Open transaction environment

The open transaction environment (OTE) is an environment where threadsafe application code can run on its own TCB inside the CICS address space without interference from other transactions. Applications that use the OTE can run on a class of TCB called an open TCB, or on the quasi-reentrant TCB (QR TCB).

The use of an open TCB provides the following advantages over the use of the QR TCB:

• No dispatching of other CICS tasks occurs on an open TCB.
• Multiple open TCBs can run concurrently.
• An application that runs under an open TCB can issue non CICS API requests that can involve the TCB being blocked. If blocking occurs, only this open TCB is halted, and not the whole of CICS.
• When the CICS task ends, the open TCB can be reused by another CICS task.

CICS manages open TCBs in separate pools, with each pool containing a different type (or mode) of open TCB. When applications are dispatched onto a TCB, the type of TCB depends on the combination of several CICS and resource configuration parameters:

• The storage protection setting for the CICS region
• Whether the application executes in a JVM server
• The parameters that are used during the compilation and binding process of the application
• The value of the following PROGRAM resource attributes:
  • API
  • CONCURRENCY
  • EXECKEY

For more information about the open transaction environment, see Threadsafe learning path.