多线程程序在今天的multicore-cpu机器上是如何通过linux编译运行的？

Question

I wrote multithreaded programs using PThreads. My system has 4 cores and 8 logical cores, os x84-64 and I don't know what the compiler will compile to support the multithreaded task to run on multiple cpus. I think that a multi-core CPU must have some method to execute program exactly by CPU switching. One of the cpus starts first, and then the other cpus. Is this logic done through the management of the operating system or by some intel asm instruction? I'm also not sure how this multi-core CPU boot first cpu and switches other cpus, and how the compiler generates the same multi-threaded code(written by c, by linux programming interface book) for machines with only one CPU and multiple cpus. So my words are a little messy.

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2022.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* Listing 29-1 */

#include <pthread.h>
#include "tlpi_hdr.h"

static void *
threadFunc(void *arg)
{
    char *s = arg;

    printf("%s", s);

    return (void *) strlen(s);
}

int
main(int argc, char *argv[])
{
    pthread_t t1;
    void *res;
    int s;

    s = pthread_create(&t1, NULL, threadFunc, "Hello world\n");
    if (s != 0)
        errExitEN(s, "pthread_create");

    printf("Message from main()\n");
    s = pthread_join(t1, &res);
    if (s != 0)
        errExitEN(s, "pthread_join");

    printf("Thread returned %ld\n", (long) res);

    exit(EXIT_SUCCESS);
}

Answer 1

Task switching and the usage of multiple CPUs is done by the operating system. The C compiler does nothing in that respect. Your code example is a C program that make calls to the pthread library. All the C compiler can do is to generate code that calls that library, but it has no idea what the library does. You may now ask: but the operating system is written in C and latest somewhere down in the kernel there must be code to do all the task switching and stuff? Yes. And the Linux kernel is written mostly in C, but the task switching and CPU handling is implemented based on the processor specification and the correct usage of registers and interrupts and not by C language features.

That is also the answer to the other part of your question “how the compiler generates the same multi-threaded code … for machines with only one CPU and multiple cpus“: the generated code is the same, because it's solely the job of the operating system to assign code to CPUs.