Make access() throw if another session is already locked (#11757)

Change-Id: Ic8571b0d078c3ff64e8b9914e55c51766ae49024

1 files changed, 10 insertions, 0 deletions

diff --git a/server/src/com/vaadin/ui/UI.java b/server/src/com/vaadin/ui/UI.java
index f260a6af79..6433bebbe4 100644
--- a/server/src/com/vaadin/ui/UI.java
+++ b/server/src/com/vaadin/ui/UI.java
@@ -1103,12 +1103,20 @@ public abstract class UI extends AbstractSingleComponentContainer implements
      * RPC handlers for components inside this UI do not need this method as the
      * session is automatically locked by the framework during request handling.
      * </p>
+     * <p>
+     * Note that calling this method while another session is locked by the
+     * current thread will cause an exception. This is to prevent deadlock
+     * situations when two threads have locked one session each and are both
+     * waiting for the lock for the other session.
+     * </p>
      * 
      * @param runnable
      *            the runnable which accesses the UI
      * @throws UIDetachedException
      *             if the UI is not attached to a session (and locking can
      *             therefore not be done)
+     * @throws IllegalStateException
+     *             if the current thread holds the lock for another session
      * 
      * @see #getCurrent()
      * @see VaadinSession#access(Runnable)
@@ -1123,6 +1131,8 @@ public abstract class UI extends AbstractSingleComponentContainer implements
             throw new UIDetachedException();
         }
 
+        VaadinService.verifyNoOtherSessionLocked(session);
+
         session.lock();
         try {
             if (getSession() == null) {