wp_cache_init() and WP_Object_Cache constructor has a memory leak

[MikeSchinkel]

When calling wp_cache_init() repeated in unit testing the WP_Object_Cache::contruct() repeatedly registers 'destruct' as a shutdown function, and each time it does it leaks memory.

There is a @todo comment above the register_shutdown_hook() that says the following so I would assume that this is no longer needed and we could just delete the line with the register_shutdown_hook()?

This should be moved to the PHP4 style constructor, PHP5 already calls destruct()

I will upload a patch to delete the list, and a different patch to only call register_shutdown_hook() once, depending on what is appropriate.

[MikeSchinkel]

This patch removes the call to register_shutdown_function().

[MikeSchinkel]

This patch restricts the call to register_shutdown_function() to be called only once.

[ayeshrajans]

The destructor simply returns true and doesn't clean up anything that could've prevented the said memory leak. Even the oldest state of cache.php file I could find (​https://github.com/WordPress/wordpress-develop/blob/b43712e0f79a9f5bea52217e06155e2f471c490c/src/wp-includes/cache.php, oldest checkout available 5 years ago) has the exact same code. I'm pretty sure this is dead code, which we should probably remove from the root.

With the __destruct and shut down function registration removed, the test suite still passes: ​https://travis-ci.org/Ayesh/wordpress-develop/builds/396071330

I will attach the patch for reference.

With the patch applied, PHP 7.1 test suite completed the execution and memory usage statistics from PHPUnit are identical when compared to a Travis results before the patch (​https://travis-ci.org/Ayesh/wordpress-develop/jobs/396068504)

[ayeshrajans]

Completely removes the dead __destruct and register_shutdown_function call.

[pbearne]

I can't find the code that is to be removed in the code
So suspect it has been fixed
Can I close it?