On Tue, Dec 30, 2014 at 08:55:11PM -0200, Alexandre Oliva wrote: > On Dec 30, 2014, "Carlos O'Donell" <carlos@xxxxxxxxxx> wrote: > > > Note that reetrant functions need not be AS-safe nor MT-safe. > > How? > > I suppose it might depend on the definition of reentrant, but if you can > reenter it in multiple threads, and you can reenter it within a thread > in which it is active (e.g., in a signal handler that may have > interrupted its own execution), then it definitely is reentrant. > > Conversely, if it is reentrant, then you can safely reenter it in > multiple threads (MT-Safe) and within signal handlers (AS-Safe), no? > > > What definition of reentrant could make a function be reentrant without > being both MT- and AS-Safe, or be both MT- and AS-Safe without being > reentrant? > > > I suppose there might be scenarios in which a function doesn't qualify > for AS-Safe because it doesn't support async recursion, but it could > still be reentered by means of (indirect?) recursion safely. However, I > can't see how this could be the case without the function being at least > MT-Safe. It looks like any window that could bring trouble for async > signals would also do so for other threads. Unless... Recursive locks? > Those would avoid trouble for other threads (making the function > MT-Safe), but not for async signals (so AS-Unsafe), and sync recursion > could enable reentrancy while avoid pitfalls that async signals would > bring about and that recursive locks wouldn't aovid. Is this the case > you had in mind? Is it the only one in which a function can be > Reentrant, MT-Safe and AS-Unsafe? > > Can you think of any that is AS-Safe, MT-Unsafe and Reentrant? Anything written without memory barriers but that has proper compiler barriers for AS-safety/reentrancy. > Can you think of any that is AS-Unsafe, MT-Unsafe and Reentrant? Anything written without memory or compiler barriers but that uses global state in a reentrant way. > Can you think of any that is non-Reentrant but that is MT-Safe or > AS-Safe? Non-reentrant but MT-safe: anything with non-recursive locks. Non-reentrant but AS-safe: anything that achieves AS-safety by blocking signals for the duration of the operation or any operation that accesses the same data. Rich -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
