terminate normally. MVS does not permit the subtask to issue its own DETACH. If neither ECB nor ETXR is specified in the ATTACH, the subtask is removed from the system automatically at normal termination. In this case, no DETACH should be issued.

13.2.2.2 WAIT/POST Macros

The two operating systems provide macros that synchronize task execution if one task or subtask depends upon the completion of another subtask.

Under VSE and MVS, the WAITM and WAIT macros, respectively, inform the control program that the execution of an active task cannot continue until one or more specific events, each represented by a different control block, have occurred.

The POST macro signals completion of an event. A POST issued to an (ECB) removes from the wait state a task waiting for the event to complete.

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿

VSE ￿

POST ￿ecbname ,SAVE= savearea

￿

￿

￿

￿(1)

(0)

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿ MVS ￿ POST ￿ecbaddress ,comple￿ion code

￿

￿

￿

￿(1-12)

(2-12)

￿

￿

￿

￿

(0)

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

ECBNAME: Provides the address of the particular event control block (ECB) representing the event posted as complete. The MVS ecbaddress parameter is the equivalent.

SAVE: If this operand is present, only the task identified by the address of its save area is taken out of the wait state. Although time is saved when specifying this operand, other tasks waiting for this ECB are not taken out of the wait state for this event until another POST is issued.

When a POST is issued without the SAVE operand, all tasks waiting for the ECB are taken out of the wait state, and the highest-priority task regains control. You can use the completion code parameter of the MVS POST macro to pass information to the waiting subtask or tasks. These tasks can then interrogate the code set in the ECB to determine a continuation of the wait or a return to execution.

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿

￿

￿

ecb1,ecb2,...

￿

￿ VSE ￿ WAIT ￿

lis￿name

￿

￿

￿

￿

(1)

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿ MVS ￿ WAIT ￿

number of even￿s,ECB = address

￿

￿

￿

￿

(2-12)

(1-12)

￿

￿

￿

￿

(0)

ECBLIST=address

￿

￿

￿

￿

 

(1-12)

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

The systems provide different facilities. Because of the use of ECB bits under MVS, only one WAIT macro can refer to an ECB at one time. An additional MVS facility, specified through the number of events parameter, permits the task to be taken out of the wait state after the specified number of events has been posted

Chapter 13. A s s e m b l e r 285

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IBM OS/390 manual WAIT/POST Macros, Ecb1,ecb2 VSE Wait Lisname, Number of evens,ECB = address ECBLIST=address

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.