RFR: 8295146: Clean up native code with newer C/C++ language features [v3]

[David Holmes]

On Tue, 29 Nov 2022 17:07:02 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> Digging into this some more, the friend declaration exists to provide access to the private `os::win32::enum Ept`.
>> 
>> One obvious and cheap solution to that would be to make that enum public.  I think that would be an improvement vs the current friend declaration.  But there are some other things one could complain about there, such as the type of the function requiring a complicated function pointer cast where it's used.  Here's a patch that I think cleans this up.
>> 
>> 
>> diff --git a/src/hotspot/os/windows/os_windows.cpp b/src/hotspot/os/windows/os_windows.cpp
>> index 0651f0868f3..bf9e759b1d6 100644
>> --- a/src/hotspot/os/windows/os_windows.cpp
>> +++ b/src/hotspot/os/windows/os_windows.cpp
>> @@ -511,7 +511,9 @@ JNIEXPORT
>>  LONG WINAPI topLevelExceptionFilter(struct _EXCEPTION_POINTERS* exceptionInfo);
>>  
>>  // Thread start routine for all newly created threads
>> -static unsigned __stdcall thread_native_entry(Thread* thread) {
>> +// Called with the associated Thread* as the argument.
>> +unsigned __stdcall os::win32::thread_native_entry(void* t) {
>> +  Thread* thread = static_cast<Thread*>(t);
>>  
>>    thread->record_stack_base_and_size();
>>    thread->initialize_thread_current();
>> @@ -744,7 +746,7 @@ bool os::create_thread(Thread* thread, ThreadType thr_type,
>>      thread_handle =
>>        (HANDLE)_beginthreadex(NULL,
>>                               (unsigned)stack_size,
>> -                             (unsigned (__stdcall *)(void*)) thread_native_entry,
>> +                             &os::win32::thread_native_entry,
>>                               thread,
>>                               initflag,
>>                               &thread_id);
>> diff --git a/src/hotspot/os/windows/os_windows.hpp b/src/hotspot/os/windows/os_windows.hpp
>> index 94d7c3c5e2d..197797078d7 100644
>> --- a/src/hotspot/os/windows/os_windows.hpp
>> +++ b/src/hotspot/os/windows/os_windows.hpp
>> @@ -36,7 +36,6 @@ typedef void (*signal_handler_t)(int);
>>  
>>  class os::win32 {
>>    friend class os;
>> -  friend unsigned __stdcall thread_native_entry(Thread*);
>>  
>>   protected:
>>    static int    _processor_type;
>> @@ -70,6 +69,10 @@ class os::win32 {
>>    static HINSTANCE load_Windows_dll(const char* name, char *ebuf, int ebuflen);
>>  
>>   private:
>> +  // The handler passed to _beginthreadex().
>> +  // Called with the associated Thread* as the argument.
>> +  static unsigned __stdcall thread_native_entry(void*);
>> +
>>    enum Ept { EPT_THREAD, EPT_PROCESS, EPT_PROCESS_DIE };
>>    // Wrapper around _endthreadex(), exit() and _exit()
>>    static int exit_process_or_thread(Ept what, int exit_code);
>
> The issue with that would be that thread_native_entry is declared as static to the compilation unit on other other Operating Systems as well, and having it as a static member on the win32 class instead would end up breaking this convention, for which I'm not sure if there's a reason why all of them are declared like this

The thread entry functions are expected to be plain C functions as we use C library calls to create threads (`_beginthreadex`, `pthread_create`) not C++. They don't need to be visible outside the compilation unit hence static.

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PR: https://git.openjdk.org/jdk/pull/11081