Databases
StackOverflow2013
Postsdbo
PORace Condition in PHP File Writing
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PORace Condition in PHP File Writing
    primarykey
    data
    text
    <p>So I have a script for accepting and processing request from another scripts and/or applications. However, one of the task has to be done with my script is assigning each request a unique, sequential "ID" to each of them.</p> <p>For example, let's says that application A is giving a 1000 request to my script, and in the same time, application B is giving 500 request to my script. I have to give them 1500 unique, sequential number, like 2001~3500 to each of them.</p> <p>The order between them however, does not matter, so I can give them numbers like this :</p> <pre><code>#2001 for 1st request from A (henceforth, A1) #2002 for A2 #2003 for B1 #2004 for A3 #2005 for B2 ...and so on... </code></pre> <p>I've tried creating a file that stores that number and a separated lock file with a function like this :</p> <pre><code>private function get_last_id() { // Check if lock file exists... while (file_exists("LAST_ID_LOCKED")) { // Wait a little bit before checking again usleep(1000); } // Create the lock file touch("LAST_ID_LOCKED"); // Create the ID file for the first time if required if (!file_exists("LAST_ID_INDICATOR")) { file_put_contents("LAST_ID_INDICATOR", 0); } // Get the last ID $last_id = file_get_contents("LAST_ID_INDICATOR"); // Update the last ID file_put_contents("LAST_ID_INDICATOR", $last_id + 1); // Delete the lock file unlink("LAST_ID_LOCKED"); return $last_id; } </code></pre> <p>This code, however, would create a race condition, where if I send them those 1500 request, the last ID will have quite a number missings, (e.g. only reach 3211 instead of 3500).</p> <p>I've also tried using flock like this, but to no avail :</p> <pre><code>private function get_last_id() { $f = fopen("LAST_ID_INDICATOR", "rw"); while (true) { if (flock($f, LOCK_SH)) { $last_id = fread($f, 8192); flock($f, LOCK_UN); fclose($f); break; } usleep($this-&gt;config["waiting_time"]); } $f = fopen("LAST_ID_INDICATOR", "rw"); while (true) { if (flock($f, LOCK_SH)) { $last_id = fread($f, 8192); $last_id++; ftruncate($f, 0); fwrite($f, $last_id); flock($f, LOCK_UN); fclose($f); break; } usleep($this-&gt;config["waiting_time"]); } return $last_id; } </code></pre> <p>So, what else can I do to look for a solution for this situation?</p> <p><strong>Notes:</strong> Due to server limitation, I'm limited to PHP 5.2 without something like semaphores and such.</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USFurunomoe
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COYou could use `uniqid()` function to generate id, it's based of microtime. What is the purpose of the file?
      singulars
      1. PORace Condition in PHP File Writing
      1. USgwillie
    2. COUniqid won't do it, since it's random and I need the number to be sequential. The purpose of the LAST_ID_INDICATOR is simply to store the the last (largest) id number.
      singulars
      1. PORace Condition in PHP File Writing
      1. USFurunomoe
    3. CO,`uniqid()` is not all that random, while not sequential, each call to function will produce id in ascending order. use `hexdec()` to convert to decimal to see what i mean.
      singulars
      1. PORace Condition in PHP File Writing
      1. USgwillie
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload