introduce pseudo-thread mutex

used to emulate single-threaded behavior after the thread itself has
shut down.

2 files changed, 14 insertions, 2 deletions

diff --git a/fnet/src/vespa/fnet/transport_thread.cpp b/fnet/src/vespa/fnet/transport_thread.cpp
index 2c0d00b22f3..9e7a34209b4 100644
--- a/fnet/src/vespa/fnet/transport_thread.cpp
+++ b/fnet/src/vespa/fnet/transport_thread.cpp
@@ -118,7 +118,7 @@ FNET_TransportThread::PostEvent(FNET_ControlPacket *cpacket,
         std::unique_lock<std::mutex> guard(_lock);
         if (_shutdown) {
             guard.unlock();
-            DiscardEvent(cpacket, context);
+            SafeDiscardEvent(cpacket, context);
             return false;
         }
         wasEmpty = _queue.IsEmpty_NoLock();
@@ -150,6 +150,14 @@ FNET_TransportThread::DiscardEvent(FNET_ControlPacket *cpacket,
     }
 }
 
+void
+FNET_TransportThread::SafeDiscardEvent(FNET_ControlPacket *cpacket,
+                                       FNET_Context context)
+{
+    WaitFinished(); // make sure actual thread is all done
+    std::lock_guard guard(_pseudo_thread); // be the thread
+    DiscardEvent(cpacket, context);
+}
 
 void
 FNET_TransportThread::handle_add_cmd(FNET_IOComponent *ioc)
@@ -215,6 +223,7 @@ FNET_TransportThread::FNET_TransportThread(FNET_Transport &owner_in)
       _myQueue(),
       _lock(),
       _cond(),
+      _pseudo_thread(),
       _started(false),
       _shutdown(false),
       _finished(false),
diff --git a/fnet/src/vespa/fnet/transport_thread.h b/fnet/src/vespa/fnet/transport_thread.h
index 408d20619d2..4de82d802dd 100644
--- a/fnet/src/vespa/fnet/transport_thread.h
+++ b/fnet/src/vespa/fnet/transport_thread.h
@@ -46,13 +46,13 @@ private:
     FNET_PacketQueue_NoLock  _myQueue;        // inner event queue
     std::mutex               _lock;           // used for synchronization
     std::condition_variable  _cond;           // used for synchronization
+    std::recursive_mutex     _pseudo_thread;  // used after transport thread has shut down
     bool                     _started;        // event loop started ?
     bool                     _shutdown;       // should stop event loop ?
     bool                     _finished;       // event loop stopped ?
     bool                     _waitFinished;   // someone is waiting for _finished
     bool                     _deleted;        // destructor called ?
 
-
     FNET_TransportThread(const FNET_TransportThread &);
     FNET_TransportThread &operator=(const FNET_TransportThread &);
 
@@ -133,6 +133,9 @@ private:
      **/
     void DiscardEvent(FNET_ControlPacket *cpacket, FNET_Context context);
 
+    // safely discard events using the pseudo thread mutex
+    void SafeDiscardEvent(FNET_ControlPacket *cpacket, FNET_Context context);
+
 
     /**
      * Obtain a reference to the object holding the configuration for