On Mon, Sep 24, 2018 at 10:18 PM Janne Blomqvist <blomqvist.ja...@gmail.com> wrote:
> On Mon, Sep 24, 2018 at 7:48 PM Thomas Koenig <tkoe...@netcologne.de> > wrote: > >> Hi Janne, >> >> > libgfortran has a recursion check in the error handling paths. This >> > works by checking the value of a static variable, and if it matches, >> > aborting immediately instead of continuing error processing. >> > Unfortunately, in a multi-threaded program, if two threads report an >> > error at the same time, this can trigger this check, and thus the >> > underlying reason for the error is never reported. >> >> I agree that this is a problem that should be addressed. Hm... >> >> What do you think, would it be desirable / possible to keep the >> recursive error check, but ensure thread safety by a suitable >> locking mechanism? As a first step, we should probably specify >> what exactly we would like to happen. >> >> Let us assume that the aim is to keep the current behavior for normal >> processes and allow concurrent error processing for multiple threads. >> >> This could be done by making the static variable thread-local. >> I'm not sure that this would work reliably, or if some sort of >> locking mechanism (probably involving PTHREAD_MUTEX_RECURSIVE) >> would be required - only have one thread at a time process >> an error. >> >> Do we actually want to keep the current behavior for non-threaded >> programs? I'd be in favor, but I do not feel strongly about that. >> > > What I briefly was thinking about doing, was to use TLS. Or rather, since > TLS is not supported on all targets, something like I did in > intrinsics/random.c:get_rand_state(). But, since the error handling stuff > should be async-signal-safe, the allocation in the setup path should be > done separately, e.g. as part of library initialization. > > In the end I decided against it because > > 1) It's more complicated, in order to handle a quite unlikely edge case. > > 2) If recursion happens anyway, it's a bug in our error handling flow > which should be fixed and not be papered over. > > Anyway, I'm not massively against this, if people have any particular > opinion lets hear it. > PING! Any opinions on the above? -- Janne Blomqvist
