Re: MT Design Question
Chris M. Thomasson wrote:
Cross-thread exceptions seem to make things more complex. If you spawn 3
futures, and 2 of them throw, where do all of those exceptions get caught
at?
<pseudo-code>
__________________________________________________________
static unsigned g_exceptions = 0;
try
{
std::future f1 = spawn_task(...);
std::future f2 = spawn_task(...);
std::future f3 = spawn_task(...);
// wait for infinity...
Sleep(INFINITE);
}
catch (future_exception const& e)
{
++g_exceptions;
cout << "caught " << g_exceptions << " exception(s)" << endl;
}
__________________________________________________________
If `f2' and `f3' throw, should the output be:
caught 1 exception(s)
caught 2 exception(s)
? I am confused!
You are. You only get an exception when you call get() on a future that holds
one, so the above code will wait forever (unless one of the spawn_task calls
throws...or the Sleep throws :-}).
To get the result held by f1 (or an exception if it holds one), you'd do
something like this:
try {
auto result = f1.get();
// f1 held a return value, work with it here
}
catch(...) {
// f1 held an exception, handle it here
}
BTW, spawn_task is not part of (draft) C++0x, but std::async is.
Scott
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