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Two simple php questions

Hello,
      i have two simple php questions. 1) I am uploading images and rename each image file to numbers by using time () function.. images name become like this 1162411085.jpg... my question is that what if 100 people are trying to upload files simultaneously... will this cause to upload error? i think php server is multi threaded so it can take many requests at once.

second question.. i am not quite professional in php.. just switched to php.. i want to track members and guests online on the website.. in asp there is an object Application where we store this kind of information in global.asa.. is there anything similiar in php too?

Thanks
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frontpor
Asked:
frontpor
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2 Solutions
 
Raynard7Commented:
Hi,

For your first question if you have that many simultanious people trying to upload you may have conflicts.  You could get around this by trying to add the current time to a database - and if it is successfully added you can use that as the file name, otherwise you try again until a unique time is generated.  Alternativley you could append the user's name or another id to the file meaning that you should not get duplicates.

For the second option if you use the $_SESSION array (started with session_start() ) this stores information for the person who is logged in.  If you wanted to track who was online you would need to pass the information for each logged in / guest to a database or repository that you could then query when you load your pages.
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neorushCommented:

You could very well have some problems, as two iamges could be saved in the same second......just use microseconds....

$micro_time = substr(microtime(), 2, 6);
$filename = time().'.'.$micro_time.'.jpg';
echo $filename;

I'll admit this could under a very odd circumstance this could still be a problem. So you could do something like use an md5hash of the user (orginal) filename, plus this time thing....that should make it so there isn't a problem for sure

$filename = md5($_FILES["form_file_name"]["name"]);
$micro_time = substr(microtime(), 2, 6);
$filename = $filename.'.'.time().'.'.$micro_time.'.jpg';
echo $filename;
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neorushCommented:
oh and to answer the session question a little better:

<?PHP

//start save user data....
if(!isset($_SESSION)){
   session_start();
}

if(!isset($_SESSION["username"])){
   $_SESSION["username"] = 'CurrentUsername';
}

echo $_SESSION["username"];

?>

<?PHP

//if you just need to get the user data back ....
if(!isset($_SESSION)){
   session_start();
}
echo $_SESSION["username"];

?>
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frontporAuthor Commented:
neorush dont you think this will be a very long name?
$filename = md5($_FILES["form_file_name"]["name"]);
$micro_time = substr(microtime(), 2, 6);
$filename = $filename.'.'.time().'.'.$micro_time.'.jpg';
echo $filename;

i think it would be best to attach id with microsecond.. id is always unique..

my second question was how will get online members and guests number.. when my site starts i start a session.. do i need to add a counter?
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Raynard7Commented:
I think there should be a split betwen neorush and myself
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