User`s guide

program can loop and use these operations repeatedly until a successful read is completed or
until some other error is received.
The disk devices do not recognize no-wait mode on input and treat such requests as normal
input-with-wait requests.
Output Wait Modes
Normally, V+ waits for each I/O operation to be completed before continuing to the next
program instruction. For example, the instruction:
TYPE /X50
causes V+ to wait for the entire record of 50 spaces to be transmitted (about 50 milliseconds
with the terminal set to 9600 baud) before continuing to the next program instruction.
Similarly, WRITE instructions to serial lines or disk files will wait for any required physical
output to complete before continuing.
This waiting is not performed if the /N (no wait) format control is specified in an output
instruction. Instead, V+ immediately executes the next instruction. The IOSTAT function
checks whether or not the output has completed. It returns a value of zero if the previous
I/O is not complete.
If a second output instruction for a particular LUN is encountered before the first no-wait
operation has completed, the second instruction automatically waits until the first is done.
This scheme means the no-wait output is effectively double-buffered. If an error occurs in
the first operation, the second operation is canceled, and the IOSTAT value is correct for the
first operation.
With V+, the IOSTAT function can be used with a second argument of 3 to explicitly check for
the completion of a no-wait write.
Serial and Disk I/O Basics
(Undefined variable: Primary.Product_Name_V)Language User's Guide, version
17.x
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