[phobos] Making std.stdio.readf @safe

[Jakub Łabaj via phobos]

LockingTextReader does exactly so - locks in constructor, unlocks 
in destructor and sometimes calls fgetc_unlocked. This makes it a 
good candidate for @trusted I believe.

On Tuesday, 7 February 2017 at 21:37:49 UTC, Andrei Alexandrescu 
wrote:
> Here some research is necessary. What I did e.g. was to google 
> for:
>
> is fgetc_unlocked safe?
>
> and got a bunch of answers, til I got to 
> https://www.gnu.org/software/libc/manual/html_node/Character-Input.html which in turns links to "POSIX Safety Concepts" i.e. https://www.gnu.org/software/libc/manual/html_node/POSIX-Safety-Concepts.html. That document sure doesn't mince words:
>
> "MT-Unsafe, AS-Unsafe, AC-Unsafe functions are not safe to call 
> within the safety contexts described above. Calling them within 
> such contexts invokes undefined behavior."
>
> So... the *_unlocked functions are not safe. They may be, 
> however, wrapped in trusted functions (that issue the 
> appropriate locking).
>
>
> Andrei
>
> On 02/07/2017 03:19 PM, Jakub Łabaj via phobos wrote:
>> Ouch, yes, I meant fgetc_unlocked.
>>
>> Thank you for the help! As a solution I'm going to make a PR 
>> with the
>> mentioned changes, i.e. copy the approach of writef and apply 
>> @trusted
>> to LockingTextReader - I think I can do this, because its 
>> behaviour
>> ensures that functions FGETC, FLOCK, FUNLOCK are invoked in a 
>> safe manner.
>>
>> On Tuesday, 7 February 2017 at 20:04:51 UTC, Andrei 
>> Alexandrescu wrote:
>>> On 2/7/17 2:07 PM, Jakub Łabaj via phobos wrote:
>>>> I see it like this:
>>>> - flockfile - can be @trusted, because no matter when we 
>>>> call it with
>>>> correct argument, it won't do anything unsafe
>>>
>>> affirmative
>>>
>>>> - funlockfile - if called by not owning thread, the 
>>>> behaviour is
>>>> undefined - so potentially may do something unsafe (I don't 
>>>> know what
>>> > happens if called on not locked file, probably is ignored)
>>>
>>> affirmative - in C "undefined" implies "unsafe"
>>>
>>>> fgetc - when not guarded by lock it is not thread safe, 
>>>> shouldn't be
>>>> @trusted
>>>
>>> I think you mean fgetc_unlocked? fgetc issues its own locking 
>>> and
>>> unlocking.
>>>
>>>
>>> Andrei
>>
>>
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