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Requesting Nowaited Reads

Accessing Files

4–4 107365 Tandem Computers Incorporated

Requesting Nowaited

Reads

To open a file for nowaited read operations, issue a #REQUESTER call and omit the

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

error_var, read_var, and prompt_var:

#SET rslt [#REQUESTER READ file1 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 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

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

#APPEND prompt_var *start read*

To read a disk file, TACL discards the data in prompt_var, 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

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

TACL continues executing code; when you are ready to wait for completion of the

read operation, use the #WAIT built-in function to wait until read_var contains

data. To avoid writing over data that has not yet been transmitted, use #WAIT to

make sure the previous operation has finished.

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

the variables associated with the file; for example:

#REQUESTER CLOSE error_var

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

#REQUESTER function.

Use the routine in Figure 4-2, nowaited_read, to perform nowaited reads from the

file specified in the first argument in the invocation and display the records on the

terminal. To invoke this routine, load the file and type:

nowaited_read

filename

HP TACL User Manual

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