On Windows, set current thread in TLS to NULL before deleting the thread.

On Windows, set current thread in TLS to NULL before deleting the thread.

This mimics the behavior of the pthreads destructor protocol:
"At thread exit, if a key value has a non-NULL destructor pointer, and the thread has a non-NULL value associated with that key, the value of the key is set to NULL, and then the function pointed to is called with the previously associated value as its sole argument."

BUG=
R=iposva@google.com

Committed: https://github.com/dart-lang/sdk/commit/44d4d84be8d53d4b108b06bf11cadb23d5ff528f

[koda, 2015-08-21 02:36:40]

koda@google.com changed reviewers:
+ iposva@google.com, johnmccutchan@google.com

[koda, 2015-08-21 02:36:41]

This avoids having a small window where Thread::Current returns a dangling
pointer, and makes Windows behavior closer to other platforms.

[Ivan Posva, 2015-08-21 03:23:56]

https://codereview.chromium.org/1309563004/diff/1/runtime/vm/thread.cc
File runtime/vm/thread.cc (right):

https://codereview.chromium.org/1309563004/diff/1/runtime/vm/thread.cc#newcode97
runtime/vm/thread.cc:97: delete current;
Are we sure the destructor will not touch anything that tries to reference
Thread::Current()?

[koda, 2015-08-21 17:15:42]

https://codereview.chromium.org/1309563004/diff/1/runtime/vm/thread.cc
File runtime/vm/thread.cc (right):

https://codereview.chromium.org/1309563004/diff/1/runtime/vm/thread.cc#newcode97
runtime/vm/thread.cc:97: delete current;
On 2015/08/21 03:23:56, Ivan Posva wrote:
> Are we sure the destructor will not touch anything that tries to reference
> Thread::Current()?

I can't guarantee it won't, but if it did, we'd already have a problem with
pthreads on Linux and Mac. This CL just makes Windows consistent with their
behavior.

It's fine for the destructor to call Thread::Current as long as it guards
against null. The same is true for any initialization code that might run before
Thread::EnsureInit.

[Ivan Posva, 2015-08-25 22:32:43]

LGTM -ip

[koda, 2015-08-25 22:34:56]

Committed patchset #1 (id:1) manually as
44d4d84be8d53d4b108b06bf11cadb23d5ff528f (presubmit successful).