First step in refactoring out the build running from the gui for later thread fiascos.

threadtest.cpp

@@ -1,34 +1,54 @@
-#include <thread>
-#include <fmt/core.h>
-#include <chrono>
-#include <iostream>
-#include <thread>
-#include <utility>
+#include <condition_variable>
 #include <iostream>
 #include <mutex>
+#include <string>
+#include <thread>
 
-using namespace std::chrono_literals;
+std::mutex m;
+std::condition_variable cv;
+std::string data;
+bool ready = false;
+bool processed = false;
 
-std::atomic_int counter = 0;
-std::mutex counter_mutex;
+void worker_thread()
+{
+    // wait until main() sends data
+    std::unique_lock lk(m);
+    cv.wait(lk, []{ return ready; });
 
+    // after the wait, we own the lock
+    std::cout << "Worker thread is processing data\n";
+    data += " after processing";
 
-void locked_counter() {
-  for (int i = 0; i < 5; ++i)
-  {
-    std::lock_guard<std::mutex> lock(counter_mutex);
-    std::this_thread::sleep_for(100ms);
-    std::cout << "Thread 1 executing\n";
-    ++counter;
-  }
+    // send data back to main()
+    processed = true;
+    std::cout << "Worker thread signals data processing completed\n";
+
+    // manual unlocking is done before notifying, to avoid waking up
+    // the waiting thread only to block again (see notify_one for details)
+    lk.unlock();
+    cv.notify_one();
 }
 
 int main()
 {
-  std::jthread t2(locked_counter); // pass by value
+    std::thread worker(worker_thread);
 
-  for(int i = 0; i < 5; ++i) {
-    std::lock_guard<std::mutex> lock(counter_mutex);
-    std::cout << "counter is " << counter << std::endl;
-  }
+    data = "Example data";
+    // send data to the worker thread
+    {
+        std::lock_guard lk(m);
+        ready = true;
+        std::cout << "main() signals data ready for processing\n";
+    }
+    cv.notify_one();
+
+    // wait for the worker
+    {
+        std::unique_lock lk(m);
+        cv.wait(lk, []{ return processed; });
+    }
+    std::cout << "Back in main(), data = " << data << '\n';
+
+    worker.join();
 }