# lib.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/num_cpus-1.13.0/src/lib.rs`.
Keywords: rust, rustlang, rust-lang

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    //! A crate with utilities to determine the number of CPUs available on the
    //! current system.
    //!
    //! Sometimes the CPU will exaggerate the number of CPUs it contains, because it can use
    //! [processor tricks] to deliver increased performance when there are more threads. This
    //! crate provides methods to get both the logical and physical numbers of cores.
    //!
    //! This information can be used as a guide to how many tasks can be run in parallel.
    //! There are many properties of the system architecture that will affect parallelism,
    //! for example memory access speeds (for all the caches and RAM) and the physical
    //! architecture of the processor, so the number of CPUs should be used as a rough guide
    //! only.
    //!
    //!
    //! ## Examples
    //!
    //! Fetch the number of logical CPUs.
    //!
    //! ```
    //! let cpus = num_cpus::get();
    //! ```
    //!
    //! See [`rayon::Threadpool`] for an example of where the number of CPUs could be
    //! used when setting up parallel jobs (Where the threadpool example uses a fixed
    //! number 8, it could use the number of CPUs).
    //!
    //! [processor tricks]: https://en.wikipedia.org/wiki/Simultaneous_multithreading
    //! [`rayon::ThreadPool`]: https://docs.rs/rayon/1.*/rayon/struct.ThreadPool.html
    #![cfg_attr(test, deny(warnings))]
    #![deny(missing_docs)]
    #![doc(html_root_url = "https://docs.rs/num_cpus/1.13.0")]
    #![allow(non_snake_case)]

    #[cfg(not(windows))]
    extern crate libc;

    #[cfg(target_os = "hermit")]
    extern crate hermit_abi;

    #[cfg(target_os = "linux")]
    mod linux;
    #[cfg(target_os = "linux")]
    use linux::{get_num_cpus, get_num_physical_cpus};

    /// Returns the number of available CPUs of the current system.
    ///
    /// This function will get the number of logical cores. Sometimes this is different from the number
    /// of physical cores (See [Simultaneous multithreading on Wikipedia][smt]).
    ///
    /// # Examples
    ///
    /// ```
    /// let cpus = num_cpus::get();
    /// if cpus > 1 {
    ///     println!("We are on a multicore system with {} CPUs", cpus);
    /// } else {
    ///     println!("We are on a single core system");
    /// }
    /// ```
    ///
    /// # Note
    ///
    /// This will check [sched affinity] on Linux, showing a lower number of CPUs if the current
    /// thread does not have access to all the computer's CPUs.
    ///
    /// This will also check [cgroups], frequently used in containers to constrain CPU usage.
    ///
    /// [smt]: https://en.wikipedia.org/wiki/Simultaneous_multithreading
    /// [sched affinity]: http://www.gnu.org/software/libc/manual/html_node/CPU-Affinity.html
    /// [cgroups]: https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
    #[inline]
    pub fn get() -> usize {
        get_num_cpus()
    }

    /// Returns the number of physical cores of the current system.
    ///
    /// # Note
    ///
    /// Physical count is supported only on Linux, mac OS and Windows platforms.
    /// On other platforms, or if the physical count fails on supported platforms,
    /// this function returns the same as [`get()`], which is the number of logical
    /// CPUS.
    ///
    /// # Examples
    ///
    /// ```
    /// let logical_cpus = num_cpus::get();
    /// let physical_cpus = num_cpus::get_physical();
    /// if logical_cpus > physical_cpus {
    ///     println!("We have simultaneous multithreading with about {:.2} \
    ///               logical cores to 1 physical core.",
    ///               (logical_cpus as f64) / (physical_cpus as f64));
    /// } else if logical_cpus == physical_cpus {
    ///     println!("Either we don't have simultaneous multithreading, or our \
    ///               system doesn't support getting the number of physical CPUs.");
    /// } else {
    ///     println!("We have less logical CPUs than physical CPUs, maybe we only have access to \
    ///               some of the CPUs on our system.");
    /// }
    /// ```
    ///
    /// [`get()`]: fn.get.html
    #[inline]
    pub fn get_physical() -> usize {
        get_num_physical_cpus()
    }

    #[cfg(not(any(target_os = "linux", target_os = "windows", target_os="macos", target_os="openbsd")))]
    #[inline]
    fn get_num_physical_cpus() -> usize {
        // Not implemented, fall back
        get_num_cpus()
    }

    #[cfg(target_os = "windows")]
    fn get_num_physical_cpus() -> usize {
        match get_num_physical_cpus_windows() {
            Some(num) => num,
            None => get_num_cpus()
        }
    }

    #[cfg(target_os = "windows")]
    fn get_num_physical_cpus_windows() -> Option<usize> {
        // Inspired by https://msdn.microsoft.com/en-us/library/ms683194

        use std::ptr;
        use std::mem;

        #[allow(non_upper_case_globals)]
        const RelationProcessorCore: u32 = 0;

        #[repr(C)]
        #[allow(non_camel_case_types)]
        struct SYSTEM_LOGICAL_PROCESSOR_INFORMATION {
            mask: usize,
            relationship: u32,
            _unused: [u64; 2]
        }

        extern "system" {
            fn GetLogicalProcessorInformation(
                info: *mut SYSTEM_LOGICAL_PROCESSOR_INFORMATION,
                length: &mut u32
            ) -> u32;
        }

        // First we need to determine how much space to reserve.

        // The required size of the buffer, in bytes.
        let mut needed_size = 0;

        unsafe {
            GetLogicalProcessorInformation(ptr::null_mut(), &mut needed_size);
        }

        let struct_size = mem::size_of::<SYSTEM_LOGICAL_PROCESSOR_INFORMATION>() as u32;

        // Could be 0, or some other bogus size.
        if needed_size == 0 || needed_size < struct_size || needed_size % struct_size != 0 {
            return None;
        }

        let count = needed_size / struct_size;

        // Allocate some memory where we will store the processor info.
        let mut buf = Vec::with_capacity(count as usize);

        let result;

        unsafe {
            result = GetLogicalProcessorInformation(buf.as_mut_ptr(), &mut needed_size);
        }

        // Failed for any reason.
        if result == 0 {
            return None;
        }

        let count = needed_size / struct_size;

        unsafe {
            buf.set_len(count as usize);
        }

        let phys_proc_count = buf.iter()
            // Only interested in processor packages (physical processors.)
            .filter(|proc_info| proc_info.relationship == RelationProcessorCore)
            .count();

        if phys_proc_count == 0 {
            None
        } else {
            Some(phys_proc_count)
        }
    }

    #[cfg(windows)]
    fn get_num_cpus() -> usize {
        #[repr(C)]
        struct SYSTEM_INFO {
            wProcessorArchitecture: u16,
            wReserved: u16,
            dwPageSize: u32,
            lpMinimumApplicationAddress: *mut u8,
            lpMaximumApplicationAddress: *mut u8,
            dwActiveProcessorMask: *mut u8,
            dwNumberOfProcessors: u32,
            dwProcessorType: u32,
            dwAllocationGranularity: u32,
            wProcessorLevel: u16,
            wProcessorRevision: u16,
        }

        extern "system" {
            fn GetSystemInfo(lpSystemInfo: *mut SYSTEM_INFO);
        }

        unsafe {
            let mut sysinfo: SYSTEM_INFO = std::mem::zeroed();
            GetSystemInfo(&mut sysinfo);
            sysinfo.dwNumberOfProcessors as usize
        }
    }

    #[cfg(any(target_os = "freebsd",
              target_os = "dragonfly",
              target_os = "netbsd"))]
    fn get_num_cpus() -> usize {
        use std::ptr;

        let mut cpus: libc::c_uint = 0;
        let mut cpus_size = std::mem::size_of_val(&cpus);

        unsafe {
            cpus = libc::sysconf(libc::_SC_NPROCESSORS_ONLN) as libc::c_uint;
        }
        if cpus < 1 {
            let mut mib = [libc::CTL_HW, libc::HW_NCPU, 0, 0];
            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);
            }
            if cpus < 1 {
                cpus = 1;
            }
        }
        cpus as usize
    }

    #[cfg(target_os = "openbsd")]
    fn get_num_cpus() -> usize {
        use std::ptr;

        let mut cpus: libc::c_uint = 0;
        let mut cpus_size = std::mem::size_of_val(&cpus);
        let mut mib = [libc::CTL_HW, libc::HW_NCPUONLINE, 0, 0];
        let rc: libc::c_int;

        unsafe {
            rc = libc::sysctl(mib.as_mut_ptr(),
                              2,
                              &mut cpus as *mut _ as *mut _,
                              &mut cpus_size as *mut _ as *mut _,
                              ptr::null_mut(),
                              0);
        }
        if rc < 0 {
            cpus = 1;
        }
        cpus as usize
    }

    #[cfg(target_os = "openbsd")]
    fn get_num_physical_cpus() -> usize {
        use std::ptr;

        let mut cpus: libc::c_uint = 0;
        let mut cpus_size = std::mem::size_of_val(&cpus);
        let mut mib = [libc::CTL_HW, libc::HW_NCPU, 0, 0];
        let rc: libc::c_int;

        unsafe {
            rc = libc::sysctl(mib.as_mut_ptr(),
                              2,
                              &mut cpus as *mut _ as *mut _,
                              &mut cpus_size as *mut _ as *mut _,
                              ptr::null_mut(),
                              0);
        }
        if rc < 0 {
            cpus = 1;
        }
        cpus as usize
    }

    #[cfg(target_os = "macos")]
    fn get_num_physical_cpus() -> usize {
        use std::ffi::CStr;
        use std::ptr;

        let mut cpus: i32 = 0;
        let mut cpus_size = std::mem::size_of_val(&cpus);

        let sysctl_name = CStr::from_bytes_with_nul(b"hw.physicalcpu\0")
            .expect("byte literal is missing NUL");

        unsafe {
            if 0 != libc::sysctlbyname(sysctl_name.as_ptr(),
                                       &mut cpus as *mut _ as *mut _,
                                       &mut cpus_size as *mut _ as *mut _,
                                       ptr::null_mut(),
                                       0) {
                return get_num_cpus();
            }
        }
        cpus as usize
    }

    #[cfg(any(
        target_os = "nacl",
        target_os = "macos",
        target_os = "ios",
        target_os = "android",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia")
    )]
    fn get_num_cpus() -> usize {
        // On ARM targets, processors could be turned off to save power.
        // Use `_SC_NPROCESSORS_CONF` to get the real number.
        #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
        const CONF_NAME: libc::c_int = libc::_SC_NPROCESSORS_CONF;
        #[cfg(not(any(target_arch = "arm", target_arch = "aarch64")))]
        const CONF_NAME: libc::c_int = libc::_SC_NPROCESSORS_ONLN;

        let cpus = unsafe { libc::sysconf(CONF_NAME) };
        if cpus < 1 {
            1
        } else {
            cpus as usize
        }
    }

    #[cfg(target_os = "haiku")]
    fn get_num_cpus() -> usize {
        use std::mem;

        #[allow(non_camel_case_types)]
        type bigtime_t = i64;
        #[allow(non_camel_case_types)]
        type status_t = i32;

        #[repr(C)]
        pub struct system_info {
            pub boot_time: bigtime_t,
            pub cpu_count: u32,
            pub max_pages: u64,
            pub used_pages: u64,
            pub cached_pages: u64,
            pub block_cache_pages: u64,
            pub ignored_pages: u64,
            pub needed_memory: u64,
            pub free_memory: u64,
            pub max_swap_pages: u64,
            pub free_swap_pages: u64,
            pub page_faults: u32,
            pub max_sems: u32,
            pub used_sems: u32,
            pub max_ports: u32,
            pub used_ports: u32,
            pub max_threads: u32,
            pub used_threads: u32,
            pub max_teams: u32,
            pub used_teams: u32,
            pub kernel_name: [::std::os::raw::c_char; 256usize],
            pub kernel_build_date: [::std::os::raw::c_char; 32usize],
            pub kernel_build_time: [::std::os::raw::c_char; 32usize],
            pub kernel_version: i64,
            pub abi: u32,
        }

        extern {
            fn get_system_info(info: *mut system_info) -> status_t;
        }

        let mut info: system_info = unsafe { mem::zeroed() };
        let status = unsafe { get_system_info(&mut info as *mut _) };
        if status == 0 {
            info.cpu_count as usize
        } else {
            1
        }
    }

    #[cfg(target_os = "hermit")]
    fn get_num_cpus() -> usize {
        unsafe { hermit_abi::get_processor_count() }
    }

    #[cfg(not(any(
        target_os = "nacl",
        target_os = "macos",
        target_os = "ios",
        target_os = "android",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia",
        target_os = "linux",
        target_os = "openbsd",
        target_os = "freebsd",
        target_os = "dragonfly",
        target_os = "netbsd",
        target_os = "haiku",
        target_os = "hermit",
        windows,
    )))]
    fn get_num_cpus() -> usize {
        1
    }

    #[cfg(test)]
    mod tests {
        fn env_var(name: &'static str) -> Option<usize> {
            ::std::env::var(name).ok().map(|val| val.parse().unwrap())
        }

        #[test]
        fn test_get() {
            let num = super::get();
            if let Some(n) = env_var("NUM_CPUS_TEST_GET") {
                assert_eq!(num, n);
            } else {
                assert!(num > 0);
                assert!(num < 236_451);
            }
        }

        #[test]
        fn test_get_physical() {
            let num = super::get_physical();
            if let Some(n) = env_var("NUM_CPUS_TEST_GET_PHYSICAL") {
                assert_eq!(num, n);
            } else {
                assert!(num > 0);
                assert!(num < 236_451);
            }
        }
    }