fix(DEC): MCOL-5602 fixing potentially endless loop in DEC (#3049)

dbcon/joblist/distributedenginecomm.cpp

@@ -356,8 +356,6 @@ int32_t DistributedEngineComm::Setup()
 
   fWlock.swap(newLocks);
   fPmConnections.swap(newClients);
-  // memory barrier to prevent the pmCount assignment migrating upward
-  atomicops::atomicMb();
   pmCount = newPmCount;
 
   newLocks.clear();
@@ -419,14 +417,14 @@ Error:
   for (map_tok = fSessionMessages.begin(); map_tok != fSessionMessages.end(); ++map_tok)
   {
     map_tok->second->queue.clear();
-    (void)atomicops::atomicInc(&map_tok->second->unackedWork[0]);
+    ++map_tok->second->unackedWork[0];
     map_tok->second->queue.push(sbs);
   }
   lk.unlock();
 
   if (fIsExeMgr)
   {
-    decltype(pmCount) originalPMCount = pmCount;
+    const uint32_t originalPMCount = pmCount;
     // Re-establish if a remote PM restarted.
     std::this_thread::sleep_for(std::chrono::seconds(3));
     auto rc = Setup();
@@ -455,7 +453,7 @@ void DistributedEngineComm::addQueue(uint32_t key, bool sendACKs)
   mqe->throttled = false;
 
   std::lock_guard lk(fMlock);
-  b = fSessionMessages.insert(pair<uint32_t, boost::shared_ptr<MQE> >(key, mqe)).second;
+  b = fSessionMessages.insert(pair<uint32_t, boost::shared_ptr<MQE>>(key, mqe)).second;
 
   if (!b)
   {
@@ -635,7 +633,7 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
                                      size_t queueSize)
 {
   ISMPacketHeader* ism;
-  uint32_t l_msgCount = msgs.size();
+  size_t l_msgCount = msgs.size();
 
   /* If the current queue size > target, do nothing.
    * If the original queue size > target, ACK the msgs below the target.
@@ -643,14 +641,13 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
   if (!mqe->throttled || queueSize >= mqe->targetQueueSize)
   {
     /* no acks will be sent, but update unackedwork to keep the #s accurate */
-    uint16_t numack = 0;
     uint32_t sockidx = 0;
 
     while (l_msgCount > 0)
     {
-      nextPMToACK(mqe, l_msgCount, &sockidx, &numack);
+      size_t numAcked = subsMsgCounterAndRotatePM(mqe, l_msgCount, &sockidx);
-      idbassert(numack <= l_msgCount);
+      idbassert(numAcked <= l_msgCount);
-      l_msgCount -= numack;
+      l_msgCount -= numAcked;
     }
 
     return;
@@ -665,9 +662,8 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
   {
     /* update unackedwork for the overage that will never be acked */
     int64_t overage = queueSize + totalMsgSize - mqe->targetQueueSize;
-    uint16_t numack = 0;
     uint32_t sockidx = 0;
-    uint32_t msgsToIgnore;
+    size_t msgsToIgnore;
 
     for (msgsToIgnore = 0; overage >= 0; msgsToIgnore++)
       overage -= msgs[msgsToIgnore]->lengthWithHdrOverhead();
@@ -679,16 +675,15 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
 
     while (msgsToIgnore > 0)
     {
-      nextPMToACK(mqe, msgsToIgnore, &sockidx, &numack);
+      size_t numAcked = subsMsgCounterAndRotatePM(mqe, msgsToIgnore, &sockidx);
-      idbassert(numack <= msgsToIgnore);
+      idbassert(numAcked <= msgsToIgnore);
-      msgsToIgnore -= numack;
+      msgsToIgnore -= numAcked;
     }
   }
 
   if (l_msgCount > 0)
   {
     SBS msg(new ByteStream(sizeof(ISMPacketHeader)));
-    uint16_t* toAck;
     vector<bool> pmAcked(pmCount, false);
 
     ism = (ISMPacketHeader*)msg->getInputPtr();
@@ -698,7 +693,6 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
 
     ism->Interleave = uniqueID;
     ism->Command = BATCH_PRIMITIVE_ACK;
-    toAck = &ism->Size;
 
     msg->advanceInputPtr(sizeof(ISMPacketHeader));
     // There must be only one local connection here.
@@ -710,9 +704,20 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
 
       /* This will reset the ACK field in the Bytestream directly, and nothing
        * else needs to change if multiple msgs are sent. */
-      nextPMToACK(mqe, l_msgCount, &sockIndex, toAck);
+      size_t numAcked = subsMsgCounterAndRotatePM(mqe, l_msgCount, &sockIndex);
-      idbassert(*toAck <= l_msgCount);
+      // Potential truncation here from size_t to 16 bits.
-      l_msgCount -= *toAck;
+      ism->Size = static_cast<uint16_t>(
+          std::min(static_cast<size_t>(std::numeric_limits<uint16_t>::max()), numAcked));
+      idbassert(numAcked <= l_msgCount);
+      l_msgCount -= numAcked;
+
+      // We get some logs if the above mentioned truncation happens.
+      if (numAcked > std::numeric_limits<uint16_t>::max())
+      {
+        cerr << "DEC::sendAcks(): msgs acked number [" << numAcked
+             << "] overflows PrimMsg protocol header field capacity 2^16." << std::endl;
+      }
+
       if (sockIndex == localConnectionId_ && fIsExeMgr)
       {
         sendToLocal = true;
@@ -739,7 +744,7 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
 
       if (totalUnackedWork == 0)
       {
-        *toAck = 1;
+        ism->Size = 1;  // size of the batch acked
 
         for (uint32_t i = 0; i < pmCount; ++i)
         {
@@ -761,8 +766,8 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
   }
 }
 
-void DistributedEngineComm::nextPMToACK(boost::shared_ptr<MQE> mqe, uint32_t maxAck, uint32_t* sockIndex,
+size_t DistributedEngineComm::subsMsgCounterAndRotatePM(boost::shared_ptr<MQE> mqe, const size_t maxAck,
-                                        uint16_t* numToAck)
+                                                        uint32_t* sockIndex)
 {
   uint32_t& nextIndex = mqe->ackSocketIndex;
 
@@ -770,56 +775,57 @@ void DistributedEngineComm::nextPMToACK(boost::shared_ptr<MQE> mqe, uint32_t max
    * the locking env, mqe->unackedWork can only grow; whatever gets latched in this fcn
    * is a safe minimum at the point of use. */
 
-  if (mqe->unackedWork[nextIndex] >= maxAck)
+  if (mqe->unackedWork[nextIndex].load() >= maxAck)
   {
-    (void)atomicops::atomicSub(&mqe->unackedWork[nextIndex], maxAck);
+    atomicops::atomicSubstitute(mqe->unackedWork[nextIndex], maxAck);
     *sockIndex = nextIndex;
-    // FIXME: we're going to truncate here from 32 to 16 bits. Hopefully this will always fit...
-    *numToAck = maxAck;
 
     if (pmCount > 0)
       nextIndex = (nextIndex + 1) % pmCount;
 
-    return;
+    return maxAck;
   }
   else
   {
     for (int i = pmCount - 1; i >= 0; --i)
     {
-      uint32_t curVal = mqe->unackedWork[nextIndex];
+      const size_t curVal = mqe->unackedWork[nextIndex].load();
-      uint32_t unackedWork = (curVal > maxAck ? maxAck : curVal);
+      const size_t unackedWork = std::min(curVal, maxAck);
-
       if (unackedWork > 0)
       {
-        (void)atomicops::atomicSub(&mqe->unackedWork[nextIndex], unackedWork);
+        atomicops::atomicSubstitute(mqe->unackedWork[nextIndex], unackedWork);
+
         *sockIndex = nextIndex;
-        *numToAck = unackedWork;
 
         if (pmCount > 0)
           nextIndex = (nextIndex + 1) % pmCount;
 
-        return;
+        return unackedWork;
       }
 
       if (pmCount > 0)
         nextIndex = (nextIndex + 1) % pmCount;
     }
 
-    cerr << "DEC::nextPMToACK(): Couldn't find a PM to ACK! ";
+    cerr << "DEC::subsMsgCounterAndRotatePM(): Couldn't find a PM to ACK! ";
 
     for (int i = pmCount - 1; i >= 0; --i)
       cerr << mqe->unackedWork[i] << " ";
 
-    cerr << " max: " << maxAck;
+    cerr << " max: " << maxAck << endl;
-    cerr << endl;
     // make sure the returned vars are legitimate
     *sockIndex = nextIndex;
-    *numToAck = maxAck / pmCount;
 
-    if (pmCount > 0)
+    // This will potentially results in invalid pmCount but it's better than crashing on 0 div.
-      nextIndex = (nextIndex + 1) % pmCount;
+    const uint32_t localPmCount = pmCount.load();
+    if (localPmCount > 0)
+    {
+      nextIndex = (nextIndex + 1) % localPmCount;
+      return maxAck / localPmCount;
+    }
 
-    return;
+    cerr << "DEC::subsMsgCounterAndRotatePM(): The number of PMs is 0.";
+    return maxAck;
   }
 }
 
@@ -970,7 +976,7 @@ void DistributedEngineComm::addDataToOutput(SBS sbs, uint32_t connIndex, Stats*
 
   if (pmCount > 0)
   {
-    (void)atomicops::atomicInc(&mqe->unackedWork[connIndex % pmCount]);
+    ++mqe->unackedWork[connIndex % pmCount];
   }
 
   TSQSize_t queueSize = mqe->queue.push(sbs);
@@ -1092,7 +1098,7 @@ int DistributedEngineComm::writeToClient(size_t aPMIndex, const SBS& bs, uint32_
     for (map_tok = fSessionMessages.begin(); map_tok != fSessionMessages.end(); ++map_tok)
     {
       map_tok->second->queue.clear();
-      (void)atomicops::atomicInc(&map_tok->second->unackedWork[0]);
+      ++map_tok->second->unackedWork[0];
       map_tok->second->queue.push(sbs);
     }
 
@@ -1120,37 +1126,6 @@ int DistributedEngineComm::writeToClient(size_t aPMIndex, const SBS& bs, uint32_
 
     // Connection was established.
     return 1;
-    /*
-                    // reconfig the connection array
-                    ClientList tempConns;
-                    {
-                            //cout << "WARNING: DEC WRITE BROKEN PIPE " <<
-    fPmConnections[index]->otherEnd()<< endl; boost::mutex::scoped_lock onErrLock(fOnErrMutex); string
-    moduleName = fPmConnections[index]->moduleName();
-                            //cout << "module name = " << moduleName << endl;
-                            if (index >= fPmConnections.size()) return 0;
-
-                            for (uint32_t i = 0; i < fPmConnections.size(); i++)
-                            {
-                                    if (moduleName != fPmConnections[i]->moduleName())
-                                            tempConns.push_back(fPmConnections[i]);
-                            }
-                            if (tempConns.size() == fPmConnections.size()) return 0;
-                            fPmConnections.swap(tempConns);
-                            pmCount = (pmCount == 0 ? 0 : pmCount - 1);
-                    }
-    // send alarm
-    ALARMManager alarmMgr;
-    string alarmItem("UNKNOWN");
-
-    if (index < fPmConnections.size())
-    {
-        alarmItem = fPmConnections[index]->addr2String();
-    }
-
-    alarmItem.append(" PrimProc");
-    alarmMgr.sendAlarmReport(alarmItem.c_str(), oam::CONN_FAILURE, SET);
-    */
   }
   return 0;
 }
@@ -1206,9 +1181,15 @@ DistributedEngineComm::MQE::MQE(const uint32_t pCount, const uint32_t initialInt
                                 const uint64_t flowControlEnableBytesThresh)
  : ackSocketIndex(0), pmCount(pCount), hasBigMsgs(false), targetQueueSize(flowControlEnableBytesThresh)
 {
-  unackedWork.reset(new volatile uint32_t[pmCount]);
   interleaver.reset(new uint32_t[pmCount]);
-  memset((void*)unackedWork.get(), 0, pmCount * sizeof(uint32_t));
+  const uint32_t localPmCount = pmCount;
+  AtomicSizeVec s(localPmCount);
+  for (size_t i = 0; i < localPmCount; ++i)
+  {
+    s[i].store(0);
+  }
+  unackedWork.swap(s);
+
   uint32_t interleaverValue = initialInterleaverValue;
   initialConnectionId = initialInterleaverValue;
   for (size_t pmId = 0; pmId < pmCount; ++pmId)

dbcon/joblist/distributedenginecomm.h

@@ -225,6 +225,7 @@ class DistributedEngineComm
 
   // A queue of ByteStreams coming in from PrimProc heading for a JobStep
   typedef ThreadSafeQueue<messageqcpp::SBS> StepMsgQueue;
+  using AtomicSizeVec = std::vector<std::atomic<size_t>>;
 
   /* To keep some state associated with the connection.  These aren't copyable. */
   struct MQE : public boost::noncopyable
@@ -235,7 +236,7 @@ class DistributedEngineComm
     messageqcpp::Stats stats;
     StepMsgQueue queue;
     uint32_t ackSocketIndex;
-    boost::scoped_array<volatile uint32_t> unackedWork;
+    AtomicSizeVec unackedWork;
     boost::scoped_array<uint32_t> interleaver;
     uint32_t initialConnectionId;
     uint32_t pmCount;
@@ -283,7 +284,7 @@ class DistributedEngineComm
   std::mutex fMlock;     // sessionMessages mutex
   std::vector<std::shared_ptr<std::mutex>> fWlock;  // PrimProc socket write mutexes
   bool fBusy;
-  volatile uint32_t pmCount;
+  std::atomic<uint32_t> pmCount;
   boost::mutex fOnErrMutex;  // to lock function scope to reset pmconnections under error condition
   boost::mutex fSetupMutex;
 
@@ -305,7 +306,7 @@ class DistributedEngineComm
 
   void sendAcks(uint32_t uniqueID, const std::vector<messageqcpp::SBS>& msgs, boost::shared_ptr<MQE> mqe,
                 size_t qSize);
-  void nextPMToACK(boost::shared_ptr<MQE> mqe, uint32_t maxAck, uint32_t* sockIndex, uint16_t* numToAck);
+  size_t subsMsgCounterAndRotatePM(boost::shared_ptr<MQE> mqe, const size_t maxAck, uint32_t* sockIndex);
   void setFlowControl(bool enable, uint32_t uniqueID, boost::shared_ptr<MQE> mqe);
   void doHasBigMsgs(boost::shared_ptr<MQE> mqe, uint64_t targetSize);
   boost::mutex ackLock;

utils/common/atomicops.h

@@ -22,6 +22,7 @@
 #include <unistd.h>
 #include <stdint.h>
 #include <sched.h>
+#include <atomic>
 
 /*
 This is an attempt to wrap the differneces between Windows and Linux around atomic ops.
@@ -92,4 +93,15 @@ inline void atomicYield()
   sched_yield();
 }
 
+// This f assumes decrement is smaller than minuend.
+template <typename T>
+inline void atomicSubstitute(typename std::atomic<T>& minuend, T decrement)
+{
+  T expected = minuend.load();
+  do
+  {
+    expected = minuend.load();
+  } while (!minuend.compare_exchange_weak(expected, expected - decrement));
+}
+
 }  // namespace atomicops