TransferMode

Note: modern Kotlin/Native memory manager allows to share objects between threads without additional ceremonies, so TransferMode has effect only in legacy memory manager.

Object Transfer Basics.

Objects can be passed between threads in one of two possible modes.

• SAFE - object subgraph is checked to be not reachable by other globals or locals, and passed if so, otherwise an exception is thrown

• UNSAFE - object is blindly passed to another worker, if there are references left in the passing worker - it may lead to crash or program malfunction

Safe mode checks if object is no longer used in passing worker, using memory-management specific algorithm (ARC implementation relies on trial deletion on object graph rooted in passed object), and throws an IllegalStateException if object graph rooted in transferred object is reachable by some other means,

Unsafe mode is intended for most performance critical operations, where object graph ownership is expected to be correct (such as application debugged earlier in SAFE mode), just transfers ownership without further checks.

Note, that for some cases cycle collection need to be done to ensure that dead cycles do not affect reachability of passed object graph.

See also