Memory Leak Fix In GetCurrentState Methods Improper Unsubscribe Timing

October 14, 2025 by StackCamp Team 71 views

Hey guys! Let's dive into a fascinating bug fix related to memory leaks in the getCurrentState methods. This issue was found and resolved in the bolt-to-github project, and it's a great example of how important proper subscription management is. So, grab your favorite beverage, and let’s get started!

Description

The getCurrentState methods in both the fileChanges and projectSettings stores were causing memory leaks. The culprit? Calling unsubscribe() inside the subscription callback instead of after the Promise resolved. This seemingly small oversight led to a big problem: store subscriptions weren't being cleaned up properly. As time went on, this resulted in accumulated memory usage, which, as you might guess, isn't a good thing.

Commit Link

Fixed in commit: 127b9d3bbdfd46dc3e73fff74539c3bc41746aeb

If you're curious, you can check out the specific commit on GitHub to see the exact code changes. It's always a good idea to peek at the code to get a deeper understanding of what’s going on!

Comprehensive Analysis

Why This Is Considered a Bug

This, my friends, is a critical memory leak bug. It directly impacts the Chrome extension's performance and stability. Here’s a breakdown of why it's such a big deal:

Memory Accumulation: Each time getCurrentState() is called, a new subscription is created. Because of the incorrect timing of unsubscribe(), these subscriptions weren't being cleaned up, leading to a buildup over time.
Resource Exhaustion: All those accumulated subscriptions start to eat up memory. Imagine a sink with a slow drain – eventually, it's going to overflow. Similarly, if memory isn't managed properly, it leads to resource exhaustion.
Performance Degradation: As the number of active subscriptions grows, store updates become sluggish. It's like trying to run a marathon with weights on your ankles – it slows you down.
Extension Instability: In severe cases, this can lead to the Chrome extension becoming unresponsive or even crashing. Nobody wants a crashed extension, right?

How to Reproduce

Want to see this bug in action? Here’s how you can reproduce it:

Setup: Load the Chrome extension and navigate to a bolt.new project. This sets the stage for our experiment.
Trigger the bug: Call getCurrentState() multiple times on either store. Here's some TypeScript code to illustrate:
```
// This would cause memory leaks
await fileChangesActions.getCurrentState();
await fileChangesActions.getCurrentState();
await fileChangesActions.getCurrentState();
// Each call leaves a subscription active
```
Each call to getCurrentState() in this scenario leaves an active subscription hanging around, contributing to the memory leak.
Observe: Monitor memory usage in Chrome DevTools. You’ll notice it continuously increasing. Chrome DevTools is your friend here – use it to keep an eye on what's happening under the hood.
Verify: Check that store subscriptions are not being cleaned up properly. This confirms our suspicions that the subscriptions are the problem.

Root Cause Analysis

The heart of the matter lies in the timing of the unsubscribe call. The original implementation looked something like this:

// ❌ BUGGY CODE - unsubscribe called inside callback
async getCurrentState(): Promise<FileChangesState> {
  return new Promise((resolve) => {
    const unsubscribe = fileChangesStore.subscribe((state) => {
      unsubscribe(); // ❌ Called too early - before resolve()
      resolve(state);
    });
  });
}

Let’s break down why this was problematic:

unsubscribe() is called immediately when the first state change occurs. This means we're unsubscribing almost as soon as we subscribe.
The subscription is cleaned up before the Promise resolves. The Promise is left hanging, waiting for something that won't happen.
If the store updates again before the Promise resolves, a new subscription is created. We're creating subscriptions faster than we're cleaning them up.
Multiple rapid calls create multiple active subscriptions. It's a subscription party, but not the fun kind.

The key takeaway here is that the unsubscribe was happening too early in the lifecycle of the subscription.

The Fix

The corrected implementation moves unsubscribe() outside the callback:

// ✅ FIXED CODE - unsubscribe called after Promise setup
async getCurrentState(): Promise<FileChangesState> {
  return new Promise((resolve) => {
    const unsubscribe = fileChangesStore.subscribe((state) => {
      resolve(state);
    });
    unsubscribe(); // ✅ Called after subscription setup
  });
}

So, why does this work?

The subscription is created and immediately cleaned up. It's a quick in-and-out, leaving no trace.
Only one subscription exists at a time. We're keeping things tidy and efficient.
The Promise resolves with the current state. The Promise gets the information it needs and can move on.
No memory leaks occur. Huzzah! We've plugged the leak.

Moving the unsubscribe call ensures that the subscription is active just long enough to capture the current state and then promptly cleaned up. This prevents the accumulation of subscriptions and, thus, the memory leak.

Exact Code Changes

Let’s get down to the nitty-gritty and look at the precise code changes. This is where the magic happens!

File: src/lib/stores/fileChanges.ts

async getCurrentState(): Promise<FileChangesState> {
  return new Promise((resolve) => {
    const unsubscribe = fileChangesStore.subscribe((state) => {
-     unsubscribe();
      resolve(state);
    });
+   unsubscribe();
  });
}

File: src/lib/stores/projectSettings.ts

async getCurrentState(): Promise<ProjectSettingsState> {
  return new Promise((resolve) => {
    const unsubscribe = projectSettingsStore.subscribe((state) => {
-     unsubscribe();
      resolve(state);
    });
+   unsubscribe();
  });
}

See that tiny but oh-so-important move? That's the fix that saved the day! By moving the unsubscribe() call, we ensure that the subscription is cleaned up right after it's set up, preventing memory leaks.

Importance of the Fix

Why should we care about this fix? Well, here’s why:

Memory Management: Prevents memory leaks that could crash the extension. A stable extension is a happy extension.
Performance: Eliminates unnecessary subscription overhead. A lean, mean extension performs better.
Reliability: Ensures the extension remains stable during long usage sessions. You can use the extension for hours without worrying about crashes.
User Experience: Prevents extension slowdowns and potential crashes. Happy users are loyal users.
Resource Efficiency: Reduces Chrome's memory footprint. Less memory usage means a smoother browsing experience.

Testing Coverage

To make sure the fix works like a charm, it was thoroughly tested with the following test cases:

Basic functionality: getCurrentState() returns the correct current state. We need to make sure the method does what it’s supposed to do.
State isolation: Multiple calls don't interfere with each other. Each call should be independent and not mess with others.
Memory safety: No subscription leaks occur. This is the core of the fix – no leaks allowed!
Integration: Works correctly with other store operations. The fix needs to play nicely with the rest of the code.

These tests provide confidence that the fix not only addresses the memory leak but also doesn't introduce any new issues.

Impact Assessment

Let’s assess the impact of this fix:

Severity: High – Memory leaks can cause system instability. This is a serious issue that needs to be addressed promptly.
Scope: Affects both fileChanges and projectSettings stores. The bug was present in multiple parts of the code.
User Impact: Prevents extension crashes and performance degradation. Users will experience a more stable and responsive extension.
Developer Impact: Cleaner code with proper resource management. Developers benefit from a codebase that is easier to maintain and reason about.

In conclusion, this fix is a big win for everyone involved. It ensures the Chrome extension maintains optimal performance and stability throughout its lifecycle.

This deep dive into the memory leak fix in the getCurrentState methods highlights the importance of proper subscription management. By carefully timing the unsubscribe() call, we were able to prevent memory leaks and ensure the stability and performance of the Chrome extension. Keep an eye out for these kinds of issues in your own code, and happy coding, guys!