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Ulm's Oberon Library:
PersistentNodes

NAME

SYNOPSIS

CONST dbfailure = 0;
CONST dbinconsistent = 1;
CONST transfailure = 2;
CONST noroot = 3;
CONST linkwithoutparent = 4;
CONST nonunique = 5;
CONST badlink = 6;
CONST errors = 7;
TYPE ErrorCode = SHORTINT; (* dbfailure ... *)
TYPE ErrorEvent = POINTER TO ErrorEventRec;
TYPE ErrorEventRec =
      RECORD
         (Events.EventRec)
         errorcode: ErrorCode;
      END;
VAR errormsg: ARRAY errors OF Events.Message;
VAR error: Events.EventType;



PROCEDURE Init(container: Containers.Container;
               permissions: Names.Permissions) : BOOLEAN;



PROCEDURE Open(VAR root: Names.Node;
               container: Containers.Container) : BOOLEAN;

DESCRIPTION

• Names.Insert accepts nodes from other implementations or other containers. However, these connections are not persistent and are lost as soon as the container is re-opened. RobustObjects is recommended to let such objects reappear automatically as soon as the persistent nodes reappear.
• Names.Destroy does not permit the root object to be destroyed. This is rejected independent from the configured Shards pot for the Names.destroy access mode. In case of an attempt to destroy a node by terminating it using Resources.Notify, all subsequent operations on any persistent node from the same container will fail until the container is re-opened again.
• Nodes that become unreachable by Names.Delete or Names.Destroy operations will be garbage collected by the next Open operation.

Init prepares a container for subsequent use of this module. This causes all present objects in the container to be deleted and an empty root node to be inserted with the given set of access permissions.

Open opens container and, if successful, makes its root node available. Some notes:

• Containers that are passed to Open are for exclusive use of PersistentNodes only.
• PersistentNodes maintains a transaction (see ObjectTransactions) for each opened container which does not permit any operations on container in parallel.
• All nodes that are retrieved from the container terminate as soon as the container terminates.

DIAGNOSTICS

dbfailure

an operation on the underlying container failed.

dbinconsistent

inconsistencies were found by Open within the container

transfailure

the transaction object of ObjectTransactions which is used for the container generated an error

noroot

no root object was found within the container (special case of a database inconsistency)

linkwithoutparent

a link without a valid parent node was found within the container (special case of a database inconsistency)

nonunique

two links shared the same name and belonged to the same parent node (special case of a database inconsistency)

badlink

a link with an invalid reference was found within the container (special case of a database inconsistency)

SEE ALSO

Containers

abstraction for persistent object databases

Names

Oberon name spaces

Shards

general abstraction for authorizations

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