Improve the algorithm progression example with zarr multiprocess

This writes a single value at the maximum axes locations before fanning
out to multiple processes.

examples/algorithm_progression.py

@@ -42,7 +42,7 @@ def __init__(self, algorithm, input_filename, input_params, param_order,
 
         self.combos = list(itertools.product(*[p['range'] for p in input_params.values()]))
 
-    def getOverallSink(self):
+    def getOverallSink(self, maxValues=None):
         msg = 'Not implemented'
         raise Exception(msg)
 
@@ -118,7 +118,10 @@ def applyAlgorithm(self, sink, params):
 
     def run(self):
         starttime = time.time()
-        sink = self.getOverallSink()
+        source = large_image.open(self.input_filename)
+        maxValues = {'x': source.sizeX, 'y': source.sizeY, 's': source.metadata['bandCount']}
+        maxValues.update({p['axis']: len(p['range']) for p in self.param_order.values()})
+        sink = self.getOverallSink(maxValues)
 
         print(f'Beginning {len(self.combos)} runs on {self.max_workers} workers...')
         num_done = 0
@@ -149,7 +152,7 @@ def run(self):
 
 
 class SweepAlgorithmMulti(SweepAlgorithm):
-    def getOverallSink(self):
+    def getOverallSink(self, maxValues=None):
         os.makedirs(os.path.splitext(self.output_filename)[0], exist_ok=True)
         algorithm_name = self.algorithm.__name__.replace('_', ' ').title()
         self.yaml_dict = {
@@ -270,10 +273,20 @@ def addTile(self, tilesink, *args, **kwargs):
 
 
 class SweepAlgorithmZarr(SweepAlgorithm):
-    def getOverallSink(self):
+    def getOverallSink(self, maxValues=None):
+        """
+        Return the main sink for the entire image.  If maxValues is specified,
+        add a single black pixel at the maximum location for all axes.  This
+        causes the array of axes values in the zarr sink to be allocated and
+        tracked, whereas, otherwise, they could be ignored.
+        """
         import large_image_source_zarr
 
-        return large_image_source_zarr.new()
+        sink = large_image_source_zarr.new()
+        if maxValues:
+            sink.addTile(np.zeros((1, 1, maxValues.get('s', 1))),
+                         **{k: v - 1 for k, v in maxValues.items() if k != 's'})
+        return sink
 
     def writeOverallSink(self, sink):
         sink.write(self.output_filename, lossy=self.lossy)