On 7/28/23 17:36, Pedro Alves wrote:
> On 2023-07-28 11:59, Tom de Vries via Gdb-patches wrote:
>> I wrote a patch using is_main_thread (), and found it returning false in the
>> main thread due to main_thread_id not being initialized yet.
>>
>> Initialization currently takes place in _initialize_run_on_main_thread, but
>> that's too late for earlier uses.
>>
>> Fix this by also initializing on first use.
>>
>> Tested on x86_64-linux.
>> ---
>>   gdb/run-on-main-thread.c | 17 ++++++++++++++++-
>>   1 file changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/gdb/run-on-main-thread.c b/gdb/run-on-main-thread.c
>> index 91d25dae28f..bee5885d9a6 100644
>> --- a/gdb/run-on-main-thread.c
>> +++ b/gdb/run-on-main-thread.c
>> @@ -94,12 +94,27 @@ run_on_main_thread (std::function<void ()> &&func)
>>     serial_event_set (runnable_event);
>>   }
>>   
>> +#if CXX_STD_THREAD
>> +static void
>> +initialize_main_thread_id (void)
>> +{
>> +  static bool initialized = false;
>> +
>> +  if (initialized)
>> +    return;
>> +  initialized = true;
>> +
>> +  main_thread_id = std::this_thread::get_id ();
>> +}
>> +#endif
>> +
>>   /* See run-on-main-thread.h.  */
>>   
>>   bool
>>   is_main_thread ()
>>   {
>>   #if CXX_STD_THREAD
>> +  initialize_main_thread_id ();
> 

Hi Pedro,

thanks for the review.

> This is assuming that is_main_thread() will always be called once by
> the main thread, before any other thread could call it.  Otherwise if
> is_main_thread is called by some other thread first,
> is_main_thread -> initialize_main_thread_id will record the wrong thread
> id in the main_thread_id.  At least a comment somewhere would
> be warranted.  I think putting:
> 
>    gdb_assert (is_main_thread ());
> 
> somewhere in the early main code would be good.  It would prevent such
> situation from ever happening undetected.
> 

Updated accordingly.  Any further comments?

Thanks,
- Tom