SYNAD Synchronous Error Routine Exit

The SYNAD parameter of the DCB or DCBE macro specifies the address of an error routine that is to be given control when an input/output error occurs. You can use this routine to analyze exceptional conditions or uncorrectable errors. I/O errors usually occur asynchronously to your program, but the access method calls your SYNAD routine synchronously to macros that your program issues.

If an I/O error occurs during data transmission, standard error recovery procedures that are provided by the operating system try to correct the error before returning control to your program. These error recovery procedures generally are asynchronous to your program. An uncorrectable error usually causes an abnormal termination of the task. However, if you specify the address of an error analysis routine (called a SYNAD routine) in the DCB or DCBE macro, that routine can try to correct or ignore the error and prevent an abnormal termination. The routine is given control when the application program issues the access method macro that requires the buffer that received the uncorrectable error. For the queued access methods this generally means after enough PUT or GET macros to fill BUFNO-1 buffers past the failing block. For the basic access methods this means when your program issues a CHECK macro for the failing DECB.

For BDAM, BSAM, BPAM, and QSAM, the control program provides a pointer to the status indicators shown in Figure 1. The block being read or written can be accepted or skipped, or processing can be terminated.

Table 1 shows the exception code bits for QISAM.

Table 1. Exception code bits—QISAM
Exception Field	Code Bit	CLOSE	Code GET	Set PUT	by PUTX	SETL	Condition If On
DCBEXCD1	0					Type K	Record Not Found
	1					Type I	Nonvalid actual address for lower limit
	2	X					Space not found for adding a record
	3					X	Nonvalid request
	4		X				Uncorrectable input error
	5	X		X	X		Uncorrectable output error
	6		X			X	Block could not be reached (input)
	7	X	X				Block could not be reached (update)
DCBEXCD2	0			X			Sequence check
	1			X			Duplicate record
	2	X					Data control block closed when error routine entered
	3		X				Overflow record
	4			X			Incorrect record length
	5-7						Reserved for future use

Descriptions of the conditions in Table 1 follow:

Record Not Found: The logical record with the specified key is not found in the data set. This happens if the specified key is higher than the highest key in the highest-level index or if the record is not in either the primary area or the overflow area of the data set.
Invalid Actual Address for Lower Limit condition is reported if the specified lower limit address is outside the space allocated to the data set.
Space Not Found for Adding a Record: The space allocated to the data set is already filled. In locate mode, a buffer segment address is not provided. In move mode, data is not moved.
Invalid Request: (1) The data set is already being referred to sequentially by the application program, (2) the buffer cannot contain the key and the data, or (3) the specified type is not also specified in the DCBMACRF field of the data control block.
Uncorrectable Input Error: The control program's error recovery procedures encounter an uncorrectable error when transferring a block from secondary storage to an input buffer. The buffer address is placed in register 1, and the SYNAD exit routine is given control when a GET macro instruction is issued for the first logical record.
Uncorrectable Output Error: The control program's error recovery procedures encounter an uncorrectable error when transferring a block from an output buffer to secondary storage. If the error is encountered during closing of the data control block, bit 2 of DCBEXCD2 is set to 1 and the SYNAD exit routine is given control immediately. Otherwise, control program action depends on whether load mode or scan mode is being used.
If a data set is being created (load mode), the SYNAD exit routine is given control when the next PUT or CLOSE macro instruction is issued. If a failure to write a data block occurs, register 1 contains the address of the output buffer, and register 0 contains the address of a work area containing the first 16 bytes of the IOB; for other errors, the contents of register 1 are meaningless. After appropriate analysis, the SYNAD exit routine should close the data set or end the job step. If records are to be subsequently added to the data set using the queued indexed sequential access method (QISAM), the job step should be terminated by issuing an abend macro instruction. (Abend closes all open data sets. However, an ISAM data set is only partially closed, and it can be reopened in a later job to add additional records by using QISAM.) Subsequent execution of a PUT macro instruction would cause reentry to the SYNAD exit routine, because an attempt to continue loading the data set would produce unpredictable results.

If a data set is being processed (scan mode), the address of the output buffer in error is placed in register 1, the address of a work area containing the first 16 bytes of the IOB is placed in register 0, and the SYNAD exit routine is given control when the next GET macro instruction is issued. Buffer scheduling is suspended until the next GET macro instruction is reissued.
Block Could Not Be Reached (Input) condition is reported if the control program's error recovery procedures encounter an uncorrectable error in searching an index or overflow chain. The SYNAD exit routine is given control when a GET macro instruction is issued for the first logical record of the unreachable block.
Block Could Not Be Reached (Update): The control program's error recovery procedures encounter an uncorrectable error in searching an index or overflow chain.
If the error is encountered during closing of the data control block, bit 2 of DCBEXCD2 is set to 1 and the SYNAD exit routine is given control immediately. Otherwise, the SYNAD exit routine is given control when the next GET macro instruction is issued.
Sequence Check: A PUT macro instruction refers to a record whose key has a smaller numeric value than the key of the record previously referred to by a PUT macro instruction. The SYNAD exit routine is given control immediately; the record is not transferred to secondary storage.
Duplicate Record: A PUT macro instruction refers to a record whose key duplicates the record previously referred to by a PUT macro instruction. The SYNAD exit routine is given control immediately; the record is not transferred to secondary storage.
Data Control Block Closed When Error Routine Entered: The control program's error recovery procedures encounter an uncorrectable output error during closing of the data control block. Bit 5 or 7 of DCBEXCD1 is set to 1, and the SYNAD exit routine is immediately given control. After appropriate analysis, the SYNAD routine must branch to the address in return register 14 so that the control program can finish closing the data control block.
Overflow Record: The input record is an overflow record. The SYNAD exit routine is entered only if bit 4, 5, 6, or 7 of DCBEXCD1 is also on.
Incorrect Record Length: The length of the record as specified in the record-descriptor word (RDW) is larger than the value in the DCBLRECL field of the data control block.