net: remove race condition on Close.

net: remove race condition on Close.

Previously a netFd could be queued for reading/writing in the channel,
but close(2)'ed before pollServer got to it. In this case, the kernel
would consider the descriptor closed and the attempt to add it to the
epoll set would fail and panic.

This patch makes Close a roundtrip to the pollServer, although the
actual close(2) still occurs elsewhere to avoid blocking the
pollServer.

Fixes issue 143.

[agl1, 2009-11-17 19:27:09]

We chatted about also fixing the races in Read and Write. I've started looking
at that, but I think that it's a different patch. One needs to add SHUT_* to
syscall, edit os.File to expose it etc.

So I think this patch is self contained and should probably land with its
current scope. I'll do a follow up to fix the other race.

[rsc, 2009-11-18 07:02:48]

LGTM

http://codereview.appspot.com/152130/diff/1001/1002
File src/pkg/net/fd.go (right):

http://codereview.appspot.com/152130/diff/1001/1002#newcode121
src/pkg/net/fd.go:121: // Thus fd.fd mirrors the kernel's view of the file
descriptor.
add

// TODO(rsc,agl): There is still a race in Read and Write,
// because they optimistically try to use the fd and don't
// call into the PollServer unless they get EAGAIN.

[agl1, 2009-11-18 21:18:35]

*** Submitted as http://code.google.com/p/go/source/detail?r=ca5c1a5682f8 ***

net: remove race condition on Close.

Previously a netFd could be queued for reading/writing in the channel,
but close(2)'ed before pollServer got to it. In this case, the kernel
would consider the descriptor closed and the attempt to add it to the
epoll set would fail and panic.

This patch makes Close a roundtrip to the pollServer, although the
actual close(2) still occurs elsewhere to avoid blocking the
pollServer.

Fixes issue 143.

R=rsc
CC=golang-dev
http://codereview.appspot.com/152130

Committer: Adam Langley <agl@golang.org>