bool CacheAllocator::moveForSlabRelease()

in cachelib/allocator/CacheAllocator-inl.h [2395:2467]
56 lines of code
9 McCabe index (conditional complexity)

bool CacheAllocator<CacheTrait>::moveForSlabRelease(
    const SlabReleaseContext& ctx, Item& oldItem, util::Throttler& throttler) {
  if (!config_.moveCb) {
    return false;
  }

  bool isMoved = false;
  auto startTime = util::getCurrentTimeSec();
  WriteHandle newItemHdl = allocateNewItemForOldItem(oldItem);

  for (unsigned int itemMovingAttempts = 0;
       itemMovingAttempts < config_.movingTries;
       ++itemMovingAttempts) {
    stats_.numMoveAttempts.inc();

    // Nothing to move and the key is likely also bogus for chained items.
    if (oldItem.isOnlyMoving()) {
      oldItem.unmarkMoving();
      const auto res =
          releaseBackToAllocator(oldItem, RemoveContext::kNormal, false);
      XDCHECK(res == ReleaseRes::kReleased);
      return true;
    }

    if (!newItemHdl) {
      // try to allocate again if it previously wasn't successful
      newItemHdl = allocateNewItemForOldItem(oldItem);
    }

    // if we have a valid handle, try to move, if not, we retry.
    if (newItemHdl) {
      isMoved = tryMovingForSlabRelease(oldItem, newItemHdl);
      if (isMoved) {
        break;
      }
    }

    throttleWith(throttler, [&] {
      XLOGF(WARN,
            "Spent {} seconds, slab release still trying to move Item: {}. "
            "Pool: {}, Class: {}.",
            util::getCurrentTimeSec() - startTime, oldItem.toString(),
            ctx.getPoolId(), ctx.getClassId());
    });
  }

  // Return false if we've exhausted moving tries.
  if (!isMoved) {
    return false;
  }

  // Since item has been moved, we can directly free it. We don't need to
  // worry about any stats related changes, because there is another item
  // that's identical to this one to replace it. Here we just need to wait
  // until all users have dropped the item handles before we can proceed.
  startTime = util::getCurrentTimeSec();
  while (!oldItem.isOnlyMoving()) {
    throttleWith(throttler, [&] {
      XLOGF(WARN,
            "Spent {} seconds, slab release still waiting for refcount to "
            "drain Item: {}. Pool: {}, Class: {}.",
            util::getCurrentTimeSec() - startTime, oldItem.toString(),
            ctx.getPoolId(), ctx.getClassId());
    });
  }
  const auto allocInfo = allocator_->getAllocInfo(oldItem.getMemory());
  allocator_->free(&oldItem);

  (*stats_.fragmentationSize)[allocInfo.poolId][allocInfo.classId].sub(
      util::getFragmentation(*this, oldItem));
  stats_.numMoveSuccesses.inc();
  return true;
}