/
LazyFields.java
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/
LazyFields.java
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/*
* Copyright 2020 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.
*/
package functions;
// [START functions_tips_lazy_globals]
// [START cloudrun_tips_global_lazy]
// [START run_tips_global_lazy]
import com.google.cloud.functions.HttpFunction;
import com.google.cloud.functions.HttpRequest;
import com.google.cloud.functions.HttpResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
public class LazyFields implements HttpFunction {
// 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 NON_LAZY_GLOBAL = fileWideComputation();
// Declared at cold-start, but only initialized if/when the function executes
// Uses the "initialization-on-demand holder" idiom
// More information: https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
private static class LazyGlobalHolder {
// Making the default constructor private prohibits instantiation of this class
private LazyGlobalHolder() {}
// This value is initialized only if (and when) the getLazyGlobal() function below is called
private static final Integer INSTANCE = functionSpecificComputation();
private static Integer getInstance() {
return LazyGlobalHolder.INSTANCE;
}
}
@Override
public void service(HttpRequest request, HttpResponse response)
throws IOException {
Integer lazyGlobal = LazyGlobalHolder.getInstance();
var writer = new PrintWriter(response.getWriter());
writer.printf("Lazy global: %s; non-lazy global: %s%n", lazyGlobal, NON_LAZY_GLOBAL);
}
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 cloudrun_tips_global_lazy]
// [END functions_tips_lazy_globals]