Statelessness

An example of what variable state function instances do (and don't) store.

Code sample

C#

To authenticate to Cloud Run functions, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

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

namespace ExecutionCount;

public class Function : IHttpFunction
{
    // Note that this variable must be static, because a new instance is
    // created for each request. An alternative approach would be to use
    // dependency injection with a singleton resource injected into the function
    // constructor.
    private static int _count;

    public async Task HandleAsync(HttpContext context)
    {
        // Note: the total function invocation count across
        // all servers may not be equal to this value!
        int currentCount = Interlocked.Increment(ref _count);
        await context.Response.WriteAsync($"Server execution count: {currentCount}", context.RequestAborted);
    }
}

Go

To authenticate to Cloud Run functions, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

// Package http provides a set of HTTP Cloud Functions samples.
package http

import (
	"fmt"
	"net/http"

	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
)

// count is a global variable, but only shared within a function instance.
var count = 0

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

// ExecutionCount is an HTTP Cloud Function that counts how many times it
// is executed within a specific instance.
func ExecutionCount(w http.ResponseWriter, r *http.Request) {
	count++

	// Note: the total function invocation count across
	// all instances may not be equal to this value!
	fmt.Fprintf(w, "Instance execution count: %d", count)
}

Java

To authenticate to Cloud Run functions, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

import com.google.cloud.functions.HttpFunction;
import com.google.cloud.functions.HttpRequest;
import com.google.cloud.functions.HttpResponse;
import java.io.BufferedWriter;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicInteger;

public class ExecutionCount implements HttpFunction {

  private final AtomicInteger count = new AtomicInteger(0);

  @Override
  public void service(HttpRequest request, HttpResponse response)
      throws IOException {
    count.getAndIncrement();

    // Note: the total function invocation count across
    // all instances may not be equal to this value!
    BufferedWriter writer = response.getWriter();
    writer.write("Instance execution count: " + count);
  }
}

Node.js

To authenticate to Cloud Run functions, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

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

// Global variable, but only shared within function instance.
let count = 0;

/**
 * HTTP Cloud Function that counts how many times
 * it is executed within a specific instance.
 *
 * @param {Object} req Cloud Function request context.
 * @param {Object} res Cloud Function response context.
 */
functions.http('executionCount', (req, res) => {
  count++;

  // Note: the total function invocation count across
  // all instances may not be equal to this value!
  res.send(`Instance execution count: ${count}`);
});

Python

To authenticate to Cloud Run functions, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

import functions_framework


# Global variable, modified within the function by using the global keyword.
count = 0


@functions_framework.http
def statelessness(request):
    """
    HTTP Cloud Function that counts how many times it is executed
    within a specific instance.
    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 count
    count += 1

    # Note: the total function invocation count across
    # all instances may not be equal to this value!
    return f"Instance execution count: {count}"

Ruby

To authenticate to Cloud Run functions, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

require "functions_framework"

# Global variable, but scoped only within one function instance.
$count = 0

FunctionsFramework.http "execution_count" do |_request|
  $count += 1

  # NOTE: the total function invocation count across all instances
  # may not be equal to this value!
  "Instance execution count: #{$count}"
end

What's next

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