4 files changed, 48 insertions, 4 deletions

diff --git a/application/bookmark/BookmarkIO.php b/application/bookmark/BookmarkIO.php
index c78dbe41..8439d470 100644
--- a/application/bookmark/BookmarkIO.php
+++ b/application/bookmark/BookmarkIO.php
@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace Shaarli\Bookmark;
 
+use malkusch\lock\exception\LockAcquireException;
 use malkusch\lock\mutex\Mutex;
 use malkusch\lock\mutex\NoMutex;
 use Shaarli\Bookmark\Exception\DatastoreNotInitializedException;
@@ -80,7 +81,7 @@ class BookmarkIO
         }
 
         $content = null;
-        $this->mutex->synchronized(function () use (&$content) {
+        $this->synchronized(function () use (&$content) {
             $content = file_get_contents($this->datastore);
         });
 
@@ -119,11 +120,28 @@ class BookmarkIO
 
         $data = self::$phpPrefix . base64_encode(gzdeflate(serialize($links))) . self::$phpSuffix;
 
-        $this->mutex->synchronized(function () use ($data) {
+        $this->synchronized(function () use ($data) {
             file_put_contents(
                 $this->datastore,
                 $data
             );
         });
     }
+
+    /**
+     * Wrapper applying mutex to provided function.
+     * If the lock can't be acquired (e.g. some shared hosting provider), we execute the function without mutex.
+     *
+     * @see https://github.com/shaarli/Shaarli/issues/1650
+     *
+     * @param callable $function
+     */
+    protected function synchronized(callable $function): void
+    {
+        try {
+            $this->mutex->synchronized($function);
+        } catch (LockAcquireException $exception) {
+            $function();
+        }
+    }
 }
diff --git a/application/front/controller/admin/ServerController.php b/application/front/controller/admin/ServerController.php
index fabeaf2f..4b74f4a9 100644
--- a/application/front/controller/admin/ServerController.php
+++ b/application/front/controller/admin/ServerController.php
@@ -39,11 +39,16 @@ class ServerController extends ShaarliAdminController
         $currentVersion = $currentVersion === 'dev' ? $currentVersion : 'v' . $currentVersion;
         $phpEol = new \DateTimeImmutable(ApplicationUtils::getPhpEol(PHP_VERSION));
 
+        $permissions = array_merge(
+            ApplicationUtils::checkResourcePermissions($this->container->conf),
+            ApplicationUtils::checkDatastoreMutex()
+        );
+
         $this->assignView('php_version', PHP_VERSION);
         $this->assignView('php_eol', format_date($phpEol, false));
         $this->assignView('php_has_reached_eol', $phpEol < new \DateTimeImmutable());
         $this->assignView('php_extensions', ApplicationUtils::getPhpExtensionsRequirement());
-        $this->assignView('permissions', ApplicationUtils::checkResourcePermissions($this->container->conf));
+        $this->assignView('permissions', $permissions);
         $this->assignView('release_url', $releaseUrl);
         $this->assignView('latest_version', $latestVersion);
         $this->assignView('current_version', $currentVersion);
diff --git a/application/front/controller/visitor/InstallController.php b/application/front/controller/visitor/InstallController.php
index bf965929..418d4a49 100644
--- a/application/front/controller/visitor/InstallController.php
+++ b/application/front/controller/visitor/InstallController.php
@@ -56,11 +56,16 @@ class InstallController extends ShaarliVisitorController
 
         $phpEol = new \DateTimeImmutable(ApplicationUtils::getPhpEol(PHP_VERSION));
 
+        $permissions = array_merge(
+            ApplicationUtils::checkResourcePermissions($this->container->conf),
+            ApplicationUtils::checkDatastoreMutex()
+        );
+
         $this->assignView('php_version', PHP_VERSION);
         $this->assignView('php_eol', format_date($phpEol, false));
         $this->assignView('php_has_reached_eol', $phpEol < new \DateTimeImmutable());
         $this->assignView('php_extensions', ApplicationUtils::getPhpExtensionsRequirement());
-        $this->assignView('permissions', ApplicationUtils::checkResourcePermissions($this->container->conf));
+        $this->assignView('permissions', $permissions);
 
         $this->assignView('pagetitle', t('Install Shaarli'));
 
diff --git a/application/helper/ApplicationUtils.php b/application/helper/ApplicationUtils.php
index 212dd8e2..a6c03aae 100644
--- a/application/helper/ApplicationUtils.php
+++ b/application/helper/ApplicationUtils.php
@@ -3,6 +3,8 @@
 namespace Shaarli\Helper;
 
 use Exception;
+use malkusch\lock\exception\LockAcquireException;
+use malkusch\lock\mutex\FlockMutex;
 use Shaarli\Config\ConfigManager;
 
 /**
@@ -252,6 +254,20 @@ class ApplicationUtils
         return $errors;
     }
 
+    public static function checkDatastoreMutex(): array
+    {
+        $mutex = new FlockMutex(fopen(SHAARLI_MUTEX_FILE, 'r'), 2);
+        try {
+            $mutex->synchronized(function () {
+                return true;
+            });
+        } catch (LockAcquireException $e) {
+            $errors[] = t('Lock can not be acquired on the datastore. You might encounter concurrent access issues.');
+        }
+
+        return $errors ?? [];
+    }
+
     /**
      * Returns a salted hash representing the current Shaarli version.
      *