[SYCL] Fix library destructor priority value (#3054)

Author: Alexander Batashev

sycl/doc/GlobalObjectsInRuntime.md

@@ -57,10 +57,13 @@ destruction of nested `std::unique_ptr`s.
 
 ### Linux
 
-On Linux DPC++ runtime uses `__attribute__((destructor))` property with maximum
-possible priority value 65535. This approach does not guarantee, that
-`GlobalHandler` destructor is the last thing to run, as user code may contain
-a similar function with the same priority value.
+On Linux DPC++ runtime uses `__attribute__((destructor))` property with low
+priority value 110. This approach does not guarantee, that `GlobalHandler`
+destructor is the last thing to run, as user code may contain a similar function
+with the same priority value. At the same time, users may specify priorities
+within [101, 109] range in order to run destructor after SYCL runtime has been
+de-initialized. A destructor without specific priority value is going to be
+executed before runtime shutdown mechanisms.
 
 Another approach would be to leak global objects. This would guarantee user,
 that global objects live long enough. But some global objects allocate heap

sycl/source/detail/global_handler.cpp

@@ -154,9 +154,11 @@ BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpReserved) {
   return TRUE; // Successful DLL_PROCESS_ATTACH.
 }
 #else
-// Setting maximum priority on destructor ensures it runs after all other global
-// destructors.
-__attribute__((destructor(65535))) static void syclUnload() { shutdown(); }
+// Setting low priority on destructor ensures it runs after all other global
+// destructors. Priorities 0-100 are reserved by the compiler. The priority
+// value 110 allows SYCL users to run their destructors after runtime library
+// deinitialization.
+__attribute__((destructor(110))) static void syclUnload() { shutdown(); }
 #endif
 } // namespace detail
 } // namespace sycl