Statelessness

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

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Code sample

C#

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}");
        }
    }
}

C++

#include <google/cloud/functions/http_request.h>
#include <google/cloud/functions/http_response.h>
#include <atomic>
#include <string>

namespace gcf = ::google::cloud::functions;

namespace {
std::atomic<int> count{0};
}  // namespace

gcf::HttpResponse concepts_stateless(gcf::HttpRequest /*request*/) {  // NOLINT
  return gcf::HttpResponse{}.set_payload("Instance execution count: " +
                                         std::to_string(++count));
}

Go


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

import (
	"fmt"
	"net/http"
)

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

// 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


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

// 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.
 */
exports.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

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


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 'Instance execution count: {}'.format(count)

Ruby

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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