Allow the user to supply a reason string when canceling a task (useful for debugging)

include/fc/thread/future.hpp

@@ -13,6 +13,13 @@
 # define FC_TASK_NAME_DEFAULT_ARG = "?"
 #endif
 
+#define FC_CANCELATION_REASONS_ARE_MANDATORY 1
+#ifdef FC_CANCELATION_REASONS_ARE_MANDATORY
+# define FC_CANCELATION_REASON_DEFAULT_ARG
+#else
+# define FC_CANCELATION_REASON_DEFAULT_ARG = nullptr
+#endif
+
 namespace fc {
   class abstract_thread;
   struct void_t{};
@@ -58,7 +65,7 @@ namespace fc {
 
       const char* get_desc()const;
                    
-      virtual void cancel();
+      virtual void cancel(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG);
       bool canceled()const { return _canceled; }
       bool ready()const;
       bool error()const;
@@ -91,6 +98,7 @@ namespace fc {
       time_point                  _timeout;
       fc::exception_ptr           _exceptp;
       bool                        _canceled;
+      const char*                 _cancellation_reason;
       const char*                 _desc;
       detail::completion_handler* _compl;
   };
@@ -210,14 +218,14 @@ namespace fc {
       /// @pre valid()
       bool error()const { return m_prom->error(); }
 
-      void cancel()const { if( m_prom ) m_prom->cancel(); }
+      void cancel(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG) const { if( m_prom ) m_prom->cancel(reason); }
       bool canceled()const { if( m_prom ) return m_prom->canceled(); else return true;}
 
-      void cancel_and_wait()
+      void cancel_and_wait(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG)
       {
          if( valid() )
          {
-            cancel();
+            cancel(reason);
             try
             {
               wait();
@@ -276,9 +284,9 @@ namespace fc {
       bool valid()const    { return !!m_prom;           }
       bool canceled()const { return m_prom ? m_prom->canceled() : true; }
 
-      void cancel_and_wait() 
+      void cancel_and_wait(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG) 
       {
-        cancel();
+        cancel(reason);
         try
         {
           wait();
@@ -294,7 +302,7 @@ namespace fc {
       /// @pre valid()
       bool error()const { return m_prom->error(); }
 
-      void cancel()const { if( m_prom ) m_prom->cancel(); }
+      void cancel(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG) const { if( m_prom ) m_prom->cancel(reason); }
 
       template<typename CompletionHandler>
       void on_complete( CompletionHandler&& c ) {

include/fc/thread/task.hpp

@@ -30,7 +30,7 @@ namespace fc {
   class task_base : virtual public promise_base {
     public:
               void run(); 
-      virtual void cancel() override;
+      virtual void cancel(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG) override;
 
     protected:
       ~task_base();
@@ -99,7 +99,7 @@ namespace fc {
         _promise_impl = static_cast<promise<R>*>(this);
         _run_functor  = &detail::functor_run<FunctorType>::run;
       }
-      virtual void cancel() override { task_base::cancel(); }
+      virtual void cancel(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG) override { task_base::cancel(reason); }
 
       aligned<FunctorSize> _functor;
     private:
@@ -119,7 +119,7 @@ namespace fc {
         _promise_impl = static_cast<promise<void>*>(this);
         _run_functor  = &detail::void_functor_run<FunctorType>::run;
       }
-      virtual void cancel() override { task_base::cancel(); }
+      virtual void cancel(const char* reason FC_CANCELATION_REASON_DEFAULT_ARG) override { task_base::cancel(reason); }
 
       aligned<FunctorSize> _functor;      
     private:

src/log/file_appender.cpp

@@ -82,7 +82,7 @@ namespace fc {
          {
             try
             {
-              _rotation_task.cancel_and_wait();
+              _rotation_task.cancel_and_wait("file_appender is destructing");
             }
             catch( ... )
             {

src/network/ntp.cpp

@@ -139,7 +139,7 @@ namespace fc
     my->_ntp_thread.async([=](){
       try
       {
-        my->_request_time_task_done.cancel_and_wait();
+        my->_request_time_task_done.cancel_and_wait("ntp object is destructing");
       }
       catch ( const fc::exception& e )
       {
@@ -152,7 +152,7 @@ namespace fc
       
       try 
       {
-        my->_read_loop_done.cancel();
+        my->_read_loop_done.cancel("ntp object is destructing");
         my->_sock.close();
         my->_read_loop_done.wait();
       } 

src/network/udt_socket.cpp

@@ -36,7 +36,7 @@ namespace fc {
 
          ~udt_epoll_service()
          {
-            _epoll_loop.cancel();
+            _epoll_loop.cancel("udt_epoll_service is destructing");
             _epoll_loop.wait();
             UDT::cleanup();
          }

src/rpc/json_connection.cpp

@@ -243,7 +243,7 @@ namespace fc { namespace rpc {
       {
          if( my->_done.valid() && !my->_done.ready() )
          {
-            my->_done.cancel();
+            my->_done.cancel("json_connection is destructing");
             my->_out->close();
             my->_done.wait();
          }

src/thread/context.hpp

@@ -48,6 +48,9 @@ namespace fc {
       next(0), 
       ctx_thread(t),
       canceled(false),
+#ifndef NDEBUG
+      cancellation_reason(nullptr),
+#endif
       complete(false),
       cur_task(0)
     {
@@ -78,6 +81,9 @@ namespace fc {
      next(0), 
      ctx_thread(t),
      canceled(false),
+#ifndef NDEBUG
+     cancellation_reason(nullptr),
+#endif
      complete(false),
      cur_task(0)
     {}
@@ -192,6 +198,9 @@ namespace fc {
     fc::context*                next;
     fc::thread*                 ctx_thread;
     bool                         canceled;
+#ifndef NDEBUG
+    const char*                  cancellation_reason;
+#endif
     bool                         complete;
     task_base*                   cur_task;
   };

src/thread/future.cpp

@@ -17,6 +17,9 @@ namespace fc {
 #endif
    _timeout(time_point::maximum()),
    _canceled(false),
+#ifndef NDEBUG
+   _cancellation_reason(nullptr),
+#endif
    _desc(desc),
    _compl(nullptr)
   { }
@@ -25,9 +28,12 @@ namespace fc {
     return _desc; 
   }
                
-  void promise_base::cancel(){
+  void promise_base::cancel(const char* reason /* = nullptr */){
 //      wlog("${desc} canceled!", ("desc", _desc? _desc : ""));
     _canceled = true;
+#ifndef NDEBUG
+    _cancellation_reason = reason;
+#endif
   }
   bool promise_base::ready()const {
     return _ready;

src/thread/task.cpp

@@ -54,12 +54,15 @@ namespace fc {
     }
   }
 
-  void task_base::cancel()
+  void task_base::cancel(const char* reason /* = nullptr */)
   {
-    promise_base::cancel();
+    promise_base::cancel(reason);
     if (_active_context)
     {
       _active_context->canceled = true;
+#ifndef NDEBUG
+      _active_context->cancellation_reason = reason;
+#endif
     }
   }
 

tests/task_cancel.cpp

@@ -18,7 +18,7 @@ BOOST_AUTO_TEST_CASE( leave_mutex_locked )
         fc::usleep(fc::seconds(1));
     }, "test_task");
     fc::usleep(fc::seconds(3));
-    test_task.cancel_and_wait();
+    test_task.cancel_and_wait("cancel called directly by test");
   }
   BOOST_TEST_PASSPOINT();
 }
@@ -57,7 +57,7 @@ BOOST_AUTO_TEST_CASE( cancel_task_blocked_on_mutex)
     }
     fc::usleep(fc::seconds(3));
 
-    test_task.cancel_and_wait();
+    test_task.cancel_and_wait("cleaning up test");
   }
 }
 
@@ -115,7 +115,7 @@ BOOST_AUTO_TEST_CASE( cancel_an_active_task )
   fc::usleep(fc::milliseconds(100));
 
   BOOST_TEST_MESSAGE("Canceling task");
-  task.cancel();
+  task.cancel("canceling to test if cancel works");
   try
   {
     task_result result = task.wait();
@@ -149,7 +149,7 @@ BOOST_AUTO_TEST_CASE( cleanup_cancelled_task )
   BOOST_CHECK_MESSAGE(!weak_string_ptr.expired(), "Weak pointer should still be valid because async task should be holding the strong pointer");
   fc::usleep(fc::milliseconds(100));
   BOOST_TEST_MESSAGE("Canceling task");
-  task.cancel();
+  task.cancel("canceling to test if cancel works");
   try
   {
     task.wait();
@@ -181,7 +181,7 @@ BOOST_AUTO_TEST_CASE( cancel_scheduled_task )
     simple_task();
     simple_task();
     fc::usleep(fc::seconds(4));
-    simple_task_done.cancel();
+    simple_task_done.cancel("canceling scheduled task to test if cancel works");
     simple_task_done.wait();
   } 
   catch ( const fc::exception& e )