waitid() function is required to be cancellable by the standard. The
wait6() and ppoll() follow the other syscalls in their groups.
Reviewed by: jhb, jilles (previous versions)
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Use list for the cancellation points enumeration. Move notes about
functions into the list inline.
The discussion of the idiomatic use of cancellation facilities does
not belong to RETURN VALUES section, move it to NOTES.
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Note that to cancel blocked kevent(2) call, changelist must be empty,
since we cannot cancel a call which already made changes to the
process state. And in reverse, call which only makes changes to the
kqueue state, without waiting for an event, is not cancellable. This
makes a natural usage model to migrate kqueue loop to support
cancellation, where existing single kevent(2) call must be split into
two: first uncancellable update of kqueue, then cancellable wait for
events.
Note that this is ABI-incompatible change, but it is believed that
there is no cancel-safe code that relies on kevent(2) not being a
cancellation point. Option to preserve the ABI would be to keep
kevent(2) as is, but add new call with flags to specify cancellation
behaviour, which only value seems to add complications.
Suggested and reviewed by: jilles
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
This helps to reduce code size in statically linked applications.
Submitted by: Sebastian Huber <sebastian.huber@embedded-brains.de>
MFC after: 2 weeks
create a new code block and thus must be balanced at the same lexical
scope. (This is also a requirement in POSIX.)
PR: 194280
Submitted by: dr2867.business@pacbell.net
MFC after: 1 week
- Create a separate 'return values' section and move some statements about
return values to that section.
- Note that each invocation of va_start() and va_copy() must be paired with
va_end() in the same function.
MFC after: 1 week
These are largely syntactic sugar. However, they improve code
readability where an RB_FOREACH() or RB_FOREACH_REVERSE()
traversal has been interrupted and must be resumed. Performance
is improved by avoiding unnecessary traversal from the head node.
optionally start the traversal from a previously found element by passing the
element in as "var". Passing a NULL "var" retains the same semantics as the
regular FOREACH macros.
Kudos to phk for suggesting the "FROM" suffix instead of my original proposal.
Reviewed by: jhb (previous version), rpaulo
MFC after: 1 week
Regular LISTs have been implemented in such a way that the prev-pointer
does not point to the previous element, but to the next-pointer stored
in the previous element. This is done to simplify LIST_REMOVE(). This
macro can be implemented without knowing the address of the list head.
Unfortunately this makes it harder to implement LIST_PREV(), which is
why this macro was never here. Still, it is possible to implement this
macro. If the prev-pointer points to the list head, we return NULL.
Otherwise we simply subtract the offset of the prev-pointer within the
structure.
It's not as efficient as traversing forward of course, but in practice
it shouldn't be that bad. In almost all use cases, people will want to
compare the value returned by LIST_PREV() against NULL, so an optimizing
compiler will not emit code that does more branching than TAILQs.
While there, make the code a bit more readable by introducing
__member2struct(). This makes STAILQ_LAST() far more readable.
MFC after: 1 month
quotation. Also make sure we have the same amount of columns in each row as
the number of columns we specify in the head arguments.
Reviewed by: brueffer
