TPF 
Coupling Facility 
Support 

CF Overview 

• 	Shared storage accessible to multiple 
connections 
• 	
Supports cache and list data structures -Currently, TPF supports only the list model 

• 	
Data is stored as logical entities 

-	Accessed by key, name, etc., instead of by address 

• 	
Supports allocation of multiple structures 




What's Inside a CF? 

Multiple structures, each containing: 
• 	
An optional lock table 

• 	
A set of lists or queues. Each list contains: -A set of entries containing data 


CF List Structure 

Connection 1 
Connection 2 
Connection 3 

Lock 
List Entry

Tab 

Header 
Data 


List 0 Header  
List 1 Header  


Controls
Entry Controls  
Data 


Facilities Provided by the CF 

• 
List entry operations 
-Add entries to lists 
-Delete entries from lists 
-Read entries on lists 
-Conditionally update entries 

• 
Lock operations to serialize list access 

• 
Empty to non-empty list transition monitor 



TPF Support for the CF 

• 	
Add multiple CFs to a complex 

• 	
Allocate a structure in a specified CF 

• 
Connect to a structure 

• 	
Monitor lists for empty to non-empty transitions 

• 	
Issue commands to the CF, handle responses, and perform error recovery 

• 
Currently there is no API to place or access data in the CF (restricted interfaces). 


Possible Uses for CF List 
Structures 

Message passing and communication 
• 
Sender creates a list entry containing the message 

• 
Recipient monitors list waiting for entries 

• 
When entry is created, recipient reads and deletes entry and processes message 


Possible Uses for CF List 
Structures 

Shared queues for work distribution 
• 	
Lists correspond to particular work states 

• 	
Users queue list entries representing work units 

• 	
Users read entries to process work 

• 	
Users move entries from list to list 

• 	
Users delete entries when work is complete 



Possible Uses for CF List 
Structures 

Locking 
• 	
Users create list entries representing locks held 

• 	
If entry already exists, lock is held 

-	Users can join list of holders (if shared lock) or wait on lock 

• 	
Users delete a list entry to unhold a lock -Lock can be granted to waiters -Waiters can be notified using list monitoring 





Summary 

• 
CF support establishes the framework for TPF to exploit the coupling facility 

• 
CF support provides a foundation for an API to allow applications to access and manipulate data