#5345: Add TaskQueue which sequentially executes the queued tasks usi…

…ng std::async.

libs/TaskQueue.h

@@ -0,0 +1,84 @@
+#pragma once
+
+#include <mutex>
+#include <list>
+#include <functional>
+#include <future>
+
+namespace util
+{
+
+class TaskQueue
+{
+private:
+    std::mutex _lock;
+
+    std::list<std::function<void()>> _queue;
+
+    std::future<void> _current;
+
+public:
+    ~TaskQueue()
+    {
+        clear();
+    }
+
+    // Adds the given task to the queue. This will launch the task
+    // immediately if no other task is currently processed
+    void enqueue(const std::function<void()>& task)
+    {
+        {
+            std::lock_guard<std::mutex> lock(_lock);
+            _queue.push_front(task);
+        }
+
+        if (isIdle())
+        {
+            startNextTask();
+        }
+    }
+
+    // Clears the queue. This might block waiting for any currently 
+    // active taks to finish
+    void clear()
+    {
+        {
+            // Lock the queue and remove any tasks such that no new ones are added
+            std::lock_guard<std::mutex> lock(_lock);
+            _queue.clear();
+        }
+
+        // Clear (and possibly) wait for the currently active future object
+        _current = std::future<void>();
+    }
+
+private:
+    bool isIdle() const
+    {
+        return !_current.valid() || 
+            _current.wait_for(std::chrono::seconds(0)) == std::future_status::ready;
+    }
+
+    void startNextTask()
+    {
+        std::lock_guard<std::mutex> lock(_lock);
+
+        if (_queue.empty())
+        {
+            return;
+        }
+
+        // No active task, dispatch a new one
+        auto frontOfQueue = _queue.front();
+        _queue.pop_front();
+
+        // Wrap the given task in our own lambda to start the next task right afterwards
+        _current = std::async(std::launch::async, [this, frontOfQueue]()
+        {
+            frontOfQueue();
+            startNextTask();
+        });
+    }
+};
+
+}

tools/msvc/libs.vcxproj

@@ -235,6 +235,7 @@
     <ClInclude Include="..\..\libs\string\tokeniser.h" />
     <ClInclude Include="..\..\libs\string\trim.h" />
     <ClInclude Include="..\..\libs\SurfaceShader.h" />
+    <ClInclude Include="..\..\libs\TaskQueue.h" />
     <ClInclude Include="..\..\libs\texturelib.h" />
     <ClInclude Include="..\..\libs\ThreadedDefLoader.h" />
     <ClInclude Include="..\..\libs\time\ScopeTimer.h" />

tools/msvc/libs.vcxproj.filters

@@ -261,6 +261,7 @@
     <ClInclude Include="..\..\libs\selection\SelectionVolume.h">
       <Filter>selection</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\libs\TaskQueue.h" />
   </ItemGroup>
   <ItemGroup>
     <Filter Include="util">