From e71c24ea9b70a700d8f0f605bf78c9c680423041 Mon Sep 17 00:00:00 2001
From: Nuno Campos <nuno@langchain.dev>
Date: Mon, 23 Sep 2024 08:41:57 -0700
Subject: [PATCH] Raise exception if sync method on async checkpointer is
 called from main thread

- The thread running the event loop can block waiting for a coro to run, only background threads can
---
 .../langgraph/checkpoint/postgres/aio.py             | 12 ++++++++++++
 .../langgraph/checkpoint/sqlite/aio.py               | 12 ++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py b/libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py
index 5a5206f3c..59ee7cbf9 100644
--- a/libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py
+++ b/libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py
@@ -393,6 +393,18 @@ class AsyncPostgresSaver(BasePostgresSaver):
         Returns:
             Optional[CheckpointTuple]: The retrieved checkpoint tuple, or None if no matching checkpoint was found.
         """
+        try:
+            # check if we are in the main thread, only bg threads can block
+            # we don't check in other methods to avoid the overhead
+            if asyncio.get_running_loop() is self.loop:
+                raise asyncio.InvalidStateError(
+                    "Synchronous calls to AsyncPostgresSaver are only allowed from a "
+                    "different thread. From the main thread, use the async interface."
+                    "For example, use `await checkpointer.aget_tuple(...)` or `await "
+                    "graph.ainvoke(...)`."
+                )
+        except RuntimeError:
+            pass
         return asyncio.run_coroutine_threadsafe(
             self.aget_tuple(config), self.loop
         ).result()
diff --git a/libs/checkpoint-sqlite/langgraph/checkpoint/sqlite/aio.py b/libs/checkpoint-sqlite/langgraph/checkpoint/sqlite/aio.py
index d2347006e..21cde06e0 100644
--- a/libs/checkpoint-sqlite/langgraph/checkpoint/sqlite/aio.py
+++ b/libs/checkpoint-sqlite/langgraph/checkpoint/sqlite/aio.py
@@ -153,6 +153,18 @@ class AsyncSqliteSaver(BaseCheckpointSaver[str]):
         Returns:
             Optional[CheckpointTuple]: The retrieved checkpoint tuple, or None if no matching checkpoint was found.
         """
+        try:
+            # check if we are in the main thread, only bg threads can block
+            # we don't check in other methods to avoid the overhead
+            if asyncio.get_running_loop() is self.loop:
+                raise asyncio.InvalidStateError(
+                    "Synchronous calls to AsyncSqliteSaver are only allowed from a "
+                    "different thread. From the main thread, use the async interface."
+                    "For example, use `await checkpointer.aget_tuple(...)` or `await "
+                    "graph.ainvoke(...)`."
+                )
+        except RuntimeError:
+            pass
         return asyncio.run_coroutine_threadsafe(
             self.aget_tuple(config), self.loop
         ).result()