// GetOrCreateShard will return the shard object, or create one if it doesn't
// already exist. Note the shard creation is protected by a keyspace Lock.
func GetOrCreateShard(ctx context.Context, ts topo.Server, keyspace, shard string) (*topo.ShardInfo, error) {
si, finalErr := ts.GetShard(ctx, keyspace, shard)
if finalErr == topo.ErrNoNode {
// create the keyspace, maybe it already exists
if err := ts.CreateKeyspace(ctx, keyspace, &pb.Keyspace{}); err != nil && err != topo.ErrNodeExists {
return nil, fmt.Errorf("CreateKeyspace(%v) failed: %v", keyspace, err)
}
// now we can lock the keyspace
node := actionnode.KeyspaceCreateShard()
lockPath, err := node.LockKeyspace(ctx, ts, keyspace)
if err != nil {
return nil, fmt.Errorf("LockKeyspace failed: %v", err)
}
// now try to create within the lock, may already exist
if err := ts.CreateShard(ctx, keyspace, shard); err != nil && err != topo.ErrNodeExists {
return nil, node.UnlockKeyspace(ctx, ts, keyspace, lockPath, fmt.Errorf("CreateShard(%v/%v) failed: %v", keyspace, shard, err))
}
// try to read the shard again, maybe someone created it
// in between the original GetShard and the LockKeyspace
si, finalErr = ts.GetShard(ctx, keyspace, shard)
// and unlock
if err := node.UnlockKeyspace(ctx, ts, keyspace, lockPath, finalErr); err != nil {
return nil, fmt.Errorf("UnlockKeyspace failed: %v", err)
}
}
return si, finalErr
}
// CreateShard will create the shard, while holding the keyspace lock
func CreateShard(ctx context.Context, ts topo.Server, keyspace, shard string) error {
// Lock the keyspace
node := actionnode.KeyspaceCreateShard()
lockPath, err := node.LockKeyspace(ctx, ts, keyspace)
if err != nil {
return fmt.Errorf("LockKeyspace failed: %v", err)
}
// now try to create within the lock, may already exist
err = ts.CreateShard(ctx, keyspace, shard)
// and unlock and return
return node.UnlockKeyspace(ctx, ts, keyspace, lockPath, err)
}