Graceful shutdown running async jobs

Former-commit-id: 2ce5b94741d384b2dfd6d3b347fa1582cd45df8f

src/AsyncWorkQueue.cpp

@@ -73,6 +73,18 @@ bool AsyncWorkQueue::removeClientAsyncWrites(client *c)
     return fFound;
 }
 
+void AsyncWorkQueue::shutdown()
+{
+    std::unique_lock<std::mutex> lock(m_mutex);
+    serverAssert(!GlobalLocksAcquired());
+    m_fQuitting = true;
+    m_cvWakeup.notify_all();
+    lock.unlock();
+
+    for (auto &thread : m_vecthreads)
+        thread.join();
+}
+
 void AsyncWorkQueue::abandonThreads()
 {
     std::unique_lock<std::mutex> lock(m_mutex);

src/AsyncWorkQueue.h

@@ -34,5 +34,7 @@ public:
     void AddWorkFunction(std::function<void()> &&fnAsync, bool fHiPri = false);
     bool removeClientAsyncWrites(struct client *c);
 
+    void shutdown();
+
     void abandonThreads();
 };

src/server.cpp

@@ -4225,6 +4225,13 @@ int prepareForShutdown(int flags) {
     /* Close the listening sockets. Apparently this allows faster restarts. */
     closeListeningSockets(1);
 
+    if (g_pserver->asyncworkqueue)
+    {
+        aeReleaseLock();
+        g_pserver->asyncworkqueue->shutdown();
+        aeAcquireLock();
+    }
+
     for (int iel = 0; iel < cserver.cthreads; ++iel)
     {
         aePostFunction(g_pserver->rgthreadvar[iel].el, [iel]{