Optimize multiple dispatches on JobSystem done via TaskGraph

Source/Engine/Threading/JobSystem.cpp

@@ -87,6 +87,7 @@ namespace
     JobSystemService JobSystemInstance;
     Thread* Threads[32] = {};
     int32 ThreadsCount = 0;
+    bool JobStartingOnDispatch = true;
     volatile int64 ExitFlag = 0;
     volatile int64 DoneLabel = 0;
     volatile int64 NextLabel = 0;
@@ -234,10 +235,13 @@ int64 JobSystem::Dispatch(const Function<void(int32)>& job, int32 jobCount)
     LOG(Info, "Job enqueue time: {0} cycles", (int64)(Platform::GetTimeCycles() - start));
 #endif
 
+    if (JobStartingOnDispatch)
+    {
         if (jobCount == 1)
             JobsSignal.NotifyOne();
         else
             JobsSignal.NotifyAll();
+    }
 
     return label;
 #else
@@ -278,3 +282,21 @@ void JobSystem::Wait(int64 label)
 #endif
 #endif
 }
+
+void JobSystem::SetJobStartingOnDispatch(bool value)
+{
+#if JOB_SYSTEM_ENABLED
+    JobStartingOnDispatch = value;
+
+    if (value)
+    {
+        JobsLocker.Lock();
+        const int32 count = Jobs.Count();
+        JobsLocker.Unlock();
+        if (count == 1)
+            JobsSignal.NotifyOne();
+        else if (count != 0)
+            JobsSignal.NotifyAll();
+    }
+#endif
+}

Source/Engine/Threading/JobSystem.h

@@ -29,4 +29,9 @@ DECLARE_SCRIPTING_TYPE_MINIMAL(JobSystem);
     /// </summary>
     /// <param name="label">The label.</param>
     API_FUNCTION() static void Wait(int64 label);
+
+    /// <summary>
+    /// Sets whether automatically start jobs execution on Dispatch. If disabled jobs won't be executed until it gets re-enabled. Can be used to optimize execution of multiple dispatches that should overlap.
+    /// </summary>
+    API_FUNCTION() static void SetJobStartingOnDispatch(bool value);
 };

Source/Engine/Threading/TaskGraph.cpp

@@ -94,6 +94,7 @@ void TaskGraph::Execute()
 
         // Execute in order
         Sorting::QuickSort(_queue.Get(), _queue.Count(), &SortTaskGraphSystem);
+        JobSystem::SetJobStartingOnDispatch(false);
         _currentLabel = 0;
         for (int32 i = 0; i < _queue.Count(); i++)
         {
@@ -104,6 +105,7 @@ void TaskGraph::Execute()
         _queue.Clear();
 
         // Wait for async jobs to finish
+        JobSystem::SetJobStartingOnDispatch(true);
         JobSystem::Wait(_currentLabel);
     }