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CICS GDS ALLOCATE - General Data Stream Allocation

CICS GDS ALLOCATE is a command used to establish a general data stream (GDS) session for Advanced Program-to-Program Communication (APPC) in CICS environments. It enables structured data exchange between CICS systems.

What is CICS GDS ALLOCATE?

CICS GDS ALLOCATE establishes a communication session using the General Data Stream protocol for APPC conversations. It allocates resources needed for structured data exchange between CICS systems or between CICS and other APPC-compatible systems.

Command Syntax

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EXEC CICS GDS ALLOCATE
    SYSID(system-id)
    CONVID(conversation-id)
    SESSION(session-name)
    MODE(mode-name)
    PARTNER(partner-name)
    RESP(response-code)
    RESP2(response-code-2)
END-EXEC.

Parameters Explained

SYSID Parameter

Specifies the target system identifier:

  • Identifies the remote CICS system
  • Must be defined in CICS system definitions
  • Used for cross-system communication
  • Must match partner system configuration

CONVID Parameter

Returns the conversation identifier:

  • Unique identifier for the conversation
  • Used in subsequent GDS commands
  • Must be stored for conversation management
  • Required for data transfer operations

SESSION Parameter

Specifies the session name:

  • Defines the communication session
  • Must be predefined in CICS
  • Determines communication characteristics
  • Links to partner system configuration

MODE Parameter

Specifies the conversation mode:

  • Defines conversation characteristics
  • Determines data transfer capabilities
  • Must match partner system mode
  • Affects performance and security

PARTNER Parameter

Specifies the partner program name:

  • Identifies the target program
  • Must exist on partner system
  • Used for program-to-program communication
  • Must be authorized for execution

Implementation Example

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WORKING-STORAGE SECTION.
01 WS-CONVERSATION-ID     PIC S9(8) COMP.
01 WS-RESPONSE            PIC S9(8) COMP.
01 WS-RESPONSE2           PIC S9(8) COMP.
01 WS-SYSTEM-ID           PIC X(8) VALUE 'REMOTE01'.
01 WS-SESSION-NAME        PIC X(8) VALUE 'SESS001'.
01 WS-MODE-NAME           PIC X(8) VALUE 'MODE001'.
01 WS-PARTNER-NAME        PIC X(8) VALUE 'PARTNER1'.
 
PROCEDURE DIVISION.
    EXEC CICS GDS ALLOCATE
        SYSID(WS-SYSTEM-ID)
        CONVID(WS-CONVERSATION-ID)
        SESSION(WS-SESSION-NAME)
        MODE(WS-MODE-NAME)
        PARTNER(WS-PARTNER-NAME)
        RESP(WS-RESPONSE)
        RESP2(WS-RESPONSE2)
    END-EXEC.
    
    IF WS-RESPONSE NOT EQUAL DFHRESP(NORMAL)
        EXEC CICS WRITE OPERATOR
            TEXT('GDS ALLOCATE failed')
        END-EXEC
        EXEC CICS RETURN END-EXEC
    END-IF.
    
    * Conversation established successfully
    * Continue with data transfer operations
WORKING-STORAGE SECTION. 01 WS-CONVERSATION-ID PIC S9(8) COMP. 01 WS-RESPONSE PIC S9(8) COMP. 01 WS-RESPONSE2 PIC S9(8) COMP. 01 WS-SYSTEM-ID PIC X(8) VALUE 'REMOTE01'. 01 WS-SESSION-NAME PIC X(8) VALUE 'SESS001'. 01 WS-MODE-NAME PIC X(8) VALUE 'MODE001'. 01 WS-PARTNER-NAME PIC X(8) VALUE 'PARTNER1'. PROCEDURE DIVISION. EXEC CICS GDS ALLOCATE SYSID(WS-SYSTEM-ID) CONVID(WS-CONVERSATION-ID) SESSION(WS-SESSION-NAME) MODE(WS-MODE-NAME) PARTNER(WS-PARTNER-NAME) RESP(WS-RESPONSE) RESP2(WS-RESPONSE2) END-EXEC. IF WS-RESPONSE NOT EQUAL DFHRESP(NORMAL) EXEC CICS WRITE OPERATOR TEXT('GDS ALLOCATE failed') END-EXEC EXEC CICS RETURN END-EXEC END-IF. * Conversation established successfully * Continue with data transfer operations

GDS Communication Flow

1. Allocation Phase

The allocation process involves:

  • Session establishment
  • Resource allocation
  • Security validation
  • Conversation initialization

2. Data Transfer Phase

After successful allocation:

  • Use GDS SEND for data transmission
  • Use GDS RECEIVE for data reception
  • Use GDS WAIT for synchronization
  • Manage conversation state

3. Termination Phase

Conversation cleanup involves:

  • Use GDS FREE to release resources
  • Clean up conversation state
  • Release allocated storage
  • Log conversation completion

Common Response Codes

Success Response Codes

  • NORMAL (0): Allocation successful
  • CONVERSATION (4): Conversation established

Error Response Codes

  • INVREQ (16): Invalid request
  • NOTFND (20): Session not found
  • NOTAUTH (22): Not authorized
  • SESSION (24): Session error
  • SYSTEM (28): System error

Best Practices

1. Resource Management

  • Always check response codes
  • Handle allocation failures gracefully
  • Free resources when done
  • Monitor conversation state

2. Error Handling

  • Implement comprehensive error handling
  • Log allocation failures
  • Provide meaningful error messages
  • Implement retry mechanisms

3. Security Considerations

  • Validate partner authorization
  • Use secure session definitions
  • Implement access controls
  • Monitor conversation activity

Explain It Like I'm 5 Years Old

Imagine you want to talk to your friend on the phone:

Before you can talk to your friend, you need to call them and make sure they answer. CICS GDS ALLOCATE is like making that phone call - it's the first step to start talking to another computer program.

Just like you need to know your friend's phone number, the computer needs to know which other computer to talk to (SYSID), what kind of conversation to have (SESSION), and what rules to follow (MODE).

Once the "phone call" is connected successfully, both computers can start sending messages back and forth, just like you and your friend can start talking. When you're done talking, you hang up the phone - that's like using GDS FREE to end the conversation.

Exercises

Exercise 1: GDS Allocation

Write a CICS GDS ALLOCATE command to establish a conversation with system 'REMOTE01' using session 'SESS001' and mode 'MODE001' to communicate with partner program 'PARTNER1'.

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EXEC CICS GDS ALLOCATE
    SYSID('REMOTE01')
    CONVID(WS-CONVERSATION-ID)
    SESSION('SESS001')
    MODE('MODE001')
    PARTNER('PARTNER1')
    RESP(WS-RESPONSE)
END-EXEC.
EXEC CICS GDS ALLOCATE SYSID('REMOTE01') CONVID(WS-CONVERSATION-ID) SESSION('SESS001') MODE('MODE001') PARTNER('PARTNER1') RESP(WS-RESPONSE) END-EXEC.

Exercise 2: Error Handling

Design error handling for GDS ALLOCATE failures. What response codes should be checked, and what actions should be taken for each?

Answer: Check for INVREQ, NOTFND, NOTAUTH, SESSION, and SYSTEM errors. Implement logging, user notification, and graceful termination with appropriate error messages for each condition.

Quiz

Question 1

What does GDS stand for in CICS GDS ALLOCATE?

Answer: A) General Data Stream

Question 2

Which parameter returns the conversation identifier?

Answer: B) CONVID

Related Concepts

CICS APPC Communication

Advanced Program-to-Program Communication in CICS environments

CICS GDS Commands

General Data Stream commands for structured data exchange

CICS Session Management

Managing communication sessions in CICS systems