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Posted by Jim Michaels on 04/24/06 01:50
"Gordon Burditt" <gordonb.a2nrk@burditt.org> wrote in message
news:124mac1o4mf8f6d@corp.supernews.com...
>>> >I need to generate 2 random numbers in rapid sequence from either PHP
>>> >or
>>>>mysql.
>>>
>>> Same page hit or different page hits? I cannot explain why you
>>> would get the same number in rapid sequence from several calls on
>>> the same hit.
>>
>>
>>same page hit on the webserver to a .html file, which has 2 <img
>>src=img.php> elements.
>>on a multiprocessor webserver, this may be occurring simultaneously.
>
this is essentially what I had before I switched over to something that I
found out later only works on NS :-/
<?php
function makeThumbnail($o_file, /*$t_ht = 150*/$t_wd=150) {
$image_info = getimagesize($o_file); // see EXIF for faster way
switch ($image_info['mime']) {
case 'image/gif':
if (imagetypes() & IMG_GIF) { // not the same as IMAGETYPE
$o_im = imagecreatefromgif($o_file) ;
} else {
$ermsg = 'GIF images are not supported<br />';
}
break;
case 'image/jpeg':
if (imagetypes() & IMG_JPG) {
$o_im = imagecreatefromjpeg($o_file) ;
} else {
$ermsg = 'JPEG images are not supported<br />';
}
break;
case 'image/png':
if (imagetypes() & IMG_PNG) {
$o_im = imagecreatefrompng($o_file) ;
} else {
$ermsg = 'PNG images are not supported<br />';
}
break;
case 'image/wbmp':
if (imagetypes() & IMG_WBMP) {
$o_im = imagecreatefromwbmp($o_file) ;
} else {
$ermsg = 'WBMP images are not supported<br />';
}
break;
default:
$ermsg = $image_info['mime'].' images are not supported<br />';
break;
}
if (!isset($ermsg)) {
$o_wd = imagesx($o_im) ;
$o_ht = imagesy($o_im) ;
// thumbnail width = target * original width / original height
//$t_wd = round($o_wd * $t_ht / $o_ht) ;
$t_ht = round($o_ht * $t_wd / $o_wd);
$t_im = imagecreatetruecolor($t_wd,$t_ht);
imagecopyresampled($t_im, $o_im, 0, 0, 0, 0, $t_wd, $t_ht, $o_wd,
$o_ht);
imagejpeg($t_im); //output to browser
imagedestroy($o_im);
imagedestroy($t_im);
}
return isset($ermsg)?$ermsg:NULL;
}
function make_seed()
{
list($usec, $sec) = explode(' ', microtime());
return (float) $sec + ((float) $usec * 100000);
}
//get next row from pictures table since we can't do random
$q2=mysql_query("SELECT pictures.pid AS pid
FROM pictures,idx
WHERE pictures.pid>idx.pid
LIMIT 1", $link2);
if ($row2=mysql_fetch_assoc($q2)) {
mysql_query("UPDATE idx SET pid=$row2[pid]", $link2);
$n=$row2['pid'];
} else { //reached end of table. wrap to beginning.
mysql_query("UPDATE idx SET pid=1", $link2);
$n=1;
}
mysql_free_result($q2);
//try random anyway. overwrite results of "nextrow".
$q3=mysql_query("SELECT MAX(pid) AS a FROM cpg133_pictures", $link2);
if ($row=mysql_fetch_assoc($q3)) {
//tried commenting out the line below. no difference.
mt_srand(make_seed()+getmypid()/*+$_SERVER['UNIQUE_ID']*/);
$n=mt_rand(1,$row['a']);
//$n=rand(1,$row['a']); //for some reason, causes code to break
}
mysql_free_result($q3);
$result = mysql_query("SELECT filepath,filename,pwidth,pheight FROM pictures
WHERE pid=$n", $link2);
if ($row = mysql_fetch_assoc($result)) {
//determine mime type from extension on filename
$ext=strrchr($row['filename'],'.');
switch($ext){
case '.jp2':
case '.jpg':
case '.jpeg':
default: $mimetype='image/jpeg';break;
case '.gif': $mimetype='image/gif';break;
case '.png': $mimetype='image/x-png';break;
}
$fname=$_SERVER['DOCUMENT_ROOT'] . '/pix/' . $row['filepath'] .
$row['filename'];
}
mysql_free_result($result);
mysql_close($link2);
if (isset($_GET['width'])) {
makeThumbnail($fname, $_GET['width']);
} else {
makeThumbnail($fname);
}
?>
//example: <img src="img.php?width=150" width=150>
> Show the code for generating the two <img src= tags. Since PHP is
> a procedural and uni-tasking (within any page, unless you start
> calling fork()) language, these should NOT be done simultaneously,
> even on a multi-processor system, although they might be done fast
> enough that microtime() doesn't advance. Also show all the calls to get
> random numbers and set seeds.
>
IE requests/loads images in series-parallel very rapidly. Have you ever
watched it? That's where it's coming from I think.
> Are you sure you're not seeding twice with the same seed? SEED ONLY ONCE.
>
> Look at the source HTML code. Are you getting:
>
> - the same image number (e.g. 1) all the time?
> - random first image number but the second is always the same as the
> first?
>
>>> Things to use for a seed (jumble them all together, as in concatenate,
>>> then take md5 of result, then convert some of md5 result to integer):
>>> microtime()
>>> getmypid()
>>
>>believe it or not, on these 2 I get the same pictures. frustrating.
>
> Are you running Apache 2.0? It may be using threads instead of
> processes, even for PHP. Is PHP even supposed to work with Apache
> 2.0 yet? On a multiprocessor system?
>
>>> $_SERVER['UNIQUE_ID'] (Apache only, and may need a module turned on)
>>
>>Don't think I have that option. sure sounds good though.
>
> The module name is mod_unique_id.
>
>>
>>> $_SERVER['REMOTE_ADDR']
>>> $_SERVER['REMOTE_PORT']
>>
>>these two won't make it unique, because both images are going to be all on
>>the same page.
>> mt_srand(make_seed()+getmypid()+$_SERVER['UNIQUE_ID']);
>> $n=mt_rand(1,$row['a']);
>
> Show me the code to generate the SECOND id. You don't repeat both
> of those lines of code, do you? SEED ONLY ONCE!
>
>>tried this, but still doesn't do it. I don't even get an error on
>>$_SERVER['UNIQUE_ID']. I think it's NULL. is $_SERVER['UNIQUE_ID'] a
>>string I should hash, or an integer?
>
> It's a string. Try printing it just to see if it's getting set at all.
> If it is getting set, it's probably being interpreted as the integer 0
> because you're trying to use it as a number.
>
> Please verify your code:
>
> 1) There is at most one call to microtime() in any of the files used
> by this page. This call is NOT inside a function. More specifically,
> this call is NOT inside make_seed(). Delete that function and
> expand it in line (ONCE) if desired.
> 2) There is at most one call to any function to set a seed (srand,
> mt_srand). This call is NOT inside a function.
>
> Gordon L. Burditt
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