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Re: Thread safe logging (or protecting global variables)

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On 09/08/2011 10:00 PM, Jef Driesen wrote:

>>>>> Can I even go one step futher and use simple a simple flag (like the
>>>>> g_loglevel variable above) that can only be modified from the
>>>>> message_set_*() functions, and which is only checked in the message()
>>>>> function but not modified.
>>>>
>>>> Will work on x86, but there is no guarantee it won't break on any other
>>>> CPU or on some new hardware a couple years later.
>>>>
>>>> An atomic would be enough - either the new standard, or find an
>>>> assembly that makes one for the target CPU, a couple of libraries have
>>>> been doing that for a long time. For example, logging libraries.
>>>
>>> I understand (in theory at least) how atomic operations can be used to
>>> protect a single variable like the g_loglevel flag in my example code.
>>> But how does this work (if that's even possible) if the logging state
>>> consists of multiple variables?
>>
>> I do not see why a logging library would need to access atomically
>> a structure containing both log levels and the sink.
>>
>> If you do not care about optimisations (for the 'logging off' case),
>> then you can create a larger structure and make it atomic.
>>
>> Atomics are supported by CPUs up to some size; if larger they need to be
>> emulated, usually by locking a mutex (or a spinlock) and using
>> the data in the structure
>
> Can you explain in a little more detail what you mean here? I'm a little
> lost.

Which part?

The first one and the second one is 'why do you want to do that?'. How
are you going to write your logging framework? With a single level?
With a hierarchy of loggers? Just global structures, or each logger
having a flag?

The third one explains how atomicity is done for many variables -
as long as they can be packed in one structure.

Edek

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Thread

Thread safe logging (or protecting global variables) Jef Driesen <jefdriesen@hotmail.com.invalid> - 2011-09-05 20:19 +0200
  Re: Thread safe logging (or protecting global variables) Edek <edek.pienkowski@gmail.com> - 2011-09-05 20:30 +0200
    Re: Thread safe logging (or protecting global variables) Jef Driesen <jefdriesen@hotmail.com.invalid> - 2011-09-06 18:48 +0200
      Re: Thread safe logging (or protecting global variables) Edek <edek.pienkowski@gmail.com> - 2011-09-07 10:34 +0200
        Re: Thread safe logging (or protecting global variables) Jef Driesen <jefdriesen@hotmail.com.invalid> - 2011-09-08 22:00 +0200
          Re: Thread safe logging (or protecting global variables) Edek <edek.pienkowski@gmail.com> - 2011-09-09 18:13 +0200
            Re: Thread safe logging (or protecting global variables) Jef Driesen <jefdriesen@hotmail.com.invalid> - 2011-09-13 17:58 +0200
              Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-13 13:18 -0700
                Re: Thread safe logging (or protecting global variables) Jef Driesen <jefdriesen@hotmail.com.invalid> - 2011-09-14 07:16 +0200
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-14 13:18 -0700
                Re: Thread safe logging (or protecting global variables) Edek <edek.pienkowski@gmail.com> - 2011-09-14 09:33 +0200
                Re: Thread safe logging (or protecting global variables) Alexander Terekhov <terekhov@web.de> - 2011-09-14 13:17 +0200
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-14 13:03 -0700
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-14 13:19 -0700
                Re: Thread safe logging (or protecting global variables) "James" <no@spam.invalid> - 2011-09-14 19:19 -0700
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-14 21:03 -0700
                Re: Thread safe logging (or protecting global variables) Alexander Terekhov <terekhov@web.de> - 2011-09-15 13:12 +0200
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-15 12:24 -0700
                Re: Thread safe logging (or protecting global variables) Alexander Terekhov <terekhov@web.de> - 2011-09-15 22:22 +0200
                Re: Thread safe logging (or protecting global variables) "James" <no@spam.invalid> - 2011-09-15 13:33 -0700
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-15 15:36 -0700
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-15 15:36 -0700
                Re: Thread safe logging (or protecting global variables) Alexander Terekhov <terekhov@web.de> - 2011-09-16 16:28 +0200
                Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-16 15:06 -0700
                Re: Thread safe logging (or protecting global variables) Alexander Terekhov <terekhov@web.de> - 2011-09-17 12:50 +0200
                Re: Thread safe logging (or protecting global variables) Alexander Terekhov <terekhov@web.de> - 2011-09-15 12:50 +0200
              Re: Thread safe logging (or protecting global variables) Edek <edek.pienkowski@gmail.com> - 2011-09-14 09:17 +0200
  Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-08 16:28 -0700
    Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-08 16:33 -0700
      Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-08 20:55 -0700
    Re: Thread safe logging (or protecting global variables) Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-12 00:45 -0700

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