Bun 'next Dev' Crash: Multiple Threads Issue

by Alex Johnson 45 views

Experiencing crashes when running bun next dev can be frustrating. This article delves into a specific crash scenario: "Bun internal multiple threads crashed," providing insights into the problem, potential causes, and troubleshooting steps. We'll break down a real-world example and guide you through understanding and resolving this issue.

Understanding the "Bun internal multiple threads crashed" Error

When you encounter the "Bun internal multiple threads crashed" error while using Bun with Next.js, it indicates a critical problem within Bun's runtime environment. This error signifies that multiple threads within Bun's core processes have terminated unexpectedly, leading to a crash. This is often a segmentation fault, meaning the program tried to access a memory location it shouldn't have. Identifying the root cause can be tricky, but the error message and associated details provide valuable clues.

Key Indicators from the Crash Report

The crash report provides crucial information for diagnosing the issue. Let's dissect a sample report:

Bun v1.3.3 (274e01c7) Windows x64
Windows v.win10_cu
CPU: sse42 avx avx2
Args: "C:\Users\Muhammad Ali\.bun\bin\bun.exe" "--bun" "F:\Ali\downloads\khushbu\node_modules\next\dist\server\lib\start-server.js"
Features: Bun.stderr(2) Bun.stdout(2) fetch(2) http_server jsc spawn transpiler_cache(20) tsconfig tsconfig_paths process_dlopen 
Builtins: ... (list of built-in modules)
Elapsed: 18641ms | User: 4031ms | Sys: 1734ms
RSS: 0.47GB | Peak: 0.48GB | Commit: 0.80GB | Faults: 196801 | Machine: 8.26GB

panic(tokio-runtime-worker): Segmentation fault at address 0x1A380940014
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

To send a redacted crash report to Bun's team,
please file a GitHub issue using the link below:

 https://bun.report/1.3.3/...
  • Bun Version and Platform: This section confirms the Bun version (e.g., 1.3.3) and the operating system (Windows x64). This is vital for identifying version-specific bugs.
  • CPU and Features: Details about CPU capabilities (SSE42, AVX, AVX2) and Bun's enabled features (fetch, HTTP server, transpiler cache, etc.) can highlight potential compatibility issues.
  • Arguments: The Args line shows the exact command executed, which in this case is running next dev using Bun. This helps confirm the context of the crash.
  • Resource Usage: Information like elapsed time, user/system CPU time, memory usage (RSS, Peak, Commit), and page faults can indicate resource contention or memory leaks.
  • Panic Message: The crucial line, panic(tokio-runtime-worker): Segmentation fault at address 0x1A380940014, points to the root cause: a segmentation fault within the Tokio runtime worker. Tokio is an asynchronous runtime for Rust, suggesting the crash occurred in a part of Bun's codebase that handles asynchronous operations.

Common Causes of the Crash

Based on the error message and related information, here are some common culprits:

  1. Bun Bugs: Bun is a relatively new runtime, and like any software, it may contain bugs. Segmentation faults often indicate underlying issues in memory management or concurrency handling within Bun itself.
  2. Incompatible Dependencies: Certain npm packages or native modules might not be fully compatible with Bun's runtime environment, leading to conflicts and crashes. This is especially true for packages that rely on native code or system-level APIs.
  3. Transpilation Issues: Bun uses its own JavaScript and TypeScript transpiler. Bugs in the transpiler or issues with specific code patterns in your project can sometimes cause crashes during the build process.
  4. Resource Limits: While less common, exceeding system resource limits (memory, file handles, etc.) could lead to crashes, particularly in resource-intensive operations like development builds.

Troubleshooting Steps

Now that we have a better understanding of the error, let's explore practical troubleshooting steps.

1. Update Bun to the Latest Version

One of the first steps is to ensure you are running the latest version of Bun. The Bun team actively fixes bugs and improves stability in each release. Updating might resolve the crash if it's due to a known issue.

bun update

After updating, try running bun next dev again to see if the problem persists.

2. Check for Incompatible Dependencies

Incompatible dependencies are a common cause of crashes. To identify potential issues:

  • Review Recent Package Updates: If the crash started occurring after updating specific packages, those packages might be the cause. Try downgrading them to previous versions to see if the problem resolves.
  • Focus on Native Modules: Packages that include native code (e.g., those requiring compilation during installation) are more likely to cause issues. Investigate any such packages in your project and check their compatibility with Bun.
  • Experiment with Minimal Dependencies: Create a minimal Next.js project with only essential dependencies and try running bun next dev. If it works, gradually add your project's dependencies back in to identify the problematic package.

3. Clear Bun's Cache

Bun aggressively caches transpiled code and other build artifacts to improve performance. However, sometimes the cache can become corrupted or outdated, leading to unexpected behavior. Clearing the cache can help resolve these issues.

While Bun doesn't have a dedicated command for clearing the entire cache, you can often achieve the same effect by deleting the relevant directories. Be cautious when deleting files, and make sure you understand what you're removing.

Typically, Bun's cache is located in a directory like ~/.bun/. You can try deleting the transpiler_cache directory within this location:

rm -rf ~/.bun/transpiler_cache

(Note: The exact cache location and directory name may vary depending on your operating system and Bun configuration.)

After clearing the cache, try running bun next dev again.

4. Simplify Your Code

Sometimes, complex code patterns or specific language features can trigger bugs in Bun's transpiler or runtime. Simplifying your code can help identify if a particular code construct is causing the crash.

  • Isolate Components: If the crash occurs when rendering a specific component, try isolating that component and running it in a simpler context.
  • Remove Complex Logic: Temporarily remove complex logic, such as asynchronous operations or advanced TypeScript features, to see if the crash disappears.
  • Check for Infinite Loops: Infinite loops or runaway recursion can exhaust resources and lead to crashes. Review your code for such issues.

5. Review System Resource Usage

Although less common, resource exhaustion can cause crashes. Monitor your system's CPU, memory, and disk usage while running bun next dev.

  • Memory Usage: If memory usage is consistently high, try increasing the Node.js memory limit using the NODE_OPTIONS environment variable:

    NODE_OPTIONS='--max_old_space_size=4096' bun next dev

    This sets the maximum old space size to 4GB. Adjust the value as needed.

  • File Handles: If you suspect file handle exhaustion, you may need to increase the system's file handle limit. The process for doing this varies depending on your operating system.

6. Report the Issue to the Bun Team

If you've tried the above steps and the crash persists, it's crucial to report the issue to the Bun team. Bun's developers rely on user reports to identify and fix bugs.

  1. Create a Minimal Reproduction: Try to create a minimal, reproducible example that demonstrates the crash. This makes it much easier for the Bun team to diagnose the issue.
  2. Gather Information: Collect as much information as possible, including:
    • Bun version
    • Operating system
    • Node.js version (if applicable)
    • Dependencies used in your project
    • The crash report
    • Steps to reproduce the crash
  3. File a GitHub Issue: The best way to report a Bun bug is to file an issue on the official Bun GitHub repository. Provide all the information you've gathered and a link to your minimal reproduction, if possible.

Example Scenario and Solution

Let's consider a real-world scenario based on the initial bug report:

Problem: A user encountered the "Bun internal multiple threads crashed" error while running bun next dev for their Next.js application on Windows. The crash report indicated a segmentation fault within the Tokio runtime worker.

Troubleshooting Steps:

  1. Updated Bun: The user was already running Bun v1.3.3, which was the latest version at the time.
  2. Checked Dependencies: The user reviewed their recent package updates but didn't identify any immediately suspicious packages.
  3. Cleared Transpiler Cache: The user cleared Bun's transpiler cache by deleting the ~/.bun/transpiler_cache directory.
  4. Simplified Code: The user began to simplify their Next.js components, focusing on the ones that had recently been modified.

Solution:

After simplifying their code, the user discovered that the crash was triggered by a specific component that used a complex combination of asynchronous operations and state updates. The component was making heavy use of useEffect hooks and data fetching, leading to race conditions and memory corruption within Bun's runtime.

By refactoring the component to use a more straightforward data fetching approach and simplifying the state updates, the user was able to resolve the crash.

Conclusion

The "Bun internal multiple threads crashed" error can be a challenging issue to diagnose, but by understanding the error message, following a systematic troubleshooting process, and providing detailed bug reports, you can often identify and resolve the problem. Remember to keep Bun updated, check for incompatible dependencies, clear the cache, simplify your code, and monitor system resources. If all else fails, don't hesitate to report the issue to the Bun team.

For more information on Bun and its features, you can visit the official Bun website. You may also find helpful resources and discussions on the official Bun Discord server.