MBCA - Transient data buffer control

       DESCRIPTIVE NAME = Transient Data Buffer Control
                          CICS/ESA AP Domain
           Licensed Materials - Property of IBM
            Restricted Materials of IBM 
           5655-Y04
           (C) Copyright IBM Corp. 1982, 1994 
      FUNCTION =
           Copybook DFHMBCPS provides structures, DFHMBCA and
           DFHMBCB and DFHMQCB.
           DFHMBCA describes the Buffer Common Area (MBCA),
           only one MBCA is allocated.
           DFHMBCB describes the Buffer Control Block (MBCB),
           one MBCB is allocated for each I/O buffer.
           DFHMQCB describes the Queue Control Block (MQCB),
           one MQCB is allocated for each I/O buffer. MQCBs
           are used to optimize the search for I/O buffers
           containing records for a given queue.
      LIFETIME =
           The lifetime of the control blocks and I/O buffers
           is essentially that of CICS.
      STORAGE CLASS =
           The control blocks are located in storage allocated
           from the DFHTDG31 subpool.
           The I/O buffers, if required, are located in storage
           allocated from the DFHTDIOB subpool.
           Note that the number of I/O buffers is defined as
           a SIT parameter / override.
           Note also that the number of I/O buffers allocated
           may exceed the number requests where this does not
           cause further pages to be allocated.
      LOCATION =
           The MBCA is located from the TDST.
           MBCBs are located on one of three bi-directional
           chains whose anchors are located in the MBCA
             1. unallocated, I/O buffer is (logically) empty
             2. unallocated, I/O buffer contains valid data
             3. allocated, I/O buffer is (logically) modified
           MQCBs are located on one of many bi-directional
           chains
             1. anchor located in the MBCA when the associated
                MBCB is on chain 1
             2. anchor located in the relevant DCTE when the
                associated MBCB is on chain 2 or chain 3.
           Each MQCB may be located from its associated MBCB
           and vice versa.
      INNER CONTROL BLOCKS =
           There are no inner control blocks.
      NOTES :
       DEPENDENCIES =
           S/370
       RESTRICTIONS =
           There are no restrictions.
       MODULE TYPE =
           Control block definition.
                 MULTIPLE BUFFERS - BUFFER COMMON AREA (MBCA)

                 MULTIPLE BUFFERS - BUFFER CONTROL BLOCK (MBCB)

                 MULTIPLE BUFFERS - QUEUE CONTROL BLOCK (MQCB)