Add comments, remove some redundant template fiddling

Also make ThreadSafeQueueSPSC not copyable and non movable

src/slic3r/GUI/Jobs/BoostThreadWorker.hpp

@@ -67,6 +67,11 @@ class BoostThreadWorker : public Worker, private Job::Ctl
         void deliver(BoostThreadWorker &runner);
     };
 
+    // The m_running state flag needs special attention. Previously, it was set simply in the run()
+    // method whenever a new job was taken from the input queue and unset after the finalize message
+    // was pushed into the output queue. This was not correct. It must not be possible to consume
+    // the finalize message before the flag gets unset, these two operations must be done atomically
+    // So the underlying queues are here extended to support handling of this m_running flag.
     template<class El>
     class RawQueue: public std::deque<El> {
         std::atomic<bool> *m_running_ptr;
@@ -79,6 +84,7 @@ class BoostThreadWorker : public Worker, private Job::Ctl
         void set_stopped() { m_running_ptr->store(false); }
     };
 
+    // The running flag is set if a job is popped from the queue
     template<class El>
     class RawJobQueue: public RawQueue<El> {
     public:
@@ -90,6 +96,7 @@ class BoostThreadWorker : public Worker, private Job::Ctl
         }
     };
 
+    // The running flag is unset when the finalize message is pushed into the queue
     template<class El>
     class RawMsgQueue: public RawQueue<El> {
     public:

src/slic3r/GUI/Jobs/ThreadSafeQueue.hpp

@@ -21,10 +21,6 @@ struct BlockingWait
     unsigned timeout_ms = 0;
 };
 
-template<class T, class... Args>
-using NonSpecialMembersOnly = std::enable_if_t<
-    (sizeof...(Args) >= 1) && !(... || std::is_convertible_v<Args, T>)>;
-
 // A thread safe queue for one producer and one consumer.
 template<class T,
          template<class, class...> class Container = std::deque,
@@ -36,15 +32,16 @@ class ThreadSafeQueueSPSC
     std::condition_variable m_cond_var;
 
 public:
-    template<class...Qargs, class = NonSpecialMembersOnly<ThreadSafeQueueSPSC, Qargs...>>
+
+    // Forward arguments to the underlying queue
+    template<class...Qargs>
     ThreadSafeQueueSPSC(Qargs &&...qargs)
         : m_queue{Container<T, ContainerArgs...>{std::forward<Qargs>(qargs)...}} {}
 
-    ThreadSafeQueueSPSC() = default;
-    ThreadSafeQueueSPSC(const ThreadSafeQueueSPSC&) = default;
-    ThreadSafeQueueSPSC(ThreadSafeQueueSPSC&&) = default;
-    ThreadSafeQueueSPSC& operator=(const ThreadSafeQueueSPSC&) = default;
-    ThreadSafeQueueSPSC& operator=(ThreadSafeQueueSPSC &&) = default;
+    ThreadSafeQueueSPSC(const ThreadSafeQueueSPSC&) = delete;
+    ThreadSafeQueueSPSC(ThreadSafeQueueSPSC&&) = delete;
+    ThreadSafeQueueSPSC& operator=(const ThreadSafeQueueSPSC&) = delete;
+    ThreadSafeQueueSPSC& operator=(ThreadSafeQueueSPSC &&) = delete;
 
     // Consume one element, block if the queue is empty.
     template<class Fn>