Re: C++ fluency
On May 9, 4:00 pm, Jerry Coffin <jcof...@taeus.com> wrote:
In article <dc701cc4-c712-4c50-b357-
2e6a2cbdc...@o30g2000vbc.googlegroups.com>, james.ka...@gmail.com
says...
[ ... ]
Except that they don't. They define policies, but they
certainly don't allow you to control exactly when the context
swaps occur.
It's certainly possible to do so in Windows, and I'm pretty
sure it is in (at least most) UNIX as well. It's decidedly
non-trivial though. To do it in Windows, you turn your test
harness into a real debugger -- i.e. you set breakpoints in
the client code and use those to give you control over the
relative order of code execution.
On the face of it, that sounds fairly complex, but in reality
it's really much worse. The problem is that the test harness
needs knowledge of the client code to ensure that it doesn't
force a context switch at a time that it couldn't happen under
normal circumstances. For example, it has to track all usage
of critical sections, to be able to force context switches
between threads that don't depend on the same critical
section, but ensure against context switches among threads
that do depend on the same critical section.
In short, before you have a working test harness, you've
duplicated a large part of the functionality of a complete
multitasking operating system. Worse, there's almost no real
scaling factor -- which is to say that the test harness is
tremendously huge and complex even if the code under test is
tiny.
I'm sure that if you're willing to write a complete OS (or just
the kernel, if you have some means of using the rest of an
existing OS with your kernel), it could be done. I'm just
unaware of any existing package or tool which does it. (And as
you say, it's a bit too much to integrate into the debugging of
a single application, if no tool exists.)
It's an interesting thought, however, because if you do have
access to the kernel (because, say, you're Microsoft, or you're
working on the Linux kernel), it shouldn't be that hard to add
some sort of controls which would support it. (I'd guess, here,
the most difficult part would be specifying exactly what the
interface should be.)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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