Background

IntentRegistry::killConflictingOperations (src/mongo/db/repl/intent_registry.cpp) runs the kill-and-drain work on a std::async(std::launch::async, ...) thread and returns a std::future<ReplicationStateTransitionGuard>. Evaluate replacing std::async with our internal library stdx::thread, and decide whether the differences in behavior are acceptable.

Proposed change (to be evaluated)

Replace std::async with a stdx::thread plus a std::promise<ReplicationStateTransitionGuard>. By keeping public return type std::future, callers will stay unaffected. SERVER-137356 introduced a SigAltStackController workaround, which can be removed at this point.

Acceptance Criteria

• Evaluate the behavioral differences between std::async and stdx::thread; understand(and mitigate as needed) the implications of switching to stdx::thread.
  • A std::async future blocks in its destructor until the thread finishes, but stdx does not. 
  • std::async captures exceptions in the future, stdx would need to try/catch
• Consider having server programmability look over this change
• Run a sys-perf patch to confirm this change isn't a perf regression