Re: c++ static initialization

["Hill, Bruce" <bhill@slac.stanford.edu>]

Good points, Ben.   I concur.

- Bruce

----- Reply message -----
From: "Benjamin Franksen" <benjamin.franksen@helmholtz-berlin.de>
Date: Tue, Aug 9, 2011 3:25 pm
Subject: c++ static initialization
To: "core-talk@aps.anl.gov" <core-talk@aps.anl.gov>

Hi Jeff

you asked for opinions, here is mine:

Am Dienstag, 9. August 2011, um 22:42:37 schrieb Jeff Hill:
> Ref: http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.14
>
> Of course C++ is really different from C in that some significant code can
> run during static initialization. The above FAQ mentions how to avoid some
> really serious issues. All of this is pretty common knowledge, but one has
> to be careful, and I have definitely seen this bug biting in EPICS base
> before.

(1) Static objects should be avoided wherever possible.

(2) If static objects are used, the constructor should be trivial, i.e. not
perform anything except setting members to default values.

(3) Non-trivial initialization for complex objects should be done in a regular
method either lazily ("Construct On First Use") or by an explicit call from
some startup routine. The latter has the advantage of a well-defined order of
initialization; the former is sometimes more convenient.

> However there is still a related issue which should be well understood; not
> everyone agrees if threads should be started during C++ static
> initialization or not.

(4) Starting threads inside static initialization is a bad idea and should not
be allowed (see rule 2).

> If multiple threads are running during c++ static
> initialization then the solution in the above FAQ doesn't apply and the
> only solution is epicsThreadOnce,

(5) epicsThreadOnce should also be avoided wherever possible. Using it means
objects cannot be freely passed between threads which is detriment to
composability.

Cheers
Ben

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