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Requesting Waited Reads

Accessing Files

4–2 107365 Tandem Computers Incorporated

Table 4-1 lists functions related to #REQUESTER operation.

Table 4-1. Functions Used With #REQUESTER

Function Description

#APPEND, #APPENDV Adds lines to a variable.

#EXTRACT, #EXTRACTV Retrieves lines from a variable.

Requesting Waited

Reads

To open a file for waited read operations, issue a #REQUESTER call and include the

WAIT option; for example, the following statement opens FILE1 and initializes

error_var, read_var, and prompt_var:

#SET rslt [#REQUESTER /WAIT/ READ file1 error_var read_var

prompt_var]

You can also use the WAIT option to specify the size of the text buffer. To specify

shared, protected, or exclusive access to the file, use the EXCLUSION option; the

default for a read operation is shared. For example:

#REQUESTER /EXCLUSION PROTECTED/ READ file2 error_var &

read_var prompt_var

Note It is very important to check the results of the open operation; otherwise, you will not know if the open

request received an error.

To initiate a read operation, append data to the prompt variable:

#APPEND prompt_var *start read*

When reading a disk file, TACL discards the data in prompt_var; you can specify any

non-null data. TACL reads a record from FILE1 and places it into read_var. You can

use #EXTRACT(V) to retrieve data from read_var; as you #EXTRACT records,

TACL deletes them from read_var.

Each time you append a line to prompt_var, the TACL process reads a record from

the disk file FILE1 and appends it to read_var. TACL then performs a READ

operation. TACL continues executing code until it encounters an #APPEND(V) or

#EXTRACT(V) call that refers to one of the #REQUESTER variables. TACL then waits

until the current read operation is complete before initiating the next read operation.

When you are finished reading from the file, issue a CLOSE request and supply one of

the variable levels associated with the file; for example:

#REQUESTER CLOSE read_var

This operation closes FILE1 (associated with read_var) and terminates the

#REQUESTER function.

HP TACL User Manual

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