why using mutex->thread_holding rather than this_ethread()?

[????????]

Hi,

Thanks in advanced.

May I ask a question here?

 

In a continuation's hanlder, take the code piece below for example,

HostDBContinuation::dnsEvent {

...

EThread *thread = mutex->thread_holding;    // here

MUTEX_TRY_LOCK_FOR(lock, action.mutex, thread, action.continuation);

...

}

Why do we use mutex->thread_holding rather than this_ethread()?

Is it due to the performance reason? pthread_getspecific is slow?

I googled a lot, seems in x86/x64 Linux, there isn't too much cost. it just 
implemented with some special register, i.e. GS/FS.

So, what's the reason?

 

Thanks again,

Xin