Minz allow parallel sessions (#3096)

* Minz allow parallel sessions

#fix https://github.com/FreshRSS/FreshRSS/issues/3093

* Array optimisation

* Array optimisation missing

* Reduce direct access to $_SESSION except in install process

* Fix session start headers warning

* Use cookie only the first time the session is started:
`PHP Warning:  session_start(): Cannot start session when headers
already sent in /var/www/FreshRSS/lib/Minz/Session.php on line 39`

* New concept of volatile session for API calls

Optimisation: do not use cookies or local storage at all for API calls
without a Web session
Fix warning:

```
PHP Warning:  session_destroy(): Trying to destroy uninitialized session
in Unknown on line 0
```

* Only call Minz_Session::init once in our index

It was called twice (once indirectly via FreshRSS->init())

* Whitespace

* Mutex for notifications

Implement mutex for notifications
https://github.com/FreshRSS/FreshRSS/pull/3208#discussion_r499509809

* Typo

* Install script is not ready for using Minz_Session

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/Minz/Request.php b/lib/Minz/Request.php
index fc333244f..271bcf738 100644
--- a/lib/Minz/Request.php
+++ b/lib/Minz/Request.php
@@ -269,13 +269,14 @@ class Minz_Request {
 	}
 
 	private static function setNotification($type, $content) {
-		//TODO: Will need to ensure non-concurrency when landing https://github.com/FreshRSS/FreshRSS/pull/3096
+		Minz_Session::lock();
 		$requests = Minz_Session::param('requests', []);
 		$requests[self::requestId()] = [
 				'time' => time(),
 				'notification' => [ 'type' => $type, 'content' => $content ],
 			];
 		Minz_Session::_param('requests', $requests);
+		Minz_Session::unlock();
 	}
 
 	public static function setGoodNotification($content) {
@@ -288,7 +289,7 @@ class Minz_Request {
 
 	public static function getNotification() {
 		$notif = null;
-		//TODO: Will need to ensure non-concurrency when landing https://github.com/FreshRSS/FreshRSS/pull/3096
+		Minz_Session::lock();
 		$requests = Minz_Session::param('requests');
 		if ($requests) {
 			//Delete abandonned notifications
@@ -301,6 +302,7 @@ class Minz_Request {
 			}
 			Minz_Session::_param('requests', $requests);
 		}
+		Minz_Session::unlock();
 		return $notif;
 	}