locking so that we can avoid locking every time we inject a single or scoped instance.
See Dagger's DoubleCheck for an example in Java that is widely employed: https://github.com/google/dagger/blob/f8a09b29683687720ae3e0e5ac241f3a4a054d6e/java/dagger/internal/DoubleCheck.java#L29
Example implementation
// In SingleInstanceFactory
@Volatile
private var value: T? = null
override fun get(context: InstanceContext): T {
// Fast path to avoid locking if this instance is already initialized
if (!isCreated(context)) {
KoinPlatformTools.synchronized(this) {
if (!isCreated(context)) {
value = create(context)
}
}
}
return getValue()
}Note that the multiplatform @Volatile is necessary for this to be correct on JVM and native platforms.