Tengo una aplicación Gui en swing que imprime un ticket en una impresora térmica en serie. Cuando presiono el botón que inicia esta acción, mi GUI está congelada. Creo que eso es porque el código se ejecuta en el EDT. Usé jstack para estar seguro, pero no entiendo los resultados a continuación:

Full thread dump Java HotSpot(TM) Client VM (23.3-b01 mixed mode, sharing):

"Thread-12" prio=6 tid=0x03012000 nid=0xd04 runnable [0x038ef000]
java.lang.Thread.State: RUNNABLE
    at gnu.io.RXTXPort.eventLoop(Native Method)
    at gnu.io.RXTXPort$MonitorThread.run(RXTXPort.java:1575)

"Thread-6" prio=6 tid=0x0302c400 nid=0x1b0 waiting on condition [0x039ef000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at posO2.Threads.ThreadHorloge.run(ThreadHorloge.java:46)

"Thread-5" prio=6 tid=0x03511c00 nid=0x9e4 waiting on condition [0x0399f000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at posO2.Threads.ThreadIgor.run(ThreadIgor.java:29)

"Thread-7" prio=6 tid=0x034b9800 nid=0xb40 waiting on condition [0x0394f000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at posO2.Threads.ThreadHorloge.run(ThreadHorloge.java:46)
    at java.lang.Thread.run(Unknown Source)

"Thread-4" prio=6 tid=0x0318ec00 nid=0xa08 waiting on condition [0x0323f000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at posO2.Threads.ThreadMajProduits.run(ThreadMajProduits.java:49)

"TimerQueue" daemon prio=6 tid=0x03036400 nid=0x9b8 waiting on condition [0x0344
f000]
java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x27e76778> (a java.util.concurrent.locks.Abstra
ctQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(Unknown Source)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject
.await(Unknown Source)
    at java.util.concurrent.DelayQueue.take(Unknown Source)
    at javax.swing.TimerQueue.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

"DestroyJavaVM" prio=6 tid=0x003c8400 nid=0xfe4 waiting on condition [0x00000000
]
java.lang.Thread.State: RUNNABLE

"AWT-EventQueue-0" prio=6 tid=0x02b6e000 nid=0xcbc runnable [0x033fe000]
java.lang.Thread.State: RUNNABLE
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(Unknown Source)
    at java.net.SocketInputStream.read(Unknown Source)
    at java.io.BufferedInputStream.fill(Unknown Source)
    at java.io.BufferedInputStream.read(Unknown Source)
    - locked <0x22f33f30> (a java.io.BufferedInputStream)
    at java.io.DataInputStream.readByte(Unknown Source)
    at org.hsqldb.result.Result.newResult(Unknown Source)
    at org.hsqldb.ClientConnection.read(Unknown Source)
    at org.hsqldb.ClientConnection.execute(Unknown Source)
    - locked <0x22f32700> (a org.hsqldb.ClientConnection)
    at org.hsqldb.jdbc.JDBCStatement.fetchResult(Unknown Source)
    at org.hsqldb.jdbc.JDBCStatement.executeQuery(Unknown Source)
    - locked <0x22be23b0> (a org.hsqldb.jdbc.JDBCStatement)
    at posO2.Printer.flash(Printer.java:1058)
    at posO2.Printer.bigFlash(Printer.java:1111)
    at posO2.Panels.Accueil$5.actionPerformed(Accueil.java:314)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

"AWT-Shutdown" prio=6 tid=0x02b81800 nid=0xefc in Object.wait() [0x033af000]
java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x27c707c0> (a java.lang.Object)
    at java.lang.Object.wait(Object.java:503)
    at sun.awt.AWTAutoShutdown.run(Unknown Source)
    - locked <0x27c707c0> (a java.lang.Object)
    at java.lang.Thread.run(Unknown Source)

"AWT-Windows" daemon prio=6 tid=0x03002800 nid=0xe58 runnable [0x0328f000]
java.lang.Thread.State: RUNNABLE
    at sun.awt.windows.WToolkit.eventLoop(Native Method)
    at sun.awt.windows.WToolkit.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

 "Java2D Disposer" daemon prio=10 tid=0x03000400 nid=0x4d0 in Object.wait() [0x03
1ef000]
java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x27c2bf18> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(Unknown Source)
    - locked <0x27c2bf18> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(Unknown Source)
    at sun.java2d.Disposer.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

"Service Thread" daemon prio=6 tid=0x02b63000 nid=0xb94 runnable [0x00000000]
java.lang.Thread.State: RUNNABLE

"C1 CompilerThread0" daemon prio=10 tid=0x02b54c00 nid=0x3f0 waiting on conditio
n [0x00000000]
java.lang.Thread.State: RUNNABLE

"Attach Listener" daemon prio=10 tid=0x02b53400 nid=0x924 waiting on condition [
0x00000000]
java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" daemon prio=10 tid=0x02b52000 nid=0xb88 runnable [0x00000000
]
java.lang.Thread.State: RUNNABLE

"Finalizer" daemon prio=8 tid=0x02b43c00 nid=0xfc8 in Object.wait() [0x02dff000]

java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x27c2c148> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(Unknown Source)
    - locked <0x27c2c148> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(Unknown Source)
    at java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)

"Reference Handler" daemon prio=10 tid=0x02b3f000 nid=0x488 in Object.wait() [0x
02daf000]
java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x27c2bdd8> (a java.lang.ref.Reference$Lock)
    at java.lang.Object.wait(Object.java:503)
    at java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)
    - locked <0x27c2bdd8> (a java.lang.ref.Reference$Lock)

"VM Thread" prio=10 tid=0x02b3d400 nid=0xa6c runnable

"VM Periodic Task Thread" prio=10 tid=0x02b76800 nid=0xf30 waiting on condition


JNI global references: 426

Alguien me puede explicar dónde puedo ver que mi GUI está congelada debido al primer hilo "Thread-12".

Y en segundo lugar, ¿cuál es la diferencia entre "Thread-6" y "Thread-7" siempre y cuando esté seguro de que solo ejecuté este hilo una vez?