PHP同时生成相同的随机数（以秒为单位）

Question

I'm using random number function in a PHP script while uploading files. Because I wanted to avoid overwrite files with same name. So following is the script potion is used while upload the file.

$filename = rand(0,100000).strtolower($_FILES['file']['name']);
$dir="/file/upload/directory/".$filename;
move_uploaded_file($_FILES["user_file"]["tmp_name"], $dir);

This application expected to have large amount of concurrent users. So QA testing this application with different automated tools by applying high concurrent visit. That point the random number seems generating the same value within the same seconds.

Then we test the random number separately this same random number on same time was clearly identified.

While search on web some post suggest on mt_rand() but still it is same on milli second level.

Is there any way of generating random number in time independent way in PHP?

Answer 1

Random numbers are generated with time. But for this particular issue we need to write few lines of code. If we check for file existence and apply incremental number to the file name it will be a fixed solution. The code can be like follows.

$filename = strtolower($_FILES['file']['name']);
$dir="/file/upload/directory/";
$i = 1;

while(is_file($dir . $i . $filename))
{
   $i++;
}

move_uploaded_file($_FILES["user_file"]["tmp_name"], $dir . $i . $filename);

Even though loop is inefficient. This will make sure the file overwrite won't happen.