Make nested iterator request test solid for max conn count changes

m-kuhn · m-kuhn · commit ec4a327502c8 · 2018-08-08T07:18:30.000+02:00
diff --git a/tests/src/python/test_provider_postgres.py b/tests/src/python/test_provider_postgres.py
@@ -1141,6 +1141,32 @@ def testCurveToMultipolygon(self):
         self.assertEqual(g.childCount(), 1)
         self.assertTrue(g.childGeometry(0).vertexCount() > 3)
 
+    def testConcurrency(self):
+        """
+        The connection pool has a maximum of 4 connections defined (+2 spare connections)
+        Make sure that if we exhaust those 4 connections and force another connection
+        it is actually using the spare connections and does not freeze.
+        This situation normally happens when (at least) 4 rendering threads are active
+        in parallel and one requires an expression to be evaluated.
+        """
+        vl = QgsVectorLayer('{conn} srid=4326 table="qgis_test".{table} (geom) sql='.format(conn=self.dbconn, table='someData'), "testgeom", "postgres")
+        self.assertTrue(vl.isValid())
+        QgsProject.instance().addMapLayer(vl)
+
+        # Acquire the maximum amount of concurrent connections
+        iterators = list()
+        for i in range(QgsApplication.instance().maxConcurrentConnectionsPerPool()):
+            iterators.append(vl.getFeatures())
+
+        # Run an expression that will also do a request and should use a spare
+        # connection. It just should not deadlock here.
+
+        feat = next(it)
+        context = QgsExpressionContext()
+        context.setFeature(feat)
+        exp = QgsExpression('get_feature(\'{layer}\', \'pk\', 5)'.format(layer=vl.id()))
+        exp.evaluate(context)
+
 
 class TestPyQgsPostgresProviderCompoundKey(unittest.TestCase, ProviderTestCase):
 
