[OSM-dev] [Tile-serving] mod_tile causes segfault on debian 7.0

[Tom Hughes]

On 22/05/13 17:47, Kai Krueger wrote:

> So, unless you are using the memcached backend, this commit in theory
> should be fine and I have done a bunch of load testing with ab to
> confirm this. (Although limited ab testing can't properly simulate real
> world load). I'll have another look through the file system backend, if
> I can see anything that might be thread unsafe.

I can...

The call to get_storage_backend comes from the translate_name hook which 
I believe is called for each request. If the stores array does not exist 
yet then it will try to create it by allocating from a memory pool that 
is shared by all threads in that process.

So if a new child is started, and multiple requests arrive more or less 
simultaneously to different threads in that process, then they will both 
try and allocate the stores array which means they will both be trying 
to manipulate the memory pool at the same time.

Tom

-- 
Tom Hughes (tom at compton.nu)
http://compton.nu/