diff --git a/changelog.in b/changelog.in
index 5a4e863f65..d08794e5fe 100644
--- a/changelog.in
+++ b/changelog.in
@@ -68,7 +68,7 @@
 
 [RELEASE]
 Version: 6.0.0
-Date: 2018-02-07
+Date: 2018-02-´23
 [DESCRIPTION]
 This major release fixes many bugs, adds quite some new
 functionality, and changes how cloning works (most likely the
@@ -81,6 +81,21 @@ by an array of variables), a new much faster implementation of
 extensional constraints using tuple sets, and support for tracing
 search engines.
 
+[ENTRY]
+Module: search
+What:   bug
+Rank:   minor
+[DESCRIPTION]
+The statistics for parallel search engines was wrong.
+
+[ENTRY]
+Module: search
+What:   bug
+Rank:   major
+[DESCRIPTION]
+Fixed several race conditions during the termination of parallel
+search engines.
+
 [ENTRY]
 Module: support
 What:   change
diff --git a/gecode/kernel/memory/manager.cpp b/gecode/kernel/memory/manager.cpp
index f725bc0849..6c3305cc8f 100644
--- a/gecode/kernel/memory/manager.cpp
+++ b/gecode/kernel/memory/manager.cpp
@@ -39,7 +39,10 @@
 
 namespace Gecode { namespace Kernel {
 
-  Support::Mutex SharedMemory::m;
+  Support::Mutex& SharedMemory::m(void) {
+    static Support::Mutex _m;
+    return _m;
+  }
 
   void
   MemoryManager::alloc_refill(SharedMemory& sm, size_t sz) {
diff --git a/gecode/kernel/memory/manager.hpp b/gecode/kernel/memory/manager.hpp
index 0ab427b411..ca0cfe281a 100755
--- a/gecode/kernel/memory/manager.hpp
+++ b/gecode/kernel/memory/manager.hpp
@@ -71,7 +71,7 @@ namespace Gecode { namespace Kernel {
       HeapChunk* hc;
     } heap;
     /// A mutex for access
-    GECODE_KERNEL_EXPORT static Support::Mutex m;
+    GECODE_KERNEL_EXPORT static Support::Mutex& m(void);
   public:
     /// Initialize
     SharedMemory(void);
@@ -200,7 +200,7 @@ namespace Gecode { namespace Kernel {
 
   forceinline HeapChunk*
   SharedMemory::alloc(size_t s, size_t l) {
-    m.acquire();
+    m().acquire();
     while ((heap.hc != NULL) && (heap.hc->size < l)) {
       heap.n_hc--;
       HeapChunk* hc = heap.hc;
@@ -217,19 +217,19 @@ namespace Gecode { namespace Kernel {
       hc = heap.hc;
       heap.hc = static_cast<HeapChunk*>(hc->next);
     }
-    m.release();
+    m().release();
     return hc;
   }
   forceinline void
   SharedMemory::free(HeapChunk* hc) {
-    m.acquire();
+    m().acquire();
     if (heap.n_hc == MemoryConfig::n_hc_cache) {
       Gecode::heap.rfree(hc);
     } else {
       heap.n_hc++;
       hc->next = heap.hc; heap.hc = hc;
     }
-    m.release();
+    m().release();
   }
 
 
diff --git a/gecode/kernel/memory/region.hpp b/gecode/kernel/memory/region.hpp
index 358f5fad33..84ce6fec97 100755
--- a/gecode/kernel/memory/region.hpp
+++ b/gecode/kernel/memory/region.hpp
@@ -92,7 +92,7 @@ namespace Gecode {
       ~Pool(void);
     };
     /// Just use a single static pool for heap chunks
-    GECODE_KERNEL_EXPORT Pool& pool();
+    GECODE_KERNEL_EXPORT static Pool& pool();
     /// Heap information data structure
     class HeapInfo {
     public:
diff --git a/gecode/search/par/bab.hpp b/gecode/search/par/bab.hpp
index d499342169..963608a0dd 100644
--- a/gecode/search/par/bab.hpp
+++ b/gecode/search/par/bab.hpp
@@ -165,7 +165,9 @@ namespace Gecode { namespace Search { namespace Par {
         mark = 0;
         if (best != NULL)
           cur->constrain(*best);
+        Statistics t = *this;
         Search::Worker::reset(r_d);
+        (*this) += t;
         m.release();
         return;
       }
@@ -240,8 +242,7 @@ namespace Gecode { namespace Search { namespace Par {
         engine().ack_terminate();
         // Wait until termination can proceed
         engine().wait_terminate();
-        // Terminate thread
-        engine().terminated();
+        // Thread will be terminated by returning from run
         return;
       case C_RESET:
         // Acknowledge reset request
diff --git a/gecode/search/par/dfs.hpp b/gecode/search/par/dfs.hpp
index 338534dd96..5bdc651d07 100644
--- a/gecode/search/par/dfs.hpp
+++ b/gecode/search/par/dfs.hpp
@@ -136,7 +136,9 @@ namespace Gecode { namespace Search { namespace Par {
         path.ngdl(0);
         d = 0;
         cur = s;
+        Statistics t = *this;
         Search::Worker::reset(r_d);
+        (*this) += t;
         m.release();
         return;
       }
@@ -188,8 +190,7 @@ namespace Gecode { namespace Search { namespace Par {
         engine().ack_terminate();
         // Wait until termination can proceed
         engine().wait_terminate();
-        // Terminate thread
-        engine().terminated();
+        // Thread will be terminated by returning from run
         return;
       case C_RESET:
         // Acknowledge reset request
diff --git a/gecode/search/par/engine.hh b/gecode/search/par/engine.hh
index 9bc1fa8a58..74ca6c44af 100644
--- a/gecode/search/par/engine.hh
+++ b/gecode/search/par/engine.hh
@@ -47,7 +47,7 @@ namespace Gecode { namespace Search { namespace Par {
 
   /// %Parallel depth-first search engine
   template<class Tracer>
-  class Engine : public Search::Engine {
+  class Engine : public Search::Engine, public Support::Terminator {
   protected:
     /// %Parallel depth-first search worker
     class Worker : public Search::Worker, public Support::Runnable {
@@ -80,6 +80,8 @@ namespace Gecode { namespace Search { namespace Par {
       NoGoods& nogoods(void);
       /// Destructor
       virtual ~Worker(void);
+      /// Terminator (engine)
+      virtual Support::Terminator* terminator(void) const;
     };
     /// Search options
     Options _opt;
@@ -133,7 +135,7 @@ namespace Gecode { namespace Search { namespace Par {
     /// For worker to acknowledge termination command
     void ack_terminate(void);
     /// For worker to register termination
-    void terminated(void);
+    virtual void terminated(void);
     /// For worker to wait until termination is legal
     void wait_terminate(void);
     /// For engine to peform thread termination
diff --git a/gecode/search/par/engine.hpp b/gecode/search/par/engine.hpp
index 09c72c7342..db629cc446 100644
--- a/gecode/search/par/engine.hpp
+++ b/gecode/search/par/engine.hpp
@@ -231,8 +231,6 @@ namespace Gecode { namespace Search { namespace Par {
     // Now all threads are terminated!
   }
 
-
-
   /*
    * Engine: reset control
    */
@@ -351,6 +349,12 @@ namespace Gecode { namespace Search { namespace Par {
     return NULL;
   }
 
+  template<class Tracer>
+  Support::Terminator* 
+  Engine<Tracer>::Worker::terminator(void) const {
+    return &_engine;
+  }
+
   /*
    * Termination and deletion
    */
diff --git a/gecode/support/thread.hpp b/gecode/support/thread.hpp
index ed5b3054fe..087393239e 100755
--- a/gecode/support/thread.hpp
+++ b/gecode/support/thread.hpp
@@ -104,13 +104,17 @@ namespace Gecode { namespace Support {
    */
   class Mutex {
   private:
-#ifdef GECODE_THREADS_WINDOWS
+#if defined(GECODE_THREADS_WINDOWS)
     /// Use a simple but more efficient critical section on Windows
     CRITICAL_SECTION w_cs;
-#endif
-#ifdef GECODE_THREADS_PTHREADS
+#elif defined(GECODE_THREADS_OSX_UNFAIR)
+    /// Use unfair lock on macOS
+    os_unfair_lock lck;
+#elif defined(GECODE_THREADS_PTHREADS)
     /// The Pthread mutex
     pthread_mutex_t p_m;
+#else
+#error No suitable mutex implementation found
 #endif
   public:
     /// Initialize mutex
@@ -134,15 +138,11 @@ namespace Gecode { namespace Support {
     void operator=(const Mutex&) {}
   };
 
-#if defined(GECODE_THREADS_WINDOWS) || !defined(GECODE_THREADS_PTHREADS)
+#ifndef GECODE_THREADS_PTHREADS_SPINLOCK
 
   typedef Mutex FastMutex;
 
-#endif
-
-#ifdef GECODE_THREADS_PTHREADS
-
-#if defined(GECODE_THREADS_OSX) || defined(GECODE_THREADS_OSX_UNFAIR) || defined(GECODE_THREADS_PTHREADS_SPINLOCK)
+#else
 
   /**
    * \brief A fast mutex for mutual exclausion among several threads
@@ -160,16 +160,8 @@ namespace Gecode { namespace Support {
    */
   class FastMutex {
   private:
-#ifdef GECODE_THREADS_OSX
-    /// The OSX spin lock
-    OSSpinLock lck;
-#elif defined(GECODE_THREADS_OSX_UNFAIR)
-    /// The OSX spin lock
-    os_unfair_lock lck;
-#else
     /// The Pthread spinlock
     pthread_spinlock_t p_s;
-#endif
   public:
     /// Initialize mutex
     FastMutex(void);
@@ -192,12 +184,6 @@ namespace Gecode { namespace Support {
     void operator=(const FastMutex&) {}
   };
 
-#else
-
-  typedef Mutex FastMutex;
-
-#endif
-
 #endif
 
   /**
@@ -259,6 +245,20 @@ namespace Gecode { namespace Support {
     void operator=(const Event&) {}
   };
 
+  /**
+   * \brief An interface for objects that can be called after a
+   *        thread has terminated (after running the thread's destructor)
+   *
+   * \ingroup FuncSupportThread
+   */
+  class Terminator {
+  public:
+    /// Destructor
+    virtual ~Terminator() {}
+    /// The function that is called when the thread has terminated
+    virtual void terminated(void) = 0;
+  };
+
   /**
    * \brief An interface for objects that can be run by a thread
    *
@@ -275,6 +275,8 @@ namespace Gecode { namespace Support {
     void todelete(bool d);
     /// Return whether to be deleted upon termination
     bool todelete(void) const;
+    /// Return terminator object
+    virtual Terminator* terminator(void) const { return NULL; }
     /// The function that is executed when the thread starts
     virtual void run(void) = 0;
     /// Destructor
diff --git a/gecode/support/thread/pthreads.hpp b/gecode/support/thread/pthreads.hpp
index 81264e7270..da085f8fac 100755
--- a/gecode/support/thread/pthreads.hpp
+++ b/gecode/support/thread/pthreads.hpp
@@ -43,6 +43,30 @@
 
 namespace Gecode { namespace Support {
 
+#ifdef GECODE_THREADS_OSX_UNFAIR
+
+  /*
+  * Mutex
+  */
+  forceinline
+  Mutex::Mutex(void) : lck(OS_UNFAIR_LOCK_INIT)  {}
+  forceinline void
+  Mutex::acquire(void) {
+    os_unfair_lock_lock(&lck);
+  }
+  forceinline bool
+  Mutex::tryacquire(void) {
+    return os_unfair_lock_trylock(&lck);
+  }
+  forceinline void
+  Mutex::release(void) {
+    os_unfair_lock_unlock(&lck);
+  }
+  forceinline
+  Mutex::~Mutex(void) {}
+
+#else
+
   /*
    * Mutex
    */
@@ -73,55 +97,8 @@ namespace Gecode { namespace Support {
       std::terminate();
     }
   }
-
-#ifdef GECODE_THREADS_OSX
-
-  /*
-   * FastMutex
-   */
-  forceinline
-  FastMutex::FastMutex(void) : lck(OS_SPINLOCK_INIT) {}
-  forceinline void
-  FastMutex::acquire(void) {
-    OSSpinLockLock(&lck);
-  }
-  forceinline bool
-  FastMutex::tryacquire(void) {
-    return OSSpinLockTry(&lck);
-  }
-  forceinline void
-  FastMutex::release(void) {
-    OSSpinLockUnlock(&lck);
-  }
-  forceinline
-  FastMutex::~FastMutex(void) {}
-
-#endif
-
-#ifdef GECODE_THREADS_OSX_UNFAIR
-
-  /*
-   * FastMutex
-   */
-  forceinline
-  FastMutex::FastMutex(void) {}
-  forceinline void
-  FastMutex::acquire(void) {
-    os_unfair_lock_lock(&lck);
-  }
-  forceinline bool
-  FastMutex::tryacquire(void) {
-    return os_unfair_lock_trylock(&lck);
-  }
-  forceinline void
-  FastMutex::release(void) {
-    os_unfair_lock_unlock(&lck);
-  }
-  forceinline
-  FastMutex::~FastMutex(void) {}
-
 #endif
-
+  
 #ifdef GECODE_THREADS_PTHREADS_SPINLOCK
 
   /*
diff --git a/gecode/support/thread/thread.cpp b/gecode/support/thread/thread.cpp
index a0cfde1dab..7f0a92f716 100755
--- a/gecode/support/thread/thread.cpp
+++ b/gecode/support/thread/thread.cpp
@@ -61,8 +61,12 @@ namespace Gecode { namespace Support {
         m.release();
         assert(e != NULL);
         e->run();
-        if (e->todelete())
+        if (e->todelete()) {
+          Terminator* t = e->terminator();
           delete e;
+          if (t)
+            t->terminated();
+        }
       }
       // Put into idle stack
       Thread::m()->acquire();
diff --git a/gecode/support/thread/thread.hpp b/gecode/support/thread/thread.hpp
index a66ba2b9d4..caf3d636ea 100755
--- a/gecode/support/thread/thread.hpp
+++ b/gecode/support/thread/thread.hpp
@@ -60,7 +60,6 @@ namespace Gecode { namespace Support {
     return heap.ralloc(s);
   }
 
-
   /*
    * Mutexes
    *
@@ -75,7 +74,7 @@ namespace Gecode { namespace Support {
     Gecode::heap.rfree(p);
   }
 
-#if defined(GECODE_THREADS_OSX) || defined(GECODE_THREADS_OSX_UNFAIR) || defined(GECODE_THREADS_PTHREADS_SPINLOCK)
+#if ! ( defined(GECODE_THREADS_WINDOWS) || defined(GECODE_THREADS_OSX_UNFAIR) || !defined(GECODE_THREADS_PTHREADS_SPINLOCK) )
 
   /*
    * Fast mutexes