跳至主要内容

如何取消执行

先决条件

本指南假设您熟悉以下概念

在构建更长时间运行的链或 LangGraph 代理时，您可能希望在某些情况下中断执行，例如用户离开您的应用程序或提交新的查询。

LangChain 表达式语言 (LCEL) 支持通过运行时 信号 选项中止正在进行的 Runnable。

兼容性

内置信号支持需要 @langchain/core>=0.2.20。有关升级指南，请参见此处：安装集成包指南。

注意： 聊天模型或检索器等各个集成可能缺少或存在不同的中止执行实现。本指南中所述的信号支持将在链的步骤之间应用。

要了解其工作原理，请构建如下所示的链，该链执行 检索增强生成。它通过首先使用 Tavily 搜索网络，然后将结果传递给聊天模型以生成最终答案来回答问题。

选择您的聊天模型

安装依赖项

提示

参见 有关安装集成包的常规说明，请参见本节.

yarn add @langchain/openai

添加环境变量

OPENAI_API_KEY=your-api-key

实例化模型

import { ChatOpenAI } from "@langchain/openai";

const model = new ChatOpenAI({
  model: "gpt-4o-mini",
  temperature: 0
});
import { TavilySearchAPIRetriever } from "@langchain/community/retrievers/tavily_search_api";
import type { Document } from "@langchain/core/documents";
import { StringOutputParser } from "@langchain/core/output_parsers";
import { ChatPromptTemplate } from "@langchain/core/prompts";
import {
  RunnablePassthrough,
  RunnableSequence,
} from "@langchain/core/runnables";

const formatDocsAsString = (docs: Document[]) => {
  return docs.map((doc) => doc.pageContent).join("\n\n");
};

const retriever = new TavilySearchAPIRetriever({
  k: 3,
});

const prompt = ChatPromptTemplate.fromTemplate(`
Use the following context to answer questions to the best of your ability:

<context>
{context}
</context>

Question: {question}`);

const chain = RunnableSequence.from([
  {
    context: retriever.pipe(formatDocsAsString),
    question: new RunnablePassthrough(),
  },
  prompt,
  llm,
  new StringOutputParser(),
]);

如果您按常规调用它，您可以看到它返回最新信息

await chain.invoke("what is the current weather in SF?");
Based on the provided context, the current weather in San Francisco is:

Temperature: 17.6°C (63.7°F)
Condition: Sunny
Wind: 14.4 km/h (8.9 mph) from WSW direction
Humidity: 74%
Cloud cover: 15%

The information indicates it's a sunny day with mild temperatures and light winds. The data appears to be from August 2, 2024, at 17:00 local time.

现在，让我们尽早中断它。初始化一个 AbortController 并将其 signal 属性传递到链执行中。为了说明取消尽快发生的这一事实，请设置 100 毫秒的超时

const controller = new AbortController();

const startTimer = console.time("timer1");

setTimeout(() => controller.abort(), 100);

try {
  await chain.invoke("what is the current weather in SF?", {
    signal: controller.signal,
  });
} catch (e) {
  console.log(e);
}

console.timeEnd("timer1");
Error: Aborted
    at EventTarget.<anonymous> (/Users/jacoblee/langchain/langchainjs/langchain-core/dist/utils/signal.cjs:19:24)
    at [nodejs.internal.kHybridDispatch] (node:internal/event_target:825:20)
    at EventTarget.dispatchEvent (node:internal/event_target:760:26)
    at abortSignal (node:internal/abort_controller:370:10)
    at AbortController.abort (node:internal/abort_controller:392:5)
    at Timeout._onTimeout (evalmachine.<anonymous>:7:29)
    at listOnTimeout (node:internal/timers:573:17)
    at process.processTimers (node:internal/timers:514:7)
timer1: 103.204ms

您可以看到执行在 100 毫秒后结束。查看 此 LangSmith 跟踪，您可以看到模型从未被调用。

流式传输​

您也可以在流式传输时传递 signal。这使您可以更好地控制在 for await... of 循环中使用 break 语句来取消当前运行，这将仅在最终输出已开始流式传输后触发。以下示例使用 break 语句——请注意取消发生之前经过的时间

const startTimer2 = console.time("timer2");

const stream = await chain.stream("what is the current weather in SF?");

for await (const chunk of stream) {
  console.log("chunk", chunk);
  break;
}

console.timeEnd("timer2");
chunk
timer2: 3.990s

现在将此与使用信号进行比较。请注意，您需要将流包装在 try/catch 块中

const controllerForStream = new AbortController();

const startTimer3 = console.time("timer3");

setTimeout(() => controllerForStream.abort(), 100);

try {
  const streamWithSignal = await chain.stream(
    "what is the current weather in SF?",
    {
      signal: controllerForStream.signal,
    }
  );
  for await (const chunk of streamWithSignal) {
    console.log(chunk);
    break;
  }
} catch (e) {
  console.log(e);
}

console.timeEnd("timer3");
Error: Aborted
    at EventTarget.<anonymous> (/Users/jacoblee/langchain/langchainjs/langchain-core/dist/utils/signal.cjs:19:24)
    at [nodejs.internal.kHybridDispatch] (node:internal/event_target:825:20)
    at EventTarget.dispatchEvent (node:internal/event_target:760:26)
    at abortSignal (node:internal/abort_controller:370:10)
    at AbortController.abort (node:internal/abort_controller:392:5)
    at Timeout._onTimeout (evalmachine.<anonymous>:7:38)
    at listOnTimeout (node:internal/timers:573:17)
    at process.processTimers (node:internal/timers:514:7)
timer3: 100.684ms

此页面是否有帮助？


您也可以留下详细的反馈 在 GitHub 上.