SerialMonitor: limit buffering without autoscroll

When the "autoscroll" checkbox is deselected the buffer may continue
to grow up to twice of the maximum size.

This is a compromise to ensure a better user experience and, at the
same time, reduce the chance to lose data and get "holes" in the
serial stream.

See #2491

Author: cmaglie

app/src/processing/app/SerialMonitor.java

@@ -69,7 +69,7 @@ public void actionPerformed(ActionEvent e) {
     Font editorFont = Preferences.getFont("editor.font");
     Font font = new Font(consoleFont.getName(), consoleFont.getStyle(), editorFont.getSize());
 
-    textArea = new TextAreaFIFO(4000000);
+    textArea = new TextAreaFIFO(8000000);
     textArea.setRows(16);
     textArea.setColumns(40);
     textArea.setEditable(false);    
@@ -244,11 +244,11 @@ public void actionPerformed(ActionEvent e) {
     final String s = consumeUpdateBuffer();
     if (s.length() > 0) {
       //System.out.println("gui append " + s.length());
-      boolean scroll = autoscrollBox.isSelected();
-      textArea.allowTrim(scroll);
-      textArea.append(s);
-      if (scroll) {
+      if (autoscrollBox.isSelected()) {
+        textArea.appendTrim(s);
         textArea.setCaretPosition(textArea.getDocument().getLength());
+      } else {
+        textArea.appendNoTrim(s);
       }
     }
   }

app/src/processing/app/debug/TextAreaFIFO.java

@@ -30,22 +30,20 @@
 
 public class TextAreaFIFO extends JTextArea implements DocumentListener {
   private int maxChars;
+  private int trimMaxChars;
 
   private int updateCount; // limit how often we trim the document
 
   private boolean doTrim;
 
   public TextAreaFIFO(int max) {
     maxChars = max;
+    trimMaxChars = max / 2;
     updateCount = 0;
     doTrim = true;
     getDocument().addDocumentListener(this);
   }
 
-  public void allowTrim(boolean trim) {
-    doTrim = trim;
-  }
-
   public void insertUpdate(DocumentEvent e) {
     if (++updateCount > 150 && doTrim) {
       updateCount = 0;
@@ -66,13 +64,29 @@ public void changedUpdate(DocumentEvent e) {
   public void trimDocument() {
     int len = 0;
     len = getDocument().getLength();
-    if (len > maxChars) {
-      int n = len - maxChars;
+    if (len > trimMaxChars) {
+      int n = len - trimMaxChars;
       //System.out.println("trimDocument: remove " + n + " chars");
       try {
         getDocument().remove(0, n);
       } catch (BadLocationException ble) {
       }
     }
   }
+
+  public void appendNoTrim(String s) {
+    int free = maxChars - getDocument().getLength();
+    if (free <= 0)
+      return;
+    if (s.length() > free)
+      append(s.substring(0, free));
+    else
+      append(s);
+    doTrim = false;
+  }
+
+  public void appendTrim(String str) {
+    append(str);
+    doTrim = true;
+  }
 }