Move available_concurrency implementation to sys

library/std/src/sys/hermit/thread.rs

@@ -1,8 +1,10 @@
 #![allow(dead_code)]
 
+use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
 use crate::mem;
+use crate::num::NonZeroUsize;
 use crate::sys::hermit::abi;
 use crate::sys::hermit::thread_local_dtor::run_dtors;
 use crate::time::Duration;
@@ -95,6 +97,10 @@ impl Thread {
     }
 }
 
+pub fn available_concurrency() -> io::Result<NonZeroUsize> {
+    unsupported()
+}
+
 pub mod guard {
     pub type Guard = !;
     pub unsafe fn current() -> Option<Guard> {

library/std/src/sys/sgx/thread.rs

@@ -1,6 +1,8 @@
 #![cfg_attr(test, allow(dead_code))] // why is this necessary?
+use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
+use crate::num::NonZeroUsize;
 use crate::time::Duration;
 
 use super::abi::usercalls;
@@ -135,6 +137,10 @@ impl Thread {
     }
 }
 
+pub fn available_concurrency() -> io::Result<NonZeroUsize> {
+    unsupported()
+}
+
 pub mod guard {
     pub type Guard = !;
     pub unsafe fn current() -> Option<Guard> {

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

@@ -2,6 +2,7 @@ use crate::cmp;
 use crate::ffi::CStr;
 use crate::io;
 use crate::mem;
+use crate::num::NonZeroUsize;
 use crate::ptr;
 use crate::sys::{os, stack_overflow};
 use crate::time::Duration;
@@ -198,6 +199,88 @@ impl Drop for Thread {
     }
 }
 
+pub fn available_concurrency() -> io::Result<NonZeroUsize> {
+    cfg_if::cfg_if! {
+        if #[cfg(any(
+            target_os = "android",
+            target_os = "emscripten",
+            target_os = "fuchsia",
+            target_os = "ios",
+            target_os = "linux",
+            target_os = "macos",
+            target_os = "solaris",
+            target_os = "illumos",
+        ))] {
+            match unsafe { libc::sysconf(libc::_SC_NPROCESSORS_ONLN) } {
+                -1 => Err(io::Error::last_os_error()),
+                0 => Err(io::Error::new_const(io::ErrorKind::NotFound, &"The number of hardware threads is not known for the target platform")),
+                cpus => Ok(unsafe { NonZeroUsize::new_unchecked(cpus as usize) }),
+            }
+        } else if #[cfg(any(target_os = "freebsd", target_os = "dragonfly", target_os = "netbsd"))] {
+            use crate::ptr;
+
+            let mut cpus: libc::c_uint = 0;
+            let mut cpus_size = crate::mem::size_of_val(&cpus);
+
+            unsafe {
+                cpus = libc::sysconf(libc::_SC_NPROCESSORS_ONLN) as libc::c_uint;
+            }
+
+            // Fallback approach in case of errors or no hardware threads.
+            if cpus < 1 {
+                let mut mib = [libc::CTL_HW, libc::HW_NCPU, 0, 0];
+                let res = unsafe {
+                    libc::sysctl(
+                        mib.as_mut_ptr(),
+                        2,
+                        &mut cpus as *mut _ as *mut _,
+                        &mut cpus_size as *mut _ as *mut _,
+                        ptr::null_mut(),
+                        0,
+                    )
+                };
+
+                // Handle errors if any.
+                if res == -1 {
+                    return Err(io::Error::last_os_error());
+                } else if cpus == 0 {
+                    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(cpus as usize) })
+        } else if #[cfg(target_os = "openbsd")] {
+            use crate::ptr;
+
+            let mut cpus: libc::c_uint = 0;
+            let mut cpus_size = crate::mem::size_of_val(&cpus);
+            let mut mib = [libc::CTL_HW, libc::HW_NCPU, 0, 0];
+
+            let res = unsafe {
+                libc::sysctl(
+                    mib.as_mut_ptr(),
+                    2,
+                    &mut cpus as *mut _ as *mut _,
+                    &mut cpus_size as *mut _ as *mut _,
+                    ptr::null_mut(),
+                    0,
+                )
+            };
+
+            // Handle errors if any.
+            if res == -1 {
+                return Err(io::Error::last_os_error());
+            } else if cpus == 0 {
+                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(cpus as usize) })
+        } else {
+            // FIXME: implement on vxWorks, Redox, Haiku, l4re
+            Err(io::Error::new_const(io::ErrorKind::Unsupported, &"Getting the number of hardware threads is not supported on the target platform"))
+        }
+    }
+}
+
 #[cfg(all(
     not(target_os = "linux"),
     not(target_os = "freebsd"),

library/std/src/sys/unsupported/thread.rs

@@ -1,6 +1,7 @@
 use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
+use crate::num::NonZeroUsize;
 use crate::time::Duration;
 
 pub struct Thread(!);
@@ -30,6 +31,10 @@ impl Thread {
     }
 }
 
+pub fn available_concurrency() -> io::Result<NonZeroUsize> {
+    unsupported()
+}
+
 pub mod guard {
     pub type Guard = !;
     pub unsafe fn current() -> Option<Guard> {

library/std/src/sys/wasi/thread.rs

@@ -3,6 +3,7 @@
 use crate::ffi::CStr;
 use crate::io;
 use crate::mem;
+use crate::num::NonZeroUsize;
 use crate::sys::unsupported;
 use crate::time::Duration;
 
@@ -63,6 +64,10 @@ impl Thread {
     }
 }
 
+pub fn available_concurrency() -> io::Result<NonZeroUsize> {
+    unsupported()
+}
+
 pub mod guard {
     pub type Guard = !;
     pub unsafe fn current() -> Option<Guard> {

library/std/src/sys/wasm/atomics/thread.rs

@@ -1,5 +1,7 @@
+use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
+use crate::num::NonZeroUsize;
 use crate::sys::unsupported;
 use crate::time::Duration;
 
@@ -39,6 +41,10 @@ impl Thread {
     pub fn join(self) {}
 }
 
+pub fn available_concurrency() -> io::Result<NonZeroUsize> {
+    unsupported()
+}
+
 pub mod guard {
     pub type Guard = !;
     pub unsafe fn current() -> Option<Guard> {

library/std/src/sys/windows/c.rs

@@ -13,6 +13,7 @@ use libc::{c_void, size_t, wchar_t};
 pub use self::EXCEPTION_DISPOSITION::*;
 pub use self::FILE_INFO_BY_HANDLE_CLASS::*;
 
+pub type DWORD_PTR = ULONG_PTR;
 pub type DWORD = c_ulong;
 pub type NonZeroDWORD = NonZero_c_ulong;
 pub type HANDLE = LPVOID;
@@ -53,6 +54,7 @@ pub type LPWSADATA = *mut WSADATA;
 pub type LPWSAPROTOCOL_INFO = *mut WSAPROTOCOL_INFO;
 pub type LPWSTR = *mut WCHAR;
 pub type LPFILETIME = *mut FILETIME;
+pub type LPSYSTEM_INFO = *mut SYSTEM_INFO;
 pub type LPWSABUF = *mut WSABUF;
 pub type LPWSAOVERLAPPED = *mut c_void;
 pub type LPWSAOVERLAPPED_COMPLETION_ROUTINE = *mut c_void;
@@ -533,6 +535,21 @@ pub struct FILETIME {
     pub dwHighDateTime: DWORD,
 }
 
+#[repr(C)]
+pub struct SYSTEM_INFO {
+    pub wProcessorArchitecture: WORD,
+    pub wReserved: WORD,
+    pub dwPageSize: DWORD,
+    pub lpMinimumApplicationAddress: LPVOID,
+    pub lpMaximumApplicationAddress: LPVOID,
+    pub dwActiveProcessorMask: DWORD_PTR,
+    pub dwNumberOfProcessors: DWORD,
+    pub dwProcessorType: DWORD,
+    pub dwAllocationGranularity: DWORD,
+    pub wProcessorLevel: WORD,
+    pub wProcessorRevision: WORD,
+}
+
 #[repr(C)]
 pub struct OVERLAPPED {
     pub Internal: *mut c_ulong,
@@ -934,6 +951,7 @@ extern "system" {
     pub fn GetModuleHandleW(lpModuleName: LPCWSTR) -> HMODULE;
 
     pub fn GetSystemTimeAsFileTime(lpSystemTimeAsFileTime: LPFILETIME);
+    pub fn GetSystemInfo(lpSystemInfo: LPSYSTEM_INFO);
 
     pub fn CreateEventW(
         lpEventAttributes: LPSECURITY_ATTRIBUTES,

library/std/src/sys/windows/thread.rs

@@ -1,5 +1,6 @@
 use crate::ffi::CStr;
 use crate::io;
+use crate::num::NonZeroUsize;
 use crate::ptr;
 use crate::sys::c;
 use crate::sys::handle::Handle;
@@ -98,6 +99,21 @@ impl Thread {
     }
 }
 
+pub fn available_concurrency() -> io::Result<NonZeroUsize> {
+    let res = unsafe {
+        let mut sysinfo: c::SYSTEM_INFO = crate::mem::zeroed();
+        c::GetSystemInfo(&mut sysinfo);
+        sysinfo.dwNumberOfProcessors as usize
+    };
+    match res {
+        0 => Err(io::Error::new_const(
+            io::ErrorKind::NotFound,
+            &"The number of hardware threads is not known for the target platform",
+        )),
+        cpus => Ok(unsafe { NonZeroUsize::new_unchecked(cpus) }),
+    }
+}
+
 #[cfg_attr(test, allow(dead_code))]
 pub mod guard {
     pub type Guard = !;