Document revision date: 19 July 1999

On VAX systems, is the client interface to the DIGITAL Distributed Name Service.

The $DNSW service completes synchronously; that is, it returns to the caller after the operation completes.

For asynchronous completion, use the $DNS service, which returns to the caller immediately after making a name service call. The return status to the client call indicates whether a request was successfully queued to the name service.

In all other respects, $DNSW is identical to $DNS. Refer to the $DNS description for complete information about the $DNSW service.

Format

SYS$DNSW [efn] ,func ,itmlst [,dnsb] [,astadr] [,astprm]

Ends a transaction by attempting to commit it, and returns the outcome of the transaction.

Format

SYS$END_TRANS [efn] ,[flags] ,iosb [,[astadr] ,[astprm] ,[tid]]

C Prototype

int sys$end_trans (unsigned int efn, unsigned int flags, struct _iosb *iosb,...);

Arguments

efn

OpenVMS usage:	ef_number
type:	longword (unsigned)
access:	read only
mechanism:	by value

Number of the event flag that is set when the service completes. If this argument is omitted, event flag 0 is set.

flags

OpenVMS usage:	mask_longword
type:	longword (unsigned)
access:	read only
mechanism:	by value

Flags specifying options for the service. The flags argument is a longword bit mask in which each bit corresponds to an option flag. The $DDTMDEF macro defines symbolic names for these option flags. The flag currently defined is shown in the following table. All undefined bits must be 0. If this argument is omitted, no flag is set.

Flag	Description
DDTM$M_SYNC	Set this flag to specify that successful synchronous completion is to be indicated by returning SS$_SYNCH. When SS$_SYNCH is returned, the asynchronous system trap (AST) routine is not called, the event flag is not set, and the I/O status block is not filled in.

iosb

OpenVMS usage:	io_status_block
type:	quadword (unsigned)
access:	write only
mechanism:	by reference

I/O status block in which the following information is returned:

• The completion status of the service. This is returned as a condition value. See the Condition Values Returned section.
• The outcome of the transaction.
  If the service returns SS$_NORMAL, the outcome of the transaction is commit. If the service returns SS$_ABORT, the outcome of the transaction is abort.
• An abort reason code that gives one reason why the transaction aborted, if the completion status of the service is SS$_ABORT.

The $DDTMMSGDEF macro defines symbolic names for these abort reason codes; those currently defined are shown in the following table:

Symbolic Name	Description
DDTM$_ABORTED	The application aborted the transaction.
DDTM$_COMM_FAIL	A communications link failed.
DDTM$_INTEGRITY	A resource manager integrity constraint check failed.
DDTM$_LOG_FAIL	A write operation to the transaction log failed.
DDTM$_PART_SERIAL	A resource manager serialization check failed.
DDTM$_PART_TIMEOUT	The timeout specified by a resource manager expired.
DDTM$_SEG_FAIL	A process or image terminated.
DDTM$_SERIALIZATION	A DECdtm transaction manager serialization check failed.
DDTM$_SYNC_FAIL	The transaction was not globally synchronized.
DDTM$_TIMEOUT	The timeout specified on $START_TRANS expired.
DDTM$_UNKNOWN	The reason is unknown.
DDTM$_VETOED	A resource manager was unable to commit the transaction.

The following diagram shows the structure of the I/O status block.

astadr

astprm

tid

If this argument is omitted, $END_TRANS ends the default transaction of the calling process.

Description

The End Transaction service ends a transaction by attempting to commit it, and returns the outcome of the transaction.

$END_TRANS initiates the commit protocol to determine whether the outcome of the transaction is commit or abort.

Caution Do not call $END_TRANS while any transaction operations are still in progress. If there are any of these operations in progress when $END_TRANS is called, an unintended set of operations could be committed, invalidating the data managed by the resource managers participating in the transaction.

$END_TRANS returns the outcome of the transaction. If it completes successfully, the outcome of the transaction is commit. If it returns the SS$_ABORT error, the outcome is abort, and the I/O status block contains one reason why the transaction aborted.

$END_TRANS must be called from the process that started the transaction. The access mode of the caller must be the same as or more privileged than that specified in the call to $START_TRANS that started the transaction.

$END_TRANS does not complete either successfully or with the SS$_ABORT error until all quotas allocated for the transaction by calls on the local node to DECdtm services have been returned.

$END_TRANS will not complete successfully (that is, the event flag will not be set, the AST routine will not be called, and the I/O status block will not be filled in) while the calling process is either:

• In an access mode that is more privileged than the DECdtm calls made by any resource manager participant in the transaction.
  RMS Journaling calls DECdtm in executive mode. Oracle Rdb and Oracle CODASYL DBMS call DECdtm in user mode.
• At AST level (in any access mode).

For example, if Oracle Rdb is a participant in the transaction, $END_TRANS will not complete successfully while the calling process is in supervisor, executive, or kernel mode, or while the calling process is at AST level.

Required Access or Privileges

None

Required Quotas

ASTLM

Related Services

$ABORT_TRANS, $ABORT_TRANSW, $END_TRANSW, $START_TRANS, $START_TRANSW

Condition Values Returned

SS$_NORMAL	If this was returned in R0, the request was successfully queued. If it was returned in the I/O status block, the service completed successfully.
SS$_SYNCH	The service completed successfully and synchronously (returned only if the DDTM$M_SYNC flag is set).
SS$_ABORT	The transaction aborted (see the abort reason code returned in the I/O status block for one reason why the transaction aborted).
SS$_ACCVIO	An argument was not accessible by the caller.
SS$_BADPARAM	The options flags were invalid.
SS$_CURTIDCHANGE	The tid argument was omitted and a call to change the default transaction of the calling process was in progress.
SS$_EXASTLM	The process AST limit (ASTLM) was exceeded.
SS$_ILLEFC	The event flag number was invalid.
SS$_INSFARGS	Not enough arguments were supplied.
SS$_INSFMEM	There was insufficient system dynamic memory for the operation.
SS$_NOCURTID	An attempt was made to end the default transaction (the tid argument was omitted), but the calling process did not have a default transaction.
SS$_NOLOG	The local node did not have a transaction log.
SS$_NOSUCHTID	A transaction with the specified transaction identifier does not exist.
SS$_NOTORIGIN	The calling process did not start the transaction.
SS$_TPDISABLED	The TP_SERVER process was not running on the local node.
SS$_WRONGACMODE	The access mode of the caller was less privileged than the mode specified in the call to $START_TRANS.
SS$_WRONGSTATE	The calling process had already called either $ABORT_TRANS or $END_TRANS to end the transaction, and processing had not completed.

Ends a transaction by attempting to commit it, and returns the outcome of the transaction.

$END_TRANSW always waits for the request to complete before returning to the caller. Other than this, it is identical to $END_TRANS.

Do not call $END_TRANSW from asynchronous system trap (AST) level, or from an access mode that is more privileged than the DECdtm calls made by any resource manager participant in the transaction. If you do, the $END_TRANSW service will wait indefinitely.

Format

SYS$END_TRANSW [efn] ,[flags] ,iosb [,[astadr] ,[astprm] ,[tid]]

C Prototype

int sys$end_transw (unsigned int efn, unsigned int flags, struct _iosb *iosb,...);

Queues a new lock or lock conversion on a resource.

The $ENQ, $ENQW, $DEQ (Dequeue Lock Request), and $GETLKI (Get Lock Information) services together provide the user interface to the Lock Management facility. Refer to the descriptions of these other services for additional information about lock management.

On Alpha systems, this service accepts 64-bit addresses.

For additional information about system service completion, refer to the Synchronize ($SYNCH) service.

Format

SYS$ENQ [efn] ,lkmode ,lksb ,[flags] ,[resnam] ,[parid] ,[astadr] ,[astprm] ,[blkast] ,[acmode] ,[rsdm_id] ,[nullarg]

C Prototype

int sys$enq (unsigned int efn, unsigned int lkmode, struct _lksb *lksb, unsigned int flags, void *resnam, unsigned int parid, void (*astadr)(__unknown_params), unsigned int acmode, unsigned int rsdm_id,...);

Arguments

efn

OpenVMS usage:	ef_number
type:	longword (unsigned)
access:	read only
mechanism:	by value

Number of the event flag to be set when the request has been granted or canceled. Cancellation occurs if you use $DEQ with the cancel modifier or if the waiting request is chosen to break a deadlock. The efn argument is a longword containing this number; however, $ENQ uses only the low-order byte.

Upon request initiation, $ENQ clears the specified event flag (or event flag 0 if efn was not specified). Then, when the lock request is granted, the specified event flag (or event flag 0) is set unless you specified the LCK$M_SYNCSTS flag in the flags argument.

lkmode

OpenVMS usage:	longword_unsigned
type:	longword (unsigned)
access:	read only
mechanism:	by value

Lock mode requested. The lkmode argument is a longword specifying this lock mode.

Each lock mode has a symbolic name. The $LCKDEF macro defines these symbolic names. The following table gives the symbolic name and description for each lock mode.

Lock Mode	Description
LCK$K_NLMODE	Null mode. This mode grants no access to the resource but serves as a placeholder and indicator of future interest in the resource. The null mode does not inhibit locking at other lock modes; further, it prevents the deletion of the resource and lock value block, which would otherwise occur if the locks held at the other lock modes were dequeued.
LCK$K_CRMODE	Concurrent read. This mode grants the caller read access to the resource while permitting write access to the resource by other users. This mode is used to read data from a resource in an unprotected manner, because other users can modify that data as it is being read. This mode is typically used when additional locking is being performed at a finer granularity with sublocks.
LCK$K_CWMODE	Concurrent write. This mode grants the caller write access to the resource while permitting write access to the resource by other users. This mode is used to write data to a resource in an unprotected fashion, because other users can simultaneously write data to the resource. This mode is typically used when additional locking is being performed at a finer granularity with sublocks.
LCK$K_PRMODE	Protected read. This mode grants the caller read access to the resource while permitting only read access to the resource by other users. Write access is not allowed. This is the traditional share lock.
LCK$K_PWMODE	Protected write. This mode grants the caller write access to the resource while permitting only read access to the resource by other users; the other users must have specified concurrent read mode access. No other writers are allowed access to the resource. This is the traditional update lock.
LCK$K_EXMODE	Exclusive. The exclusive mode grants the caller write access to the resource and allows no access to the resource by other users. This is the traditional exclusive lock.

lksb

OpenVMS usage:	lock_status_block
type:	longword (unsigned)
access:	write only
mechanism:	by 32- or 64-bit reference (Alpha)
mechanism:	by 32-bit reference (VAX)

Lock status block in which $ENQ writes the final completion status of the operation. The lksb argument is the 32- or 64-bit address (on Alpha systems) or the 32-bit address (on VAX systems) of the 8-byte lock status block.

The lock status block can optionally contain a 16-byte lock value block. The initial value of the lock value block is zero (0). When you specify the LCK$M_VALBLK flag in the flags argument, the lock status block contains a lock value block. In this case, the 16-byte lock value block appears at the beginning of the first byte following the eighth byte of the lock status block, bringing the total length of the lock status block to 24 bytes.

The following diagram shows the format of the lock status block and the optional lock value block.

The following table defines the status block fields.

Status Block Field	Definition
Condition value	A word in which $ENQ writes a condition value describing the final disposition of the lock request; for example, whether the lock was granted, converted, and so on. The condition values returned in this field are described in the Condition Values Returned in the Lock Status Block section, which appears following the list of condition values returned in R0.
Reserved	A word reserved by Compaq.
Lock identification	A longword containing the identification of the lock. For a new lock, $ENQ writes the lock identification of the requested lock into this longword when the lock request is queued. For a lock conversion on an existing lock, you must supply the lock identification of the existing lock in this field.
Lock value block	A user-defined, 16-byte structure containing information about the resource. This information is interpreted only by the user program. When a process acquires a lock on a resource, the lock management facility provides that process with a process-private copy of the lock value block associated with the resource, provided that process has specified the LCK$M_VALBLK flag in the flags argument. The copy provided to the process is a copy of the lock value block stored in the lock manager's database. The copy of the lock value block maintained in the lock database is either read into or updated from the caller's lock value block. The method used depends on the lock mode of the lock that was granted, and on the mode of the original lock held, if the operation was a conversion. In general, a grant or a conversion to an equal-level or higher-level lock mode reads the lock value from the lock database into the caller's lock value block. This occurs while either a lock dequeue or a lock conversion from EX-mode or PW-mode to an equal-level or lower-level lock mode causes the contents of the caller's lock value block to be written into the lock database. The specific behavior of the lock conversion is documented in the OpenVMS Programming Concepts Manual in the table entitled, "Effect of Lock Conversion on Lock Value Block".

Callers of $ENQ are provided with copies of the updated lock value block from the lock database in the following way: when $ENQ grants a new lock to the caller or converts the caller's existing lock to the same lock mode or a higher lock mode, $ENQ copies the lock value block from the lock database to the caller's lock value block, provided the caller has specified the LCK$M_VALBLK flag.

The Description section describes events that can cause the lock value block to become invalid.

flags

The $LCKDEF macro defines a symbolic name for each flag bit. The following table describes each flag.

Flag	Description
LCK$M_NOQUEUE	When this flag is specified, $ENQ does not queue the lock request unless the lock can be granted immediately. By default, $ENQ always queues the request. If you specify LCK$M_NOQUEUE in a lock conversion operation and the conversion cannot be granted immediately, the lock remains in the original lock mode.
LCK$M_SYNCSTS	When you specify this flag, $ENQ returns the successful condition value SS$_SYNCH in R0 if the lock request is granted immediately; in this case, no completion asynchronous system trap (AST) is delivered and no event flag is set. If the lock request is queued successfully but cannot be granted immediately, $ENQ returns the condition value SS$_NORMAL in R0; then when the request is granted, $ENQ sets the event flag and queues an AST if the astadr argument was specified.
LCK$M_SYSTEM	When you specify this flag, the resource name is interpreted as systemwide. By default, resource names are qualified by the user identification code (UIC) group number of the creating process. This flag is ignored in lock conversions.
LCK$M_VALBLK	When you specify this flag, the lock status block contains a lock value block. The initial value of the lock value block is zero (0). See the description of the lksb argument for more information.
LCK$M_CONVERT	When you specify this flag, $ENQ performs a lock conversion. In this case, the caller must supply (in the second longword of the lock status block) the lock identification of the lock to be converted.
LCK$M_NODLCKWT	By specifying this flag, a process indicates to the lock management services that it is not blocked from execution while waiting for the lock request to complete. For example, a lock request might be left outstanding on the waiting queue as a signaling device between processes. This flag helps to prevent false deadlocks by providing the lock management services with additional information about the process issuing the lock request. When you set this flag, the lock management services do not consider this lock when trying to detect deadlock conditions.
	A process should specify the LCK$M_NODLCKWT flag only in a call to the $ENQ system service. The $ENQW system service waits for the lock request to be granted before returning to the caller; therefore, specifying the LCK$M_NODLCKWT flag in a call to the $ENQW system service defeats the purpose of the flag and can result in a genuine deadlock being ignored. The lock management services make use of the LCK$M_NODLCKWT flag only when the lock specified by the call to $ENQ is in either the waiting or the conversion queue. Improper use of the LCK$M_NODLCKWT flag can result in the lock management services ignoring genuine deadlocks.
LCK$M_NODLCKBLK	By specifying this flag, a process indicates to the lock management services that, if this lock is blocking another lock request, the process intends to give up this lock on demand. When you specify this flag, the lock management services do not consider this lock as blocking other locks when trying to detect deadlock conditions. A process typically specifies the LCK$M_NODLCKBLK flag only when it also specifies a blocking AST. Blocking ASTs notify processes with granted locks that another process with an incompatible lock mode has been queued to access the same resource. Use of blocking ASTs can cause false deadlocks, because the lock management services detect a blocking condition, even though a blocking AST has been specified; however, the blocking condition will disappear as soon as the process holding the lock executes, receives the blocking AST, and dequeues the lock. Specifying the LCK$M_NODLCKBLK flag prevents this type of false deadlock.
	To enable blocking ASTs, the blkast argument of the $ENQ system service must contain the address of a blocking AST service routine. If the process specifies the LCK$M_NODLCKBLK flag, the blocking AST service routine should either dequeue the lock or convert it to a lower lock mode without issuing any new lock requests. If the blocking AST routine does otherwise, a genuine deadlock could be ignored. The lock management services make use of the LCK$M_NODLCKBLK flag only when the lock specified by the call to $ENQ has been granted. Improper use of the LCK$M_NODLCKBLK flag can result in the lock management services ignoring genuine deadlocks.
LCK$M_NOQUOTA	This flag is reserved by Compaq. When you set this flag, the calling process is not charged Enqueue Limit (ENQLM) quota for this new lock. The calling process must be running in executive or kernel mode to set this flag. This flag is ignored for lock conversions.
LCK$M_CVTSYS	This flag is reserved by Compaq. When you set this flag, the lock is converted from a process-owned lock to a system-owned lock. The calling process must be running in executive or kernel mode to set this flag.
LCK$M_EXPEDITE	This flag is valid only for new lock requests. Specifying this flag allows a request to be granted immediately, provided the requested mode when granted would not block any currently queued requests in the resource conversion and wait queues. Currently, this flag is valid only for NLMODE requests. If this flag is specified for any other lock mode, the request will fail and an error of SS$_UNSUPPORTED will be returned.
LCK$M_QUECVT	This flag is valid only for conversion operations. A conversion request with the LCK$M_QUECVT flag set will be forced to wait behind any already queued conversions. The conversion request is granted immediately, if there are no already queued conversions. The QUECVT behavior is valid only for a subset of all possible conversions. Table SYS-8 defines the legal set of conversion requests for LCK$M_QUECVT. Illegal conversion requests are failed with SS$_BADPARAM returned.

Table SYS-8 Legal QUECVT Conversions

Lock Mode	Lock Mode to Which Lock Is Converted
at Which Lock Is Held	NL	CR	CW	PR	PW	EX
NL	No	Yes	Yes	Yes	Yes	Yes
CR	No	No	Yes	Yes	Yes	Yes
CW	No	No	No	Yes	Yes	Yes
PR	No	No	Yes	No	Yes	Yes
PW	No	No	No	No	No	Yes
EX	No	No	No	No	No	No

• NL---Null lock
• CR---Concurrent read
• CW---Concurrent write
• PR---Protected read
• PW---Protected write
• EX---Exclusive lock

resnam

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