code review 8459043: runtime: fix deadlock in network poller

runtime: fix deadlock in network poller
The invariant is that there must be at least one running P or a thread polling network.
It was broken.
Fixes issue 5216.

[dvyukov, 2013-04-07 03:41:26]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://dvyukov%40google.com@code.google.com/p/go/

[bradfitz, 2013-04-07 03:49:47]

https://codereview.appspot.com/8459043/diff/3/src/pkg/runtime/proc.c
File src/pkg/runtime/proc.c (right):

https://codereview.appspot.com/8459043/diff/3/src/pkg/runtime/proc.c#newcode881
src/pkg/runtime/proc.c:881: runtime·unlock(&runtime·sched);
same block of code as the one above, if you wanted to combine them.  it's
probably fine for documentation purposes to have them separate, though.

[dvyukov, 2013-04-07 03:55:43]

https://codereview.appspot.com/8459043/diff/3/src/pkg/runtime/proc.c
File src/pkg/runtime/proc.c (right):

https://codereview.appspot.com/8459043/diff/3/src/pkg/runtime/proc.c#newcode881
src/pkg/runtime/proc.c:881: runtime·unlock(&runtime·sched);
Yes, that was the intent.
The conditions and the comment are more important than the 3 trivial lines of
code.
And if I combine them and add comments in between, it will be ugly.

[r, 2013-04-07 05:10:11]

LGTM

[dvyukov, 2013-04-07 05:28:15]

*** Submitted as https://code.google.com/p/go/source/detail?r=34f14e209a2e ***

runtime: fix deadlock in network poller
The invariant is that there must be at least one running P or a thread polling
network.
It was broken.
Fixes issue 5216.

R=golang-dev, bradfitz, r
CC=golang-dev
https://codereview.appspot.com/8459043