Assemblyscript: Memory leak in `Map#clear`

[jtenner]

https://github.com/AssemblyScript/assemblyscript/blob/master/std/assembly/map.ts#L61

Memory leak here at Map#clear

Proposed fix:

  clear(): void {
    const bucketsSize = INITIAL_CAPACITY * <i32>BUCKET_SIZE;

    // check to see if buckets exists and free it before setting it to a new array buffer
    if (this.buckets != null) memory.free(changetype<usize>(this.buckets));
    this.buckets = new ArrayBuffer(bucketsSize);
    this.bucketsMask = INITIAL_CAPACITY - 1;
    const entriesSize = INITIAL_CAPACITY * <i32>ENTRY_SIZE<K,V>();

    // check to see if entries exists and free it before setting it to a new array buffer
    if (this.entries!= null) memory.free(changetype<usize>(this.entries));
    this.entries = new ArrayBuffer(entriesSize, true);
    this.entriesCapacity = INITIAL_CAPACITY;
    this.entriesOffset = 0;
    this.entriesCount = 0;
  }

[jtenner]

I don't want to submit a new pull request without making sure I know what I'm talking about. Any ideas?

[dcodeIO]

Current stdlib anticipates the presence of GC, and ArrayBuffer is a managed object so is cleared by GC, not manually. Have you tried using ITCM with manual gc.collect() calls?

[jtenner]

@dcodeIO I'm at a complete loss for how to do this sort of thing. I don't know what ITCM is, or how the gc works. Is there documentation on this?

I'm guessing this is something I need to learn and I don't know where to find this information.

[dcodeIO]

To use the GC, do:

import "allocator/tlsf";
import "collector/itcm";

and whenever you need to free memory (this can only be done manually currently), do

gc.collect();

[jtenner]

I've imported the gc as you have suggested, and now I run into a runtime error. It looks like there's a problem within the step() function inside the gc. Is there something I'm missing?

index.js:210 Uncaught (in promise) RuntimeError: function signature mismatch
    at ~lib/collector/itcm/step (wasm-function[37]:172)
    at ~lib/collector/itcm/__gc_allocate (wasm-function[38]:15)
    at ~lib/array/Array<i32>#constructor (wasm-function[77]:53)
    at assembly/primitives/CanvasMap/CanvasRenderingContext2DInitializer#getOptimized (wasm-function[99]:93)
    at assembly/example/init (wasm-function[102]:8)
    at Object.wrap [as init] (http://localhost:1234/demo-src.e31bb0bc.js:4437:12)
    at _callee$ (http://localhost:1234/demo-src.e31bb0bc.js:4727:50)
    at tryCatch (http://localhost:1234/demo-src.e31bb0bc.js:152:40)
    at Generator.invoke [as _invoke] (http://localhost:1234/demo-src.e31bb0bc.js:378:22)
    at Generator.prototype.(anonymous function) [as next] (http://localhost:1234/demo-src.e31bb0bc.js:204:21)

I notice that it's calling ~lib/array/Array<i32>#constructor, and I'm definitely not constructing an Array<i32>. I assume that's because it's trying to initialize an array of references. Are there pitfalls I need to avoid, or is there a bug here?

The source starts here on this line:
https://github.com/jtenner/canvas-as/blob/master/assembly/primitives/CanvasMap.ts#L19

[dcodeIO]

It's not well tested, yet, so there might be issues. What about the array at public used: string[] = new Array<string>(0);?

[jtenner]

I don't think so, because the error occurs when I call getOptimized() like it suggests in the stack trace. It's saying that an array is being constructed in a function that isn't even constructing an array:

    at ~lib/array/Array<i32>#constructor (:1234/wasm-function[70]:36)
    at assembly/primitives/CanvasMap/CanvasRenderingContext2DInitializer#getOptimized (:1234/wasm-function[98]:196)
    at assembly/example/init (:1234/wasm-function[101]:8)

Edit: Just to make sure, I commented out the property and the if statements that use the string array. It looks like it's not related.

The untouched wat file shows construction of an Array here:
https://github.com/jtenner/canvas-as/blob/master/build/untouched.wat#L5532

Looks like those might be the culprits.

[dcodeIO]

GC itself doesn't construct managed objects, so it must be something else. For example OptimizedCanvasRenderingContext2D, which is instantiated there, contains a lot of arrays on its private properties that, since OptimizedCanvasRenderingContext2D doesn't have a constructor, are constructed and assigned on new OptimizedCanvasRenderingContext2D.

[jtenner]

When it generates an Array<enum> it would be generating an Array<i32> as a consequence. It must be one of those. You are right. I just can't seem to replicate the problem on wasm studio as an example.

Edit: Yes it's inlining the "default" constructor because no constructor exists.

[dcodeIO]

Closing this issue for now as it hasn't received any replies recently. Feel free to reopen it if necessary!