Subj : Re: Can C++ local static objects be made thread safe?
To   : comp.programming.threads
From : Marcin 'Qrczak' Kowalczyk
Date : Sat Feb 05 2005 12:30 am

Giancarlo Niccolai <searchforme@ingoogle.com> writes:

>>> Suppose that read_unicode_database_from_file() requires ANOTHER static
>>> initializer, or is replaced in the MT code with something different. In
>>> example, suppose that read_unicode_database_from_file() requires a locked
>>> variable to be prepared by the thread that calls
>>> lookup_unicode_char_by_name(). Then, chances are that
>>> read_unicode_database_from_file() will deadlock.
>> 
>> If there was a cyclic dependency between local static objects, then the
>> library would have been already broken in a single-threaded environment.
>
> The cyclic dependency is introduced in MT code; ST code cannot have cyclic
> dependency.

If you introduced a cyclic dependency, you broke the code, and it has
nothing to do with making initialization of static local objects
thread-aware.

Please show how it's broken when thread local static objects are
initialized in a thread-aware way, and at the same time it works when
they are initialized using an traditional guard variable.

> In example, are you really sure that it's a "smart" programming technique to
> open and setup a database environment as a by-product of a very commonly
> used routine? How will you manage errors? With try-catches? are you really
> sure you want to try-catch all your access to a unicode-translation
> functions to prevent a lazy initialization failure to abort your program?

This has nothing to do with MT. If you don't like static local
variables with non-trivial initialization, don't use them, but why do
you advocate a broken semantics of these variables when they are used
in multiple threads?

> I repeat myself, but you are trying to solve an unexisting problem;
> correctly built MT programs just works another way, and ST programs going
> MT just must be redesigned in some area;

Not all programs must be redesigned. There is a chance that making
initialization of local static objects thread-aware is the only thing
needed to make them working.

-- 
   __("<         Marcin Kowalczyk
   \__/       qrczak@knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/

.