// returns the most recent val
Object lock(Ref ref) {
// can't upgrade readLock, so release it
releaseIfEnsured(ref);
boolean unlocked = true;
try {
tryWriteLock(ref);
unlocked = false;
if (ref.tvals != null && ref.tvals.point > readPoint) throw retryex;
Info refinfo = ref.tinfo;
// write lock conflict
if (refinfo != null && refinfo != info && refinfo.running()) {
if (!barge(refinfo)) {
ref.lock.writeLock().unlock();
unlocked = true;
return blockAndBail(refinfo);
}
}
ref.tinfo = info;
return ref.tvals == null ? null : ref.tvals.val;
} finally {
if (!unlocked) ref.lock.writeLock().unlock();
}
}
