[SYCL] Fix unloading of shared images on Windows

After #17869, Windows will not unload
images during the runtime of the program. However, this means that
shared libraries that are dynamically loaded and unloaded will leave
dangling pointers to their images. If somehow these images get picked
up, e.g. if another library is loaded with overlapping symbols, the
runtime may try to dereference the dangling device image pointers. This
commit reenables Windows unloading with the caveat that once the global
handler is dead the runtime assumes that shutdown has begun.

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/source/detail/global_handler.cpp

@@ -134,6 +134,10 @@ GlobalHandler &GlobalHandler::instance() {
   return *RTGlobalObjHandler;
 }
 
+bool GlobalHandler::isInstanceAlive() {
+  return GlobalHandler::getInstancePtr();
+}
+
 template <typename T, typename... Types>
 T &GlobalHandler::getOrCreate(InstWithLock<T> &IWL, Types &&...Args) {
   const LockGuard Lock{IWL.Lock};

sycl/source/detail/global_handler.hpp

@@ -52,6 +52,9 @@ class GlobalHandler {
   /// `__attribute__((destructor))` is called).
   static GlobalHandler &instance();
 
+  /// \return true if the instance has not been deallocated yet.
+  static bool isInstanceAlive();
+
   GlobalHandler(const GlobalHandler &) = delete;
   GlobalHandler(GlobalHandler &&) = delete;
   GlobalHandler &operator=(const GlobalHandler &) = delete;

sycl/source/detail/program_manager/program_manager.cpp

@@ -3927,9 +3927,8 @@ extern "C" void __sycl_register_lib(sycl_device_binaries desc) {
 // Executed as a part of current module's (.exe, .dll) static initialization
 extern "C" void __sycl_unregister_lib(sycl_device_binaries desc) {
   // Partial cleanup is not necessary at shutdown
-#ifndef _WIN32
-  if (!sycl::detail::GlobalHandler::instance().isOkToDefer())
+  if (!sycl::detail::GlobalHandler::isInstanceAlive() ||
+      !sycl::detail::GlobalHandler::instance().isOkToDefer())
     return;
   sycl::detail::ProgramManager::getInstance().removeImages(desc);
-#endif
 }