Using posix timers "timer_tracker" as base class for timerfd was flawed.
Posix timers are not inherited by child processes and don't survive
execve. The method used by posix timers didn't allow to share timers
between processes. The timers were still per-process timers and worked
entirely separate from each other. Reading from these timers via
different descriptors was only synchronized within the same process.
This does not reflect the timerfd semantics in Linux: The per-file
timers can be dup'ed and survive fork and execve. They are still just
descriptors pointing to the same timer object originally created by
timerfd_create. Synchronization is performed between all descriptor
instances of the same timer, system-wide.
Thus, reimplement timerfd using a timer instance in shared memory,
a kernel timer, and a handful of sync objects.
Every process maintains a per-process timerfd struct on the cygheap
maintaining a per-process thread. Every process sharing the same
timerfd will run this thread checking the state of the timer, similar
to the posix timer thread, just working on the shared objects and
synchronizing its job with each other thread.
Drop the timerfd implementation in the posix timer code and move the
public API to fhandler_timerfd.c. Keep the ttstart timer_tracker
anchor out of "NO_COPY" since the fixup_after_fork code should run to
avoid memory leakage.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
Linux returns EINVAL, "fd is attached to an object which is unsuitable
for writing". If we don't handle write locally, write returns EBADF.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
- Puzzeling: Commit ec98d19a08c2e4678e8a6f40fea0c9bbeaa4a2c7
changed ttstart to NO_COPY but kept all the code to handle
fixup after fork. Revert to not-NO_COPY and make timerfd
fork work.
- On fixup_after_fork, keep timerfd timers and restart thread
if they were armed in the parent.
- Move timerfd timer_trackers to cygheap. Overload timer_tracker
new and delete methods to handle timers accordingly. This is not
exactly required for fork, but exec will be grateful.
- Give up on TFD_TIMER_CANCEL_ON_SET for now. There's no easy way
to recognize a discontinuous change in a clock.
- Be paranoid when cleaning out ttstart.
- Fix some minor issues.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
First cut of a timerfd implementation.
Still TODO:
- fork/exec semantics
- timerfd_settime TFD_TIMER_CANCEL_ON_SET flag
- ioctl(TFD_IOC_SET_TICKS)
- bug fixes
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
