Added the unregister_thread_end_handler() function and also used it to

fix a bug that can trigger when the thread_specific_data object is destructed.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402483

dlib/threads/thread_specific_data_extension.h

@@ -31,6 +31,9 @@ namespace dlib
         ~thread_specific_data (
         )
         {
+            unregister_thread_end_handler(const_cast<thread_specific_data&>(*this),&thread_specific_data::thread_end_handler);
+
+            auto_mutex M(m);
             items.reset();
             while (items.move_next())
             {
@@ -94,8 +97,11 @@ namespace dlib
             thread_id_type junk;
             T* item;
             auto_mutex M(m);
-            items.remove(id,junk,item);
-            delete item;
+            if (items[id])
+            {
+                items.remove(id,junk,item);
+                delete item;
+            }
         }
 
         mutable typename binary_search_tree<thread_id_type,T*>::kernel_2a items;

dlib/threads/threads_kernel_abstract.h

@@ -113,6 +113,26 @@ namespace dlib
               If this exception is thrown then the call to this function had no effect.
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T
+        >
+    void unregister_thread_end_handler (
+        T& obj,
+        void (T::*handler)()
+    );
+    /*!
+        requires
+            - handler == a valid member function pointer for class T
+        ensures
+            - Undoes all previous calls to register_thread_end_handler(obj,handler).  
+              So the given handler won't be called when any threads end.
+        throws
+            - std::bad_alloc
+              If this exception is thrown then the call to this function had no effect.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     template <

dlib/threads/threads_kernel_shared.h

@@ -81,6 +81,32 @@ namespace dlib
                 void* param
             );
 
+            template <
+                typename T
+                >
+            void unregister_thread_end_handler (
+                T& obj,
+                void (T::*handler)()
+            )
+            {
+                member_function_pointer<>::kernel_1a mfp, junk_mfp;
+                mfp.set(obj,handler);
+
+                thread_id_type junk_id;
+
+                // find any member function pointers in the registry that point to the same
+                // thing as mfp and remove them
+                auto_mutex M(reg.m);
+                reg.reg.reset();
+                while (reg.reg.move_next())
+                {
+                    while (reg.reg.current_element_valid() && reg.reg.element().value() == mfp)
+                    {
+                        reg.reg.remove_current_element(junk_id, junk_mfp);
+                    }
+                }
+            }
+
             template <
                 typename T
                 >
@@ -202,6 +228,19 @@ namespace dlib
         threads_kernel_shared::thread_pool().register_thread_end_handler(obj,handler);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T
+        >
+    inline void unregister_thread_end_handler (
+        T& obj,
+        void (T::*handler)()
+    )
+    {
+        threads_kernel_shared::thread_pool().unregister_thread_end_handler(obj,handler);
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <