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Date: Thu, 16 Dec 2010 11:28:22 +0300
Lines: 47
Subject: Re: [PHP-DEV] Re: PHP Performance in Apache: Multi-Process vs Multi-Threaded
From: dmda@yandex.ru ("jvlad")

>> No. Php if we talk about php with all its extensions is not threadsafe
>> at
>> all. Many of the extensions allocate static data and inherently
>> non-thread-safe.
>
> PHP is, if compiled with ZTS/TSRM, thread-safe. Some libraries used by
> some extensions might not be thread safe, but basically all "usually"
> used ones are thread-safe. While it is a bit complicated as some
> libraries could either be compiled thread-safe or not or some might be
> not thread-safe on specific systems ... but that's not PHP itself ;-)
>
> johannes
>

Dear Johannes,

I'm not sure why you repeated what I stated in my post. So I'm repeating it 
after you too :)
Yes, php core is developed with threadsafe techniques in mind, some 
extensions are safe too, and some extensions which are using 3rd party 
libraries are definitely not safe.

The only thing I'd kindly ask you to pay more attention to is using 
"usually" word together with "safe" in one sentence. In my opinion they 
should never be used both if we talk about production servers, or at least 
servers where crashes are not welcome.

Just to illustrate the issue with "usually", do you consider openssl, a 
widely used php extension, as a "usually threadsafe" extension?
If you do, please take a look at this page 
http://www.openssl.org/docs/crypto/threads.html and these words in 
particular:

OpenSSL can safely be used in multi-threaded applications provided that at 
least two callback functions are set, locking_function and threadid_func. 
locking_function(int mode, int n, const char *file, int line) is needed to 
perform locking on shared data structures. (Note that OpenSSL uses a number 
of global data structures that will be implicitly shared whenever multiple 
threads use OpenSSL.) Multi-threaded applications will crash at random if it 
is not set


Do you think any locking function is implemented in openssl php extension?

-j