pvac: ensure that listeners are done in ClientChannel

ensure no concurrent callback in progress
when removing listeners.

src/client/client.cpp

@@ -5,6 +5,7 @@
 
 #include <epicsMutex.h>
 #include <epicsGuard.h>
+#include <epicsEvent.h>
 
 #include <pv/pvData.h>
 #include <pv/bitSet.h>
@@ -20,6 +21,7 @@ namespace pvd = epics::pvData;
 namespace pva = epics::pvAccess;
 
 typedef epicsGuard<epicsMutex> Guard;
+typedef epicsGuardRelease<epicsMutex> UnGuard;
 
 namespace pvac {
 
@@ -35,10 +37,12 @@ struct ClientChannel::Impl : public pva::ChannelRequester,
     // assume few listeners per channel, store in vector
     typedef std::vector<ClientChannel::ConnectCallback*> listeners_t;
     listeners_t listeners;
+    bool listeners_inprogress;
+    epicsEvent listeners_done;
 
     static size_t num_instances;
 
-    Impl() {REFTRACE_INCREMENT(num_instances);}
+    Impl() :listeners_inprogress(false) {REFTRACE_INCREMENT(num_instances);}
     virtual ~Impl() {REFTRACE_DECREMENT(num_instances);}
 
     // called automatically via wrapped_shared_from_this
@@ -47,6 +51,10 @@ struct ClientChannel::Impl : public pva::ChannelRequester,
         // ClientChannel destroy implicitly removes all callbacks,
         // but doesn't destroy the Channel or cancel Operations
         Guard G(mutex);
+        while(listeners_inprogress) {
+            UnGuard U(G);
+            listeners_done.wait();
+        }
         listeners.clear();
     }
 
@@ -60,25 +68,39 @@ struct ClientChannel::Impl : public pva::ChannelRequester,
         {
             Guard G(mutex);
             notify = listeners; // copy vector
+            listeners_inprogress = true;
         }
-        ConnectEvent evt;
-        evt.connected = connectionState==pva::Channel::CONNECTED;
-        for(listeners_t::const_iterator it=notify.begin(), end=notify.end(); it!=end; ++it)
-        {
-            try {
-                (*it)->connectEvent(evt);
-            }catch(std::exception& e){
-                LOG(pva::logLevelError, "Unhandled exception in connection state listener: %s\n", e.what());
+        try {
+            ConnectEvent evt;
+            evt.connected = connectionState==pva::Channel::CONNECTED;
+            for(listeners_t::const_iterator it=notify.begin(), end=notify.end(); it!=end; ++it)
+            {
+                try {
+                    (*it)->connectEvent(evt);
+                }catch(std::exception& e){
+                    LOG(pva::logLevelError, "Unhandled exception in connection state listener: %s\n", e.what());
 
-                Guard G(mutex);
-                for(listeners_t::iterator it2=listeners.begin(), end2=listeners.end(); it2!=end2; ++it2) {
-                    if(*it==*it2) {
-                        listeners.erase(it2);
-                        break;
+                    Guard G(mutex);
+                    for(listeners_t::iterator it2=listeners.begin(), end2=listeners.end(); it2!=end2; ++it2) {
+                        if(*it==*it2) {
+                            listeners.erase(it2);
+                            break;
+                        }
                     }
                 }
             }
+        }catch(...){
+            {
+                Guard G(mutex);
+                listeners_inprogress = false;
+            }
+            listeners_done.signal();
         }
+        {
+            Guard G(mutex);
+            listeners_inprogress = false;
+        }
+        listeners_done.signal();
     }
 };
 
@@ -159,6 +181,12 @@ void ClientChannel::removeConnectListener(ConnectCallback* cb)
     if(!impl) throw std::logic_error("Dead Channel");
     Guard G(impl->mutex);
 
+    // ensure no in-progress callbacks
+    while(impl->listeners_inprogress) {
+        UnGuard U(G);
+        impl->listeners_done.wait();
+    }
+
     for(Impl::listeners_t::iterator it=impl->listeners.begin(), end=impl->listeners.end(); it!=end; ++it)
     {
         if(cb==*it) {