move away from mutex to atomic variables

arangod/VocBase/document-collection.cpp

@@ -123,6 +123,7 @@ TRI_document_collection_t::TRI_document_collection_t ()
     _headersPtr(nullptr),
     _keyGenerator(nullptr),
     _uncollectedLogfileEntries(0),
+    _currentWriterThread(0),
     _cleanupIndexes(0) {
 
   _tickMax = 0;
@@ -199,13 +200,8 @@ int TRI_document_collection_t::beginWrite () {
   // std::cout << "BeginWrite: " << document->_info._name << std::endl;
   TRI_WRITE_LOCK_DOCUMENTS_INDEXES_PRIMARY_COLLECTION(this);
 
-  try {
+  // register writer 
-    _vocbase->_deadlockDetector.setWriterStarted(this);
+  _currentWriterThread.store(TRI_CurrentThreadId());
-  }
-  catch (...) {
-    TRI_WRITE_UNLOCK_DOCUMENTS_INDEXES_PRIMARY_COLLECTION(this);
-    return TRI_ERROR_OUT_OF_MEMORY;
-  }
 
   return TRI_ERROR_NO_ERROR;
 }
@@ -229,11 +225,8 @@ int TRI_document_collection_t::endWrite () {
   // std::cout << "EndWrite: " << document->_info._name << std::endl;
   TRI_WRITE_UNLOCK_DOCUMENTS_INDEXES_PRIMARY_COLLECTION(this);
  
-  try { 
+  // unregister writer
-    _vocbase->_deadlockDetector.setWriterFinished(this);
+  _currentWriterThread.store(0);
-  }
-  catch (...) {
-  }
 
   return TRI_ERROR_NO_ERROR;
 }
@@ -390,14 +383,9 @@ int TRI_document_collection_t::beginWriteTimed (uint64_t timeout,
   if (wasBlocked) {      
     _vocbase->_deadlockDetector.setReaderUnblocked(this);
   }
-  
+ 
-  try {
+  // register writer 
-    _vocbase->_deadlockDetector.setWriterStarted(this);
+  _currentWriterThread.store(TRI_CurrentThreadId());
-  }
-  catch (...) {
-    TRI_WRITE_UNLOCK_DOCUMENTS_INDEXES_PRIMARY_COLLECTION(this);
-    return TRI_ERROR_OUT_OF_MEMORY;
-  }
 
   return TRI_ERROR_NO_ERROR;
 }

arangod/VocBase/document-collection.h

@@ -357,6 +357,7 @@ TRI_doc_collection_info_t;
 ////////////////////////////////////////////////////////////////////////////////
 
 struct TRI_document_collection_t : public TRI_collection_t {
+
   // ...........................................................................
   // this lock protects the indexes and _headers attributes
   // ...........................................................................
@@ -380,6 +381,10 @@ public:
   VocShaper* getShaper () const;
 #endif
 
+  inline TRI_tid_t getCurrentWriterThread () const {
+    return _currentWriterThread.load();
+  }
+
   inline bool useSecondaryIndexes () const {
     return _useSecondaryIndexes;
   }
@@ -421,6 +426,8 @@ public:
   TRI_read_write_lock_t                  _compactionLock;
   double                                 _lastCompaction;
 
+  std::atomic<TRI_tid_t>                 _currentWriterThread;
+
   // ...........................................................................
   // this condition variable protects the _journalsCondition
   // ...........................................................................

lib/Basics/DeadlockDetector.h

@@ -69,18 +69,10 @@ namespace triagens {
 
           std::vector<TRI_tid_t> stack;
 
-          TRI_tid_t writerTid;
+          TRI_tid_t writerTid = value->getCurrentWriterThread();
 
-          {
+          if (writerTid == 0) {
-            MUTEX_LOCKER(_writersLock);
+            return false;
-            // find responsible writer
-            auto it = _writers.find(value); 
-
-            if (it == _writers.end()) {
-              return false;
-            }
-
-            writerTid = (*it).second;
           }
             
           stack.push_back(writerTid);
@@ -121,18 +113,10 @@ namespace triagens {
 
           std::vector<TRI_tid_t> stack;
 
-          TRI_tid_t writerTid;
+          TRI_tid_t writerTid = value->getCurrentWriterThread();
 
-          {
+          if (writerTid == 0) {
-            MUTEX_LOCKER(_writersLock);
+            return false;
-            // find responsible writer
-            auto it = _writers.find(value); 
-
-            if (it == _writers.end()) {
-              return false;
-            }
-
-            writerTid = (*it).second;
           }
             
           stack.push_back(writerTid);
@@ -186,48 +170,12 @@ namespace triagens {
           }
         }
 
-////////////////////////////////////////////////////////////////////////////////
-/// @brief inserts a writer into the list of writers
-////////////////////////////////////////////////////////////////////////////////
-
-        void setWriterStarted (T const* value) {
-          auto tid = TRI_CurrentThreadId();
-
-          MUTEX_LOCKER(_writersLock);
-          _writers.emplace(value, tid);
-        }
-
-////////////////////////////////////////////////////////////////////////////////
-/// @brief removes a writers from the list of writers
-////////////////////////////////////////////////////////////////////////////////
-
-        void setWriterFinished (T const* value) noexcept {
-          try {
-            MUTEX_LOCKER(_writersLock);
-            _writers.erase(value);
-          }
-          catch (...) {
-          }
-        }
-
 // -----------------------------------------------------------------------------
 // --SECTION--                                                 private variables
 // -----------------------------------------------------------------------------
 
       private:
 
-////////////////////////////////////////////////////////////////////////////////
-/// @brief lock for managing the writers
-////////////////////////////////////////////////////////////////////////////////
-
-        triagens::basics::Mutex _writersLock;
-
-////////////////////////////////////////////////////////////////////////////////
-/// @brief all operating writers
-////////////////////////////////////////////////////////////////////////////////
-
-        std::unordered_map<T const*, TRI_tid_t> _writers;
-
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief lock for managing the readers
 ////////////////////////////////////////////////////////////////////////////////