[development] problems with shutdown function in search module

[Khalid Baheyeldin]

> I am not sure I understand the problem.
> If you want to make sure only one process runs at a time, we can use a
> locking
> mechanism like I do in one module:
>
> Making sure we get the lock prevents a race condition, a problem that make
> poormanscron.module currently unuseable (see link in code comment).
>
> /**
> * Implementation of hook_cron().
> */
> function hook_cron() {
>   // Check if we have another instance of cron running.
>   if (variable_get('hook_cron_running', 0)) {
>     return;
>   }
>   // hook_cron is not already running.
>   // See if we can get the lock before another process does.
>   // Algorithm found here: http://drupal.org/node/43511.
>   $result = db_query("UPDATE {variable} SET value = 'i:1;' WHERE name =
> 'hook_cron_running' AND value = 'i:0;'");
>   if (db_affected_rows() != 1) {
>     // We didn't get the lock. Another process outran us.
>     watchdog('hook_cron', 'This cron process was outraced.');
>     return;
>   }
>   // Do stuff here...
>
>   // then, at the end:
>   // Unlock.
>   variable_set('hook_cron_running', 0);
>   return;
> }
>

Wouldn't the second process be blocked until the first one completes,
instead
of returning immediately? There is no equivalent to Oracle's NOWAIT in MySQL
as far as I recall.
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