As far as I see, you pass c.id to go_readcallback, which gets the stream from streamsMap.
Why unsafe.Pointer and uintptr? Why not just a simple int or uint32 ? For map key, they're indifferent, and the unsafe.Pointer is totally uneeded here. 2020. július 9., csütörtök 18:58:52 UTC+2 időpontban Hraban Luyat a következőt írta: > > Hi all, > > In package github.com/hraban/opus (currently 57179df), if I run go test > -race I get an error: > > fatal error: checkptr: unsafe pointer arithmetic > > The offending line is: > > https://github.com/hraban/opus/blob/v2/stream.go#L108: > > oggfile := C.op_open_callbacks( > unsafe.Pointer(s.id), // <-- this guy > &C.callbacks, > nil, > 0, > &errno) > > Background: I need to pass a reference to a go struct to that C call, so > when it calls my callback function, that callback function can find the Go > struct. The C function expects a void *, but I have a map[uintptr]myType > locally with a fresh int for every new struct. I cast that uintptr to an > unsafe.Pointer, pass that to the C call, and once the callback is called, I > cast it back to a uintptr, and use that to fetch the relevant struct from > the map. That's what the "s.id" thing is. > > If I understand correctly, since 1.14 (?) go test -race includes > -d=checkptr, and checkptr does not like arbitrary uintptrs to be case to > unsafe.Pointer. However, as far as I understand, that error is spurious in > my specific case, because nobody ever dereferences the pointer at all, or > does any arithmetic on it; it's only cast straight back to a uintptr. > > Question 1: Is my map[uintptr]myType rigmarole even necessary? It came > about from my understanding of > https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md, > but maybe I misunderstood. > > Question 2: if it is necessary, is this "arbitrary uintptr in void *" > valid? As far as I understand the C standard, it is, but again maybe I > misunderstood. > > Question 3: If it is valid, what can / should I do about go test -race? > > Related: > https://groups.google.com/g/golang-nuts/c/FAOZoQzodAI/m/IF_xKit2DXYJ , > seems like a similar issue, and the reply suggests the approach is valid. > > Thanks all and kind regards > > Hraban > > > Full go test -race output: > > fatal error: checkptr: unsafe pointer arithmetic > > goroutine 56 [running]: > runtime.throw(0x42354f9, 0x23) > /usr/local/opt/go/libexec/src/runtime/panic.go:1116 +0x72 > fp=0xc000048ce0 sp=0xc000048cb0 pc=0x4034c22 > runtime.checkptrArithmetic(0x40, 0x0, 0x0, 0x0) > /usr/local/opt/go/libexec/src/runtime/checkptr.go:26 +0xce > fp=0xc000048d10 sp=0xc000048ce0 pc=0x400859e > _/Users/hraban/code/personal/opus.(*Stream).Init.func1(0xc0001525c0, > 0xc000128758, 0x1) > /Users/hraban/code/personal/opus/stream.go:108 +0x6a fp=0xc000048d68 > sp=0xc000048d10 pc=0x419ddba > _/Users/hraban/code/personal/opus.(*Stream).Init(0xc0001525c0, 0x42630c0, > 0xc0001323e0, 0x0, 0x0) > /Users/hraban/code/personal/opus/stream.go:112 +0x277 fp=0xc000048e38 > sp=0xc000048d68 pc=0x419a9c7 > _/Users/hraban/code/personal/opus.NewStream(0x42630c0, 0xc0001323e0, 0x0, > 0x0, 0x0) > /Users/hraban/code/personal/opus/stream.go:75 +0xa0 fp=0xc000048e88 > sp=0xc000048e38 pc=0x419a6b0 > _/Users/hraban/code/personal/opus.TestStreamIllegal(0xc0002fcb40) > /Users/hraban/code/personal/opus/stream_test.go:20 +0xc0 > fp=0xc000048ed0 sp=0xc000048e88 pc=0x4194320 > testing.tRunner(0xc0002fcb40, 0x4238c08) > /usr/local/opt/go/libexec/src/testing/testing.go:991 +0x1ec > fp=0xc000048fd0 sp=0xc000048ed0 pc=0x41270ec > runtime.goexit() > /usr/local/opt/go/libexec/src/runtime/asm_amd64.s:1373 +0x1 > fp=0xc000048fd8 sp=0xc000048fd0 pc=0x4066851 > created by testing.(*T).Run > /usr/local/opt/go/libexec/src/testing/testing.go:1042 +0x661 > > goroutine 1 [chan receive]: > testing.(*T).Run(0xc000156000, 0x4230a45, 0x11, 0x4238c08, 0x1) > /usr/local/opt/go/libexec/src/testing/testing.go:1043 +0x699 > testing.runTests.func1(0xc000156000) > /usr/local/opt/go/libexec/src/testing/testing.go:1284 +0xa7 > testing.tRunner(0xc000156000, 0xc00013bd50) > /usr/local/opt/go/libexec/src/testing/testing.go:991 +0x1ec > testing.runTests(0xc000132040, 0x437c680, 0x1d, 0x1d, 0x0) > /usr/local/opt/go/libexec/src/testing/testing.go:1282 +0x528 > testing.(*M).Run(0xc000154000, 0x0) > /usr/local/opt/go/libexec/src/testing/testing.go:1199 +0x300 > main.main() > _testmain.go:100 +0x224 > exit status 2 > FAIL _/Users/hraban/code/personal/opus 0.231s > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/54b0696e-c95e-4dfb-905e-76c42604db75o%40googlegroups.com.
