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docs: deferred nodes (#4759)

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Sydney Runkle
2025-05-20 13:07:11 -04:00
committed by GitHub
parent 4a04ca7268
commit bd52b1faa1
2 changed files with 13 additions and 23 deletions
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docs/docs/how-tos/graph-api.ipynb
+12 -23
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@@ -1785,18 +1785,19 @@
},
{
"cell_type": "markdown",
"id": "205ff836-0f97-4ee8-9830-6bd8368e48c9",
"id": "48731230",
"metadata": {},
"source": [
"<details class=\"example\"><summary>Extended example: unequal length branches</summary>\n",
"### Defer node execution\n",
"\n",
"The above example showed how to fan-out and fan-in when each path was only one step. But what if one path had more than one step? Let's add a node <code>b_2</code> in the \"b\" branch:\n",
"<br>"
"Deferring node execution is useful when you want to delay the execution of a node until all other pending tasks are completed. This is particularly relevant when branches have different lengths, which is common in workflows like map-reduce flows.\n",
"\n",
"The above example showed how to fan-out and fan-in when each path was only one step. But what if one branch had more than one step? Let's add a node `\"b_2\"` in the `\"b\"` branch:"
]
},
{
"cell_type": "code",
"execution_count": 1,
"execution_count": 26,
"id": "3890af2f-fb14-4569-b48d-a91db2d3f026",
"metadata": {},
"outputs": [],
@@ -1844,13 +1845,14 @@
"builder.add_node(b)\n",
"builder.add_node(b_2)\n",
"builder.add_node(c)\n",
"builder.add_node(d)\n",
"# highlight-next-line\n",
"builder.add_node(d, defer=True)\n",
"builder.add_edge(START, \"a\")\n",
"builder.add_edge(\"a\", \"b\")\n",
"builder.add_edge(\"a\", \"c\")\n",
"builder.add_edge(\"b\", \"b_2\")\n",
"# highlight-next-line\n",
"builder.add_edge([\"b_2\", \"c\"], \"d\")\n",
"builder.add_edge(\"b_2\", \"d\")\n",
"builder.add_edge(\"c\", \"d\")\n",
"builder.add_edge(\"d\", END)\n",
"graph = builder.compile()"
]
@@ -1912,23 +1914,10 @@
},
{
"cell_type": "markdown",
"id": "903f0da5-8c2c-4a7e-96fb-0b16b4756eff",
"id": "70e67ced",
"metadata": {},
"source": [
"<div class=\"admonition note\">\n",
" <p class=\"admonition-title\">Note</p>\n",
"<p>In the above example, nodes <code>\"b\"</code> and <code>\"c\"</code> are executed concurrently in the same [superstep](../../concepts/low_level/#graphs). What happens in the next step?</p>\n",
" <p>We use <code>add_edge([\"b_2\", \"c\"], \"d\")</code> here to force node <code>\"d\"</code> to only run when both nodes <code>\"b_2\"</code> and <code>\"c\"</code> have finished execution. If we added two separate edges,\n",
" node <code>\"d\"</code> would run twice: after node <code>b2</code> finishes and once again after node <code>c</code> (in whichever order those nodes finish).</p>\n",
"</div>"
]
},
{
"cell_type": "markdown",
"id": "c1653341-3215-4ca0-b0e7-9be22f0adaa1",
"metadata": {},
"source": [
"</details>"
"In the above example, nodes `\"b\"` and `\"c\"` are executed concurrently in the same superstep. We set `defer=True` on node `d` so it will not execute until all pending tasks are finished. In this case, this means that `\"d\"` waits to execute until the entire `\"b\"` branch is finished."
]
},
{
libs/langgraph/langgraph/graph/state.py
+1
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@@ -304,6 +304,7 @@ class StateGraph(Graph):
If a string is provided, it will be used as the node name, and action will be used as the function or runnable.
action: The action associated with the node. (default: None)
Will be used as the node function or runnable if `node` is a string (node name).
defer: Whether to defer the execution of the node until the run is about to end.
metadata: The metadata associated with the node. (default: None)
input: The input schema for the node. (default: the graph's input schema)
retry: The policy for retrying the node. (default: None)