code review 74440044: os: relax the way we kill processes on Plan 9

os: relax the way we kill processes on Plan 9

Previously, we wrote "kill" to the process control file
to kill a program. This is problematic because it doesn't
let the program gracefully exit.

This matters especially if the process we're killing is a
Go program. On Unix, sending SIGKILL to a Go program will
automatically kill all runtime threads. On Plan 9, there
are no threads so when the program wants to exit it has to
somehow signal all of the runtime processes. It can't do
this if we mercilessly kill it by writing to it's control
file.

Instead, we now send it a note to invoke it's note handler
and let it perform any cleanup before exiting.

[ality, 2014-03-12 12:08:39]

Hello rsc@golang.org, 0intro@gmail.com (cc:
golang-codereviews@googlegroups.com),

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

[0intro, 2014-03-12 18:57:10]

It looks fine to me. It doesn't fix the net/http/cgi test by itself, but it does
after applying 9796043.

[rsc, 2014-03-12 20:33:45]

LGTM

[ality, 2014-03-13 01:13:20]

*** Submitted as https://code.google.com/p/go/source/detail?r=35d1f708a0d2 ***

os: relax the way we kill processes on Plan 9

Previously, we wrote "kill" to the process control file
to kill a program. This is problematic because it doesn't
let the program gracefully exit.

This matters especially if the process we're killing is a
Go program. On Unix, sending SIGKILL to a Go program will
automatically kill all runtime threads. On Plan 9, there
are no threads so when the program wants to exit it has to
somehow signal all of the runtime processes. It can't do
this if we mercilessly kill it by writing to it's control
file.

Instead, we now send it a note to invoke it's note handler
and let it perform any cleanup before exiting.

LGTM=rsc
R=rsc, 0intro
CC=golang-codereviews
https://codereview.appspot.com/74440044

[gobot, 2014-03-13 03:01:58]

This CL appears to have broken the windows-386-ec2 builder.