Serial port can take a while to close (especially on latest MacOSX) take this fact in account.

Author: cmaglie

app/src/processing/app/SerialMonitor.java

@@ -139,9 +139,12 @@ public void actionPerformed(ActionEvent event) {
         Preferences.set("serial.debug_rate", rateString);
         closeSerialPort();
         try {
+          Thread.sleep(100); // Wait for serial port to properly close
           openSerialPort();
         } catch (SerialException e) {
           System.err.println(e);
+        } catch (InterruptedException e) {
+          e.printStackTrace();
         }
       }});
 

app/src/processing/app/debug/BasicUploader.java

@@ -141,10 +141,14 @@ public boolean uploadUsingPreferences(String buildPath, String className,
           while (timeout > System.currentTimeMillis()) {
             List<String> portList = Serial.list();
             if (portList.contains(uploadPort)) {
-              Serial.touchPort(uploadPort, 9600);
-              break;
+              try {
+                Serial.touchPort(uploadPort, 9600);
+                break;
+              } catch (SerialException e) {
+                // Port already in use
+              }
             }
-            Thread.sleep(100);
+            Thread.sleep(250);
           }
         } else {
           Serial.touchPort(uploadPort, 9600);