cmake: add DllMain() into each OpenCV DLL

to detect process termination after ExitProcess() call

cmake/OpenCVModule.cmake

@@ -909,6 +909,13 @@ macro(_ocv_create_module)
       source_group("Src" FILES "${_VS_VERSION_FILE}")
     endif()
   endif()
+  if(WIN32 AND NOT ("${the_module}" STREQUAL "opencv_core" OR "${the_module}" STREQUAL "opencv_world")
+      AND (BUILD_SHARED_LIBS AND NOT "x${OPENCV_MODULE_TYPE}" STREQUAL "xSTATIC")
+      AND NOT OPENCV_SKIP_DLLMAIN_GENERATION
+  )
+      set(_DLLMAIN_FILE "${CMAKE_CURRENT_BINARY_DIR}/${the_module}_main.cpp")
+      configure_file("${OpenCV_SOURCE_DIR}/cmake/templates/dllmain.cpp.in" "${_DLLMAIN_FILE}" @ONLY)
+  endif()
 
   source_group("Include" FILES "${OPENCV_CONFIG_FILE_INCLUDE_DIR}/cvconfig.h" "${OPENCV_CONFIG_FILE_INCLUDE_DIR}/opencv2/opencv_modules.hpp")
   source_group("Src" FILES "${${the_module}_pch}")
@@ -918,6 +925,7 @@ macro(_ocv_create_module)
     "${OPENCV_CONFIG_FILE_INCLUDE_DIR}/cvconfig.h" "${OPENCV_CONFIG_FILE_INCLUDE_DIR}/opencv2/opencv_modules.hpp"
     ${${the_module}_pch}
     ${_VS_VERSION_FILE}
+    ${_DLLMAIN_FILE}
   )
   set_target_properties(${the_module} PROPERTIES LABELS "${OPENCV_MODULE_${the_module}_LABEL};Module")
   set_source_files_properties(${OPENCV_MODULE_${the_module}_HEADERS} ${OPENCV_MODULE_${the_module}_SOURCES} ${${the_module}_pch}

cmake/templates/dllmain.cpp.in

@@ -0,0 +1,36 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+
+#ifndef _WIN32
+#error "Build configuration error"
+#endif
+#ifndef CVAPI_EXPORTS
+#error "Build configuration error"
+#endif
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+#define OPENCV_MODULE_S "@the_module@"
+
+namespace cv {
+extern __declspec(dllimport) bool __termination;  // Details: #12750
+}
+
+extern "C"
+BOOL WINAPI DllMain(HINSTANCE, DWORD fdwReason, LPVOID lpReserved);
+
+extern "C"
+BOOL WINAPI DllMain(HINSTANCE, DWORD fdwReason, LPVOID lpReserved)
+{
+    if (fdwReason == DLL_THREAD_DETACH || fdwReason == DLL_PROCESS_DETACH)
+    {
+        if (lpReserved != NULL) // called after ExitProcess() call
+        {
+            //printf("OpenCV: terminating: " OPENCV_MODULE_S "\n");
+            cv::__termination = true;
+        }
+    }
+    return TRUE;
+}

modules/core/src/precomp.hpp

@@ -308,8 +308,9 @@ TLSData<CoreTLSData>& getCoreTlsData();
 #define CL_RUNTIME_EXPORT
 #endif
 
-extern bool __termination; // skip some cleanups, because process is terminating
-                           // (for example, if ExitProcess() was already called)
+extern CV_EXPORTS
+bool __termination;  // skip some cleanups, because process is terminating
+                     // (for example, if ExitProcess() was already called)
 
 cv::Mutex& getInitializationMutex();