如何在Linux上使用clone()创建真正的线程？

Question

我正在尝试使用clone()创建一个新线程.使用以下代码(...):

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define _SCHED_H 1
#define __USE_GNU 1
#include <bits/sched.h>

#define STACK_SIZE 4096

int func(void *arg) {
    printf("Inside func.\n");
    sleep(1);
    printf("Terminating func...\n");

    return 0;
}

int main() {
    printf("This process pid: %u\n", getpid());
    char status_file[] = "/proc/self/status";
    void *child_stack = malloc(STACK_SIZE);
    int thread_pid;

    printf("Creating new thread...\n");
    thread_pid = clone(&func, child_stack+STACK_SIZE, CLONE_SIGHAND|CLONE_FS|CLONE_VM|CLONE_FILES, NULL);
    printf("Done! Thread pid: %d\n", thread_pid);

    FILE *fp = fopen(status_file, "rb");

    printf("Looking into %s...\n", status_file);

    while(1) {
        char ch = fgetc(fp);
        if(feof(fp)) break;
        printf("%c", ch);
    }

    fclose(fp);

    getchar();

    return 0;
}

我得到以下内容:

This process pid: 10839
Creating new thread...
Done! Thread pid: 10840
Inside func.
Looking into /proc/self/status...
Name:   threadTest02
State:  R (running)
Tgid:   10839
Pid:    10839
PPid:   4777
TracerPid:      0
Uid:    1000    1000    1000    1000
Gid:    1000    1000    1000    1000
FDSize: 256
Groups: 4 20 24 27 30 46 107 123 124 1000 
VmPeak:     4300 kB
VmSize:     4300 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:       356 kB
VmRSS:       356 kB
VmData:      188 kB
VmStk:       136 kB
VmExe:         4 kB
VmLib:      1884 kB
VmPTE:        32 kB
VmSwap:        0 kB
Threads:        1
SigQ:   0/22869
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
Cpus_allowed:   3
Cpus_allowed_list:      0-1
Mems_allowed:   00000000,00000001
Mems_allowed_list:      0
voluntary_ctxt_switches:        1
nonvoluntary_ctxt_switches:     1
Terminating func...

那么,简而言之,我的计划做了什么？它创建一个新的线程clone并打印它/proc/self/status,以便我可以看到它的状态.由于我的线程休眠1秒钟,它在/proc/self/status打印时仍然存在.

但是,至少有两件事使我的线程不像普通线程.首先,正如您在上面看到的,进程'pid是10839而我的线程的pid是10840.因此,进程和我的线程没有相同的pid,就像在一个共同的线程中一样.其次,即使在我的线程创建之后,Threads:我的进程' /proc/self/status文件的字段仍然是1.所以,我的线程似乎不被识别为线程.

我的问题是,我的代码中缺少什么？我需要做些什么才能使我的线程像普通线程一样？第三个参数中clone是否缺少任何选项？

Answer 1

您可能希望看到标志CLONE_THREAD,它会将新线程放在与调用进程相同的线程组中.

一旦你给了CLONE_THREAD,它将使新线程与调用进程具有相同的pid和ppid.它用于posix线程.以下是我系统的输出.LWP专栏说这是一个轻量级的过程,具有不同的TID

UID        PID  PPID   LWP  C NLWP    SZ   RSS PSR STIME TTY          TIME CMD
anukalp  18398  9638 18398  0    2   464   456   0 10:56 pts/3    00:00:00 ./a.out
anukalp  18398  9638 18399  0    2   464   456   1 10:56 pts/3    00:00:00 ./a.out

此外,/ proc/self/status的输出发生了变化,我添加了几个printfs:

[anukalp @ localhost~] $ ./a.out

This process pid: 18398
Creating new thread...
Done! Thread pid: 18399 /* This is now thread id, available to caller of clone */
getpid(): ad pid: 18399
Inside func.
getpid(): 18398
getppid(): 9638
Looking into /proc/self/status...
Name:   a.out
State:  R (running)
Tgid:   18398
Pid:    18398
PPid:   9638
TracerPid:      0
Uid:    500     500     500     500
Gid:    500     500     500     500
FDSize: 256
Groups: 7 19 22 80 81 82 83 100 490 500 
VmPeak:     1856 kB
VmSize:     1856 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:       248 kB
VmRSS:       248 kB
VmData:      168 kB
VmStk:       140 kB
VmExe:         4 kB
VmLib:      1516 kB
VmPTE:        16 kB
VmSwap:        0 kB
Threads:        2
SigQ:   1/14050
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
Cpus_allowed:   00000000,000000ff
Cpus_allowed_list:      0-7
voluntary_ctxt_switches:        1
nonvoluntary_ctxt_switches:     0
Inside thread: thread pid = 18398
Inside thread: thread ppid = 9638

请让我知道这可不可以帮你!