是nice()用于更改线程优先级或进程优先级的吗? [英] is nice() used to change the thread priority or the process priority?

问题描述

nice的手册页上说:"nice()将inc添加到调用过程的好值.因此，我们可以使用它来更改<创建的线程的好值吗? c1>?

The man page for nice says "nice() adds inc to the nice value for the calling process. So, can we use it to change the nice value for a thread created by pthread_create?

看来我们可以为每个线程设置好值.

It seems that we do can set the nice value per thread.

我编写了一个应用程序，为不同的线程设置了不同的值，并观察到"nicer"线程的调度优先级较低.检查输出，我发现字符串"high priority ................"的输出频率更高.

I wrote a application ,setting different nice value for different thread, and observed that the "nicer" thread has been scheduled with lower priority. Checking the output, I found that the string "high priority ................" get outputted more frequently.

void * thread_function1(void *arg)
{

 pid_t tid = syscall(SYS_gettid);

 int ret = setpriority(PRIO_PROCESS, tid, -10);
 printf("tid of high priority thread %d , %d\n",tid ,getpriority(PRIO_PROCESS,tid));
 while(1){
  printf("high priority ................\n");
    }

}


void * thread_function(void *arg)
{
 pid_t tid = syscall(SYS_gettid);
 int ret = setpriority(PRIO_PROCESS, tid, 10);
 printf("tid of low priority thread %d , %d \n",tid ,getpriority(PRIO_PROCESS,tid));
while(1) 
{

  printf("lower priority\n");
}
}


int main()
{

pthread_t id1;
pthread_t id2;

pid_t pid = getpid();
pid_t tid = syscall(SYS_gettid);

printf("main thread : pid = %d , tid = %d \n" , pid, tid);
pthread_create(&id1, NULL, thread_function1,  NULL);
pthread_create(&id2, NULL,thread_function,   NULL);

pthread_join(id1, NULL);
pthread_join(id2, NULL);


}

推荐答案

pthread手册页说:

POSIX.1还要求线程共享一系列其他属性 (即，这些属性是进程范围的，而不是每个线程的):

POSIX.1 also requires that threads share a range of other attributes (i.e., these attributes are process-wide rather than per-thread):

[...]

• 很好的值(setpriority(2))

• nice value (setpriority(2))

因此，从理论上讲，"niceness"值是该进程的全局值，并由所有线程共享，因此您不应为一个或多个单独的线程设置特定的niceness.

So, theoretically, the "niceness" value is global to the process and shared by all threads, and you should not be able to set a specific niceness for one or more individual threads.

但是，相同的手册页也显示:

However, the very same man page also says:

LinuxThreads

此实现的显着特征如下:

The notable features of this implementation are the following:

[...]

• 线程不共享通用的nice值.

NPTL

[...]

NPTL与POSIX.1仍有一些不符之处:

NPTL still has a few non-conformances with POSIX.1:

• 线程不共享一个通用的nice值.

因此，事实证明Linux上的两个线程实现(LinuxThreads和NPTL)实际上都违反了POSIX.1，您可以通过将tid传递给

So it turns out that both threading implementations on Linux (LinuxThreads and NPTL) actually violate POSIX.1, and you can set a specific niceness for one or more individual threads by passing a tid to setpriority() on these systems.

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