Add test case for SessionHandler causing a deadlocked session

Author: cs278

ext/session/tests/user_session_module/sessionhandler_stuck_open.phpt

@@ -0,0 +1,51 @@
+--TEST--
+Test SessionHandler with serialization failure locks session
+--EXTENSIONS--
+session
+--SKIPIF--
+<?php if (!is_dir('/proc/self/fd')) die('skip /proc/self/fd does not exist');
+--FILE--
+<?php
+
+$savePath = __DIR__;
+
+session_set_save_handler(new \SessionHandler(), true);
+
+session_start([
+    'save_path' => $savePath,
+]);
+
+$sessionFile = $savePath.'/sess_'.session_id();
+
+$_SESSION['test'] = function () {};
+
+try {
+    session_write_close();
+} catch (\Throwable $e) {
+    echo $e->getMessage(), "\n";
+}
+
+// At this point the session handler should have closed the file handle, unlocking
+// the session for the next request.
+
+$dir = '/proc/self/fd/';
+$h = opendir($dir);
+
+while (false !== $entry = readdir($h)) {
+    $target = realpath($dir.$entry);
+
+    if ($target === $sessionFile) {
+        echo "Fail session `{$sessionFile}` is still open\n";
+        @unlink($sessionFile);
+
+        return;
+    }
+}
+
+echo "Passed\n";
+@unlink($sessionFile);
+
+?>
+--EXPECT--
+Serialization of 'Closure' is not allowed
+Passed