Don't synchronize command lists and queues that were destroyed

lib/level-zero/cmdlist.jl

@@ -91,11 +91,12 @@ mutable struct ZeImmediateCommandList <: AbstractZeCommandList
                 @warn "Leaking an immediate command list still busy after $(FINALIZER_SYNC_TIMEOUT_NS ÷ 1_000_000_000)s to avoid blocking finalization" maxlog = 1
                 return
             end
-            zeCommandListDestroy(obj)
-            release(obj.context)
-            # mark destroyed: the stream registry can still reach this list, and
-            # synchronizing a destroyed handle crashes in the driver
+            # mark the list as destroyed before destroying it: it can still be reached and
+            # synchronized (see `destroyed`), which crashes in the driver on a destroyed handle
+            handle = obj.handle
             obj.handle = ze_command_list_handle_t(C_NULL)
+            zeCommandListDestroy(handle)
+            release(obj.context)
         end
         obj
     end

lib/level-zero/cmdqueue.jl

@@ -62,14 +62,12 @@ mutable struct ZeCommandQueue
             for (_, fence) in Iterators.flatten((obj.submitted, obj.spare, obj.failed))
                 zeFenceDestroy(fence)
             end
-            zeCommandQueueDestroy(obj)
+            # mark the queue as destroyed before destroying it: it can still be reached and
+            # synchronized (see `destroyed`), which crashes in the driver on a destroyed handle
+            handle = obj.handle
+            obj.handle = ze_command_queue_handle_t(C_NULL)
+            zeCommandQueueDestroy(handle)
             release(obj.context)
-            if LTS[]
-                # mark the queue as destroyed: it can still be weakly reachable (e.g. from
-                # the stream registry used by `synchronize_all_streams`), and synchronizing a
-                # destroyed handle crashes in the driver.
-                obj.handle = ze_command_queue_handle_t(C_NULL)
-            end
         end
         obj
     end

lib/level-zero/synchronization.jl

@@ -22,15 +22,23 @@ function check_done(res::ze_result_t)
         throw_api_error(res)
     end
 end
+# Lists and queues are only destroyed by their finalizers, which first wait for their work
+# where the driver doesn't. They can still be waited for afterwards: an object finalized in the same GC cycle as one
+# of them can make it reachable again (e.g. memory freed then recording its last user), and
+# synchronizing a destroyed handle crashes in the driver.
+destroyed(obj::Union{ZeImmediateCommandList, ZeCommandQueue}) = obj.handle == C_NULL
+
 Base.isdone(list::ZeImmediateCommandList) =
-    check_done(unchecked_zeCommandListHostSynchronize(list, 0))
+    destroyed(list) || check_done(unchecked_zeCommandListHostSynchronize(list, 0))
 Base.isdone(queue::ZeCommandQueue) =
-    check_done(unchecked_zeCommandQueueSynchronize(queue, 0))
+    destroyed(queue) || check_done(unchecked_zeCommandQueueSynchronize(queue, 0))
 
 # the blocking synchronization (GC-safe, like all Level Zero calls)
 gcsafe_synchronize(list::ZeImmediateCommandList) =
+    destroyed(list) ? RESULT_SUCCESS :
     unchecked_zeCommandListHostSynchronize(list, typemax(UInt64))
 gcsafe_synchronize(queue::ZeCommandQueue) =
+    destroyed(queue) ? RESULT_SUCCESS :
     unchecked_zeCommandQueueSynchronize(queue, typemax(UInt64))
 gcsafe_synchronize(event::ZeEvent) =
     unchecked_zeEventHostSynchronize(event, typemax(UInt64))

test/array.jl

@@ -313,6 +313,20 @@ end
   synchronize()
   @test Array(b) == ones(Float32, n_chunk)
 
+  # memory last used by a task that's done is collected together with that task's stream,
+  # whose command list then gets destroyed, and can be reused regardless. (the task is
+  # created in a function, as the testset would keep it alive.)
+  upload_in_task() = fetch(@async oneAPI.device_pointer(oneArray(ones(Float32, n_chunk))))
+  ptr = upload_in_task()
+  GC.gc(true)
+  ys = []
+  for _ in 1:64
+    push!(ys, oneArray(fill(2f0, n_chunk)))
+    oneAPI.device_pointer(last(ys)) == ptr && break
+  end
+  oneAPI.POOL[] && @test oneAPI.device_pointer(last(ys)) == ptr
+  @test all(y -> Array(y) == fill(2f0, n_chunk), ys)
+
   # many small arrays keep their contents, also when unused memory is given back
   xs = [oneArray(fill(Float32(i), i)) for i in 1:300]
   for i in 1:2:300