- Memory Leak Issue: Node.js timeouts can easily create memory leaks.
-
Timeout API: Unlike browsers, where
setTimeout
returns a number, Node.js returns aTimeout
object. - Timeout Object: This object includes several properties and can retain references, causing memory issues.
Example of Memory Leak
class MyThing {
constructor() {
this.timeout = setTimeout(() => { ... }, INTERVAL);
}
clearTimeout() {
clearTimeout(this.timeout);
}
}
-
Problem: The
Timeout
object remains even afterclearTimeout
or timeout completion, holding references that prevent garbage collection.
Impact of AsyncLocalStorage
- AsyncLocalStorage: Attaches state to timeouts, making leaks worse.
- Example:
const { AsyncLocalStorage } = require('node:async_hooks');
const als = new AsyncLocalStorage();
let t;
als.run([...Array(10000)], () => {
t = setTimeout(() => {
const theArray = als.getStore();
}, 100);
});
- Result: Timeout holds a reference to a large array, exacerbating the memory issue.
Suggested Fix
- Use ID Instead of Object:
class MyThing {
constructor() {
this.timeout = +setTimeout(() => { ... }, INTERVAL);
}
clearTimeout() {
clearTimeout(this.timeout);
}
}
- Problem: Current Node.js bug makes this approach cause an unrecoverable memory leak.
Workaround
- Aggressive Nullification:
class MyThing {
constructor() {
this.timeout = setTimeout(() => {
this.timeout = null;
}, INTERVAL);
}
clearTimeout() {
if (this.timeout) {
clearTimeout(this.timeout);
this.timeout = null;
}
}
}
Broader Implications
- Widespread Use: Many applications use timeouts and intervals, leading to potential memory issues.
-
Next.js: Patches
setTimeout
andsetInterval
to clear intervals, though it can encounter related bugs.
Long-Term Considerations
-
Better API Design: Node.js could improve by returning a lightweight proxy object instead of the full
Timeout
object. - AsyncLocalStorage Management: Need for APIs to prevent propagation of unnecessary state to avoid leaks.
Conclusion
- Memory Management: Developers need to be cautious with timeouts and AsyncLocalStorage to avoid memory leaks.
- Awaiting Fix: A fix for the underlying Node.js bug is crucial for long-term resolution.
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