On 6 May 2018 at 19:42, Duy Nguyen <pclouds@xxxxxxxxx> wrote: > On Sun, May 6, 2018 at 7:26 PM, Duy Nguyen <pclouds@xxxxxxxxx> wrote: >> On Sun, May 6, 2018 at 4:10 PM, Martin Ågren <martin.agren@xxxxxxxxx> wrote: >>> These `struct lock_file`s are local to their respective functions and we >>> can drop their staticness. >>> - static struct lock_file lock; >>> + struct lock_file lock = LOCK_INIT; >> >> Is it really safe to do this? I vaguely remember something about >> (global) linked list and signal handling which could trigger any time >> and probably at atexit() time too (i.e. die()). You don't want to >> depend on stack-based variables in that case. > > So I dug in a bit more about this. The original implementation does > not allow stack-based lock files at all in 415e96c8b7 ([PATCH] > Implement git-checkout-cache -u to update stat information in the > cache. - 2005-05-15). The situation has changed since 422a21c6a0 > (tempfile: remove deactivated list entries - 2017-09-05). At the end > of that second commit, Jeff mentioned "We can clean them up > individually" which I guess is what these patches do. Though I do not > know if we need to make sure to call "release" function or something/ > Either way you need more explanation and assurance than just "we can > drop their staticness" in the commit mesage. Thank you Duy for your comments. How about I write the commit message like so: After 076aa2cbd (tempfile: auto-allocate tempfiles on heap, 2017-09-05), we can have lockfiles on the stack. These `struct lock_file`s are local to their respective functions and we can drop their staticness. Each of these users either commits or rolls back the lock in every codepath, with these possible exceptions: * We bail using a call to `die()` or `exit()`. The lock will be cleaned up automatically. * We return early from a function `cmd_foo()` in builtin/, i.e., we are just about to exit. The lock will be cleaned up automatically. If I have missed some codepath where we do not exit, yet leave a locked lock around, that was so also before this patch. If we would later re-enter the same function, then before this patch, we would be retaking a lock for the very same `struct lock_file`, which feels awkward, but to the best of my reading has well-defined behavior. Whereas after this patch, we would attempt to take the lock with a completely fresh `struct lock_file`. In both cases, the result would simply be that the lock can not be taken, which is a situation we already handle.