Method internal_acquire_reader

benchmarks/tbb/spin_rw_mutex.cpp:66–82

Acquire read lock on given mutex.

//! Acquire read lock on given mutex.
void spin_rw_mutex_v3::internal_acquire_reader()
{
    ITT_NOTIFY(sync_prepare, this);
    for( internal::atomic_backoff b;;b.pause() ){
        state_t s = const_cast<volatile state_t&>(state); // ensure reloading
        if( !(s & (WRITER|WRITER_PENDING)) ) { // no writer or write requests
            state_t t = (state_t)__TBB_FetchAndAddW( &state, (intptr_t) ONE_READER );
            if( !( t&WRITER )) 
                break; // successfully stored increased number of readers
            // writer got there first, undo the increment
            __TBB_FetchAndAddW( &state, -(intptr_t)ONE_READER );
        }
    }

    ITT_NOTIFY(sync_acquired, this);
    __TBB_ASSERT( state & READERS, "invalid state of a read lock: no readers" );
}

//! Upgrade reader to become a writer.
/** Returns whether the upgrade happened without releasing and re-acquiring the lock */