Check if a file exist, report an OK if it does or an error if timeout

Question

Following the good advice on this link: How to keep checking for a file until it exists, then provide a link to it

The loop will never end if the file will never be created. In a perfect system, it should not happen, but if it does how would one exit from that loop?

I have a similar case:

/* More codes above */
  // writing on the file
  $csvfile = $foldername.$date.$version.".csv";
  $csv = fopen( $csvfile, 'w+' );

  foreach ($_POST['lists'] as $pref) {
    fputcsv($csv, $pref, ";");
  }

  // close and wait IO creation
  fclose($csv);
  sleep(1);

  // Running the Java
  $exec = shell_exec("/usr/bin/java -jar $app $csvfile");
  sleep(3);

  $xmlfile = preg_replace('/\\.[^.\\s]{3,4}$/', '.xml', $csvfile);
  if (file_exists("$csvfile") && (file_exists("$xmlfile"))){
      header("Location:index.php?msg");
exit;
      }
      else if (!file_exists("$csvfile")){
          header("Location:index.php?msgf=".basename($csvfile)." creation failed!");
exit;
      }
      else if (!file_exists("$xmlfile")){
          header("Location:index.php?msgf=".basename($xmlfile)." creation failed!");
exit;
      }
      //exit;
} // Just the end
?>

( Yes, bad idea to pass variables in the url.. I got that covered )

I use sleep(N); because I know the java takes short to create the file, same for the csv on the php.

How can I improve the check on the file, to wait the necessary time before reporting the status OK or NOT ok if the file was not created?

well for one thing, you should add `exit;` to each of your headers and the keyword here is "exit". — Funk Forty Niner, Jan 31 '17 at 16:07
@Fred-ii- True, the exit is at the end of the php, just didn't think of pasting it here - I guess I will - Thanks — aPugLife, Jan 31 '17 at 16:07
even though you say it's at the end, header could keep on wanting to execute if they're not added to each header. — Funk Forty Niner, Jan 31 '17 at 16:08
`else if` is unnecessary, it only increases the cyclomatic complexity. Where's your loop? — Gabriel Heming, Jan 31 '17 at 16:16
The code after `shell_exec()` will not execute until the `java` call has completed, so the file has either been created or it failed. — AbraCadaver, Jan 31 '17 at 16:17
@GabrielHeming well that is correct, not good to use many if, would be just a waste of time and resources, and in my case it probably does. I just wrote the first code that got to my mind, I'm still testing it so I probably will fix this too. That's why I was looking for the best loop, this part is to fix — aPugLife, Jan 31 '17 at 16:19
@AbraCadaver if it is true, i don't even need to `sleep();` here. Honestly, I haven't tried with a infinite-java-loop and see when the next php code will be executed. Well, it seems I do not need a loop that check if the file exist, then! — aPugLife, Jan 31 '17 at 16:24

Gabriel Heming · Accepted Answer · 2017-01-31T17:07:37.680

1

After reading your comments, I think "the best loop" isn't a good question to get a better answer.

The linked script just give a good approach when the script expects a file. That script will wait until the file is created or forever (but the creator ensures about the file creation).

Better than that, you could give a particular period to ensure if the file exists or not.

If after the shell_exec the java script didn't create the file (which I think is almost impossible, but is just a thought), you could use a code like above:

$cycles = 0;
while (!($isFileCreated = file_exists($filename)) && $cycles > 1000) { 
    $cycles++;
    usleep(1);
}

if (!$isFileCreated)
{
    //some action
    //throw new RuntimeException("File doesn't exists");
}

//another action

The script above will wait until the file is created or until reach a particular amount of cycles (it's better to call cycles than microseconds, because I can't ensure that each cycle will be execute in one microsecond). The number of cycles can be changed if you need more time.

edited Jan 31 '17 at 17:07

answered Jan 31 '17 at 16:33

Gabriel Heming

1,100
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The file will always be created if the content of the csv will always match the classes wrote in the Java. When A new *someting* will be inserted in the csv and the Java is not ready for that (perhaps an upgrade, I use the marshall class for converting a csv to xml), then the Java will fail and the file won't be created. I am reading your code, clear enough! let me test it (: ps. $cycles is expressed in seconds...? so a timeout of 10 second is better than one of 1000 seconds.. – aPugLife Jan 31 '17 at 16:39
Oh, You're right. I was thinking about `usleep`. It's correct now. `sleep` is in seconds, `usleep` is in micro seconds – Gabriel Heming Jan 31 '17 at 16:42
If you need to use this verification on more than one place, wrap it into a function. – Gabriel Heming Jan 31 '17 at 16:44
Ok let me test it a bit and I'll upvote/comment when i have some results (: thanks! – aPugLife Jan 31 '17 at 16:50
Ok so, im not using usleep because for my needs the sleep is good already, therefore my cicles are not 1000 but reduced to just 5. I only need 5 seconds to know if the file exists or not. the command OR does not work, I thought it was a AND, so I modified it: `while (!($isFileCreated = file_exists($xmlfile)) && $cycles < 5) { $cycles++; sleep(1); }` To be honest, what the comments on my post say are true, `shell_exec()` is released only after the -java- complete its job. So I actually do not need a loop. But I thank you for your code! and if you tell me it is right the `&&` I *** – aPugLife Jan 31 '17 at 17:04
The approach about the usleep, is to give less time between the verification (which is just a measurement). You're right (again) about the conditional operator, it's must be AND. Correct now. – Gabriel Heming Jan 31 '17 at 17:07
Well usleep is probably the best choice because less "time" to wait between seconds. Good job (: – aPugLife Jan 31 '17 at 17:09

Check if a file exist, report an OK if it does or an error if timeout

1 Answers1