crystal-lang/crystal

The Crystal programming language | http://crystal-lang.org | Fund Crystal's development: http://is.gd/X7PRtI | Docs: http://crystal-lang.org/docs/ | API: http://crystal-lang.org/api/

From IRC (bridge bot)

@FromIRC

<yxhuvud> No, it is the return code from a syscall. It is very common to let negative result values indicate error status and positive be some other type.

Quinton Miller

@HertzDevil

including posix's c libraries

or should i say api

From IRC (bridge bot)

@FromIRC

<yxhuvud> Yes. And io_uring and a bunch of others.

Quinton Miller

@HertzDevil

so @naqvis it is not so much an "issue" as it is part of c's tradition

Ali Naqvi

@naqvis

:P , yeah and C do that for reference types

i mean for FFI where you know C is returning a reference then isn't out a better choice?

From IRC (bridge bot)

@FromIRC

<yxhuvud> Not really an option for mmap.

Ali Naqvi

@naqvis

just looked into mmap manpage :P

@didactic-drunk you can do a comparison against Pointer(Void).new(-1)

Quinton Miller

@HertzDevil

for the record, that constructor calls -1.to_u64!

Ali Naqvi

@naqvis

does it ?
https://play.crystal-lang.org/#/r/bbi5

Quinton Miller

@HertzDevil

well since crystal always maps Void to Nil you can "dereference" any Pointer(Void) and it'll be nil

0xffff_ffff_ffff_ffff is definitely -1.to_u64!

Ali Naqvi

@naqvis

but isn't Pointer(Void).new(-1) equivalent to C (void *) -1?

https://cplayground.com/?p=jay-hornet-anteater

Quinton Miller

@HertzDevil

iso c says nothing about the size of a void*

crystal more or less defines the pointer size to always be 8 bytes

From IRC (bridge bot)

@FromIRC

<yxhuvud> hertzdevil: not only that, iso c doesn't even define what the value of a null pointer actually is.

Quinton Miller

@HertzDevil

0 is definitely not a null pointer on cc65 targetting the nes

Ali Naqvi

@naqvis

test.c

void* test() {
  return ((void *) -1);
}

test.cr

@[Link(ldflags: "-L#{__DIR__}/ -ltest.o ")]
lib Test
  fun test : Void*
end

p! Test.test == Pointer(Void).new(-1) # => true

Quinton Miller

@HertzDevil

that's due to the abi, not the c standard

Ali Naqvi

@naqvis

yeah true, but this does answer the original question on how to find out if mmap failed

Quinton Miller

@HertzDevil

it will break silently if c's void* is smaller than crystal's Pointer(Void) and zero extension is performed instead of sign extension

Ali Naqvi

@naqvis

https://man7.org/linux/man-pages/man2/mmap.2.html

On error, the value MAP_FAILED (that is, (void *) -1) is returned, and errno is set to indicate the error.

Quinton Miller

@HertzDevil

what's doable is still doing that and then comparing your pointer to the return value of test instead

and not to a Pointer(Void) created in crystal

for portability

Ali Naqvi

@naqvis

but invoking FFI, crystal is yielding the same result as it do for Pointer(Void)
p! Test.test # => Pointer(Void)@0xffffffffffffffff

is crystal doing some conversions behind the scenes?

didactic-drunk

@didactic-drunk

I think 0x0 is a valid mapping/success return value for mmap so -1 is used.

Ali Naqvi

@naqvis

yeah, make sense

didactic-drunk

@didactic-drunk

Will Pointer(UInt8).new(-1) end up optimized to a constant single value or should I store a copy for comparison?

Ali Naqvi

@naqvis

should be same for each invocation

as we are giving the same address

but for easy maintenance, better to have constant defined like MMAP_FAILED

Thore Bödecker

@foxxx0

Hi, I'm trying to spawn a long-running process in the background that occasionally prints something on stdout. i want to have that Fiber blocking until the next line on stdout, which works fine using #gets on the stdout pipe. however, as soon as this fiber is part of my multi-fiber application, the other fibers seem to be blocked too

source code with the problematic fiber highlighted: https://paste.foxxx0.de/ngH/crystal#n101

didactic-drunk

@didactic-drunk

Is it possible to have multiple flags type params filled using symbols? https://carc.in/#/r/bbk7

George Dietrich

@Blacksmoke16

@didactic-drunk https://carc.in/#/r/bbkt

best you can do atm, see crystal-lang/crystal#10680

Jonathan Silverman

@mixflame

my scalablepress/paypal/gbaldraw integration is live

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https://gbaldraw.fun/ please bear in mind the content on the global/empty string room is user generated by anonymous users, apologies if you see anything triggering, if that's the case, please click the link on the right instead and create your own (infinitely lasting) private room

the global room is popular with free speech exhibitionists, please excuse me for that

running Amber on Crystal 1.0.0

ported from Rails 6/Ruby 3

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