Examples with ResourceLocker org.neo4j.lock.ResourceLocker used on opensource projects

Example 1 with ResourceLocker

use of org.neo4j.lock.ResourceLocker in project neo4j by neo4j.

the class RelationshipModifier method acquireMostOfTheNodeAndGroupsLocks.

private void acquireMostOfTheNodeAndGroupsLocks(RelationshipModifications modifications, RecordAccessSet recordChanges, ResourceLocker locks, LockTracer lockTracer, MutableLongObjectMap<NodeContext> contexts, MappedNodeDataLookup nodeDataLookup) {
    /* Here we're going to figure out if we need to make changes to any node and/or relationship group records and lock them if we do. */
    // We check modifications for each node, it might need locking. The iteration here is always sorted by node id
    modifications.forEachSplit(byNode -> {
        long nodeId = byNode.nodeId();
        RecordProxy<NodeRecord, Void> nodeProxy = recordChanges.getNodeRecords().getOrLoad(nodeId, null, cursorContext);
        // optimistic (unlocked) read
        NodeRecord node = nodeProxy.forReadingLinkage();
        boolean nodeIsAddedInTx = node.isCreated();
        if (// we can not trust this as the node is not locked
        !node.isDense()) {
            if (// to avoid locking unnecessarily
            !nodeIsAddedInTx) {
                // lock and re-read, now we can trust it
                locks.acquireExclusive(lockTracer, NODE, nodeId);
                nodeProxy = recordChanges.getNodeRecords().getOrLoad(nodeId, null, cursorContext);
                node = nodeProxy.forReadingLinkage();
                if (node.isDense()) {
                    // another transaction just turned this node dense, unlock and let it be handled below
                    locks.releaseExclusive(NODE, nodeId);
                } else if (byNode.hasCreations()) {
                    // Sparse node with added relationships. We might turn this node dense, at which point the group lock will be needed, so lock it
                    locks.acquireExclusive(lockTracer, RELATIONSHIP_GROUP, nodeId);
                }
            }
        }
        if (// the node is not locked but the dense node is a one-way transform so we can trust it
        node.isDense()) {
            // Stabilize first in chains, in case they are deleted or needed for chain degrees.
            // We are preventing any changes to the group which in turn blocks any other relationship becomming the first in chain
            locks.acquireShared(lockTracer, RELATIONSHIP_GROUP, nodeId);
            // Creations
            NodeContext nodeContext = NodeContext.createNodeContext(nodeProxy, memoryTracker);
            contexts.put(nodeId, nodeContext);
            if (byNode.hasCreations()) {
                // We have some creations on a dense node. If the group exists we can use that, otherwise we create it
                byNode.forEachCreationSplit(byType -> {
                    RelationshipGroupGetter.RelationshipGroupPosition groupPosition = findRelationshipGroup(recordChanges, nodeContext, byType);
                    nodeContext.setCurrentGroup(groupPosition.group() != null ? groupPosition.group() : groupPosition.closestPrevious());
                    RecordProxy<RelationshipGroupRecord, Integer> groupProxy = groupPosition.group();
                    if (groupProxy == null) {
                        // The group did not exist
                        if (!nodeContext.hasExclusiveGroupLock()) {
                            // And we did not already have the lock, so we need to upgrade to exclusive create it
                            locks.releaseShared(RELATIONSHIP_GROUP, nodeId);
                            // Note the small window here where we dont hold any group lock, things might change so we can not trust previous group reads
                            locks.acquireExclusive(lockTracer, NODE, nodeId);
                            locks.acquireExclusive(lockTracer, RELATIONSHIP_GROUP, nodeId);
                        }
                        nodeContext.setNode(recordChanges.getNodeRecords().getOrLoad(nodeId, null, cursorContext));
                        long groupStartingId = nodeContext.node().forReadingLinkage().getNextRel();
                        long groupStartingPrevId = NULL_REFERENCE.longValue();
                        if (groupPosition.closestPrevious() != null) {
                            groupStartingId = groupPosition.closestPrevious().getKey();
                            groupStartingPrevId = groupPosition.closestPrevious().forReadingLinkage().getPrev();
                        }
                        // At this point the group is locked so we can create it
                        groupProxy = relGroupGetter.getOrCreateRelationshipGroup(nodeContext.node(), byType.type(), recordChanges.getRelGroupRecords(), groupStartingPrevId, groupStartingId);
                        // another transaction might beat us at this point, so we are not guaranteed to be the creator but we can trust it to exist
                        if (!nodeContext.hasExclusiveGroupLock()) {
                            nodeContext.markExclusiveGroupLock();
                        } else if (groupProxy.isCreated()) {
                            // When a new group is created we can no longer trust the pointers of the cache
                            nodeContext.clearDenseContext();
                        }
                    }
                    nodeContext.denseContext(byType.type()).setGroup(groupProxy);
                });
                if (!nodeContext.hasExclusiveGroupLock()) {
                    // No other path has given us the exclusive lock yet
                    byNode.forEachCreationSplitInterruptible(byType -> {
                        // But if we are creating relationships to a chain that does not exist on the group
                        // or we might need to flip the external degrees flag
                        RelationshipGroupRecord group = nodeContext.denseContext(byType.type()).group().forReadingLinkage();
                        if (byType.hasOut() && (!group.hasExternalDegreesOut() || isNull(group.getFirstOut())) || byType.hasIn() && (!group.hasExternalDegreesIn() || isNull(group.getFirstIn())) || byType.hasLoop() && (!group.hasExternalDegreesLoop() || isNull(group.getFirstLoop()))) {
                            // Then we need the exclusive lock to change it
                            locks.releaseShared(RELATIONSHIP_GROUP, nodeId);
                            // Note the small window here where we dont hold any group lock, things might change so we can not trust previous group reads
                            locks.acquireExclusive(lockTracer, RELATIONSHIP_GROUP, nodeId);
                            nodeContext.markExclusiveGroupLock();
                            // And we can abort the iteration as the group lock is protecting all relationship group records of the node
                            return true;
                        }
                        return false;
                    });
                }
            }
            // Deletions
            if (byNode.hasDeletions()) {
                if (// no need to do anything if it is already locked by additions
                !nodeContext.hasExclusiveGroupLock()) {
                    byNode.forEachDeletionSplitInterruptible(byType -> {
                        NodeContext.DenseContext denseContext = nodeContext.denseContext(byType.type());
                        RelationshipGroupRecord group = denseContext.getOrLoadGroup(relGroupGetter, nodeContext.node().forReadingLinkage(), byType.type(), recordChanges.getRelGroupRecords(), cursorContext);
                        // here we have the shared lock, so we can trust the read
                        if (byType.hasOut() && !group.hasExternalDegreesOut() || byType.hasIn() && !group.hasExternalDegreesIn() || byType.hasLoop() && !group.hasExternalDegreesLoop()) {
                            // We have deletions but without external degrees, we might need to flip that so we lock it
                            locks.releaseShared(RELATIONSHIP_GROUP, nodeId);
                            // Note the small window here where we dont hold any group lock, things might change so we can not trust previous group reads
                            locks.acquireExclusive(lockTracer, RELATIONSHIP_GROUP, nodeId);
                            nodeContext.markExclusiveGroupLock();
                            return true;
                        } else {
                            // We have deletions and only external degrees
                            boolean hasAnyFirst = batchContains(byType.out(), group.getFirstOut()) || batchContains(byType.in(), group.getFirstIn()) || batchContains(byType.loop(), group.getFirstLoop());
                            if (hasAnyFirst) {
                                // But we're deleting the first in the chain so the group needs to be updated
                                locks.releaseShared(RELATIONSHIP_GROUP, nodeId);
                                // Note the small window here where we dont hold any group lock, things might change so we can not trust previous group reads
                                locks.acquireExclusive(lockTracer, RELATIONSHIP_GROUP, nodeId);
                                nodeContext.markExclusiveGroupLock();
                                return true;
                            }
                        }
                        return false;
                    });
                }
            }
            // Look for an opportunity to delete empty groups that we noticed while looking for groups above
            if (nodeContext.hasExclusiveGroupLock() && nodeContext.hasAnyEmptyGroup()) {
                // There may be one or more empty groups that we can delete
                if (locks.tryExclusiveLock(NODE_RELATIONSHIP_GROUP_DELETE, nodeId)) {
                    // We got the EXCLUSIVE group lock so we can go ahead and try to remove any potentially empty groups
                    if (!nodeContext.hasEmptyFirstGroup() || locks.tryExclusiveLock(NODE, nodeId)) {
                        if (nodeContext.hasEmptyFirstGroup()) {
                            // It's possible that we need to delete the first group, i.e. we just now locked the node and therefore need to re-read it
                            nodeContext.setNode(recordChanges.getNodeRecords().getOrLoad(nodeId, null, cursorContext));
                        }
                        Predicate<RelationshipGroupRecord> canDeleteGroup = group -> !byNode.hasCreations(group.getType());
                        if (RelationshipGroupGetter.deleteEmptyGroups(nodeContext.node(), canDeleteGroup, nodeDataLookup)) {
                            nodeContext.clearDenseContext();
                        }
                    }
                }
            }
        }
    });
}