void reader_writer_lock::unblock_readers() {
// clear rdr interest flag, increment rdr count
__TBB_ASSERT(rdr_count_and_flags&RFLAG, NULL);
rdr_count_and_flags += RC_INCR-RFLAG;
__TBB_ASSERT(rdr_count_and_flags >= RC_INCR, NULL);
// indicate clear of window
if (rdr_count_and_flags & WFLAG1 && !(rdr_count_and_flags & WFLAG2)) {
__TBB_AtomicOR(&rdr_count_and_flags, WFLAG2);
}
// unblock waiting readers
scoped_lock_read *head = reader_head.fetch_and_store(NULL);
__TBB_ASSERT(head, NULL);
__TBB_ASSERT(head->status == waiting, NULL);
head->status = active;
}
//! Acquire write lock on the given mutex.
bool spin_rw_mutex_v3::internal_acquire_writer()
{
ITT_NOTIFY(sync_prepare, this);
for( internal::atomic_backoff backoff;;backoff.pause() ){
state_t s = const_cast<volatile state_t&>(state); // ensure reloading
if( !(s & BUSY) ) { // no readers, no writers
if( CAS(state, WRITER, s)==s )
break; // successfully stored writer flag
backoff.reset(); // we could be very close to complete op.
} else if( !(s & WRITER_PENDING) ) { // no pending writers
__TBB_AtomicOR(&state, WRITER_PENDING);
}
}
ITT_NOTIFY(sync_acquired, this);
return false;
}
void reader_writer_lock::set_next_writer(scoped_lock *W) {
writer_head = W;
if (W->status == waiting_nonblocking) {
if (rdr_count_and_flags.compare_and_swap(WFLAG1+WFLAG2, 0) == 0) {
W->status = active;
}
}
else {
if (fetch_and_or(rdr_count_and_flags, WFLAG1) & RFLAG) { // reader present
spin_wait_until_and(rdr_count_and_flags, WFLAG2); // block until readers set WFLAG2
}
else { // no reader in timing window
__TBB_AtomicOR(&rdr_count_and_flags, WFLAG2);
}
spin_wait_while_geq(rdr_count_and_flags, RC_INCR); // block until readers finish
W->status = active;
}
}
