Cloud Functions a été renommé Cloud Run Functions. Pour en savoir plus, consultez l'article de blog sur Cloud Run Functions.

Initialisation tardive des variables globales

Cette page montre comment mettre en attente l'initialisation des variables globales jusqu'à ce qu'elles soient utilisées.

En savoir plus

Pour obtenir une documentation détaillée incluant cet exemple de code, consultez les articles suivants :

Exemple de code

C#

Pour vous authentifier auprès de Cloud Run Functions, configurez le service Identifiants par défaut de l'application. Pour en savoir plus, consultez Configurer l'authentification pour un environnement de développement local.

using Google.Cloud.Functions.Framework;
using Microsoft.AspNetCore.Http;
using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace LazyFields;

public class Function : IHttpFunction
{
    // This computation runs at server cold-start.
    // Warning: Class variables used in functions code must be thread-safe.
    private static readonly int NonLazyGlobal = FileWideComputation();

    // This variable is initialized at server cold-start, but the
    // computation is only performed when the function needs the result.
    private static readonly Lazy<int> LazyGlobal = new Lazy<int>(
        FunctionSpecificComputation,
        LazyThreadSafetyMode.ExecutionAndPublication);

    public async Task HandleAsync(HttpContext context)
    {
        // In a more complex function, there might be some paths that use LazyGlobal.Value,
        // and others that don't. The computation is only performed when necessary, and
        // only once per server.
        await context.Response.WriteAsync(
            $"Lazy global: {LazyGlobal.Value}; non-lazy global: {NonLazyGlobal}",
            context.RequestAborted);
    }

    private static int FunctionSpecificComputation()
    {
        int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
        return numbers.Sum();
    }

    private static int FileWideComputation()
    {
        int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
        return numbers.Aggregate((current, next) => current * next);
    }
}

Go


// Package tips contains tips for writing Cloud Functions in Go.
package tips

import (
	"context"
	"log"
	"net/http"
	"sync"

	"cloud.google.com/go/storage"
	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
)

// client is lazily initialized by LazyGlobal.
var client *storage.Client
var clientOnce sync.Once

func init() {
	functions.HTTP("LazyGlobal", LazyGlobal)
}

// LazyGlobal is an example of lazily initializing a Google Cloud Storage client.
func LazyGlobal(w http.ResponseWriter, r *http.Request) {
	// You may wish to add different checks to see if the client is needed for
	// this request.
	clientOnce.Do(func() {
		// Pre-declare an err variable to avoid shadowing client.
		var err error
		client, err = storage.NewClient(context.Background())
		if err != nil {
			http.Error(w, "Internal error", http.StatusInternalServerError)
			log.Printf("storage.NewClient: %v", err)
			return
		}
	})
	// Use client.
}

Java


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();
  }
}

Node.js

const functions = require('@google-cloud/functions-framework');

// Always initialized (at cold-start)
const nonLazyGlobal = fileWideComputation();

// Declared at cold-start, but only initialized if/when the function executes
let lazyGlobal;

/**
 * HTTP function that uses lazy-initialized globals
 *
 * @param {Object} req request context.
 * @param {Object} res response context.
 */
functions.http('lazyGlobals', (req, res) => {
  // This value is initialized only if (and when) the function is called
  lazyGlobal = lazyGlobal || functionSpecificComputation();

  res.send(`Lazy global: ${lazyGlobal}, non-lazy global: ${nonLazyGlobal}`);
});

Python

import functions_framework

# Always initialized (at cold-start)
non_lazy_global = file_wide_computation()

# Declared at cold-start, but only initialized if/when the function executes
lazy_global = None


@functions_framework.http
def lazy_globals(request):
    """
    HTTP Cloud Function that uses lazily-initialized globals.
    Args:
        request (flask.Request): The request object.
        <http://flask.pocoo.org/docs/1.0/api/#flask.Request>
    Returns:
        The response text, or any set of values that can be turned into a
        Response object using `make_response`
        <http://flask.pocoo.org/docs/1.0/api/#flask.Flask.make_response>.
    """
    global lazy_global, non_lazy_global

    # This value is initialized only if (and when) the function is called
    if not lazy_global:
        lazy_global = function_specific_computation()

    return f"Lazy: {lazy_global}, non-lazy: {non_lazy_global}."

Ruby

FunctionsFramework.on_startup do
  # This method is called when the function is initialized, not on each
  # invocation.

  # Declare and set non_lazy_global
  set_global :non_lazy_global, file_wide_computation

  # Declare, but do not set, lazy_global
  set_global :lazy_global do
    function_specific_computation
  end
end

FunctionsFramework.http "tips_lazy" do |_request|
  # This method is called every time this function is called.

  "Lazy: #{global :lazy_global}; non_lazy: #{global :non_lazy_global}"
end

Étapes suivantes

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