Add concurrency support for run_on_dataset (#8841)

Long-term, would be better to use the lower-level batch() method(s) but
it may take me a bit longer to clean up. This unblocks in the meantime,
though it may fail when the evaluated chain raises a
`NotImplementedError` for a corresponding async method

libs/langchain/langchain/smith/evaluation/runner_utils.py

@@ -1278,6 +1278,27 @@ async def arun_on_dataset(
     }
 
 
+def _handle_coroutine(coro: Coroutine) -> Any:
+    """
+    Handles a coroutine from a sync context.
+
+    Args:
+        coro (asyncio.coroutine): The coroutine to be handled.
+
+    Returns:
+        any: The result of the executed coroutine.
+    """
+    # Check if there's a running event loop
+    try:
+        loop = asyncio.get_event_loop()
+    except RuntimeError:  # No event loop
+        return asyncio.run(coro)
+    if loop.is_running():
+        return loop.create_task(coro)
+    else:
+        return asyncio.run(coro)
+
+
 def run_on_dataset(
     client: Client,
     dataset_name: str,
@@ -1285,6 +1306,7 @@ def run_on_dataset(
     *,
     evaluation: Optional[RunEvalConfig] = None,
     num_repetitions: int = 1,
+    concurrency_level: int = 5,
     project_name: Optional[str] = None,
     verbose: bool = False,
     tags: Optional[List[str]] = None,
@@ -1303,6 +1325,7 @@ def run_on_dataset(
             independent calls on each example without carrying over state.
         evaluation: Configuration for evaluators to run on the
             results of the chain
+        concurrency_level: The number of async tasks to run concurrently.
         num_repetitions: Number of times to run the model on each example.
             This is useful when testing success rates or generating confidence
             intervals.
@@ -1403,18 +1426,35 @@ def run_on_dataset(
     llm_or_chain_factory, project_name, dataset, examples = _prepare_eval_run(
         client, dataset_name, llm_or_chain_factory, project_name
     )
-    results = _run_on_examples(
-        client,
-        examples,
-        llm_or_chain_factory,
-        num_repetitions=num_repetitions,
-        project_name=project_name,
-        verbose=verbose,
-        tags=tags,
-        evaluation=evaluation,
-        input_mapper=input_mapper,
-        data_type=dataset.data_type,
-    )
+    if concurrency_level in (0, 1):
+        results = _run_on_examples(
+            client,
+            examples,
+            llm_or_chain_factory,
+            num_repetitions=num_repetitions,
+            project_name=project_name,
+            verbose=verbose,
+            tags=tags,
+            evaluation=evaluation,
+            input_mapper=input_mapper,
+            data_type=dataset.data_type,
+        )
+    else:
+        # TODO: Use runnables and the batch method
+        coro = _arun_on_examples(
+            client,
+            examples,
+            llm_or_chain_factory,
+            concurrency_level=concurrency_level,
+            num_repetitions=num_repetitions,
+            project_name=project_name,
+            verbose=verbose,
+            tags=tags,
+            evaluation=evaluation,
+            input_mapper=input_mapper,
+            data_type=dataset.data_type,
+        )
+        results = _handle_coroutine(coro)
     return {
         "project_name": project_name,
         "results": results,