worker_lock.lock() in WorkPool::~impl() to ensure destruction order (#1026)

Author: lihuiba

thread/workerpool.cpp

@@ -57,11 +57,16 @@ class WorkPool::impl {
     ~impl() {
         for (auto num = vcpus.size(); num; --num) enqueue({});
         for (auto &worker : owned_std_threads) worker.join();
+<<<<<<< HEAD
         if (likely(CURRENT)) {
             while (vcpus.size()) thread_yield();
         } else {
             while (vcpus.size()) std::this_thread::yield();
         }
+=======
+        while (vcpus.size()) std::this_thread::yield();
+        worker_lock.lock();
+>>>>>>> c4118ca (worker_lock.lock() in WorkPool::~impl() to ensure destruction order (#1026))
     }
 
     void enqueue(Delegate<void> call, AutoContext = {}) {