Merged in camera-hang-fix (pull request #83)

Fix issue #36: BLACS freezing in IMAQdxCamera continuous acquisition.

Approved-by: David Meyer

Author: chrisjbillington

IMAQdxCamera/blacs_tabs.py

@@ -22,7 +22,7 @@
 
 import numpy as np
 
-from qtutils import UiLoader, inmain_later
+from qtutils import UiLoader, inmain_decorator
 import qtutils.icons
 from qtutils.qt import QtWidgets, QtGui, QtCore
 import pyqtgraph as pg
@@ -58,7 +58,13 @@ def __init__(self, image_view, label_fps):
         self.frame_rate = None
         self.update_event = None
 
+    @inmain_decorator(wait_for_return=True)
     def handler(self, data):
+        # Acknowledge immediately so that the worker process can begin acquiring the
+        # next frame. This increases the possible frame rate since we may render a frame
+        # whilst acquiring the next, but does not allow us to accumulate a backlog since
+        # only one call to this method may occur at a time.
+        self.send([b'ok'])
         md = json.loads(data[0])
         image = np.frombuffer(memoryview(data[1]), dtype=md['dtype'])
         image = image.reshape(md['shape'])
@@ -71,25 +77,6 @@ def handler(self, data):
             else:
                 self.frame_rate = 1 / dt
         self.last_frame_time = this_frame_time
-        # Wait for the previous update to compete so we don't accumulate a backlog:
-        if self.update_event is not None:
-            while True:
-                # Don't block, and check for self.stopping regularly in case we are
-                # shutting down. Otherwise if shutdown is called from the main thread we
-                # would deadlock.
-                try:
-                    self.update_event.get(timeout=0.1)
-                    break
-                except Empty:
-                    if self.stopping:
-                        return
-        self.update_event = inmain_later(self.update, image, self.frame_rate)
-        return [b'ok']
-
-    def update(self, image, frame_rate):
-        if not self.mainloop_thread.is_alive():
-            # We have been shut down. Nothing to do here.
-            return
         if self.image_view.image is None:
             # First time setting an image. Do autoscaling etc:
             self.image_view.setImage(image.swapaxes(-1, -2))
@@ -99,8 +86,21 @@ def update(self, image, frame_rate):
                 image.swapaxes(-1, -2), autoRange=False, autoLevels=False
             )
         # Update fps indicator:
-        if frame_rate is not None:
-            self.label_fps.setText(f"{frame_rate:.01f} fps")
+        if self.frame_rate is not None:
+            self.label_fps.setText(f"{self.frame_rate:.01f} fps")
+
+        # Tell Qt to send posted events immediately to prevent a backlog of paint events
+        # and other low-priority events. It seems that we cannot make our qtutils
+        # CallEvents (which are used to call this method in the main thread) low enough
+        # priority to ensure all other occur before our next call to self.handler()
+        # runs. This may be because the CallEvents used by qtutils.invoke_in_main have
+        # their own event handler (qtutils.invoke_in_main.Caller), perhaps posted event
+        # priorities are only meaningful within the context of a single event handler,
+        # and not for the Qt event loop as a whole. In any case, this seems to fix it.
+        # Manually calling this is usually a sign of bad coding, but I think it is the
+        # right solution to this problem. This solves issue #36.
+        QtGui.QApplication.instance().sendPostedEvents()
+        return self.NO_RESPONSE
 
 
 class IMAQdxCameraTab(DeviceTab):
@@ -286,4 +286,4 @@ def restart(self, *args, **kwargs):
         # Must manually stop the receiving server upon tab restart, otherwise it does
         # not get cleaned up:
         self.image_receiver.shutdown()
-        return DeviceTab.restart(self, *args, **kwargs)
+        return DeviceTab.restart(self, *args, **kwargs)

__init__.py

@@ -26,7 +26,7 @@
 check_version('qtutils', '2.0.0', '3.0.0')
 check_version('labscript', '2.6', '3')
 check_version('blacs', '2.7.0', '3.0.0')
-check_version('zprocess', '2.2.7', '3')
+check_version('zprocess', '2.17.0', '3')
 check_version('numpy', '1.15.1', '2')