[fpc-devel] volatile variables

[Nikolai Zhubr]

28.06.2011 19:42, Hans-Peter Diettrich wrote:
> Jonas Maebe schrieb:
>
>>> 2.) Blocking access as described in 4.11 does not address execution
>>> order.
>>
>> It does guarantee that if T1 locks the mutex, changes the value,
>> unlocks the mutex [...]
>
> Can you explain please, to what "changes the value" applies?
To some variable, not explicitly named here, but not to the mutex.

>
> I could not find a definition of the mutex struct, to determine whether
> it contains any user-alterable values. When "the value" is declared
> outside the mutex struct, it will be accessible also *without* locking
> the mutex first.
A mutex is usually treated as opaque. It is only used when 
entering/leaving critical section, not for storing any user-accessible data.

>
> However I can imagine that some mutex derived *class* (TCriticalSection)
> can have additional fields, that are inaccessible until some code
> obtains the mutex (similar to TThreadList). Otherwise a mutex cannot
> protect anything but itself.
It is responsibility of a programmer to ensure that all accesses to the 
variable in question is surrounded by proper enter/leave constructs 
involving some mutex. Such proper constructs are not enforced by pascal 
language automatically (like say in java), so mistakes are quite 
possible (and sometimes do happen).

Nikolai

>
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