fix deadlock in scoped_timer destructor (#5371)

src/util/scoped_timer.cpp

@@ -33,12 +33,14 @@ Revision History:
 #include <pthread.h>
 #endif
 
+enum scoped_timer_work_state { IDLE = 0, WORKING = 1, EXITING = 2 };
+
 struct scoped_timer_state {
     std::thread m_thread;
     std::timed_mutex m_mutex;
     event_handler * eh;
     unsigned ms;
-    std::atomic<int> work;
+    std::atomic<scoped_timer_work_state> work;
     std::condition_variable_any cv;
 };
 
@@ -49,11 +51,11 @@ static atomic<unsigned> num_workers(0);
 static void thread_func(scoped_timer_state *s) {
     workers.lock();
     while (true) {
-        s->cv.wait(workers, [=]{ return s->work > 0; });
+        s->cv.wait(workers, [=]{ return s->work > IDLE; });
         workers.unlock();
 
         // exiting..
-        if (s->work == 2)
+        if (s->work == EXITING)
             return;
 
         auto end = std::chrono::steady_clock::now() + std::chrono::milliseconds(s->ms);
@@ -68,9 +70,8 @@ static void thread_func(scoped_timer_state *s) {
         s->m_mutex.unlock();
 
     next:
-        s->work = 0;
+        s->work = IDLE;
         workers.lock();
-        available_workers.push_back(s);
     }
 }
 
@@ -97,7 +98,7 @@ struct scoped_timer::imp {
         s->ms = ms;
         s->eh = eh;
         s->m_mutex.lock();
-        s->work = 1;
+        s->work = WORKING;
         if (new_worker) {
             s->m_thread = std::thread(thread_func, s);
         } 
@@ -108,8 +109,11 @@ struct scoped_timer::imp {
 
     ~imp() {
         s->m_mutex.unlock();
-        while (s->work == 1)
+        while (s->work == WORKING)
             std::this_thread::yield();
+        workers.lock();
+        available_workers.push_back(s);
+        workers.unlock();
     }
 };
 
@@ -139,7 +143,7 @@ void scoped_timer::finalize() {
     while (deleted < num_workers) {
         workers.lock();
         for (auto w : available_workers) {
-            w->work = 2;
+            w->work = EXITING;
             w->cv.notify_one();
         }
         decltype(available_workers) cleanup_workers;