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feat(go): preventing concurrent reads/writes on streams and futures#1490

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dicej merged 1 commit into
bytecodealliance:mainfrom
asteurer:concurrent
Jan 8, 2026
Merged

feat(go): preventing concurrent reads/writes on streams and futures#1490
dicej merged 1 commit into
bytecodealliance:mainfrom
asteurer:concurrent

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@asteurer

@asteurer asteurer commented Jan 7, 2026

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Overview

This change is intended to prevent concurrent reads and writes on streams and futures

Closes #1460

Observations

Given the following guest application code:

func Handle(request *Request) Result[*Response, ErrorCode] {
	tx, rx := MakeStreamU8()

	go func() {
		defer tx.Drop()
		for i := 0; i < 100; i++ {
			tx.Write([]byte(fmt.Sprintf("Hello %d", i)))
			time.Sleep(1 * time.Millisecond)
		}
	}()

	var wg sync.WaitGroup
	for i := 0; i < 3; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			buffer := make([]uint8, 7)
			for j := 0; j < 10; j++ {
				// ERROR: READ CONCURRENTLY
				count := rx.Read(buffer)
				if count == 0 {
					break
				}

				fmt.Printf("output: %s", string(buffer))
			}
		}(i)
	}

	wg.Wait()

	return Err[*wasi_http_handler.Response](MakeErrorCodeDestinationIpUnroutable())

}

I would expect there to be a panic and have there be a "nil handle" message; however, this is the output I get:

worker error: error while executing at wasm backtrace:
    0: 0x2916ef - <unknown>!<wasm function 16>
    1: 0x182eb0 - <unknown>!wit_component_wasi_http_types.wasm_stream_read_u8
    2: 0x184933 - <unknown>!github.com_bytecodealliance_wit_bindgen_wit_types.__StreamReader_go.shape.uint8__.Read
    3: 0x1890b5 - <unknown>!wit_component_export_wasi_http_handler.Handle.func2
    4: 0x188d81 - <unknown>!wit_component_export_wasi_http_handler.Handle.gowrap1
    5: 0x12204b - <unknown>!wasm_pc_f_loop_export
    6: 0x18c0d1 - <unknown>!_async_lift_wasi_http_handler_0.3.0_rc_2025_09_16_handle
error: channel closed

This is concerning because the Goroutine appears to be moving past the panic in the wit_runtime.Handle.Take() method:

func (self *Handle) Take() int32 {
	if self.value == 0 {
		panic("nil handle")
	}
	value := self.value
	self.value = 0
	return value
}

@dicej any thoughts and/or suggestions?

@dicej

dicej commented Jan 7, 2026

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time.Sleep(1 * time.Millisecond)

time.Sleep will block the entire runtime since there's no GOOS=wasip3 yet. You'll need to use wasi:clocks@0.3.0-rc- 2025-09-26/monotonic-clock#wait-for instead (i.e. generating bindings from the WASIp3 WIT files and using those directly).

dicej
dicej requested changes Jan 7, 2026
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Comment thread crates/go/src/package/wit_types/wit_future.go Outdated
Comment thread crates/go/src/package/wit_types/wit_future.go Outdated
@asteurer asteurer requested a review from dicej January 7, 2026 22:38
@asteurer

asteurer commented Jan 7, 2026 •
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@dicej Looks like the CI/Check GH Actions workflow failed. I assume the fix for that is just re-running it? If so, would you mind doing that for me?

@dicej

dicej commented Jan 7, 2026

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@dicej Looks like the CI/Check GH Actions workflow failed. I assume the fix for that is just re-running it? If so, would you mind doing that for me?

👍

BTW, would you be able to add test coverage for this to the tests/runtime-async suite, perhaps by expanding simple-stream-payload?

@asteurer

asteurer commented Jan 8, 2026

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@dicej When you have a moment, this is ready to be reviewed

dicej
dicej approved these changes Jan 8, 2026
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Looks good, thanks! Just a few doc tweak suggestions.

Comment thread crates/go/src/package/wit_types/wit_future.go Outdated
Comment thread crates/go/src/package/wit_types/wit_future.go Outdated
Comment thread crates/go/src/package/wit_types/wit_stream.go Outdated
@asteurer @dicej
feat(go): preventing concurrent reads/writes on streams and futures
53c7c31 
Signed-off-by: Andrew Steurer <94206073+asteurer@users.noreply.github.com>

fix: adding panic for empty dst slice, removing handle reassignment for futures

Signed-off-by: Andrew Steurer <94206073+asteurer@users.noreply.github.com>

docs(go): adding package comments

Signed-off-by: Andrew Steurer <94206073+asteurer@users.noreply.github.com>

feat(go): add future read concurrency test

Signed-off-by: Andrew Steurer <94206073+asteurer@users.noreply.github.com>

feat(go): adding remaining concurrent read/write tests

Signed-off-by: Andrew Steurer <94206073+asteurer@users.noreply.github.com>

doc(go): adding comments on drop methods

Signed-off-by: Andrew Steurer <94206073+asteurer@users.noreply.github.com>

Update crates/go/src/package/wit_types/wit_stream.go

Co-authored-by: Joel Dice <joel.dice@fermyon.com>

Update crates/go/src/package/wit_types/wit_future.go

Co-authored-by: Joel Dice <joel.dice@fermyon.com>

Update crates/go/src/package/wit_types/wit_future.go

Co-authored-by: Joel Dice <joel.dice@fermyon.com>
@asteurer asteurer requested a review from dicej January 8, 2026 23:02
@dicej dicej enabled auto-merge January 8, 2026 23:03
@dicej dicej added this pull request to the merge queue Jan 8, 2026
Merged via the queue into bytecodealliance:main with commit 44225ca Jan 8, 2026
27 checks passed
@asteurer asteurer deleted the concurrent branch January 8, 2026 23:33
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go: prevent concurrent reads or writes on the same stream or future

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@asteurer @dicej