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haiku thread affinity build fix #89462

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Oct 5, 2021
Merged

haiku thread affinity build fix #89462

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16 changes: 10 additions & 6 deletions library/std/src/sys/unix/thread.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -339,14 +339,18 @@ pub fn available_concurrency() -> io::Result<NonZeroUsize> {

Ok(unsafe { NonZeroUsize::new_unchecked(cpus as usize) })
} else if #[cfg(target_os = "haiku")] {
let mut sinfo: libc::system_info = crate::mem::zeroed();
let res = libc::get_system_info(&mut sinfo);
// system_info cpu_count field gets the static data set at boot time with `smp_set_num_cpus`
// `get_system_info` calls then `smp_get_num_cpus`
unsafe {
let mut sinfo: libc::system_info = crate::mem::zeroed();
let res = libc::get_system_info(&mut sinfo);

if res != libc::B_OK {
return Err(io::Error::last_os_error());
}
if res != libc::B_OK {
return Err(io::Error::new_const(io::ErrorKind::NotFound, &"The number of hardware threads is not known for the target platform"));
}

Ok(unsafe { NonZeroUsize::new_unchecked(sinfo.cpu_count as usize) })
Ok(NonZeroUsize::new_unchecked(sinfo.cpu_count as usize))
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This escaped my attention last time, but calls of unsafe functions in new code should be annotated with comments describing why a call like this is safe. In particular I'm having trouble finding haiku documentation for get_system_info that would guarantee that the returned cpu_count will be non-zero. A reference here would be great.

See e.g.

rust/library/core/src/ptr/unique.rs

Line 88 in 673d0db

// SAFETY: the caller must guarantee that `ptr` is non-null.
for an example of what I mean

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Or you could use a checked constructor instead, too.

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The cpu_count field is filled with the number of cpus at boot time set here https://github.com/haiku/haiku/blob/04be20a75a6e09d9c2f801fc0e6ffd4e5b486950/src/system/kernel/main.cpp#L114 and taken here afterwards https://github.com/haiku/haiku/blob/8f16317a5b6db5c672f331814273e5857555020f/src/system/kernel/smp.cpp#L1481

}
} else {
// FIXME: implement on vxWorks, Redox, l4re
Err(io::Error::new_const(io::ErrorKind::Unsupported, &"Getting the number of hardware threads is not supported on the target platform"))
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