4.1 Multi-User Shared Persistent Store Fragments

These fragments can be split up into several groups:

1. The persistentstore library. See the section 'The persistent store library' below for more details.
2. Libraries important to the application programmer when implementing the client programs. These libraries are listed in the section called 'Configuration of the Client'.
3. Libraries important to the application programmer when implementing/configuring the server program. These libraries are listed in the section called 'Configuration of the Server'.
4. Libraries used by the latter two groups of libraries. These libraries are not important to application programmers. They are listed in the section called 'Utilities'.
5. Example implementations for both client and server programs can be found in the directory called 'examples'. One example is described in detail in appendix~\ref{bygexample}. Before running the examples, make sure that an ensemble deamon is running on the host(s) involved.

4.1.1 The Persistent Store Library

4.1.2 Configuration of the Client

• clientinterface.bet: This file describes the interface to a client using the shared persistent store (named PSclient). This interface file has to be included by all client programs. The PSClient pattern is subclassed in the notification.bet file in order to yield the NPSClient pattern. This pattern has to be used instead of the PSClient pattern, when the client wants to subscribe to notifications.
• serverinterface.bet: This file contains the interface to the server, the PersistentStoreManager. This interface file has to be included in all client and server programs.
• sharedpersistentstore.bet: This file contains the sharedpersistentstore library. It provides concurrency control for a persistent store. This library has to be included by the client program, if a persistent store is being accessed in a multi-user environment.
• transaction.bet: This file contains the transaction library for the shared persistent store. It has to be included by the clients if they want to use transactions.
• notification.bet: This file is a library containing the declarations used when using notifications. This file has to be included by the clients, if they want to subscribe to notifications.

4.2 Configuration of the Server

• serverinterface.bet: This file contains the interface to the server, the PersistentStoreManager. This interface file has to be included in all client and server programs.
• notificationmanager.bet: This file contains the interface to a notification manager serving notification control. A server wishing to provide notification control has to include this file in order to run an instance of the notificationmanager.
• lockmanager.bet: This file contains the interface to a lock manager serving concurrency control. This file is included by the file serverinterface.bet, because every server starts a lockmanager.

4.2.1 Utilities

• samefile.bet: This file contains the method samefile, which returns true, if the two entered files are the same and false otherwise. This library is used instead of file1name[]->file2name.equal because the same file can have different names depending on the machine, where a process starts. F.eks. /a/home/scandium9/jojo/speciale/pstore1 and ~jojo/speciale/pstore1 are the same files, but would result in false, if using the equal-operation.
• perslib.bet: This fragment is a library containing the pattern declarations used to save the lock information on disk. This is done in order to facilitate recovery from a server crash.
• sharedPSnotifications.bet: This file is included by the sharedpersistentstore library in order to send notifications to the server. Notifications are only sent if a notificationmanger is started by the server. If a notificationmanager is started, notifications are sent automatically by the shared persistent store and not explicitly by the user.

4.2.2 Example Programs

• PSManager.bet: This file contains an example implemenation of the server, the PersistentStoreManager. It provides only a lock manager, no extra functionality. This is the smallest possible server implementation.
• NPSManager.bet: This file contains an example implemenation of the server, the PersistentStoreManager. It provides not only a lock manager, but also a notification manager serving notfication control.
• recordlib.bet: This fragment is a library containing the declarations of record, person and register. It is used in order to store registers containing persons in a persistentstore. The client example implementations use this library.
• simpleclient.bet: This file contains an example implementation of the client. The client opens a shared persistent store. The client does not make use of transactions or notifications. The user can determine the used lock mode and lock policy.
• notclient.bet: This file contains an example implementation of the client. It opens a shared persistent store and subscribes to UPDATE and WAITFORLOCK notifications for it. When being notified, the client displays the notification on the screen. The access to the persistent store is done using transactions. The user can determine the used lock mode and lock policy.
• regetclient.bet: This file contains an example implementation of the client. The client opens a shared persistent store. The client subscribes to UPDATE events. When receiving a notification about an UPDATE, the client regets the in-memory objects of the updated persistent store. Note: This is only done, when the client is accessing the persistent store at the same time, where the persistent store is updated (only possible if the lock policy is MRSW).