streaming: Don't accidentally serialize TLS

Author: jpsamaroo

src/stream.jl

@@ -300,7 +300,7 @@ function migrate_stream!(stream::Stream, w::Integer=myid())
 
         # TODO: Wire up listener to ferry cancel_token notifications to remote
         # worker once migrations occur during runtime
-        tls = get_tls()
+        tls = poolset(get_tls())
         @assert w == myid() "Only pull-based migration is currently supported"
         #remote_cancel_token = clone_cancel_token_remote(get_tls().cancel_token, worker_id)
 
@@ -322,8 +322,11 @@ function migrate_stream!(stream::Stream, w::Integer=myid())
                                              # Initialize the StreamStore on the destination with the unsent inputs/outputs.
                                              STREAM_THUNK_ID[] = thunk_id
                                              @assert !in_task()
-                                             set_tls!(tls)
-                                             #get_tls().cancel_token = MemPool.access_ref(identity, remote_cancel_token; local_only=true)
+
+                                             # N.B. It's not very valid to share TLS across tasks, but we do this
+                                             # so that input/output tasks have access to TID and cancel token
+                                             set_tls!(copy(MemPool.access_ref(identity, tls; local_only=true)))
+
                                              unsent_inputs, unsent_outputs = unsent
                                              for (input_uid, inputs) in unsent_inputs
                                                  input_stream = store.input_streams[input_uid]