Align docs with USE_CYCLIC_GC=0 (ed36f02c)

Co-authored-by: ilya-g <ilya.gorbunov@jetbrains.com>

CONCURRENCY.md

@@ -199,10 +199,10 @@ To achieve such functionality Kotlin/Native runtime provides two related classes
 `kotlin.native.concurrent.AtomicReference` and `kotlin.native.concurrent.FreezableAtomicReference`.
 Atomic reference holds reference to a frozen or immutable object, and its value could be updated by set
 or compare-and-swap operation. Thus, dedicated set of objects could be used to create mutable shared object graphs
-(of immutable objects). Cycles in the shared memory could be created using atomic references, and to collect them
-Kotlin/Native runtime has special concurrent cycle collector, concurrently analyzing cyclic data rooted in atomic references.
-When cycle of no longer used objects is detected, collector zeroes out reference stored in atomic reference and thus
-allows cycle to be collected.
+(of immutable objects). Cycles in the shared memory could be created using atomic references.
+Kotlin/Native runtime doesn't support garbage collecting cyclic data when reference cycle goes through
+`AtomicReference` or frozen `FreezableAtomicReference`. So to avoid memory leaks atomic references
+that are potentially parts of shared cyclic data should be zeroed out once no longer needed.
 
  If atomic reference value is attempted to be set to non-frozen value runtime exception is thrown.
 

runtime/src/main/kotlin/kotlin/native/concurrent/Atomics.kt

@@ -216,7 +216,7 @@ private fun debugString(value: Any?): String {
 /**
  * An atomic reference to a frozen Kotlin object. Can be used in concurrent scenarious
  * but frequently shall be of nullable type and be zeroed out once no longer needed.
- * Asynchronous cycle collector takes care of cyclic references of that kind.
+ * Otherwise memory leak could happen if the atomic reference is a part of a reference cycle.
  */
 @Frozen
 @LeakDetectorCandidate
@@ -292,8 +292,8 @@ public class AtomicReference<T> {
 
 /**
  * An atomic reference to a Kotlin object. Can be used in concurrent scenarious, but must be frozen first,
- * otherwise behaves as regular box for the value. Asynchronous cycle collector helps to collect the
- * cyclic garbage going through frozen instances of `FreezableAtomicReference`.
+ * otherwise behaves as regular box for the value. If frozen, shall be zeroed out once no longer needed.
+ * Otherwise memory leak could happen if atomic reference is a part of a reference cycle.
  */
 @NoReorderFields
 @LeakDetectorCandidate
@@ -377,4 +377,4 @@ public class FreezableAtomicReference<T>(private var value_: T) {
 
     @SymbolName("Kotlin_AtomicReference_compareAndSet")
     private external fun compareAndSetImpl(expected: Any?, new: Any?): Boolean
-}
+}