Обсуждение: C nitpick about pgwin32_dispatch_queued_signals()
Hello,
the current MSVC compiler deems it necessary to issue
warning C4053: one void operand for '?:'
for a line with CHECK_FOR_INTERRUPTS(). This boils down to this bit of
miscadmin.h (line 116 in master):
#define INTERRUPTS_PENDING_CONDITION() \
(unlikely(UNBLOCKED_SIGNAL_QUEUE()) ?
pgwin32_dispatch_queued_signals() : 0, \
unlikely(InterruptPending))
#endif
The C spec says that of the possible results of the :? operator, either
none or both can be void, and pgwin32_dispatch_queued_signals() is void
(and has been as far back as I can find it).
Does that matter?
--
Christian
On 11/2/2025 7:05 AM, Christian Ullrich wrote:
> Hello,
>
> the current MSVC compiler deems it necessary to issue
>
> warning C4053: one void operand for '?:'
>
> for a line with CHECK_FOR_INTERRUPTS(). This boils down to this bit of
> miscadmin.h (line 116 in master):
>
> #define INTERRUPTS_PENDING_CONDITION() \
> (unlikely(UNBLOCKED_SIGNAL_QUEUE()) ?
> pgwin32_dispatch_queued_signals() : 0, \
> unlikely(InterruptPending))
> #endif
>
> The C spec says that of the possible results of the :? operator, either
> none or both can be void, and pgwin32_dispatch_queued_signals() is void
> (and has been as far back as I can find it).
>
> Does that matter?
>
>
Yeah, this is a bug, or at least a spec violation. We should fix it in
my opinion-- it's non-conforming C. Others may disagree, though.
It happens to work because the comma operator discards the result
anyway, but MSVC is right to complain.
This isn't a new thing with modern C standards, BTW --- the rule
about not mixing void and non-void operands in ?: has been there
since C89. We've just been getting away with it because most
compilers don't complain when the result is discarded by the
comma operator anyway.
I see a couple of ways to fix it:
1. Cast both arms to void:
#define INTERRUPTS_PENDING_CONDITION() \
(unlikely(UNBLOCKED_SIGNAL_QUEUE()) ? \
(pgwin32_dispatch_queued_signals(), (void)0) : (void)0, \
unlikely(InterruptPending))
2. Restructure to use && instead of ?::
#define INTERRUPTS_PENDING_CONDITION() \
(unlikely(UNBLOCKED_SIGNAL_QUEUE()) && \
(pgwin32_dispatch_queued_signals(), true), \
unlikely(InterruptPending))
3. Just make it an inline function instead of a macro.
I'd lean towards #2 --- it's cleaner and avoids the whole issue.
The semantics are the same since we're only calling the function
for its side-effects.
Thoughts?
Bryan Green
Bryan Green <dbryan.green@gmail.com> writes:
> On 11/2/2025 7:05 AM, Christian Ullrich wrote:
>> the current MSVC compiler deems it necessary to issue
>> warning C4053: one void operand for '?:'
>> for a line with CHECK_FOR_INTERRUPTS(). This boils down to this bit of
>> miscadmin.h (line 116 in master):
>>
>> #define INTERRUPTS_PENDING_CONDITION() \
>> (unlikely(UNBLOCKED_SIGNAL_QUEUE()) ?
>> pgwin32_dispatch_queued_signals() : 0, \
>> unlikely(InterruptPending))
>> #endif
>>
>> The C spec says that of the possible results of the :? operator, either
>> none or both can be void, and pgwin32_dispatch_queued_signals() is void
>> (and has been as far back as I can find it).
> Yeah, this is a bug, or at least a spec violation. We should fix it in
> my opinion-- it's non-conforming C. Others may disagree, though.
Agreed.
> 2. Restructure to use && instead of ?::
> #define INTERRUPTS_PENDING_CONDITION() \
> (unlikely(UNBLOCKED_SIGNAL_QUEUE()) && \
> (pgwin32_dispatch_queued_signals(), true), \
> unlikely(InterruptPending))
> I'd lean towards #2 --- it's cleaner and avoids the whole issue.
I dunno, don't really like the nested comma operator here.
It's probably necessary to avoid having a void argument to &&,
but it's confusing. Let's go with your #1 (casting the 0 to void).
But can't we simplify that to just
#define INTERRUPTS_PENDING_CONDITION() \
(unlikely(UNBLOCKED_SIGNAL_QUEUE()) ?
pgwin32_dispatch_queued_signals() : (void) 0, \
unlikely(InterruptPending))
#endif
that is, the only change needed is s/0/(void) 0/.
regards, tom lane
On Sun, 2025-11-02 at 11:47 -0500, Tom Lane wrote: > Bryan Green <dbryan.green@gmail.com> writes: > > On 11/2/2025 7:05 AM, Christian Ullrich wrote: > > > the current MSVC compiler deems it necessary to issue > > > warning C4053: one void operand for '?:' > > > for a line with CHECK_FOR_INTERRUPTS(). This boils down to this bit of > > > miscadmin.h (line 116 in master): > > > > > > #define INTERRUPTS_PENDING_CONDITION() \ > > > (unlikely(UNBLOCKED_SIGNAL_QUEUE()) ? > > > pgwin32_dispatch_queued_signals() : 0, \ > > > unlikely(InterruptPending)) > > > #endif > > > > > > The C spec says that of the possible results of the :? operator, either > > > none or both can be void, and pgwin32_dispatch_queued_signals() is void > > > (and has been as far back as I can find it). > > > Yeah, this is a bug, or at least a spec violation. We should fix it in > > my opinion-- it's non-conforming C. Others may disagree, though. > > Agreed. > > > Let's go with your #1 (casting the 0 to void). > But can't we simplify that to just > > #define INTERRUPTS_PENDING_CONDITION() \ > (unlikely(UNBLOCKED_SIGNAL_QUEUE()) ? > pgwin32_dispatch_queued_signals() : (void) 0, \ > unlikely(InterruptPending)) > #endif > > that is, the only change needed is s/0/(void) 0/. +1 Laurenz Albe
On 11/2/2025 10:50 AM, Laurenz Albe wrote: > On Sun, 2025-11-02 at 11:47 -0500, Tom Lane wrote: >> Bryan Green <dbryan.green@gmail.com> writes: >>> On 11/2/2025 7:05 AM, Christian Ullrich wrote: >>>> the current MSVC compiler deems it necessary to issue >>>> warning C4053: one void operand for '?:' >>>> for a line with CHECK_FOR_INTERRUPTS(). This boils down to this bit of >>>> miscadmin.h (line 116 in master): >>>> >>>> #define INTERRUPTS_PENDING_CONDITION() \ >>>> (unlikely(UNBLOCKED_SIGNAL_QUEUE()) ? >>>> pgwin32_dispatch_queued_signals() : 0, \ >>>> unlikely(InterruptPending)) >>>> #endif >>>> >>>> The C spec says that of the possible results of the :? operator, either >>>> none or both can be void, and pgwin32_dispatch_queued_signals() is void >>>> (and has been as far back as I can find it). >> >>> Yeah, this is a bug, or at least a spec violation. We should fix it in >>> my opinion-- it's non-conforming C. Others may disagree, though. >> >> Agreed. >> >> >> Let's go with your #1 (casting the 0 to void). >> But can't we simplify that to just >> >> #define INTERRUPTS_PENDING_CONDITION() \ >> (unlikely(UNBLOCKED_SIGNAL_QUEUE()) ? >> pgwin32_dispatch_queued_signals() : (void) 0, \ >> unlikely(InterruptPending)) >> #endif >> >> that is, the only change needed is s/0/(void) 0/. > > +1 > > Laurenz Albe Option 1 works for me as well. Hopefully, it works for Christian as well.