In release mode, there seems to be nothing to prevent this.
In debug mode, the "Verify" call waits for the sweeper, but there is still a race between the task count update and the ExitIsolateAsHelper call, which could cause problems.
Fix both of these, and add more assertions and verbose error messages.
- make sweeper task cleanly exit isolate *before* notifying
- wait for sweeper before shutting down isolate
- verbose pthread failures
BUG=
R=asiva@google.com
Review URL: https://codereview.chromium.org//1233563004 .
Daniel Andersson