Assert profile locks before writing

This fixes the potential edge case where a frozen then unfrozen qTox instance could have its locks delete by a new qTox instance.

We now check that we still own our locks, restoring them if we can, before saving

src/core/core.cpp

@@ -947,6 +947,8 @@ void Core::saveConfiguration()
     if (!isReady())
         return;
 
+    ProfileLocker::assertLock();
+
     QString dir = Settings::getSettingsDirPath();
     QDir directory(dir);
     if (!directory.exists() && !directory.mkpath(directory.absolutePath()))

src/profilelocker.cpp

@@ -67,3 +67,33 @@ void ProfileLocker::clearAllLocks()
         file.remove();
     }
 }
+
+void ProfileLocker::assertLock()
+{
+    if (!lockfile)
+    {
+        qCritical() << "ProfileLocker::assertLock: We don't seem to own any lock!";
+        deathByBrokenLock();
+    }
+
+    if (!QFile(lockPathFromName(curLockName)).exists())
+    {
+        QString tmp = curLockName;
+        unlock();
+        if (lock(tmp))
+        {
+            qCritical() << "ProfileLocker::assertLock: Lock file was lost, but could be restored";
+        }
+        else
+        {
+            qCritical() << "ProfileLocker::assertLock: Lock file was lost, and could *NOT* be restored";
+            deathByBrokenLock();
+        }
+    }
+}
+
+void ProfileLocker::deathByBrokenLock()
+{
+    qCritical() << "ProfileLocker: Lock is *BROKEN*, exiting immediately";
+    abort();
+}

src/profilelocker.h

@@ -28,9 +28,15 @@ public:
     /// DO NOT call unless all we're the only qTox instance
     /// and we don't hold any lock yet.
     static void clearAllLocks();
+    /// Check that we actually own the lock
+    /// In case the file was deleted on disk, restore it
+    /// If we can't get a lock, exit qTox immediately
+    /// If we never had a lock in the firt place, exit immediately
+    static void assertLock();
 
 private:
     static QString lockPathFromName(const QString& name);
+    static void deathByBrokenLock(); ///< Print an error then exit immediately
 
 private:
     static std::unique_ptr<QLockFile> lockfile;