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c: ClosureData, GoClosure #28

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Merged
xushiwei merged 1 commit into from
Sep 6, 2026
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c: ClosureData, GoClosure #28

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12 changes: 12 additions & 0 deletions c/c.go
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Original file line number Diff line number Diff line change
Expand Up @@ -191,6 +191,18 @@ func GoDeferData() Pointer

// -----------------------------------------------------------------------------

func ClosureData[ClosureT any](closure ClosureT) Pointer {

@fennoai fennoai Bot Sep 6, 2026

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[P2] Document ClosureData's unsafe contract (GC lifetime + exported doc comment)

ClosureData is an exported function with no doc comment, unlike neighbors such as GoString (line 180). Beyond golint/godoc convention, the lifetime contract is non-obvious: new(ClosureT) allocates a Go-managed object returned as a bare unsafe.Pointer. Once handed to C, the GC no longer sees a typed reference, so if C retains the pointer past the last Go reference the backing object can be collected or moved, leaving a dangling pointer. Recommend a doc comment stating (1) the purpose and (2) that the caller must keep the returned Pointer's backing allocation reachable (e.g. via runtime.KeepAlive/runtime.Pinner) for as long as C uses it.

ret := new(ClosureT)
*ret = closure
return Pointer(ret)
}

func GoClosure[ClosureT any](data Pointer) (closure ClosureT) {

@fennoai fennoai Bot Sep 6, 2026

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[P2] Document GoClosure's unchecked type reinterpretation + nil precondition

GoClosure is exported with no doc comment and performs *(*ClosureT)(data), blindly reinterpreting data as *ClosureT. Because ClosureT is inferred independently at each call site and is invisible in the raw Pointer, a mismatch between the type used at ClosureData and here is silent memory corruption with no compiler/runtime guard. Additionally, a nil data (common for a C callback's opaque user-data slot) dereferences nil and crashes. Recommend a doc comment stating that data must originate from ClosureData with the same ClosureT and must be non-nil (and/or add an early nil guard).

return *(*ClosureT)(data)
}

// -----------------------------------------------------------------------------

//go:linkname AllocaSigjmpBuf llgo.sigjmpbuf
func AllocaSigjmpBuf() Pointer

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