Accessing the Zend Application Bootstrap _init Functions After Bootstrapping

Question

I have written a Zend Framework based cron service for parallel tasks, and ran into issues with the child threads sharing resources with the parent . I solved the database connection issue , but I'm now seeing periodic issues with Zend_Db_Table_Abstract failing to save table metadata to metadata cache.

Failed saving metadata to metadataCache

I initialize the metadata cache during bootstrap. Rather than copying my code from the bootstrap and executing after forking, I thought that it might be better to call the Bootstrap->_init[...] functions by using $application->bootstrap('[...]') .

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UPDATE

Because Zend_Controller_Front::getInstance() is a Singleton, using it to get the bootstrap instance and call the functions that way returns me to the same issue with shared resources that I had already resolved.

I want to somehow keep this DRY while avoiding the issues with shared resources after forking.

Answer 1

The Zend_Controller_Front Singleton holds an instance of your bootstrap

$bootstrap = Zend_Controller_Front::getInstance()->getParam('bootstrap');
$bootstrap->bootstrap('db')

Answer 2

Zend_Controller_Front is singleton, but its constructor is protected, so you can extend that simply by creating a class called, App_Controller_Front

in that create a method for getNewInstance(), which can call constructor without checking for existence. This way you can override the singleton behavior.

Answer 3

You are 'forking' these parallel processes not with pcntl_fork, but just by running them multiple times via your crobjob, correct? That would imply that they are running as separate processes from each other, and the only shared resources (and subsequent conflicts) are system resources (especially files).

The error you're seeing could be caused on any number of things related to the files that the cache is being written to. For instance, you might see that error if the metadata file is locked by another one of your processes, a problem which might not show up until the number of parallel processes you are running is quite high.

That error can also arise when the metadata cache file can't be written to for other reasons, such as the partition it is on is out of disk space or the file permissions aren't set correctly.

Perhaps you could you elaborate more on how you have configured your metadata cache and how your script parallelization works. Also, what version of Zend Framework are you running?

Answer 4

Why each child thread reads config, caches db metadata, etc.? Use a master/worker hierarchy. Common idea:

$pid = pcntl_fork();

if ($pid == -1) {        
    // Fork failed            
    exit(1); 
} elseif ($pid) { 
    // We are the parent 
    // prepare common data, cache it, etc.
} else { 
    // We are the child 
    // create new db connection, use cached data
    // if there is no data in cache yet - sleep
    exit(0); 
}