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The implementation of the Open Transaction Environment (OTE), and the accompanying requirement for threadsafe programming, marks a radical change in CICS capabilities. When first announced, threadsafe was implemented primarily for the significant CPU savings achievable with CICS/DB2 transactions (customers report up to 30% reduction in CPU for some CICS/DB2 applications.) Now, a second wave of threadsafe implementers are finding significant advantages in converting non-DB2 applications to threadsafe, including:

  • CPU constraint relief. Use of the OTE allows CICS transactions to run on multiple processors, reducing QR TCB wait time.

  • Use of restricted options. The OTE allows full use of z/OS functionality, including macros that cause z/OS waits, or use z/OS storage.

  • Segregation of resource-intensive transactions. The OTE allows troublesome transactions to be run under their own open TCB, freeing the QR for other work.

  • Availability of OPENAPI TRUEs for non-DB2 products. IBM and most OEM vendors have been upgrading their TRUEs to embrace the OPENAPI standard. Users of IBM tools such as CICS Sockets and MQ Series should consider upgrading to the threadsafe version of the TRUE.

However, some users have suffered transaction abends and even data corruption if non-threadsafe programs are allowed to run in the OTE. Exercise caution and conduct thorough research when considering a threadsafe conversion.

For more information, click here to download the award-winning presentation Russ gave at Share on converting CICS applications to threadsafe, or here for a copy of the presentation Russ gave on exploiting the OTE without DB2.

CICS TS 4.2 (with IMS r12) now uses an OpenAPI TRUE, meaning that CICS/DLI programs can now take advantage of the OTE. Russ has an article in ETJ detailing some of the implications of this enhancement.

Russ has also written two introductory articles on CICS and Threadsafe for Technical Support, the journal of NaSpa, and recently published a series of articles in Enterprise Tech Journal on the subject.

For detailed information about what threadsafe is, how to use the OTE, and how to convert non-threadsafe programs to be threadsafe compliant, download the latest versions of the presentations Russ has developed:


Russ has written a number of articles for peer reviewed journals on the subjects of Threadsafe:




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