Overview
Client system users can issue library requests through client
applications which may be system commands, procedures, utilities, or interactive scripts. The applications generate ACSLM requests which must pass across the network and through several software layers (that is, SSI, NIs, and CSn before being processed by the ACSLM.
For each request, the ACSLM generates one or more responses which must pass through the same software layers before being received by the client application originating the request. These software layers generally are transparent to the ACSLM and the client applications.
Response Types
There are three response types generated by the ACSLM:
• Acknowledge. An acknowledge response is returned for each syntactically correct request. It indicates that the request has been received.
• Intermediate. An intennediate response is returned if interim infonnation must be returned to the requestor, or if all necessary response information cannot fit in a single response message.
• Final. A final response is returned for each request. It indicates the success or failure of the request.
Response Coordination
Any number of client applications can exist in a network, and each application asynchronously sends multiple requests to the ACSLM.
All requests are queued and processed by the ACSLM in First In First Out (FIFO) order. The ACSLM attempts to maximize library resource usage by processing as many requests as possible. As a result, the ACSLM may intermix responses to different requests from a single client application.
Library Request Processing ACSLM Processes
Enters Generates Adds applic. Transfers Receives Removes Checks application library prefIX. msg across msg& SSI prefix syntax. If request request Translates network. passes it to & adds CSI OK: Copies
with msgto CSI. prefIX. CSIpreflX,
unique network Translates applic. ID,
application format. msgto & unique
ID. server requestID
formal toacknow-Passes msg ledging to ACSLM. response.
Queues request
•
Acknowledging ResponseExtracts Removes Receives Transfers Removes Passes applic.ID SSI prefIX. msg& msg across CSI prefIX acknow~edge
& request Translates passes it to network. & adds SSI response to
ID. msgto SSIZ' prefIX. CSI.
Matches client Translates
response to system msgto Processes
request. format. network request.
May notify Passes msg format.
user of to Client request Applic. A' status.
Final Response
•
Extracts Removes . Receives Transfers Removes Passes final applic.ID SSI prefIX. msg& msg across CSI prefIX response to
& request Translates passes it to network. & adds SSI CSI.
ID. msgto SSIZ' prefIX.
Matches client Translates
response to system msgto
request. format. network
May notify Passesmsg format.
user of to Client request Applic. A' status.
Figure 2-1. Client Application - ACSLM Message Flow
ACSLM Processes Library Request Processing For example, if an application issues, in order, an audit, a mount, and a
query request, the acknowledging responses will be received in the same order, but the intennediate and fmal responses will probably be intermixed. The final responses may be returned in a different order due to the processing time required for each request. Only the order of responses within request is guaranteed.
Interaction Process
Client Application
Request
•
Figure 2-1 summarizes how a request is sent from a user to the
ACSLM through a client application. It also shows how acknowledging and final responses are returned to the client application. The arrows in the figure indicate the message flow direction.
Figure 2-2 through Figure 2-4 show the possible message flows between a client application and the ACSLM. Figure 2-2 shows how only a final response is returned from the ACSLM if it finds a syntax error in the request. ® indicates that message processing occurs at the indicated layer.
SSI NI NI CSI ACSLM
® ® ® ® •
® ® ® ®
Final ResponseFigure 2-2. Request With a Syntax Error
Library Request Processing ACSLM Processes An acknowledging response is always returned for syntactically correct requests. Figure 2-3 shows such a request with no intennediate
responses. @ indicates that message processing occurs at the indicated layer.
Client
Application SSI NI NI CSI ACSLM
Request
---~---
---~~---~.~Ac/cnowledging Response
I---~~---Final Response
~.~---~---~---~---~I---Figure 2-3. Request With No Intermediate Response Figure 2-4 shows a syntactically correct request with one or more intennediate responses. @ indicates that message processing occurs at the indicated layer.
Client
Application SSI NI NI CSI ACSLM
Request
~ ~ ~ ~
•
Acknowledging Response
•
~ ~ ~ ~Intp.nnediate Response
• ® ® ®
~. .. repeated for each intermediate response Final Response
•
~ ~ ~ ~ACSLM Processes Library Request Processing
ACSSA - ACSLM Interactions Overview
Server system users can access ACSLM services through the ACSSA Command Processor. The ACSSA translates commands from each user to equivalent ACSLM requests and multiplexes the requests to the ACSLM. The ACSSA ensures that the responses to each request are returned to the correct user.
Users must log into the special user identifier, acssa, to access the Command Processor. Any number of users can be using Command Processors at one time. The Command Processor ensures that each user issues only one command at a time; this prevents responses to several requests from being intermixed on the same terminal display.
The interaction between the ACSSA and ACSLM is the same as that between a client application and the ACSLM, but without the
intervening software layers. The ACSSA appears as a CSI to the ACSLM since the ACSSA uses the same ACSLM programmatic interface that the CSls use.
The ACSSA generally has no more, or less, privilege than a client application. The one exception is that ACSSA users are allowed to perform library operations on components in the diagnostic state. This feature allows maintenance personnel to exercise components without interference from client system users.
Interaction Process
Figure 2-5 summarizes how a request is sent from a user to the ACSLM through the ACSSA. It also shows how acknowledging and final responses are returned to the ACSSA. The arrows in the figure indicate the message flow direction.
Library Request Processing
User
Enters library request through Conunand Processor.
..
..
ACSSA
Request
Checks syntax. If OK: Sends request to ACSLM. Blocks additional requests from this Command Processor.
Acknowledging Response
Extracts and saves application ID & request ID. Matches the response to the Command Processor. Does not display acknow ledgment
Final Response
Extracts and saves application ID & request ID. Matches the response to the Command Processor & displays response.
Prompts user for new request
ACSLM Processes
ACSLM
Checks syntax. If OK: Copies request ID to acknowledging response. Queues request
Passes acknowledging response to ACSSA.
Processes request.
Passes final response to ACSSA.
Figure 2-5. ACSSA - ACSLM Message Flow
ACSLM Processes
ACSSA Request
II
ACSSA Request
II
II
Library Request Processing Figure 2-6 through Figure 2-8 show the possible message flows
between the ACSSA and ACSLM. Figure 2-6 shows how only a final response is returned from the ACSLM if it finds a syntax error in the request.
ACSLM
•
Final Response
Figure 2-6. Request Containing a Syntax Error
An acknowledging response is always returned for syntactically correct requests. Figure 2-7 shows such a request with no intennediate
responses.
ACSLM
Acknowledging Response
Final Response
Figure 2-7. Request With No Intermediate Response
Library Request Processing ACSLM Processes
ACSSA
Request
•
•
•
Figure 2-8 shows a syntactically correct request with one or more intermediate responses.
ACSLM
•
Acknowledging Response
Intermediate Response . .. repeated for each intermediate response
Final Response
Figure 2-8. Request With Intermediate Responses