Add a flush for the GUI print cache.

I tested the performance impact of this and for the GUI it seems to
be neutral, but the CLI takes a small performance hit.

src/rars/simulator/Simulator.java

@@ -240,6 +240,7 @@ private void startExecution() {
         private void stopExecution(boolean done, Reason reason) {
             this.done = done;
             this.constructReturnReason = reason;
+            SystemIO.flush(true);
             if (done) SystemIO.resetFiles(); // close any files opened in the process of simulating
             Simulator.getInstance().notifyObserversOfExecution(new SimulatorNotice(SimulatorNotice.SIMULATOR_STOP,
                     maxSteps, (Globals.getGui() != null || Globals.runSpeedPanelExists)?RunSpeedPanel.getInstance().getRunSpeed():RunSpeedPanel.UNLIMITED_SPEED,
@@ -386,6 +387,7 @@ public void run() {
             // Volatile variable initialized false but can be set true by the main thread.
             // Used to stop or pause a running program.  See stopSimulation() above.
             while (!stop) {
+                SystemIO.flush(false);
                 // Perform the RISCV instruction in synchronized block.  If external threads agree
                 // to access memory and registers only through synchronized blocks on same
                 // lock variable, then full (albeit heavy-handed) protection of memory and

src/rars/util/SystemIO.java

@@ -441,6 +441,8 @@ private static BufferedReader getInputReader() {
         return inputReader;
     }
 
+    // The GUI doesn't handle lots of small messages well so I added this hacky way of buffering
+    // Currently it checks to flush every instruction run
     private static String buffer = "";
     private static long lasttime = 0;
     private static void print2Gui(String output){
@@ -453,6 +455,19 @@ private static void print2Gui(String output){
             buffer += output;
         }
     }
+    /**
+     * Flush stdout cache
+     * Makes sure that messages don't get stuck in the print2Gui buffer for too long.
+     */
+    public static void flush(boolean force) {
+        long time = System.currentTimeMillis();
+        if (buffer != "" && (force || time > lasttime)){
+            Globals.getGui().getMessagesPane().postRunMessage(buffer);
+            buffer = "";
+            lasttime = time + 100;
+        }
+    }
+
 
     public static Data swapData(Data in){
         Data temp = new Data(false);