updated ssc doc

docs/user_guide/source/engines/ssc.rst

@@ -8,7 +8,7 @@ The SSC engine takes the following parameters:
 
 1. ``OpenTimeoutSecs``: Default **10**. Timeout in seconds for opening a stream. The SSC engine's open function will block until the RendezvousAppCount is reached, or timeout, whichever comes first. If it reaches the timeout, SSC will throw an exception.
 
-2. ``Threading``: Default **False**. SSC will use threads to hide the time cost for metadata manipulation and data transfer when this parameter is set to **true**. SSC will check if MPI is initialized with multi-thread enabled, and if not, then SSC will force this parameter to be **false**. Please do NOT enable threading when multiple I/O streams are opened in an application, as it will cause unpredictable errors.
+2. ``Threading``: Default **False**. SSC will use threads to hide the time cost for metadata manipulation and data transfer when this parameter is set to **true**. SSC will check if MPI is initialized with multi-thread enabled, and if not, then SSC will force this parameter to be **false**. Please do NOT enable threading when multiple I/O streams are opened in an application, as it will cause unpredictable errors. This parameter is only effective when writer definitions and reader selections are NOT locked. For cases definitions and reader selections are locked, SSC has a more optimized way to do data transfers, and thus it will not use this parameter.
 
 =============================== ================== ================================================
  **Key**                         **Value Format**   **Default** and Examples

source/adios2/engine/ssc/SscReader.cpp

@@ -272,19 +272,12 @@ void SscReader::EndStepFirstFlexible()
 {
     MPI_Win_free(&m_MpiWin);
     SyncReadPattern();
-}
-
-void SscReader::EndStepConsequentFlexible() { MPI_Win_free(&m_MpiWin); }
-
-void SscReader::EndBeginStepFirstFlexible()
-{
-    EndStepFirstFlexible();
     BeginStepFlexible(m_StepStatus);
 }
 
-void SscReader::EndBeginStepConsequentFlexible()
+void SscReader::EndStepConsequentFlexible()
 {
-    EndStepConsequentFlexible();
+    MPI_Win_free(&m_MpiWin);
     BeginStepFlexible(m_StepStatus);
 }
 
@@ -312,23 +305,24 @@ void SscReader::EndStep()
             if (m_Threading)
             {
                 m_EndStepThread =
-                    std::thread(&SscReader::EndBeginStepFirstFlexible, this);
+                    std::thread(&SscReader::EndStepFirstFlexible, this);
             }
             else
             {
-                EndStepFirstFlexible();
+                MPI_Win_free(&m_MpiWin);
+                SyncReadPattern();
             }
         }
         else
         {
             if (m_Threading)
             {
-                m_EndStepThread = std::thread(
-                    &SscReader::EndBeginStepConsequentFlexible, this);
+                m_EndStepThread =
+                    std::thread(&SscReader::EndStepConsequentFlexible, this);
             }
             else
             {
-                EndStepConsequentFlexible();
+                MPI_Win_free(&m_MpiWin);
             }
         }
     }

source/adios2/engine/ssc/SscReader.h

@@ -72,8 +72,6 @@ class SscReader : public Engine
     void EndStepFixed();
     void EndStepFirstFlexible();
     void EndStepConsequentFlexible();
-    void EndBeginStepFirstFlexible();
-    void EndBeginStepConsequentFlexible();
 
 #define declare_type(T)                                                        \
     void DoGetSync(Variable<T> &, T *) final;                                  \
@@ -100,7 +98,7 @@ class SscReader : public Engine
 
     int m_Verbosity = 0;
     int m_OpenTimeoutSecs = 10;
-    bool m_Threading = true;
+    bool m_Threading = false;
 };
 
 } // end namespace engine