* Yuan Ting <yuant...@ict.ac.cn> [200301 23:50]:
> I write a simple program likes below and it triggers a data race alarm with
> -race flag. But no matter how I run, this program will not panic. I know it
> is legal to receive messages from nil channels, but I don't quite
> understand why this program does not panic in the presence of data races.
>
> ch := make(chan struct{})
> go func() {
> ch = nil
> }()
> go func() {
> <-ch
> }()
I think the other responses missed the obvious here (or at least chose
more elaborate, though correct, explanations). This is a variable
assignment in one goroutine concurrent with a variable reference in
another. It is exactly the same (from the point of view of whether it
is a race or not) as this:
var a = 17
go func() {
a = 987654
}()
go func() {
fmt.Println(a)
}
In the second goroutine, the variable a might have the value 17, it
might have the value 987654, and it might have garbage that is neither
of these. This is a race condition, and it is also true of the channel
code above.
One of the other responses very correctly said that a race does not
imply that the code could panic. The integer code above will never
panic, even on architectures where a write of an integer to memory
concurrent with a read from that memory can possibly allow the read to
return partially written data. However, the above code is clearly a
race condition.
...Marvin
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