fix issue with object references for async callbacks

Author: sveseli

src/pvaccess/Channel.482.cpp

@@ -1368,17 +1368,17 @@ void Channel::asyncGetThread(Channel* channel)
 
         try {
             AsyncRequestPtr asyncRequest = channel->asyncGetRequestQueue.frontAndPop();
+
             // there were queued requests, reset poll counter
             remainingRuntime = MaxAsyncRequestWaitTimeout;
             try {
                 // Cannot allow shutdown while callback is being executed
                 pvd::Lock lock(channel->asyncGetThreadMutex);
 
                 channel->asyncConnect();
-                pvc::PvaClientGetPtr pvaGet = channel->createGetPtr(asyncRequest->requestDescriptor);
-                pvaGet->get();
-                pvd::PVStructurePtr pvStructure = pvaGet->getData()->getPVStructure();
-                PvObject pvObject(pvStructure);
+                pvc::PvaClientGetPtr asyncPvaGet = channel->createGetPtr(asyncRequest->requestDescriptor);
+                asyncPvaGet->get();
+                PvObject pvObject(asyncPvaGet->getData()->getPVStructure());
                 if (!channel->shutdownInProgress) {
                     logger.trace("Invoking async get callback");
                     channel->invokePyCallback(asyncRequest->pyCallback, pvObject);
@@ -1465,6 +1465,7 @@ void Channel::asyncPutThread(Channel* channel)
 
         try {
             AsyncRequestPtr asyncRequest = channel->asyncPutRequestQueue.frontAndPop();
+
             // there were queued requests, reset poll counter
             remainingRuntime = MaxAsyncRequestWaitTimeout;
             try {
@@ -1475,8 +1476,7 @@ void Channel::asyncPutThread(Channel* channel)
                 pvc::PvaClientPutPtr asyncPvaPut = channel->createPutPtr(asyncRequest->requestDescriptor);
                 channel->preparePut(PvObject(asyncRequest->pvStructurePtr), asyncPvaPut);
                 asyncPvaPut->put();
-                pvd::PVStructurePtr pvStructure = asyncPvaPut->getData()->getPVStructure();
-                PvObject pvObject(pvStructure);
+                PvObject pvObject(asyncPvaPut->getData()->getPVStructure());
                 if (!channel->shutdownInProgress) {
                     logger.trace("Invoking async put callback");
                     channel->invokePyCallback(asyncRequest->pyCallback, pvObject);

src/pvaccess/Channel.482.h

@@ -265,6 +265,17 @@ class Channel : public ChannelMonitorDataProcessor
         , requestDescriptor(requestDescriptor_) 
         , pvStructurePtr(pvStructurePtr_) 
         {}
+
+        // In some cases it seems like boost python object reference counts
+        // go below the minimum before destructor is called
+        ~AsyncRequest() {
+            if (pyCallback.ptr()->ob_refcnt <= 1) {
+                boost::python::incref(pyCallback.ptr());
+            }
+            if (pyErrorCallback.ptr()->ob_refcnt <= 1) {
+                boost::python::incref(pyErrorCallback.ptr());
+            }
+        }
     };
 
     typedef std::tr1::shared_ptr<AsyncRequest> AsyncRequestPtr;

test/testChannelPut.py

@@ -19,6 +19,9 @@
 
 class TestChannelPut:
 
+    def putCallback(self, pv):
+        self.putPv = pv.copy()
+
     #
     # Boolean Put
     #
@@ -389,7 +392,7 @@ def testAsyncPut_PvObject(self):
         pv = c.get('')
         pv['int'] = i
         print('\nAsync setting int field to: %s' % (i))
-        c.asyncPut(pv, None, None, '')
+        c.asyncPut(pv, self.putCallback, None, '')
         time.sleep(0.1)
         pv2 = c.get('')
         print('Testing equality: %s == %s' % (pv['int'], pv2['int']))