Simon Marlow ha scritto:
Manlio Perillo wrote:
I have some doubts about errno handling in a Concurrent Haskell program.
Let's suppose that GHC non threaded runtime is used, so that each Haskell thread is bound to an OS thread.
Let's suppose there are two threads running (`A` and `B`). Thread `A` calls a function `f`, that, in turn, calls via FFI a C function `c_f`.
Function `c_f` fails, settings errno; however the GHC scheduler suspends execution of thread `A` and switch to thread `B`, before the current value of errno is read.
Now, let's suppose thread `B` calls a function `g`, that, in turn, calls via FFI a C function `c_g`. Function `c_g`, too, fails, setting errno.
Is this possible?
It's safe, we save the value of errno when a Haskell thread is descheduled, and restore it when it is scheduled again. We do the same on Windows for GetLastError().
Thanks. I was just replying to the message, after having read the code of the scheduler. Manlio Perillo