Add lazy global snippet (GoogleCloudPlatform#1611)

averikitsch · web-flow · commit 506c8e770b56 · 2019-10-09T10:45:17.000-07:00
diff --git a/functions/snippets/src/main/java/Lazy.java b/functions/snippets/src/main/java/Lazy.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// [START functions_tips_lazy_globals]
+// [START run_tips_global_lazy]
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.Arrays;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+public class Lazy {
+  // Always initialized (at cold-start)
+  // Warning: Class variables used in Servlet classes must be thread-safe,
+  // or else might introduce race conditions in your code.
+  private static final int nonLazyGlobal = fileWideComputation();
+  // Declared at cold-start, but only initialized if/when the function executes
+  private static Integer lazyGlobal = null;
+
+  public void lazyGlobal(HttpServletRequest request, HttpServletResponse response)
+      throws IOException {
+    // This value is initialized only if (and when) the function is called
+    if (lazyGlobal == null) {
+      lazyGlobal = functionSpecificComputation();
+    }
+
+    PrintWriter writer = response.getWriter();
+    writer.write(String.format("Lazy global: %s; non-lazy global: %s", lazyGlobal, nonLazyGlobal));
+  }
+
+  private static int functionSpecificComputation() {
+    int[] numbers = new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9};
+    return Arrays.stream(numbers).sum();
+  }
+
+  private static int fileWideComputation() {
+    int[] numbers = new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9};
+    return Arrays.stream(numbers).reduce((t, x) -> t * x).getAsInt();
+  }
+}
+// [END run_tips_global_lazy]
+// [END functions_tips_lazy_globals]
diff --git a/functions/snippets/src/main/java/Scopes.java b/functions/snippets/src/main/java/Scopes.java
@@ -15,6 +15,7 @@
  */
 
 // [START functions_tips_scopes]
+// [START run_tips_global_scope]
 
 import java.io.IOException;
 import java.io.PrintWriter;
@@ -26,7 +27,7 @@ public class Scopes {
   // Global (instance-wide) scope
   // This computation runs at instance cold-start.
   // Warning: Class variables used in Servlet classes must be thread-safe,
-  // or else might introduce race conditions in your code. 
+  // or else might introduce race conditions in your code.
   private static final int InstanceVar = heavyComputation();
 
   public void scopeDemo(HttpServletRequest request, HttpServletResponse response)
@@ -38,16 +39,16 @@ public void scopeDemo(HttpServletRequest request, HttpServletResponse response)
     PrintWriter writer = response.getWriter();
     writer.write(String.format("Instance: %s; function: %s", InstanceVar, functionVar));
   }
-  
+
   private static int lightComputation() {
     int[] numbers = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
     return Arrays.stream(numbers).sum();
   }
-  
+
   private static int heavyComputation() {
     int[] numbers = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
     return Arrays.stream(numbers).reduce((t, x) -> t * x).getAsInt();
   }
 }
-
+// [END run_tips_global_scope]
 // [END functions_tips_scopes]
diff --git a/functions/snippets/src/test/java/SnippetsTests.java b/functions/snippets/src/test/java/SnippetsTests.java
@@ -163,6 +163,13 @@ public void scopesTest() throws IOException {
     assertThat(responseOut.toString(), containsString("Instance:"));
   }
 
+  @Test
+  public void lazyTest() throws IOException {
+    new Lazy().lazyGlobal(request, response);
+
+    assertThat(responseOut.toString(), containsString("Lazy global:"));
+  }
+
   @Test
   public void retrieveLogsTest() throws IOException {
     new RetrieveLogs().retrieveLogs(request, response);
@@ -177,7 +184,7 @@ public void helloBackgroundTest() throws IOException {
     when(request.getReader()).thenReturn(bodyReader);
 
     new HelloBackground().helloBackground(request, response);
-    assertThat(responseOut.toString(), containsString("Hello John!"));    
+    assertThat(responseOut.toString(), containsString("Hello John!"));
   }
 
   @Test
@@ -192,7 +199,7 @@ public void envTest() throws IOException {
     new EnvVars().envVar(request, response);
     assertThat(responseOut.toString(), containsString("BAR"));
   }
-  
+
   @Test
   public void helloExecutionCount() throws IOException {
     new Concepts().executionCount(request, response);
