Updated: 11 December 1998

OpenVMS Programming Concepts Manual

There are several other RTL routines that permit high-level access to components of the operating system. Table 7-12 lists these routines and their functions. The sections that follow give further details about some of these routines.

Table 7-12 Miscellaneous Interface Routines

Entry Point	Function
LIB$AST_IN_PROG	Indicates whether an asynchronous system trap is in progress
LIB$ASN_WTH_MBX	Assigns an I/O channel and associates it with a mailbox
LIB$CREATE_DIR	Creates a directory or subdirectory
LIB$FIND_IMAGE_SYMBOL	Reads a global symbol from the shareable image file and dynamically activates a shareable image into the P0 address space of a process
LIB$ADDX	Performs addition on signed two's complement integers of arbitrary length (multiple-precision addition)
LIB$SUBX	Performs subtraction on signed two's complement integers of arbitrary length (multiple-precision subtraction)
LIB$FILE_SCAN	Finds file names given OpenVMS RMS file access block (FAB)
LIB$FILE_SCAN_END	End-of-file scan
LIB$FIND_FILE	Finds file names given string
LIB$FIND_FILE_END	End-of-find file
LIB$INSERT_TREE	Inserts an element in a binary tree
LIB$LOOKUP_TREE	Finds an element in a binary tree
LIB$TRAVERSE_TREE	Traverses a binary tree
LIB$GET_COMMON	Gets a record from the process's COMMON storage area
LIB$PUT_COMMON	Puts a record to the process's COMMON storage area

7.7.1 Indicating Asynchronous System Trap in Progress

An asynchronous system trap (AST) is a mechanism for providing a software interrupt when an external event occurs, such as when a user presses the Ctrl/C key sequence. When an external event occurs, the operating system interrupts the execution of the current process and calls a routine that you supply. While that routine is active, the AST is said to be in progress, and the process is said to be executing at AST level. When your AST routine returns control to the original process, the AST is no longer active and execution continues where it left off.

The LIB$AST_IN_PROG routine indicates to the calling program whether an AST is currently in progress. Your program can call LIB$AST_IN_PROG to determine whether it is executing at AST level, and then take appropriate action. This routine is useful if you are writing AST-reentrant code.

For information about using ASTs, see Chapter 5.

7.7.2 Create a Directory or Subdirectory

The LIB$CREATE_DIR routine creates a directory or a subdirectory. The calling program must specify the directory specification in standard OpenVMS RMS format. This directory specification may also contain a disk specification.

In addition to the required directory specification argument, LIB$CREATE_DIR takes the following five optional arguments:

• The user identification code (UIC) of the owner of the created directory or subdirectory
• The protection enable mask
• The protection value mask
• The maximum number of versions allowed for files created in this directory or subdirectory
• The relative volume number within the volume set on which the directory or subdirectory is created

See the OpenVMS RTL Library (LIB$) Manual for a complete description of LIB$CREATE_DIR.

7.7.3 File Searching Routines

The run-time library provides two routines that your program can call to search for a file and two routines that your program can call to end a search sequence.

• When you call LIB$FILE_SCAN with a wildcard file specification and an action routine, the routine calls the action routine for each file or error, or both, found in the wildcard sequence. LIB$FILE_SCAN allows the search sequence to continue even though certain errors are present.
• When you call LIB$FIND_FILE with a wildcard file specification, it finds the next file specification that matches the wildcard specification.

In addition to the wildcard file specification, which is a required argument, LIB$FIND_FILE takes the following four optional arguments:

• The default specification.
• The related specification.
• The OpenVMS RMS secondary status value from a failing RMS operation.
• A longword containing two flag bits. If bit 1 is set, LIB$FIND_FILE performs temporary defaulting for multiple input files and the related specification argument is ignored. See the OpenVMS RTL Library (LIB$) Manual for a complete description of LIB$FIND_FILE in template format.

The LIB$FIND_FILE_END routine is called once after each call to LIB$FIND_FILE in interactive use. LIB$FIND_FILE_END prevents the temporary default values retained by the previous call to LIB$FIND_FILE from affecting the next file specification.

The LIB$FILE_SCAN routine uses an optional context argument to perform temporary defaulting for multiple input files. For example, a command such as the following would specify A, B, and C in successive calls, retaining context, so that portions of one file specification would affect the next file specification:

$ COPY [smith]A,B,C *

The LIB$FILE_SCAN_END routine is called once after each sequence of calls to LIB$FILE_SCAN. LIB$FILE_SCAN_END performs a parse of the null string to deallocate saved OpenVMS RMS context and to prevent the temporary default values retained by the previous call to LIB$FILE_SCAN from affecting the next file specification. For instance, in the previous example, LIB$FILE_SCAN_END should be called after the C file specification is parsed, so that specifications from the $COPY files do not affect file specifications in subsequent commands.

The following BLISS example illustrates the use of LIB$FIND_FILE. It prompts for a file specification and default specification. The default specification indicates the default information for the file for which you are searching. Once the routine has searched for one file, the resulting file specification determines both the related file specification and the default file specification for the next search. LIB$FIND_FILE_END is called at the end of the following BLISS program to deallocate the virtual memory used by LIB$FIND_FILE.

%TITLE 'FILE_EXAMPLE1 - Sample program using LIB$FIND_FILE' MODULE FILE_EXAMPLE1( ! Sample program using LIB$FIND_FILE IDENT = '1-001', MAIN = EXAMPLE_START ) = BEGIN %SBTTL 'Declarations' !+ ! SWITCHES: !- SWITCHES ADDRESSING_MODE (EXTERNAL = GENERAL, NONEXTERNAL = WORD_RELATIVE); !+ ! TABLE OF CONTENTS: !- FORWARD ROUTINE EXAMPLE_START; ! Main program !+ ! INCLUDE FILES: !- LIBRARY 'SYS$LIBRARY:STARLET.L32'; ! System symbols !+ ! Define facility-specific messages from shared system messages. !- $SHR_MSGDEF(CLI,3,LOCAL, (PARSEFAIL,WARNING)); !+ ! EXTERNAL REFERENCES: !- EXTERNAL ROUTINE LIB$GET_INPUT, ! Read from SYS$INPUT LIB$FIND_FILE, ! Wildcard scanning routine LIB$FIND_FILE_END, ! End find file LIB$PUT_OUTPUT, ! Write to SYS$OUTPUT STR$COPY_DX; ! String copier LITERAL TRUE = 1, ! Success FALSE = 0; ! Failure %SBTTL 'EXAMPLE_START - Sample program main routine'; ROUTINE EXAMPLE_START = BEGIN !+ ! This program reads a file specification and default file ! specification from SYS$INPUT. It then prints all the files that ! match that specification and prompts for another file specification. ! After the first file specification no default specification is requested, ! and the previous resulting file specification becomes the related ! file specification. !- LOCAL LINEDESC : $BBLOCK[DSC$C_S_BLN], ! String desc. for input line RESULT_DESC : $BBLOCK[DSC$C_S_BLN], ! String desc. for result file CONTEXT, ! LIB$FIND_FILE context pointer DEFAULT_DESC : $BBLOCK[DSC$C_S_BLN], ! String desc. for default spec RELATED_DESC : $BBLOCK[DSC$C_S_BLN], ! String desc. for related spec HAVE_DEFAULT, STATUS; !+ ! Make all string descriptors dynamic. !- CH$FILL(0,DSC$C_S_BLN,LINEDESC); LINEDESC[DSC$B_CLASS] = DSC$K_CLASS_D; CH$MOVE(DSC$C_S_BLN,LINEDESC,RESULT_DESC); CH$MOVE(DSC$C_S_BLN,LINEDESC,DEFAULT_DESC); CH$MOVE(DSC$C_S_BLN,LINEDESC,RELATED_DESC); HAVE_DEFAULT = FALSE; CONTEXT = 0; !+ ! Read file specification, default file specification, and ! related file specification. !- WHILE (STATUS = LIB$GET_INPUT(LINEDESC, $DESCRIPTOR('FILE SPECIFICATION: '))) NEQ RMS$_EOF DO BEGIN IF NOT .STATUS THEN SIGNAL_STOP(.STATUS); !+ ! If default file specification was not obtained, do so now. !- IF NOT .HAVE_DEFAULT THEN BEGIN STATUS = LIB$GET_INPUT(DEFAULT_DESC, $DESCRIPTOR('DEFAULT FILE SPECIFICATION: ')); IF NOT .STATUS THEN SIGNAL_STOP(.STATUS); HAVE_DEFAULT = TRUE; END; !+ ! CALL LIB$FIND_FILE until RMS$_NMF (no more files) is returned. ! If an error other than RMS$_NMF is returned, it is signaled. ! Print out the file specification if the call is successful. !- WHILE (STATUS = LIB$FIND_FILE(LINEDESC,RESULT_DESC,CONTEXT, DEFAULT_DESC,RELATED_DESC)) NEQ RMS$_NMF DO IF NOT .STATUS THEN SIGNAL(CLI$_PARSEFAIL,1,RESULT_DESC,.STATUS) ELSE LIB$PUT_OUTPUT(RESULT_DESC); !+ ! Make this resultant file specification the related file ! specification for next file. !- STR$COPY_DX(RELATED_DESC,LINEDESC); END; ! End of loop ! reading file specification !+ ! Call LIB$FIND_FILE_END to deallocate the virtual memory used by LIB$FIND_FILE. ! Note that we do this outside of the loop. Since the MULTIPLE bit of the ! optional user flags argument to LIB$FIND_FILE wasn't used, it is not ! necessary to call LIB$FIND_FILE_END after each call to LIB$FIND_FILE. ! (The MULTIPLE bit would have caused temporary defaulting for multiple input ! files.) !- STATUS = LIB$FIND_FILE_END (CONTEXT); IF NOT .STATUS THEN SIGNAL_STOP (.STATUS); RETURN TRUE END; ! End of main program END ! End of module ELUDOM

The following BLISS example illustrates the use of LIB$FILE_SCAN and LIB$FILE_SCAN_END.

%TITLE 'FILE_EXAMPLE2 - Sample program using LIB$FILE_SCAN' MODULE FILE_EXAMPLE1( ! Sample program using LIB$FILE_SCAN IDENT = '1-001', MAIN = EXAMPLE_START ) = BEGIN %SBTTL 'Declarations' !+ ! SWITCHES: !- SWITCHES ADDRESSING_MODE (EXTERNAL = GENERAL, NONEXTERNAL = WORD_RELATIVE); !+ ! TABLE OF CONTENTS: !- FORWARD ROUTINE EXAMPLE_START, ! Main program SUCCESS_RTN, ! Success action routine ERROR_RTN; ! Error action routine !+ ! INCLUDE FILES: !- LIBRARY 'SYS$LIBRARY:STARLET.L32'; ! System symbols !+ ! Define VMS block structures (BLOCK[,BYTE]). !- STRUCTURE BBLOCK [O, P, S, E; N] = [N] (BBLOCK + O) <P, S, E>; !+ ! EXTERNAL REFERENCES: !- EXTERNAL ROUTINE LIB$GET_INPUT, ! Read from SYS$INPUT LIB$FILE_SCAN, ! Wildcard scanning routine LIB$FILE_SCAN_END, ! End of file scan LIB$PUT_OUTPUT; ! Write to SYS$OUTPUT %SBTTL 'EXAMPLE_START - Sample program main routine'; ROUTINE EXAMPLE_START = BEGIN !+ ! This program reads the file specification, default file specification, ! and related file specification from SYS$INPUT and then displays on ! SYS$OUTPUT all files which match the specification. !- LOCAL RESULT_BUFFER : VECTOR[NAM$C_MAXRSS,BYTE], !Buffer for resultant ! name string EXPAND_BUFFER : VECTOR[NAM$C_MAXRSS,BYTE], !Buffer for expanded ! name string LINEDESC : BBLOCK[DSC$C_S_BLN], !String descriptor ! for input line RESULT_DESC : BBLOCK[DSC$C_S_BLN], !String descriptor ! for result file DEFAULT_DESC : BBLOCK[DSC$C_S_BLN], !String descriptor ! for default specification RELATED_DESC : BBLOCK[DSC$C_S_BLN], !String descriptor ! for related specification IFAB : $FAB_DECL, !FAB for file_scan INAM : $NAM_DECL, ! and a NAM block RELNAM : $NAM_DECL, ! and a related NAM block STATUS; !+ ! Make all descriptors dynamic. !- CH$FILL(0,DSC$C_S_BLN,LINEDESC); LINEDESC[DSC$B_CLASS] = DSC$K_CLASS_D; CH$MOVE(DSC$C_S_BLN,LINEDESC,RESULT_DESC); CH$MOVE(DSC$C_S_BLN,LINEDESC,DEFAULT_DESC); CH$MOVE(DSC$C_S_BLN,LINEDESC,RELATED_DESC); !+ ! Read file specification, default file specification, and related ! file specification !- STATUS = LIB$GET_INPUT(LINEDESC, $DESCRIPTOR('File specification: ')); IF NOT .STATUS THEN SIGNAL_STOP(.STATUS); STATUS = LIB$GET_INPUT(DEFAULT_DESC, $DESCRIPTOR('Default file specification: ')); IF NOT .STATUS THEN SIGNAL_STOP(.STATUS); STATUS = LIB$GET_INPUT(RELATED_DESC, $DESCRIPTOR('Related file specification: ')); IF NOT .STATUS THEN SIGNAL_STOP(.STATUS); !+ ! Initialize the FAB, NAM, and related NAM blocks. !- $FAB_INIT(FAB=IFAB, FNS=.LINEDESC[DSC$W_LENGTH], FNA=.LINEDESC[DSC$A_POINTER], DNS=.DEFAULT_DESC[DSC$W_LENGTH], DNA=.DEFAULT_DESC[DSC$A_POINTER], NAM=INAM); $NAM_INIT(NAM=INAM, RSS=NAM$C_MAXRSS, RSA=RESULT_BUFFER, ESS=NAM$C_MAXRSS, ESA=EXPAND_BUFFER, RLF=RELNAM); $NAM_INIT(NAM=RELNAM); RELNAM[NAM$B_RSL] = .RELATED_DESC[DSC$W_LENGTH]; RELNAM[NAM$L_RSA] = .RELATED_DESC[DSC$A_POINTER]; !+ ! Call LIB$FILE_SCAN. Note that errors need not be checked ! here because LIB$FILE_SCAN calls error_rtn for all errors. !- LIB$FILE_SCAN(IFAB,SUCCESS_RTN,ERROR_RTN); !+ ! Call LIB$FILE_SCAN_END to deallocate virtual memory used for ! file scan structures. !- STATUS = LIB$FILE_SCAN_END (IFAB); IF NOT .STATUS THEN SIGNAL_STOP (.STATUS); RETURN 1 END; ! End of main program ROUTINE SUCCESS_RTN (IFAB : REF BBLOCK) = BEGIN !+ ! This routine is called by LIB$FILE_SCAN for each file that it ! successfully finds in the search sequence. ! ! Inputs: ! ! IFAB Address of a fab ! ! Outputs: ! ! file specification printed on SYS$OUTPUT !- LOCAL DESC : BBLOCK[DSC$C_S_BLN]; ! A local string descriptor BIND INAM = .IFAB[FAB$L_NAM] : BBLOCK; ! Find NAM block ! from pointer in FAB CH$FILL(0,DSC$C_S_BLN,DESC); ! Make static ! string descriptor DESC[DSC$W_LENGTH] = .INAM[NAM$B_RSL]; ! Get string length ! from NAM block DESC[DSC$A_POINTER] = .INAM[NAM$L_RSA]; ! Get pointer to the string RETURN LIB$PUT_OUTPUT(DESC) ! Print name on SYS$OUTPUT ! and return END; ROUTINE ERROR_RTN (IFAB : REF BBLOCK) = BEGIN !+ ! This routine is called by LIB$FILE_SCAN for each file specification that ! produces an error. ! ! Inputs: ! ! ifab Address of a fab ! ! Outputs: ! ! Error message is signaled !- LOCAL DESC : BBLOCK[DSC$C_S_BLN]; ! A local string descriptor BIND INAM = .IFAB[FAB$L_NAM] : BBLOCK; ! Get NAM block pointer ! from FAB CH$FILL(0,DSC$C_S_BLN,DESC); ! Create static ! string descriptor DESC[DSC$W_LENGTH] = .INAM[NAM$B_RSL]; DESC[DSC$A_POINTER] = .INAM[NAM$L_RSA]; !+ ! Signal the error using the shared message PARSEFAIL ! and the CLI facility code. The second part of the SIGNAL ! is the RMS STS and STV error codes. !- RETURN SIGNAL((SHR$_PARSEFAIL+3^16),1,DESC, .IFAB[FAB$L_STS],.IFAB[FAB$L_STV]) END; END ! End of module ELUDOM

7.7.4 Inserting an Entry into a Balanced Binary Tree

Three routines allow you to manipulate the contents of a balanced binary tree:

• LIB$INSERT_TREE adds an entry to a balanced binary tree.
• LIB$LOOKUP_TREE looks up an entry in a balanced binary tree.
• LIB$TRAVERSE_TREE calls an action routine for each node in the tree.

Example

The following BLISS example illustrates all three routines. The program prompts for input from SYS$INPUT and stores each data line as an entry in a binary tree. When the user enters the end-of-file character (Ctrl/Z), the tree is printed in sorted order. The program includes three subroutines:

• The first subroutine allocates virtual memory for a node.
• The second subroutine compares a key with a node.
• The third subroutine is called during the tree traversal. It prints out the left and right subtree pointers, the current node balance, and the name of the node.

%TITLE 'TREE_EXAMPLE - Sample program using binary tree routines' MODULE TREE_EXAMPLE( ! Sample program using trees IDENT = '1-001', MAIN = TREE_START ) = BEGIN %SBTTL 'Declarations' !+ ! SWITCHES: !- SWITCHES ADDRESSING_MODE (EXTERNAL = GENERAL, NONEXTERNAL = WORD_RELATIVE); !+ ! LINKAGES: ! ! NONE ! ! TABLE OF CONTENTS: !- FORWARD ROUTINE TREE_START, ! Main program ALLOC_NODE, ! Allocate memory for a node COMPARE_NODE, ! Compare two nodes PRINT_NODE; ! Print a node (action routine ! for LIB$TRAVERSE_TREE) !+ ! INCLUDE FILES: !- LIBRARY 'SYS$LIBRARY:STARLET.L32'; ! System symbols !+ ! Define VMS block structures (BLOCK[,BYTE]). !- STRUCTURE BBLOCK [O, P, S, E; N] = [N] (BBLOCK + O) <P, S, E>; !+ ! MACROS: !- MACRO NODE$L_LEFT = 0,0,32,0%, ! Left subtree pointer in node NODE$L_RIGHT = 4,0,32,0%, ! Right subtree pointer NODE$W_BAL = 8,0,16,0%, ! Balance this node NODE$B_NAMLNG = 10,0,8,0%, ! Length of name in this node NODE$T_NAME = 11,0,0,0%; ! Start of name (variable length) LITERAL NODE$C_LENGTH = 11; ! Length of fixed part of node !+ ! EXTERNAL REFERENCES: !- EXTERNAL ROUTINE LIB$GET_INPUT, ! Read from SYS$INPUT LIB$GET_VM, ! Allocate virtual memory LIB$INSERT_TREE, ! Insert into binary tree LIB$LOOKUP_TREE, ! Lookup in binary tree LIB$PUT_OUTPUT, ! Write to SYS$OUTPUT LIB$TRAVERSE_TREE, ! Traverse a binary tree STR$UPCASE, ! Convert string to all uppercase SYS$FAO; ! Formatted ASCII output routine %SBTTL 'TREE_START - Sample program main routine'; ROUTINE TREE_START = BEGIN !+ ! This program reads from SYS$INPUT and stores each data line ! as an entry in a binary tree. When end-of-file character (CTRL/Z) ! is entered, the tree will be printed in sorted order. !- LOCAL NODE : REF BBLOCK, ! Address of allocated node TREEHEAD, ! List head of binary tree LINEDESC : BBLOCK[DSC$C_S_BLN], ! String descriptor for input line STATUS; TREEHEAD = 0; ! Zero binary tree head CH$FILL(0,DSC$C_S_BLN,LINEDESC); ! Make a dynamic descriptor LINEDESC[DSC$B_CLASS] = DSC$K_CLASS_D; ! ... !+ ! Read input lines until end of file seen. !- WHILE (STATUS = LIB$GET_INPUT(LINEDESC, ! Read input line $DESCRIPTOR('Text: '))) ! with this prompt NEQ RMS$_EOF DO IF NOT .STATUS ! Report any errors found THEN SIGNAL(.STATUS) ELSE BEGIN STR$UPCASE(LINEDESC,LINEDESC); ! Convert string ! to uppercase IF NOT (STATUS = LIB$INSERT_TREE( TREEHEAD, ! Insert good data into the tree LINEDESC, ! Data to insert %REF(1), ! Insert duplicate entries COMPARE_NODE, ! Addr. of compare routine ALLOC_NODE, ! Addr. of node allocation routine NODE, ! Return addr. of 0)) ! allocated node here THEN SIGNAL(.STATUS); END; !+ ! End of file character encountered. Print the whole tree and exit. !- IF NOT (STATUS = LIB$TRAVERSE_TREE( TREEHEAD, ! Listhead of tree PRINT_NODE, ! Action routine to print a node 0)) THEN SIGNAL(.STATUS); RETURN SS$_NORMAL END; ! End of routine tree_start ROUTINE ALLOC_NODE (KEYDESC,RETDESC,CONTEXT) = BEGIN !+ ! This routine allocates virtual memory for a node. ! ! INPUTS: ! ! KEYDESC Address of string descriptor for key ! (this is the linedesc argument passed ! to LIB$INSERT_TREE) ! RETDESC Address of location to return address of ! allocated memory ! CONTEXT Address of user context argument passed ! to LIB$INSERT_TREE (not used in this ! example) ! ! OUTPUTS: ! ! Memory address returned in longword pointed to by retdesc !- MAP KEYDESC : REF BBLOCK, RETDESC : REF VECTOR[,LONG]; LOCAL NODE : REF BBLOCK, STATUS; STATUS = LIB$GET_VM(%REF(NODE$C_LENGTH+.KEYDESC[DSC$W_LENGTH]),NODE); IF NOT .STATUS THEN RETURN .STATUS ELSE BEGIN NODE[NODE$B_NAMLNG] = .KEYDESC[DSC$W_LENGTH]; ! Set name length CH$MOVE(.KEYDESC[DSC$W_LENGTH], ! Copy in the name .KEYDESC[DSC$A_POINTER], NODE[NODE$T_NAME]); RETDESC[0] = .NODE; ! Return address to caller END; RETURN .STATUS END; ROUTINE COMPARE_NODE (KEYDESC,NODE,CONTEXT) = BEGIN !+ ! This routine compares a key with a node. ! ! INPUTS: ! ! KEYDESC Address of string descriptor for new key ! (This is the linedesc argument passed to ! LIB$INSERT_TREE) ! NODE Address of current node ! CONTEXT User context data (Not used in this example) !- MAP KEYDESC : REF BBLOCK, NODE : REF BBLOCK; RETURN CH$COMPARE(.KEYDESC[DSC$W_LENGTH], ! Compare key with ! current node .KEYDESC[DSC$A_POINTER], .NODE[NODE$B_NAMLNG], NODE[NODE$T_NAME]) END; ROUTINE PRINT_NODE (NODE,CONTEXT) = BEGIN !+ ! This routine is called during the tree traversal. It ! prints out the left and right subtree pointers, the ! current node balance, and the name of the node. !- MAP NODE : REF BBLOCK; LOCAL OUTBUF : BBLOCK[512], ! FAO output buffer OUTDESC : BBLOCK[DSC$C_S_BLN], ! Output buffer descriptor STATUS; CH$FILL(0,DSC$C_S_BLN,OUTDESC); ! Zero descriptor OUTDESC[DSC$W_LENGTH] = 512; OUTDESC[DSC$A_POINTER] = OUTBUF; IF NOT (STATUS = SYS$FAO($DESCRIPTOR('!XL !XL !XL !XW !AC'), OUTDESC,OUTDESC, .NODE,.NODE[NODE$L_LEFT], .NODE[NODE$L_RIGHT], .NODE[NODE$W_BAL], NODE[NODE$B_NAMLNG])) THEN SIGNAL(.STATUS) ELSE BEGIN STATUS = LIB$PUT_OUTPUT(OUTDESC); ! Output the line IF NOT .STATUS THEN SIGNAL(.STATUS); END; RETURN SS$_NORMAL END; END ! End of module TREE_EXAMPLE ELUDOM

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