FLAG-69: improve the performance of generate flags for patient function

api/src/main/java/org/openmrs/module/patientflags/api/impl/FlagServiceImpl.java

@@ -95,24 +95,27 @@ public List<Flag> generateFlagsForPatient(Patient patient, Map<Object, Object> c
 	/**
 	 * @see org.openmrs.module.patientflags.api.FlagService#generateFlagsForPatient(Patient, Filter, Map<Object, Object>)
 	 */
-	public List<Flag> generateFlagsForPatient(Patient patient, Filter filter, Map<Object, Object> context) {
-		List<Flag> results = new ArrayList<Flag>();
-		
+	public List<Flag> generateFlagsForPatient(final Patient patient, Filter filter, final Map<Object, Object> context) {
+		final List<Flag> results = Collections.synchronizedList(new ArrayList<>());
+
 		// we can get rid of this once onStartup is implemented
 		if (!isInitialized)
 			refreshCache();
-		
+
 		// test each Flag in the cache against the specific Patient
-		for (Flag flag : filter.filter(flagCache)) {
-			// trap bad flags so that they don't hang the system
+		filter.filter(flagCache).parallelStream().forEach(flag -> {
 			try {
-				if (flag.eval(patient, context))
+				Context.openSession();
+				if (flag.eval(patient, context)) {
 					results.add(flag);
-			}
-			catch (Exception e) {
+				}
+			} catch (Exception e) {
 				log.error("Unable to test flag " + flag.getName() + " on patient #" + patient.getId(), e);
+			} finally {
+				Context.closeSession();
 			}
-		}
+		});
+
 		return results;
 	}