ucb: NeonLockStore::stopTicker(): avoid deadlock

Tor reports that NeonLockStore::stopTicker() m_pTickerThread->join()
can deadlock with TickerThread running NeonLockStore::refreshLocks().

This can be avoided by copying m_pTickerThread to the stack, and
releasing the m_aMutex before calling join().

Change-Id: I387f83a530c5b893f79fa677b1092e0902c8af65

1 files changed, 12 insertions, 5 deletions

diff --git a/ucb/source/ucp/webdav-neon/NeonLockStore.cxx b/ucb/source/ucp/webdav-neon/NeonLockStore.cxx
index 04608a63f725..043ea7d27d72 100644
--- a/ucb/source/ucp/webdav-neon/NeonLockStore.cxx
+++ b/ucb/source/ucp/webdav-neon/NeonLockStore.cxx
@@ -128,14 +128,21 @@ void NeonLockStore::startTicker()
 
 void NeonLockStore::stopTicker()
 {
-    osl::MutexGuard aGuard( m_aMutex );
-
-    if ( m_pTickerThread.is() )
+    rtl::Reference<TickerThread> pTickerThread;
     {
-        m_pTickerThread->finish();
-        m_pTickerThread->join();
+        osl::MutexGuard aGuard( m_aMutex );
+
+        if (!m_pTickerThread.is())
+        {
+            return; // nothing to do
+        }
+        m_pTickerThread->finish(); // needs mutex
+        // the TickerThread may run refreshLocks() at most once after this
+        pTickerThread = m_pTickerThread;
         m_pTickerThread.clear();
     }
+
+    pTickerThread->join(); // without m_aMutex locked (to prevent deadlock)
 }
 
 void NeonLockStore::registerSession( HttpSession * pHttpSession )