On 10/2/24 9:36 AM, Nick Gearls wrote:
> Am I right that we can call apr_global_mutex_create() with a NULL filename
> and APR_LOCK_DEFAULT?
> In case the underlying locking mechanism needs a filename, it will generate
> one.
> Moreover, if we only support Unix & Windows, the preferred mechanism won't
> use a file at all.
> Is that correct?
Unix is a bit broad. I am not sure what the default mechanism is for each
Unix-style OS. I think for Linux it is indeed not file
based (pthread).
>
> In all cases, we don't have to generate a mktemp name ourselves, it'll be
> done in APR. Right?
Yes. Unless you have a specific requirement to store this file outside of
/tmp/. But if you provide a name be sure that the file
does not exist already. Hence apr_file_mktemp would not be good for creating
such a name because it also creates the file.
Regards
Rüdiger
>
> On 01/10/2024 14:02, Ruediger Pluem wrote:
>> On 10/1/24 9:32 AM, Ervin Hegedüs wrote:
>>> Hi there,
>>>
>>> I hope this is a good forum to ask my question.
>>>
>>> We (mod_security2 developers) use mutex locks. Thiscode snippet was added
>>> recently:
>>>
>>> https://github.com/owasp-modsecurity/ModSecurity/blob/v2/master/apache2/modsecurity.c#L125-L168
>>>
>>> As you can see, we create locks with these functions:
>>>
>>> apr_temp_dir_get()
>>> apr_file_mktemp()
>>> apr_global_mutex_create()
>>>
>>> This wrapper (acquire_global_lock()) works on Linux, but it seems to crash
>>> on FreeBSD:
>>> https://github.com/owasp-modsecurity/ModSecurity/issues/3255
>>>
>>> I did some investigation and I found that after the apr_file_mktemp()
>>> returns with success and the created file name is given to
>>> apr_global_mutex_create() then it removes that.
>>>
>>> In this comment:
>>> https://github.com/owasp-modsecurity/ModSecurity/issues/3255#issuecomment-2383132160
>>> I explained the results (with gdb and truss).
>>>
>>> My question is: what is the expected way to use file mutexes?
>>>
>>> Thanks for your help,
>> Have a look at
>>
>> https://httpd.apache.org/docs/2.4/mod/core.html#mutex
>> https://github.com/apache/httpd/blob/trunk/include/util_mutex.h#L156
>> https://github.com/apache/httpd/blob/trunk/include/util_mutex.h#L181
>>
>> and as example
>>
>> https://github.com/apache/httpd/blob/trunk/modules/ssl/mod_ssl.c#L456
>> https://github.com/apache/httpd/blob/trunk/modules/ssl/ssl_engine_mutex.c#L50
>>
>> If you want to go for an APR only approach keep in mind that the apr methods
>> create the lock file if needed
>> either with the name you specified or they create it in /tmp via
>> apr_file_mktemp
>> It should not exist.
>>
>> See
>>
>> https://github.com/apache/apr/blob/1.7.x/locks/unix/proc_mutex.c#L1051
>> https://github.com/apache/apr/blob/1.7.x/locks/unix/proc_mutex.c#L1200
>>
>>
>> Regards
>>
>> Rüdiger
>>
>
