On Tuesday, September 12, 2017 at 12:13:15 AM UTC-4, Dave Cheney wrote: > > > > On Tuesday, 12 September 2017 13:40:04 UTC+10, Shivaram Lingamneni wrote: >> >> On Monday, September 11, 2017 at 11:17:01 PM UTC-4, Dave Cheney wrote: >>> >>> The already in use is probably coming from the TCP stack which waits a >>> certain time before allowing the address to be reused. However I thought >>> that the net package already used SO_REUSEADDR to avoid the delay in close >>> to reopen. >>> >>> >>>> The question I'm really asking is not so much how to write code that >>>> works in practice (or, rather, appears to do so), but how to be certain >>>> (on >>>> the basis of the specification and API documentation) that the code is >>>> correct. >>>> >>> >>> As written the code is correct. Once the listener is closed, you can >>> reopen it, modulo TCP stack vagaries. >>> >> >> The net package is indeed setting SO_REUSEADDR, which allows re-bind on >> the address immediately after close(2). The problem is that close(2) is not >> guaranteed to occur as a result of Listener.Close(), because of reference >> counting of file descriptors. This is not an issue with the TCP stack; the >> runtime is simply failing to issue the required system call. >> > > I've had a look through the code for the TCPListener and I cannot see > where the reference count is being bumped by accept. As far as I understand > the *netFD returned from Accept is unassociated with the *netFD that is > bound to a listening socket. >
On the one hand, I am more confident in the claim that "close(2) is not guaranteed to occur as a result of Listener.Close()" than I am in the specific explanation of `Accept()` holding a reference. On the other hand, I think I found the relevant line of code: https://github.com/golang/go/blob/2d69e9e259ec0f5d5fbeb3498fbd9fed135fe869/src/internal/poll/fd_unix.go#L318 If I'm reading this correctly, this layer of Accept() acquires a readLock() on the file, which includes a reference acquire: https://github.com/golang/go/blob/2d69e9e259ec0f5d5fbeb3498fbd9fed135fe869/src/internal/poll/fd_mutex.go#L216 and then continues holding this reference when it "blocks" on `fd.pd.WaitRead`. -- 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. For more options, visit https://groups.google.com/d/optout.
