Added comment for std::atomic<bool>::exchange()

send signal runProc_coinAttached only if state changes from false true.

include/runProc.h

@@ -15,6 +15,7 @@
 #include <QDebug>
 #include "datIf.h"
 #include <QSharedMemory>
+#include <atomic>
 #include "sendWRcmd.h"
 #include "controlBus.h"
 #include "storeINdata.h"
@@ -35,6 +36,10 @@ class T_runProc : public QObject
 
     void restoreDeviceParameter(struct T_devices *deviceSettings);
 
+#ifndef THIS_IS_CA_MASTER
+    std::atomic_bool m_coinAttached{false};
+#endif
+
 private slots:
     void runProc_slotProcess(void);
     bool bl_performComplStart(void);

src/runProc.cpp

@@ -48,8 +48,15 @@ T_runProc::T_runProc()
 void T_runProc::runProc_slotProcess(void)
 {
 #ifndef THIS_IS_CA_MASTER
-    if (epi_getDI_CoinAttach()) {
-        emit runProc_coinAttached();
+    bool const coinAttached = epi_getDI_CoinAttach();
+    // exchange: (atomically) replaces the underlying value of m_coinAttached
+    // with the value of coinAttached, returns the value of m_coinAttached
+    // before the call
+    if (m_coinAttached.exchange(coinAttached) == false) {
+        if (coinAttached) {
+            // old value was false, and new value is true
+            emit runProc_coinAttached();
+        }
     }
     cash_paymentProcessing();
     doors_supervise();