Remove fake isolate from concurrent sweeper and extend lifetime of VM threads.

Remove fake isolate from concurrent sweeper and extend lifetime of VM threads.

* Use real isolate in concurrent sweeper rather than shallow copy.

The only part of the isolate, other than the page being swept, used by the sweeper is the class table (via RawObject::Size), which is now safe to read concurrently (copy-on-write).

* Do not eagerly destroy a VM thread whenever it exits an isolate.

This extends the lifetime of a VM thread across entering/exiting multiple isolates. This is necessary in case an embedder callback executes during
compilation and switches/spawns isolates.

For embedder threads, since there is no API to signal "I'm done using the VM in this thread", this means we leak the (small) Thread structure.

For our own ThreadPool threads, we explicitly clean up.

BUG=23153
R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45810

[Ivan Posva, 2015-05-15 00:33:43]

Please avoid the repeated creation/deletion of the Thread object. Can be done in
a different CL but should have priority.

The rest LGTM for the purpose of removing the shadow isolate.

-Ivan

https://codereview.chromium.org/1136143003/diff/20001/runtime/vm/gc_sweeper.cc
File runtime/vm/gc_sweeper.cc (right):

https://codereview.chromium.org/1136143003/diff/20001/runtime/vm/gc_sweeper.c...
runtime/vm/gc_sweeper.cc:147: Thread::CleanUp();
Why do we need to cleanup here? The pool thread should release the thread
structure when it is done.

[koda, 2015-05-15 12:48:58]

Committed patchset #3 (id:40001) manually as r45810 (presubmit successful).

[koda, 2015-05-15 12:50:08]

Will follow up with CL with thread destructors.

https://codereview.chromium.org/1136143003/diff/20001/runtime/vm/gc_sweeper.cc
File runtime/vm/gc_sweeper.cc (right):

https://codereview.chromium.org/1136143003/diff/20001/runtime/vm/gc_sweeper.c...
runtime/vm/gc_sweeper.cc:147: Thread::CleanUp();
On 2015/05/15 00:33:43, Ivan Posva wrote:
> Why do we need to cleanup here? The pool thread should release the thread
> structure when it is done.

Done.