fixup! Make Dagger.finish_stream() propagate downstream

src/stream.jl

@@ -40,9 +40,6 @@ function Base.put!(store::StreamStore{T,B}, value) where {T,B}
         end
         @dagdebug thunk_id :stream "adding $value ($(length(store.output_streams)) outputs)"
         for output_uid in keys(store.output_streams)
-            if !haskey(store.output_buffers, output_uid)
-                initialize_output_stream!(store, output_uid)
-            end
             buffer = store.output_buffers[output_uid]
             while isfull(buffer)
                 if !isopen(store)
@@ -257,10 +254,13 @@ function initialize_input_stream!(our_store::StreamStore{OT,OB}, input_stream::S
 end
 initialize_input_stream!(our_store::StreamStore, arg) = arg
 function initialize_output_stream!(our_store::StreamStore{T,B}, output_uid::UInt) where {T,B}
-    @assert islocked(our_store.lock)
     @dagdebug STREAM_THUNK_ID[] :stream "initializing output stream $output_uid"
-    buffer = initialize_stream_buffer(B, T, our_store.output_buffer_amount)
-    our_store.output_buffers[output_uid] = buffer
+    local buffer
+    @lock our_store.lock begin
+        buffer = initialize_stream_buffer(B, T, our_store.output_buffer_amount)
+        our_store.output_buffers[output_uid] = buffer
+    end
+
     our_uid = our_store.uid
     output_stream = our_store.output_streams[output_uid]
     output_fetcher = our_store.output_fetchers[output_uid]
@@ -595,6 +595,16 @@ function stream!(sf::StreamingFunction, uid,
     f = move(thunk_processor(), sf.f)
     counter = 0
 
+    # Initialize output streams. We can't do this in add_waiters!() because the
+    # output handlers depend on the DTaskTLS, so they have to be set up from
+    # within the DTask.
+    store = sf.stream.store
+    for output_uid in keys(store.output_streams)
+        if !haskey(store.output_buffers, output_uid)
+            initialize_output_stream!(store, output_uid)
+        end
+    end
+
     while true
         # Yield to other (streaming) tasks
         yield()

test/streaming.jl

@@ -413,6 +413,19 @@ for idx in 1:5
     # end
 
     @testset "Graceful finishing" begin
+        @test test_finishes("finish_stream() without return value") do
+            B = Dagger.spawn_streaming() do
+                A = Dagger.@spawn scope=rand(scopes) Dagger.finish_stream()
+
+                Dagger.@spawn scope=rand(scopes) accumulator(A)
+            end
+
+            fetch(B)
+            # Since we don't return any value in the call to finish_stream(), B
+            # should never execute.
+            @test isempty(ACCUMULATOR)
+        end
+
         @test test_finishes("finish_stream() with one downstream task") do
             B = Dagger.spawn_streaming() do
                 A = Dagger.@spawn scope=rand(scopes) Dagger.finish_stream(42)