c – 具有实时优先级的pthreads

我需要管理具有不同优先级的线程池,因此我编写了以下线程启动过程：

static
int startup(thrd_t *thrd,thrd_sync_t *sync,int prio)
{
    pthread_attr_t attr;
    int err;
    struct sched_param param = {
        .sched_priority = prio
    };

    assert(pthread_attr_init(&attr) == 0);
    assert(pthread_attr_setschedpolicy(&attr,SCHED_FIFO) == 0);
    assert(pthread_attr_setschedparam(&attr,&param) == 0);
    err = pthread_create(&thrd->handler,&attr,thread_routine,(void *)thrd);
    pthread_attr_destroy(&attr);

    return err;
}

原则上,不应允许非特权用户执行此代码：pthread_create()调用应返回EPERM,因为运行具有高优先级的线程具有安全隐患.

出乎意料的是,它适用于普通用户,但它根本不尊重给定的优先级.

我尝试通过删除pthread_attr_t并在创建线程后设置调度属性来修改代码：

static
int startup(thrd_t *thrd,int prio)
{
    pthread_attr_t attr;
    int err;
    struct sched_param param = {
        .sched_priority = prio
    };

    err = pthread_create(&thrd->handler,NULL /*&attr*/,(void *)thrd);
    if (err != 0) return err;

    err = pthread_setschedparam(thrd->handler,SCHED_FIFO,&param);
    if (err != 0) return err;

    return err;
}

顺便说一下,这种方法管理起来要困难得多,因为如果出现错误,我需要终止新创建的线程.至少它似乎在权限要求方面正常工作(只有root可以执行此操作),但仍然不遵守优先级.

难道我做错了什么？

编辑

我刚刚添加了以下一段由每个线程执行的代码：

static
void getinfo ()
{
    struct sched_param param;
    int policy;

    sched_getparam(0,&param);
    DEBUG_FMT("Priority of this process: %d",param.sched_priority);

    pthread_getschedparam(pthread_self(),&policy,&param);

    DEBUG_FMT("Priority of the thread: %d,current policy is: %d and should be %d",param.sched_priority,policy,SCHED_FIFO);
}

使用第一种方法(即pthread_attr_t方法),结果是pthread_attr_setschedpolicy完全无效,因为优先级为0且策略不是SCHED_FIFO.

使用第二种方法(即pthread_setschedparam方法),该函数打印预期的数据,但执行仍然以错误的方式运行.

解决方法

我认为您还必须使用pthread_attr_setinheritsched来确保考虑对优先级设置的更改.从手册页：

PTHREAD_INHERIT_SCHED
Specifies that the scheduling policy and associated attributes are
to be inherited from the creating
thread,and the scheduling attributes
in this attr argument are to be
ignored.

PTHREAD_EXPLICIT_SCHED
Specifies that the scheduling policy and associated attributes are
to be set to the corresponding values
from this attribute object.

在手册页中,您还有以下内容：

The default setting of the inherit-scheduler attribute in a newly initialized thread attributes object is PTHREAD_INHERIT_SCHED.