This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
Is a compiler allowed to interleave constructor calls when performing dynamic initialization of nonlocal objects? What I mean by interleaving is: beginning to execute a particular constructor, then going off and doing something else, then going back to the original constructor. I can't find anything explicit about this in 18.104.22.168 [basic.start.static].
I'll present a few different examples, some of which get a bit wild. But a lot of what this comes down to is exactly what the standard means when it talks about the order of initialization. If it says that some object x must be initialized before a particular event takes place, does that mean that x's constructor must be entered before that event, or does it mean that it must be exited before that event? If object x must be initialized before object y, does that mean that x's constructor must exit before y's constructor is entered?
(The answer to that question might just be common sense, but I couldn't find an answer in 22.214.171.124 [basic.start.static]. Actually, when I read 126.96.36.199 [basic.start.static] carefully, I find there are a lot of things I took for granted that aren't there.)
OK, so a few specific scenerios.
<runtime gunk> <Enter A's constructor> <Enter f> <runtime gunk> <Enter B's constructor> <Enter f> <Leave f> <Leave B's constructor> <Leave f> <Leave A's constructor>The implication of a 'yes' answer for users is that any function called by a constructor, directly or indirectly, must be reentrant.
At this point, you might be thinking we could avoid all of this nonsense by removing compilers' freedom to defer initialization until after the beginning of main(). I'd resist that, for two reasons. First, it would be a huge change to make after the standard has been out. Second, that freedom is necessary if we want to have support for dynamic libraries. I realize we don't yet say anything about dynamic libraries, but I'd hate to make decisions that would make such support even harder.