Golang default number of cores

Golang is an open source programming language designed to simplify and speed up some common programming tasks. It is widely used in cloud computing, network programming, big data processing and other fields, and also shows very good performance in some high-concurrency applications.

So, let us discuss the issue of how many cores Golang defaults to.

In Golang, you can use the following code to query the number of CPU cores of the current system:

package main

import (
    "fmt"
    "runtime"
)

func main() {
    fmt.Println(runtime.NumCPU())
}

This code can return the CPU cores of the current system by calling the NumCPU function in the runtime package. quantity. When testing on my laptop, the function returns a result of 4.

So, how is this result obtained? In fact, Golang obtains CPU information through the interface provided by the operating system. Specifically, Golang uses the getcpuinfo function based on Linux system calls to obtain CPU information:

func getcpuinfo() (uint32, error) {
        var info cpu.CacheInfo
        _, b, err := sys.RawSyscall(sys.SYS_ARCH_PRCTL, uintptr(sys.ARCH_GET_CPUID), uintptr(unsafe.Pointer(&info)), 0)
        if err != 0 {
                return 0, os.NewSyscallError("archprctl", err)
        }
        if b != 0 {
                // The kernel returned something we don't understand.
                return 0, fmt.Errorf("unknown arch_prctl result: %d", b)
        }
        // Return the highest non-zero value of cores and threads.
        return uint32(math.Max(float64(info.CoresPerPhysicalPackage), float64(info.ThreadsPerCore))), nil
}

The core of this function is to obtain the CPU cache information cpu.CacheInfo, and then obtain the CPU core number info from here .CoresPerPhysicalPackage and the number of threads info.ThreadsPerCore, and finally returns the larger value of these two quantities.

Of course, if your system is not based on the Linux kernel, then Golang will use other system calls to obtain CPU information.

To summarize, Golang queries the CPU information of the current system through the interface provided by the operating system by default, thereby determining the number of CPU cores. If you need to use multi-core parallel processing in your program, you can use Golang's goroutine and channel mechanisms, which can make your code more concise and efficient.

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