Description:
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As far as I am aware FastCGI support in APC requires all new PHP processes to be spawned as child processes of the first PHP processes launched by FastCGI. This is not valid when using PHP with FastCGI on IIS as all additional PHP processes are launched as child processes of the IIS process. Some of the detrimental effects this has are;

1) Memory is not shared between PHP processes.

2) As each PHP process stores precompiled scripts in their own memory space, there is potential for a single PHP script to exist in several different caches as PHP processes are not tied to serving all requests for individual scripts. 

3) Memory consumption potential is equal to apc.shm_size multiplied by the number of PHP processes running. 

4) When new PHP processes are launched as load increases they do not benefit from existing cached scripts which can lead to performance issues.

5) When PHP processes are recycled by FastCGI the APC cache tied to this process is lost.

Reproduce code:
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1) Using Windows 2003 operating system install IIS and Microsoft's FastCGI handler (http://www.iis.net/php).

2) Configure FastCGI for use with PHP setting MaxInstances to greater than 1 and MaxRequests to a low number (e.g. 10) to accentuate recycling issue (http://www.iis.net/articles/view.aspx/IIS7/Hosting-Web-Applications/PHP/Using-FastCGI-to-Host-PHP-Applications-on-IIS-6-0-).

3) Configure PHP to use APC extension.

4) Access PHP script while monitoring apc.php to view status of APC cache.


 

Expected result:
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APC to share memory between PHP processes.

Actual result:
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APC does not share memory between PHP processes which not only leads to loaded servers, but also potentially cause associated issues as outlined in description field.