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我是这里的新用户,我是c++的新手,所以对我来说有点难。。。所以我问你们一些问题
我正在为学校做一项工作,要求我实现线程优先级:
#include <pthread.h>
#include <stdio.h>
#include <sched.h>
int sched_yield(void);
// Parameters to print_function.
struct char_print_parms{
char character; // char to print
int count; // times to print
};
void* char_print (void* parameters){
int i;
struct char_print_parms* p;
p = (struct char_print_parms*) parameters;
for (i = 0; i < p->count; ++i){
fputc (p->character, stderr);
sched_yield();
}
return NULL;
}
int main (){
pthread_t thread1_id,thread2_id;
struct char_print_parms thread1_args,thread2_args;
// Create a new thread to print 200 x's.
thread1_args.character = 'x';
thread1_args.count = 200;
pthread_create (&thread1_id, NULL, &char_print, &thread1_args);
// Create a new thread to print 200 o's.
thread2_args.character = 'o';
thread2_args.count = 200;
pthread_create (&thread2_id, NULL,
&char_print, &thread2_args);
// main waits for the threads to complete
pthread_join(thread1_id, NULL);
pthread_join(thread2_id, NULL);
return 0;
}
这给出的是"oxoxoxo…"等
目标是获得更多的"o",直到它结束。
我所做的是:
#include <pthread.h>
#include <stdio.h>
#include <sched.h>
int sched_yield(void);
// Parameters to print_function.
struct char_print_parms{
char character; // char to print
int count; // times to print
};
void* char_print (void* parameters){
int i;
struct char_print_parms* p;
p = (struct char_print_parms*) parameters;
for (i = 0; i < p->count; ++i){
fputc (p->character, stderr);
sched_yield();
}
return NULL;
}
int main (){
pthread_t thread1_id,thread2_id;
struct char_print_parms thread1_args,thread2_args;
//new code lines
struct sched_param param;
pthread_attr_t pta;
pthread_attr_init(&pta);
pthread_attr_getschedparam(&pta, ¶m);
//end of new code lines
// Create a new thread to print 200 x's.
thread1_args.character = 'x';
thread1_args.count = 200;
//more new code lines
param.sched_priority = 0;
pthread_attr_setschedparam(&pta, ¶m);
pthread_setschedparam(thread1_id, SCHED_OTHER, ¶m);
//end of more new code lines
pthread_create (&thread1_id, NULL, &char_print, &thread1_args);
// Create a new thread to print 200 o's.
thread2_args.character = 'o';
thread2_args.count = 200;
//more new code lines 2
param.sched_priority = 10;
pthread_attr_setschedparam(&pta, ¶m);
pthread_setschedparam(thread2_id, SCHED_OTHER, ¶m);
//end of more new code lines 2
pthread_create (&thread2_id, NULL,
&char_print, &thread2_args);
// main waits for the threads to complete
pthread_join(thread1_id, NULL);
pthread_join(thread2_id, NULL);
return 0;
}
最后,我编译并尝试运行,但出现了一个错误:
分割失败(堆芯转储)
再一次,我是c++的新手,我的英语不是很好,但我想试着理解为什么这不起作用。欢迎任何帮助!
调用pthread_setschedparam
时,线程id变量尚未初始化。因此,您试图更改不确定线程上的参数。
更改优先级的最简单方法是在线程本身中执行。
关于未初始化的局部变量,在显式初始化之前,它们的值是不确定的。使用未初始化的局部变量会导致未定义的行为。
如果您在pthread_setschedparam
中看到该示例,您会看到它被pthread_self
调用以设置自己的线程优先级。您可以使用它在传递给包含优先级的线程的结构中添加一个字段,或者使用一个包装线程函数来设置优先级,然后调用实际的线程函数。
您应该首先调用pthread_create (&thread1_id, NULL, &char_print, &thread1_args);
来创建线程thread1_id
,然后您可以设置该线程的优先级。我修改了代码,它运行良好。
thread1_args.character = 'x';
thread1_args.count = 200;
pthread_create (&thread1_id, NULL, &char_print, &thread1_args);
//more new code lines
param.sched_priority = 0;
pthread_attr_setschedparam(&pta, ¶m);
pthread_setschedparam(thread1_id, SCHED_OTHER, ¶m);
// Create a new thread to print 200 o's.
thread2_args.character = 'o';
thread2_args.count = 200;
pthread_create (&thread2_id, NULL, &char_print, &thread2_args);
//more new code lines 2
param.sched_priority = 10;
pthread_attr_setschedparam(&pta, ¶m);
pthread_setschedparam(thread2_id, SCHED_OTHER, ¶m);
您可以阅读此链接:https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_MRG/2/html/Realtime_Reference_Guide/chap-Realtime_Reference_Guide-Priorities_and_policies.html.
我测试了这段代码,但每次的输出都不一样。