What does "no garbage collection" mean?

[Xe]

From the readme:

not yet supported:
...

• garbage collection

What does this mean? Does this mean that all values are on stack memory? Does this mean that all pointers are allocated on the heap and never freed?

[aykevl]

The latter. All objects are allocated and never freed. However, there is a simple heap-to-stack pass that tries to allocate objects on the stack if possible so that the most obvious cases won't leak memory.

I'm planning to implement a real garbage collector at some point, probably a simple mark-sweep collector to start with. It just hasn't been done yet.

[aykevl]

Closing as this is a question, not an issue. You are of course free to open an issue for GC support.

[Des-Nerger]

Until GC is implemented, what is the preferred approach to freeing memory, for a user? Is there a temporary API for that? I feel like region-based memory management would nicely work there. Until GC is implemented, at least.

[aykevl]

There is experimental GC support for ARM chips. You can enable it with -gc=marksweep.
Other than that, there is no way to free memory. However, you can structure the program in such a way that it never allocates on the heap in the main loop, by making sure everything can get stack allocated. For details, see: https://tinygo.readthedocs.io/en/latest/microcontrollers.html#heap-allocation

[kyegupov]

A note re wasm target: since webassembly has no stack introspection, marksweep cannot be ported to it. Three possible (all imperfect strategies are: manual free (incl. optionally delegating alloc/free to host), reference counting, semi-manual allocation of objects into "permanent" and "temporary" heaps.

[aykevl]

I think marksweep can be ported with some compiler work. LLVM has some support for it. It just needs to be done, and it isn't easy. See https://llvm.org/docs/GarbageCollection.html, the most likely candidate would be the shadow stack GC, at least initially.

[kyegupov]

@aykevl is there any timeline/roadmap for implementing garbage collection?

[aykevl]

On WebAssembly I assume?
Not really, certainly after #130 (almost finished), maybe after #104 (partially done). It's also hard to say how long the feature itself is going to take as I'm not sure how difficult it is.

[wilsonwang371]

does tinygo support GC in WASM now? Do I have to call GC in my code to get memory garbage collected?

[aykevl]

Yes, TinyGo supports GC in WebAssembly. And you don't need to call runtime.GC for it, it happens automatically.