altosuilib: Make sure only one thread is closing serial device

Multiple closers can cause a crash by freeing the libaltos device twice

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/altosuilib/AltosSerial.java b/altosuilib/AltosSerial.java
index 0632ca70..60e15bdb 100644
--- a/altosuilib/AltosSerial.java
+++ b/altosuilib/AltosSerial.java
@@ -117,7 +117,7 @@ public class AltosSerial extends AltosLink  {
 		SwingUtilities.invokeLater(r);
 	}
 
-	private void close_serial() {
+	private synchronized void close_serial() {
 		synchronized (devices_opened) {
 			devices_opened.remove(device.getPath());
 		}