Perl Print buffering flush

Question

Hi,

I have the following Perl code:

STDOUT->autoflush(1);

foreach(...)
{
    ...

    foreach(...)
    {
        print("Processing $folder");
        $|=1;
        process($folder);
    }
    ...
}

but the print statement works only in the first iteration of the loop and does not print anything after that. Any idea why?

EDIT: I found the reason and have added it in the answer also. The solution was:

I added the following line inside the loop and it worked:

select STDOUT;

I think the code in process() function should have been modifying the default output buffer. It was a code written by somebody else!

I am not sure if this is a problem with Perl which allows this or the developer who did not change it back to the default.

The final code looked like this:

foreach(...)
{
    ...

    foreach(...)
    {
        select STDOUT;

        print("Processing $folder");
        $|=1;
        process($folder);
    }
    ...
}

Thanks all...

Answer 1

I added the following line inside the loop and it worked:

select STDOUT;

I think the code in process() function should have been modifying the default output buffer. It was a code written by somebody else!

I am not sure if this is a problem with Perl which allows this or the developer who did not change it back to the default.

The final code looked like this:

foreach(...)
{
    ...

    foreach(...)
    {
        select STDOUT;

        print("Processing $folder");
        $|=1;
        process($folder);
    }
    ...
}

Thanks all...

Answer 2

Good detective work in tracking down this problem!

I'd like to suggest an alternate solution.

Rather than having select() wars with the author of process(), you could use the IO::Handle interface to STDOUT:

use IO::Handle;

foreach(...)
{
    ...

    foreach(...)
    {
        STDOUT->printflush("Processing $folder");

        process($folder);
    }
    ...
}