Stream: git-wasmtime

Topic: wasmtime / issue #10869 Memory "leak" when running a GC

Wasmtime GitHub notifications bot (May 30 2025 at 15:34):

alexcrichton opened issue #10869:

When running this program:

use wasmtime::*;

fn main() -> Result<()> {
    let mut config = Config::new();
    config.wasm_gc(true);
    let engine = Engine::new(&config)?;
    let mut store = Store::new(&engine, ());

    let module = Module::new(
        &engine,
        r#"
            (module
                (table 1 anyref)

                (func (result anyref)
                    i32.const 0
                    table.get)

            )
        "#,
    )?;

    Instance::new(&mut store, &module, &[]).unwrap();
    loop {
        store.gc(None);
    }
}

this will infinitely consume memory and eventually die. The problem here is that GC is written at the abstraction level of wasmtime-crate-exports but created those from internals requires pushing onto an internal vector. These vectors are never shrunk meaning that the memory is held until the store is dropped, meaning that a store's memory usage is O(gcs) which isn't great for long-running programs.

Wasmtime GitHub notifications bot (May 30 2025 at 15:34):

alexcrichton added the wasmtime:api label to Issue #10869.

Wasmtime GitHub notifications bot (May 30 2025 at 15:34):

alexcrichton added the wasm-proposal:gc label to Issue #10869.

Wasmtime GitHub notifications bot (Jun 03 2025 at 14:42):

alexcrichton closed issue #10869:

When running this program:

use wasmtime::*;

fn main() -> Result<()> {
    let mut config = Config::new();
    config.wasm_gc(true);
    let engine = Engine::new(&config)?;
    let mut store = Store::new(&engine, ());

    let module = Module::new(
        &engine,
        r#"
            (module
                (table 1 anyref)

                (func (result anyref)
                    i32.const 0
                    table.get)

            )
        "#,
    )?;

    Instance::new(&mut store, &module, &[]).unwrap();
    loop {
        store.gc(None);
    }
}

this will infinitely consume memory and eventually die. The problem here is that GC is written at the abstraction level of wasmtime-crate-exports but created those from internals requires pushing onto an internal vector. These vectors are never shrunk meaning that the memory is held until the store is dropped, meaning that a store's memory usage is O(gcs) which isn't great for long-running programs.

Wasmtime GitHub notifications bot (Jun 03 2025 at 14:42):

alexcrichton commented on issue #10869:

Fixed in https://github.com/bytecodealliance/wasmtime/pull/10903

Last updated: Dec 06 2025 at 07:03 UTC