Continue processing after closing connection

Question 1

Is there a way in PHP to close the connection (essentially tell a browser than there's no more data to come) but continue processing. The specific circumstance I'm thinking of is that I would want to serve up cached data, then if the cache had expired, I would still serve the cached data for a fast response, close the connection, but continue processing to regenerate and cache new data. Essentially the only purpose is to make a site appear more responsive as there wouldn't be the occasional delay while a user waits for content to be regenerated.

UPDATE:

PLuS has the closest answer to what I was looking for. To clarify for a couple of people I'm looking for something that enables the following steps:

User requests page
Connection opens to server
PHP checks if cache has expired, if still fresh, serve cache and close connection (END HERE). If expired, continue to 4.
Serve expired cache
Close connection so browser knows it's not waiting for more data.
PHP regenerates fresh data and caches it.
PHP shuts down.

UPDATE:

This is important, it must be a purely PHP solution. Installing other software is not an option.

Question 2

I finally found a solution (thanks to Google, I just had to keep trying different combinations of search terms). Thanks to the comment from arr1 on this page (it's about two thirds of the way down the page).

<?php
ob_end_clean();
header("Connection: close");
ignore_user_abort(true);
ob_start();
echo 'Text the user will see';
$size = ob_get_length();
header("Content-Length: $size");
ob_end_flush(); // All output buffers must be flushed here
flush();        // Force output to client
// Do processing here 
sleep(30);
echo('Text user will never see');

I have yet to actually test this but, in short, you send two headers: one that tells the browser exactly how much data to expect then one to tell the browser to close the connection (which it will only do after receiving the expected amount of content). I haven't tested this yet.

Question 3

Here's what worked best for me when trying to script this (in case anyone else comes across this like I did):

$ pecl -d php_suffix=5.6 install <package>
$ pecl uninstall -r <package>

$ pecl -d php_suffix=7.0 install <package>
$ pecl uninstall -r <package>

$ pecl -d php_suffix=7.1 install <package>
$ pecl uninstall -r <package>

The -d php_suffix=<version> piece allows you to set config values at run time vs pre-setting them with pecl config-set. The uninstall -r bit does not actually uninstall it (from the docs):

vagrant@homestead:~$ pecl help uninstall
pecl uninstall [options] [channel/]<package> ...
Uninstalls one or more PEAR packages.  More than one package may be
specified at once.  Prefix with channel name to uninstall from a
channel not in your default channel (pecl.php.net)

Options:
  ...
  -r, --register-only
        do not remove files, only register the packages as not installed
  ...

The uninstall line is necessary otherwise installing it will remove any previously installed version, even if it was for a different PHP version (ex: Installing an extension for PHP 7.0 would remove the 5.6 version if the package was still registered as installed).

Question 4

This workaround is basically making the service got an auto restart. That means your service will start from beginning. And yes, this is hardcoding.

Add a string argument to start() method in Service template file

mine was restart argument. This will be an extra for the activity intent to pass to onStartCommand() method that triggered by ctx.startService() method. Then put 'autoRestartService' with that restart argument value.

My .buildozer/android/platform/build-<your arch>/dists/<your app>/templates/Service.tmpl.java:

package {{ args.package }};

import android.content.Intent;
import android.content.Context;
import org.kivy.android.PythonService;


public class Service{{ name|capitalize }} extends PythonService {

    {% if sticky %}
    @Override
    public int startType() {
        return START_STICKY;
    }
    {% endif %}

    @Override
    protected int getServiceId() {
        return {{ service_id }};
    }
                                  /*add 'restart' String argument to the start() method*/
    static public void start(Context ctx, String pythonServiceArgument, String restart) {
        Intent intent = new Intent(ctx, Service{{ name|capitalize }}.class);
        String argument = ctx.getFilesDir().getAbsolutePath() + "/app";
        intent.putExtra("androidPrivate", ctx.getFilesDir().getAbsolutePath());
        intent.putExtra("androidArgument", argument);
        intent.putExtra("serviceTitle", "{{ args.name }}");
        intent.putExtra("serviceDescription", "{{ name|capitalize }}");
        intent.putExtra("serviceEntrypoint", "{{ entrypoint }}");
        intent.putExtra("pythonName", "{{ name }}");
        intent.putExtra("serviceStartAsForeground", "{{ foreground|lower }}");
        intent.putExtra("pythonHome", argument);
        intent.putExtra("pythonPath", argument + ":" + argument + "/lib");
        intent.putExtra("pythonServiceArgument", pythonServiceArgument);
        intent.putExtra("autoRestartService", restart); /*<-- add this line*/
        ctx.startService(intent);
    }

    static public void stop(Context ctx) {
        Intent intent = new Intent(ctx, Service{{ name|capitalize }}.class);
        ctx.stopService(intent);
    }
}

Set the autoRestartService value within PythonService's onStartCommand()

Take a look at PythonService's onDestroy() method below. onDestroy() method will be triggered if the service is killed (caused by closing the app or swiping from recent app). There is an option wether restart the service or not depends on autoRestartService value. So set it within the onStartCommand() method by getting it from intent extras.

My .buildozer/android/platform/build-<your arch>/dists/<your app>/src/main/org/kivy/android/PythonService.java:

package org.kivy.android;

import android.os.Build;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;
import android.app.Service;
import android.os.IBinder;
import android.os.Bundle;
import android.content.Intent;
import android.content.Context;
import android.util.Log;
import android.app.Notification;
import android.app.PendingIntent;
import android.os.Process;
import java.io.File;

//imports for channel definition
import android.app.NotificationManager;
import android.app.NotificationChannel;
import android.graphics.Color;

public class PythonService extends Service implements Runnable {

    // Thread for Python code
    private Thread pythonThread = null;

    // Python environment variables
    private String androidPrivate;
    private String androidArgument;
    private String pythonName;
    private String pythonHome;
    private String pythonPath;
    private String serviceEntrypoint;
    // Argument to pass to Python code,
    private String pythonServiceArgument;


    public static PythonService mService = null;
    private Intent startIntent = null;

    private boolean autoRestartService = false;

    public void setAutoRestartService(boolean restart) {
        autoRestartService = restart;
    }

    public int startType() {
        return START_NOT_STICKY;
    }

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        if (pythonThread != null) {
            Log.v("python service", "service exists, do not start again");
            return START_NOT_STICKY;
        }

        startIntent = intent;
        Bundle extras = intent.getExtras();
        androidPrivate = extras.getString("androidPrivate");
        androidArgument = extras.getString("androidArgument");
        serviceEntrypoint = extras.getString("serviceEntrypoint");
        pythonName = extras.getString("pythonName");
        pythonHome = extras.getString("pythonHome");
        pythonPath = extras.getString("pythonPath");
        boolean serviceStartAsForeground = (
            extras.getString("serviceStartAsForeground").equals("true")
        );
        pythonServiceArgument = extras.getString("pythonServiceArgument");
        autoRestartService = (
            extras.getString("autoRestartService").equals("true") //this will return boolean for autoRestartservice
        );
        pythonThread = new Thread(this);
        pythonThread.start();

        if (serviceStartAsForeground) {
            doStartForeground(extras);
        }

        return startType();
    }

    protected int getServiceId() {
        return 1;
    }

    protected void doStartForeground(Bundle extras) {
        String serviceTitle = extras.getString("serviceTitle");
        String serviceDescription = extras.getString("serviceDescription");
        Notification notification;
        Context context = getApplicationContext();
        Intent contextIntent = new Intent(context, PythonActivity.class);
        PendingIntent pIntent = PendingIntent.getActivity(context, 0, contextIntent,
            PendingIntent.FLAG_UPDATE_CURRENT);

        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
            notification = new Notification(
                context.getApplicationInfo().icon, serviceTitle, System.currentTimeMillis());
            try {
                // prevent using NotificationCompat, this saves 100kb on apk
                Method func = notification.getClass().getMethod(
                    "setLatestEventInfo", Context.class, CharSequence.class,
                    CharSequence.class, PendingIntent.class);
                func.invoke(notification, context, serviceTitle, serviceDescription, pIntent);
            } catch (NoSuchMethodException | IllegalAccessException |
                     IllegalArgumentException | InvocationTargetException e) {
            }
        } else {
            // for android 8+ we need to create our own channel
            // https://.com/questions/47531742/startforeground-fail-after-upgrade-to-android-8-1
            String NOTIFICATION_CHANNEL_ID = "org.kivy.p4a";    //TODO: make this configurable
            String channelName = "Background Service";                //TODO: make this configurable
            NotificationChannel chan = new NotificationChannel(NOTIFICATION_CHANNEL_ID, channelName, 
                NotificationManager.IMPORTANCE_NONE);
            
            chan.setLightColor(Color.BLUE);
            chan.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
            NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
            manager.createNotificationChannel(chan);

            Notification.Builder builder = new Notification.Builder(context, NOTIFICATION_CHANNEL_ID);
            builder.setContentTitle(serviceTitle);
            builder.setContentText(serviceDescription);
            builder.setContentIntent(pIntent);
            builder.setSmallIcon(context.getApplicationInfo().icon);
            notification = builder.build();
        }
        startForeground(getServiceId(), notification);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        pythonThread = null;
        if (autoRestartService && startIntent != null) {
            Log.v("python service", "service restart requested");
            startService(startIntent);
        }
        Process.killProcess(Process.myPid());
    }

    /**
     * Stops the task gracefully when killed.
     * Calling stopSelf() will trigger a onDestroy() call from the system.
     */
    @Override
    public void onTaskRemoved(Intent rootIntent) {
        super.onTaskRemoved(rootIntent);
        stopSelf();
    }

    @Override
    public void run(){
        String app_root =  getFilesDir().getAbsolutePath() + "/app";
        File app_root_file = new File(app_root);
        PythonUtil.loadLibraries(app_root_file,
            new File(getApplicationInfo().nativeLibraryDir));
        this.mService = this;
        nativeStart(
            androidPrivate, androidArgument,
            serviceEntrypoint, pythonName,
            pythonHome, pythonPath,
            pythonServiceArgument);
        stopSelf();
    }

    // Native part
    public static native void nativeStart(
            String androidPrivate, String androidArgument,
            String serviceEntrypoint, String pythonName,
            String pythonHome, String pythonPath,
            String pythonServiceArgument);
}

there is setAutoRestartService() method there, but we cant call it because it is non-static method.

Last thing, buildozer.spec

Add FOREGROUND_SERVICE permission and service to buildozer.spec.

android.permissions = FOREGROUND_SERVICE
...

services = myservice:./path/to/your-service.py:foreground

Now start the service by giving 'true' string as third positional argument.

activity = autoclass('org.kivy.android.PythonActivity').mActivity
service = autoclass('com.omdo.example.ServiceMyservice')
service.start(activity, '', 'true')

Note: I don't really understands Java, maybe someone can make it simpler.

Reference:

Static vs. Non-Static

Foreground vs. Background

Intents & Extras

Create python-for-android Service

Question 5

Never used any of those, but they look interesting..

Take a look at Gearman as well.. more overhead in systems like these but you get other cool stuff :) Guess it depends on your needs ..

Question 6

nohup or disown (in bash) will allow a process or job to continue in the background after the controlling shell has been killed.

Continue processing after closing connection

Answers

php