Re: File Descriptor and readLine() difficulties

Thanks Adam, that does help.

It sounds like for this interface I'm going to have to have the router job call the handling programs passing the first line of data, or I'm just going to have to prototype the IFS APIs and deal with the files directly.

Thanks for the explanation.

Wiley Ammons
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Wiley.Ammons@xxxxxxxxxxxxx

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AGlauser@xxxxxxxxxxxx wrote:

Wiley Ammons wrote on 29/06/2007 14:32:26:

I have prototyped open and close and I am using Scott's readline

almost

verbatim as an external procedure to my program. I have an interface
process that determines the type of message I have received by

reading the

header inside each file. There is a group of 3 programs that read the

list

of files, and then opens each file to see if it should process them.

The problem I am facing is that when I open, readline and close an

IFS

file in the first program, subsequent programs called by the same

parent

process open the same file and get line 2 of the file instead of line

1

like that first program. They therefore never process the

transaction. Any

help would be appreciated, thanks for your time.

The readline in the form you have it is limited to handling one file at a time, and it is not designed to partially read a file, and then re-read it from the beginning. It helps to understand that readline is in a sense 'virtualizing' access to the file. One of the main benefits of readline() is that it reads data in chunks from the file, in order to maximize I/O performance.

If it helps, here is my copy of readline:

//ReadLine - Get a line at a time from an IFS file
P $_readline B export
D $_readline PI 10I 0
D fd 10I 0 value
D text * value
D maxlen 10I 0 value

D rdbuf S 1024A static
D rdpos S 10I 0 static
D rdlen S 10I 0 static

Note the use of the 'static' keyword. That means that these variables retain their values across calls to this procedure within a given activation group. Also note that the buffer is is 1kB in size.

D p_retstr S *
D RetStr S 32766A based(p_retstr)
D len S 10I 0

c eval len = 0
c eval p_retstr = text
c eval %subst(RetStr:1:MaxLen) = *blanks
c dow 1=1
C* Load the buffer
c if rdpos>=rdlen

I'm guessing that your first line (the file header) is less than 1 kB long. Suppose your file is 2 kB long and the first line is 256 bytes long. Then, after reading the first line in program 1, you call this routine from program 2. When you hit this line, rdpos = 256, and rdlen = 1024. Therefore, we don't read from the file again, and just continue processing what is left in the buffer.

Hope this helps,
Adam

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