std::thread::available_parallelism merging linux/android/freebsd version

FreeBSD 13.1 had introduced a sched cpu affinity compatibility layer
with Linux. 13.0 and even 13.1 being EOL, we can simplify here.

Author: devnexen

library/std/src/sys/pal/unix/thread.rs

@@ -320,19 +320,22 @@ pub fn available_parallelism() -> io::Result<NonZeroUsize> {
             target_os = "solaris",
             target_os = "illumos",
             target_os = "aix",
+            target_os = "freebsd",
         ))] {
-            #[allow(unused_assignments)]
-            #[allow(unused_mut)]
-            let mut quota = usize::MAX;
-
-            #[cfg(any(target_os = "android", target_os = "linux"))]
+            #[cfg(any(target_os = "android", target_os = "linux", target_os = "freebsd"))]
             {
-                quota = cgroups::quota().max(1);
-                let mut set: libc::cpu_set_t = unsafe { mem::zeroed() };
+                #[cfg(not(target_os = "freebsd"))]
+                type cpuset = libc::cpu_set_t;
+                #[cfg(target_os = "freebsd")]
+                type cpuset = libc::cpuset_t;
+                let mut set: cpuset = unsafe { mem::zeroed() };
                 unsafe {
-                    if libc::sched_getaffinity(0, mem::size_of::<libc::cpu_set_t>(), &mut set) == 0 {
+                    if libc::sched_getaffinity(0, mem::size_of::<cpuset>(), &mut set) == 0 {
                         let count = libc::CPU_COUNT(&set) as usize;
-                        let count = count.min(quota);
+                        #[cfg(not(target_os = "freebsd"))]
+                        let count = count.min(cgroups::quota().max(1));
+                        #[cfg(target_os = "freebsd")]
+                        let count = count.min(usize::MAX);
 
                         // According to sched_getaffinity's API it should always be non-zero, but
                         // some old MIPS kernels were buggy and zero-initialized the mask if
@@ -350,37 +353,20 @@ pub fn available_parallelism() -> io::Result<NonZeroUsize> {
                 cpus => {
                     let count = cpus as usize;
                     // Cover the unusual situation where we were able to get the quota but not the affinity mask
-                    let count = count.min(quota);
+                    #[cfg(any(target_os = "linux", target_os = "android"))]
+                    let count = count.min(cgroups::quota().max(1));
+                    #[cfg(not(any(target_os = "linux", target_os = "android")))]
+                    let count = count.min(usize::MAX);
                     Ok(unsafe { NonZeroUsize::new_unchecked(count) })
                 }
             }
         } else if #[cfg(any(
-                   target_os = "freebsd",
                    target_os = "dragonfly",
                    target_os = "openbsd",
                    target_os = "netbsd",
                ))] {
             use crate::ptr;
 
-            #[cfg(target_os = "freebsd")]
-            {
-                let mut set: libc::cpuset_t = unsafe { mem::zeroed() };
-                unsafe {
-                    if libc::cpuset_getaffinity(
-                        libc::CPU_LEVEL_WHICH,
-                        libc::CPU_WHICH_PID,
-                        -1,
-                        mem::size_of::<libc::cpuset_t>(),
-                        &mut set,
-                    ) == 0 {
-                        let count = libc::CPU_COUNT(&set) as usize;
-                        if count > 0 {
-                            return Ok(NonZeroUsize::new_unchecked(count));
-                        }
-                    }
-                }
-            }
-
             #[cfg(target_os = "netbsd")]
             {
                 unsafe {