diff --git a/TermTk/TTkCore/signal.py b/TermTk/TTkCore/signal.py
index 1dbd934d..ea3a3142 100644
--- a/TermTk/TTkCore/signal.py
+++ b/TermTk/TTkCore/signal.py
@@ -59,6 +59,7 @@ __all__ = ['pyTTkSlot', 'pyTTkSignal']
 
 from inspect import getfullargspec
 from types import LambdaType
+from threading import Lock
 
 def pyTTkSlot(*args, **kwargs):
     def pyTTkSlot_d(func):
@@ -72,7 +73,7 @@ def pyTTkSignal(*args, **kwargs):
 
 class _pyTTkSignal_obj():
     _signals = []
-    __slots__ = ('_types', '_name', '_revision', '_connected_slots')
+    __slots__ = ('_types', '_name', '_revision', '_connected_slots', '_mutex')
     def __init__(self, *args, **kwargs):
         # ref: http://pyqt.sourceforge.net/Docs/PyQt5/signals_slots.html#PyQt5.QtCore.pyqtSignal
 
@@ -90,6 +91,7 @@ class _pyTTkSignal_obj():
         self._name = kwargs.get('name', None)
         self._revision = kwargs.get('revision', 0)
         self._connected_slots = {}
+        self._mutex = Lock()
         _pyTTkSignal_obj._signals.append(self)
 
     def connect(self, slot):
@@ -133,11 +135,13 @@ class _pyTTkSignal_obj():
                 del self._connected_slots[slot]
 
     def emit(self, *args, **kwargs):
+        if not self._mutex.acquire(False): return
         if len(args) != len(self._types):
             error = "func"+str(self._types)+" signal has "+str(len(self._types))+" argument(s) but "+str(len(args))+" provided"
             raise TypeError(error)
         for slot,sl in self._connected_slots.copy().items():
             slot(*args[sl], **kwargs)
+        self._mutex.release()
 
     def clear(self):
         self._connected_slots = {}
diff --git a/TermTk/TTkWidgets/scrollbar.py b/TermTk/TTkWidgets/scrollbar.py
index 81ebdb19..2780251b 100644
--- a/TermTk/TTkWidgets/scrollbar.py
+++ b/TermTk/TTkWidgets/scrollbar.py
@@ -126,12 +126,11 @@ class TTkScrollBar(TTkWidget):
 
     def wheelEvent(self, evt):
         if evt.evt == TTkK.WHEEL_Up:
-            self._value -= self._pageStep
+            value = self._value-self._pageStep
         else:
-            self._value += self._pageStep
-        self._value = max(self._minimum,min(self._maximum,self._value))
+            value = self._value+self._pageStep
+        self.setValue(max(self._minimum,min(self._maximum,value)))
         self.sliderMoved.emit(self._value)
-        self.update()
         return True
 
     def mousePressEvent(self, evt):
@@ -143,21 +142,20 @@ class TTkScrollBar(TTkWidget):
             mouse = evt.x
 
         if mouse == 0: # left/up arrow pressed
-            self._value = self._value - self._singleStep
+            self.setValue(self._value - self._singleStep)
         elif mouse == size-1: # right/down arrow pressed
-            self._value = self._value + self._singleStep
+            self.setValue(self._value + self._singleStep)
         elif self._screenPgDown[0] <= mouse < self._screenPgDown[1]:
-            self._value = self._value - self._pageStep
+            self.setValue(self._value - self._pageStep)
         elif self._screenPgUp[0] <= mouse < self._screenPgUp[1]:
-            self._value = self._value + self._pageStep
+            self.setValue(self._value + self._pageStep)
         elif self._screenScroller[0] <= mouse < self._screenScroller[1]:
             self._mouseDelta = mouse-self._screenScroller[0]
             self._draggable = True
         else:
             return False
-        self._value = max(self._minimum,min(self._maximum,self._value))
+        self.setValue(max(self._minimum,min(self._maximum,self._value)))
         self.sliderMoved.emit(self._value)
-        self.update()
         # TTkLog.debug(f"m={mouse}, md:{self._mouseDelta}, d:{self._screenPgDown},u:{self._screenPgUp},s:{self._screenScroller}")
         return True
 
@@ -176,11 +174,9 @@ class TTkScrollBar(TTkWidget):
         asciiDrawingSize = size2 - asciiStep
 
         a =  aa * (self._maximum - self._minimum) // asciiDrawingSize
-        self._value = a + self._minimum
 
-        self._value = max(self._minimum,min(self._maximum,self._value))
+        self.setValue(max(self._minimum,min(self._maximum,a+self._minimum)))
         self.sliderMoved.emit(self._value)
-        self.update()
         # TTkLog.debug(f"m={mouse}, md:{self._mouseDelta}, aa:{aa}")
         return True
 
diff --git a/tests/test.ui.006.scroll.py b/tests/test.ui.006.scroll.01.py
similarity index 100%
rename from tests/test.ui.006.scroll.py
rename to tests/test.ui.006.scroll.01.py
diff --git a/tests/test.ui.006.scroll.02.tryLoop.py b/tests/test.ui.006.scroll.02.tryLoop.py
new file mode 100755
index 00000000..c624849b
--- /dev/null
+++ b/tests/test.ui.006.scroll.02.tryLoop.py
@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+
+# MIT License
+#
+# Copyright (c) 2021 Eugenio Parodi <ceccopierangiolieugenio AT googlemail DOT com>
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+import sys, os
+
+sys.path.append(os.path.join(sys.path[0],'..'))
+import TermTk as ttk
+
+root = ttk.TTk()
+
+sb1 = ttk.TTkScrollBar(parent=root, pos=(10,2), size=(1,10))
+sb2 = ttk.TTkScrollBar(parent=root, pos=(12,2), size=(1,12))
+sb3 = ttk.TTkScrollBar(parent=root, pos=(14,2), size=(1,14))
+sb4 = ttk.TTkScrollBar(parent=root, pos=(16,2), size=(1,16))
+sb5 = ttk.TTkScrollBar(parent=root, pos=( 5,0), size=(30,1), orientation=ttk.TTkK.HORIZONTAL)
+
+sb1.valueChanged.connect(sb2.setValue)
+sb2.valueChanged.connect(sb3.setValue)
+sb3.valueChanged.connect(sb4.setValue)
+sb4.valueChanged.connect(sb5.setValue)
+sb5.valueChanged.connect(sb1.setValue)
+
+
+root.mainloop()
\ No newline at end of file
diff --git a/tools/check.import.sh b/tools/check.import.sh
index 34e268e0..8c7e41fc 100755
--- a/tools/check.import.sh
+++ b/tools/check.import.sh
@@ -9,6 +9,7 @@ __check(){
             -e "from dataclasses" \
             -e "signal.py:from inspect import getfullargspec" \
             -e "signal.py:from types import LambdaType" \
+            -e "signal.py:from threading import Lock" \
             -e "colors.py:from .colors_ansi_map" \
             -e "log.py:import inspect" \
             -e "log.py:import logging" \