[gui][viewer] add cache for the data viewer.

tomwer/gui/visualization/dataviewer.py

@@ -30,6 +30,7 @@ __date__ = "21/07/2020"
 import silx
 from silx.gui import qt
 from silx.utils.enum import Enum as _Enum
+from collections import OrderedDict
 try:
     from silx.gui.utils.signal import SignalProxy
 except ImportError:
@@ -305,7 +306,43 @@ class DisplayControl(qt.QWidget):
         self._scanQLE.setText(scan_name)
 
 
+class _CachedOrderedDict(object):
+    def __init__(self, max_size=4):
+        if max_size <= 0:
+            raise ValueError
+
+        self.max_size = max_size
+        self._items = OrderedDict()
+
+    def _move_latest(self, key):
+        # Order is in descending priority, i.e. first element
+        # is latest.
+        self._items.move_to_end(key, last=False)
+
+    def __getitem__(self, key, default=None):
+        if key not in self._items:
+            return default
+
+        value = self._items[key]
+        self._move_latest(key)
+        return value
+
+    def __setitem__(self, key, value):
+        if len(self._items) >= self.max_size:
+            keys = list(self._items.keys())
+            key_to_evict = keys[-1]
+            self._items.pop(key_to_evict)
+
+        self._items[key] = value
+        self._move_latest(key)
+
+    def __contains__(self, item):
+        return item in self._items
+
+
 class ImageStack(_ImageStack):
+    CACHE_SIZE = 15
+
     def __init__(self, parent):
         self._normFct = None
         self._url_indexes = None
@@ -315,6 +352,10 @@ class ImageStack(_ImageStack):
         self._normFct = fct
         self._url_indexes = url_indexes
 
+    def reset(self) -> None:
+        super().reset()
+        self._urlData = _CachedOrderedDict(max_size=ImageStack.CACHE_SIZE)
+
     def _urlLoaded(self) -> None:
         """