我写了一个测试程序来测试一下SCHED_FIFO。我了解到SCHED_FIFO不能被SCHED_OTHER线程抢占。但是我无法解释多次运行同一程序时获得的结果。
/* Includes */
#include <unistd.h> /* Symbolic Constants */
#include <sys/types.h> /* Primitive System Data Types */
#include <errno.h> /* Errors */
#include <stdio.h> /* Input/Output */
#include <stdlib.h> /* General Utilities */
#include <pthread.h> /* POSIX Threads */
#include <string.h> /* String handling */
#include <sched.h>
/* prototype for thread routine */
void print_message_function ( void *ptr );
void print_message_function1 ( void *ptr );
/* struct to hold data to be passed to a thread
* this shows how multiple data items can be passed to a thread
*/
typedef struct str_thdata
{
int thread_no;
int thread_value;
char message[100];
} thdata;
int main()
{
pthread_t thread1, thread2; /* thread variables */
thdata data1, data2; /* structs to be passed to threads */
/* initialize data to pass to thread 1 */
data1.thread_no = 1;
data1.thread_value = 0;
strcpy(data1.message, "Hello!");
/* initialize data to pass to thread 2 */
data2.thread_no = 2;
data2.thread_value = 10000;
strcpy(data2.message, "Hi!");
/* create threads 1 and 2 */
pthread_create (&thread1, NULL, (void *) &print_message_function, (void *) &data1);
pthread_create (&thread2, NULL, (void *) &print_message_function1, (void *) &data2);
/* Main block now waits for both threads to terminate, before it exits
* If main block exits, both threads exit, even if the threads
* have not finished their work
*/
pthread_join(thread1, NULL);
pthread_join(thread2, NULL);
/* exit */
exit(0);
} /* main() */
/**
* print_message_function is used as the start routine for the threads used
* it accepts a void pointer
**/
void print_message_function ( void *ptr )
{
thdata *data;
data = (thdata *) ptr; /* type cast to a pointer to thdata */
struct sched_param param;
//int priority=10;
/* sched_priority will be the priority of the thread */
//param.sched_priority = priority;
/* only supported policy, others will result in ENOTSUP */
int policy = SCHED_OTHER;
/* scheduling parameters of target thread */
pthread_setschedparam(pthread_self(), policy, ¶m);
printf("Thread %d says sched policy %d \n", data->thread_no, SCHED_OTHER);
pthread_getschedparam(pthread_self(),&policy,¶m);
printf("Thread %d says %s %d \n", data->thread_no, data->message,policy);
int i=0;
/* do the work */
printf("Thread %d says %s %d \n", data->thread_no, data->message,(int)pthread_self());
for(i=0;i<100;i++)
printf("Thread %d says %d \n", data->thread_no,data->thread_value++);
pthread_exit(0); /* exit */
} /* print_message_function ( void *ptr ) */
void print_message_function1 ( void *ptr )
{
thdata *data;
data = (thdata *) ptr; /* type cast to a pointer to thdata */
struct sched_param param;
int priority=10;
/* sched_priority will be the priority of the thread */
param.sched_priority = priority;
/* only supported policy, others will result in ENOTSUP */
int policy = SCHED_FIFO;
/* scheduling parameters of target thread */
pthread_setschedparam(pthread_self(), policy, ¶m);
printf("Thread %d says sched policy %d \n", data->thread_no, SCHED_FIFO);
pthread_getschedparam(pthread_self(),&policy,¶m);
printf("Thread %d says %s %d \n", data->thread_no, data->message,policy);
int i=0;
/* do the work */
printf("Thread %d says %s %d \n", data->thread_no, data->message,(int)pthread_self());
for(i=0;i<100;i++)
printf("Thread %d says %d \n", data->thread_no,data->thread_value++);
pthread_exit(0); /* exit */
} /* print_message_function ( void *ptr ) */
我在多次运行中得到了意想不到的结果，我看到线程SCHED_FIFO抢占了SCHED_OTHER，即根据程序，线程 2 处于FIFO模式，而线程 1处于SCHED_OTHER模式。我多次看到thread2被thread1抢占。
有人可以帮我找出问题吗？