Added data integrity mechanism: garbage collection signaling.

The garbage collector now sets a flag on the agent object indicating garbage collection.
The process will immediately exit when detecting garbage collection.

objectstore/Agent.cpp

@@ -44,6 +44,7 @@ void cta::objectstore::Agent::initialize() {
   m_payload.set_heartbeat(0);
   m_payload.set_timeout_us(60*1000*1000);
   m_payload.set_description("");
+  m_payload.set_being_garbage_collected(false);
   m_payloadInterpreted = true;
 }
 
@@ -138,6 +139,16 @@ bool cta::objectstore::Agent::isEmpty() {
   return true;
 }
 
+bool cta::objectstore::Agent::isBeingGarbageCollected() {
+  checkPayloadReadable();
+  return m_payload.being_garbage_collected();
+}
+
+void cta::objectstore::Agent::setBeingGarbageCollected() {
+  checkPayloadWritable();
+  m_payload.set_being_garbage_collected(true);
+}
+
 void cta::objectstore::Agent::garbageCollect(const std::string& presumedOwner, AgentReference & agentReference, log::LogContext & lc,
     cta::catalogue::Catalogue & catalogue) {
   checkPayloadWritable();

objectstore/Agent.hpp

@@ -58,6 +58,10 @@ public:
   
   bool isEmpty();
   
+  void setBeingGarbageCollected();
+  
+  bool isBeingGarbageCollected();
+  
   void garbageCollect(const std::string &presumedOwner, AgentReference & agentReference, log::LogContext & lc,
     cta::catalogue::Catalogue & catalogue) override;
   

objectstore/AgentReference.cpp

@@ -159,6 +159,12 @@ void AgentReference::queueAndExecuteAction(std::shared_ptr<Action> action, objec
       objectstore::ScopedExclusiveLock agl(ag);
       double agentLockTime = t.secs(utils::Timer::resetCounter);
       ag.fetch();
+      if (ag.isBeingGarbageCollected()) {
+        log::ScopedParamContainer params(lc);
+        params.add("agentObject", ag.getAddressIfSet());
+        lc.log(log::CRIT, "In AgentReference::queueAndExecuteAction(): agent object being garbage collected. Exiting.");
+        ::exit(EXIT_FAILURE);
+      }
       double agentFetchTime = t.secs(utils::Timer::resetCounter);
       size_t agentOwnershipSizeBefore = ag.getOwnershipListSize();
       size_t operationsCount = q->queue.size() + 1;

objectstore/GarbageCollector.cpp

@@ -172,9 +172,10 @@ void GarbageCollector::cleanupDeadAgent(const std::string & address, std::list<l
     // The agent will be removed from our ownership by the calling function: we're done.
     return;
   }
-  // Aquire ownership of the agent.
+  // Aquire ownership of the agent. Prevent further updates to it.
   m_ourAgentReference.addToOwnership(address,m_objectStore);
   agent.setOwner(m_ourAgentReference.getAgentAddress());
+  agent.setBeingGarbageCollected();
   agent.commit();
   // Update the register
   ScopedExclusiveLock arl(m_agentRegister);

objectstore/cta.proto

@@ -155,6 +155,7 @@ message Agent {
   required uint64 heartbeat = 2001;
   required uint64 timeout_us = 2002;
   repeated string ownedobjects = 2003;
+  optional bool being_garbage_collected = 2004 [default = false];
 }
 
 message AgentRegister {