我不理解这里 printf() 的行为。如果我锁定整个功能，那么打印出来就可以了。但是，如果我修改代码，使其只锁定具有数据依赖性的代码，一个线程永远不会结束？
这是代码:
queue_lock 是问题所在。
void *professor_write(int *param){
pthread_mutex_lock(&pro_id_update);
param[0]++;
int id = param[0];
pthread_mutex_unlock(&pro_id_update);
printf("STARTING Professor %d\n", id);
//Each professor assigning <num_assignings> times
for(int i = 0; i < param[1]; i++){
int num_assignments;
if(param[5] == param[4])
num_assignments = param[5];
else{
//Random number of assignments in range min_num_assignment ~ max_num_assignment
num_assignments = rand() % (param[5] - param[4]) + param[4];
}
for(int j = 0; j < num_assignments; j++){
int wait_time;
if(param[3] == param[4])
wait_time = param[3];
else{
//Random wait time in range min_prof_wait ~ max_prof_wait
wait_time = rand() % (param[3] - param[2]) + param[2];
}
sleep(wait_time);
int hours;
if(param[7] == param[6])
hours = param[6];
else{
//Random hours range in min_assignment_hours ~ max_assignment_hours
hours = rand() % (param[7] - param[6]) + param[6];
}
struct assignment tmp;
tmp.hours = hours;
tmp.numberOfStudents = param[8];
tmp.prof_id = id;
pthread_mutex_lock(&queue_lock);
//queue is full wait for students to read
while(param[9] == count)
printf("full\n");
// pthread_cond_wait(&empty, &queue_lock);
fprintf(stdout, "ASSIGN Professor %d adding Assignment %d: %d Hours\n", id, in, hours);
queue[in] = tmp;
in = (in + 1) % param[9];
count++;
//signal student the queue is not empty
// pthread_cond_signal(&fill);
pthread_mutex_unlock(&queue_lock);
}
}
printf("EXITING Professor %d\n", id);
pthread_exit(0);
}
示例输出:
num_assignings: 4
min_prof_wait: 1
max_prof_wait: 5
min_num_assignments: 1
max_num_assignments: 1
min_assignment_hours: 1
max_assignment_hours: 5
num_professors: 2
num_students: 2
students_per_assignment: 2
queue_size: 256
STARTING Professor 1
STARTING Professor 2
ASSIGN Professor 2 adding Assignment 0: 4 Hours
ASSIGN Professor 1 adding Assignment 1: 4 Hours
ASSIGN Professor 1 adding Assignment 2: 2 Hours
ASSIGN Professor 2 adding Assignment 3: 2 Hours
ASSIGN Professor 2 adding Assignment 4: 4 Hours
ASSIGN Professor 1 adding Assignment 5: 4 Hours
ASSIGN Professor 2 adding Assignment 6: 1 Hours
EXITING Professor 2
输出如果锁定整个事情:
num_assignings: 4
min_prof_wait: 1
max_prof_wait: 5
min_num_assignments: 1
max_num_assignments: 1
min_assignment_hours: 1
max_assignment_hours: 5
num_professors: 2
num_students: 2
students_per_assignment: 2
queue_size: 256
STARTING Professor 1
ASSIGN Professor 1 adding Assignment 0: 2 Hours
ASSIGN Professor 1 adding Assignment 1: 1 Hours
ASSIGN Professor 1 adding Assignment 2: 3 Hours
ASSIGN Professor 1 adding Assignment 3: 4 Hours
EXITING Professor 1
STARTING Professor 2
ASSIGN Professor 2 adding Assignment 4: 4 Hours
ASSIGN Professor 2 adding Assignment 5: 2 Hours
ASSIGN Professor 2 adding Assignment 6: 4 Hours
ASSIGN Professor 2 adding Assignment 7: 1 Hours
EXITING Professor 2
最佳答案
我已经精简了一个示例应用程序，它的行为有时与您发布的问题相同。
为了重新创建它，我“忘记”加入线程 2。
您能否确保加入所有线程，并可能发布调用线程的 block ？
根据您的评论，我认为这是最有可能的。当 prof2 在 prof1 之前完成时，我的应用程序表现出相同的行为。
In some cases, the program runs as predicted. But other times, the eighth element never updated to the queue.
#include <pthread.h>
#include <stdio.h>
pthread_mutex_t queue_lock;
void *professor_write(void *params){
int prof = ((int*)params)[0];
int runs = ((int*)params)[1];
int i;
printf("STARTING Professor %d\n", prof);
//Each professor assigning <num_assignings> times
for(i = 0; i < runs; i++){
sleep(rand() % (5));
pthread_mutex_lock(&queue_lock);
fprintf(stdout, "ASSIGN Professor %d adding Assignment %d:\n", prof, i);
pthread_mutex_unlock(&queue_lock);
}
printf("EXITING Professor %d\n", prof);
pthread_exit(0);
}
int main()
{
int prof1[2]={1,4};
int prof2[2]={2,4};
pthread_t prof2_thread;
pthread_t prof1_thread;
pthread_create(&prof1_thread, NULL, professor_write, prof1);
pthread_create(&prof2_thread, NULL, professor_write, prof2);
pthread_join(prof1_thread, NULL);
//pthread_join(prof2_thread, NULL); // commented out to force error
return 0;
}
我得到这个输出，当 prof2 首先完成时成功:
STARTING Professor 1
STARTING Professor 2
ASSIGN Professor 2 adding Assignment 0:
ASSIGN Professor 1 adding Assignment 0:
ASSIGN Professor 1 adding Assignment 1:
ASSIGN Professor 2 adding Assignment 1:
ASSIGN Professor 2 adding Assignment 2:
ASSIGN Professor 2 adding Assignment 3:
EXITING Professor 2
ASSIGN Professor 1 adding Assignment 2:
ASSIGN Professor 1 adding Assignment 3:
EXITING Professor 1
或者当 prof1 首先完成时(我更改了 rand 值以使另一个线程首先完成，或者您可以交换连接。):
STARTING Professor 1
STARTING Professor 2
ASSIGN Professor 1 adding Assignment 0:
ASSIGN Professor 2 adding Assignment 0:
ASSIGN Professor 1 adding Assignment 1:
ASSIGN Professor 2 adding Assignment 1:
ASSIGN Professor 1 adding Assignment 2:
ASSIGN Professor 2 adding Assignment 2:
ASSIGN Professor 1 adding Assignment 3:
EXITING Professor 1
关于c - 多线程的 printf()，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29112290/