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C에서 세마포어 개념을 중심으로 머리를 감싸려고 노력했지만 몇 가지 제한된 성공을 거두었습니다. 내가 이해하는 C에서 세마포 값이 0이면 sem_wait()는 해당 세마포 값이 더 이상 0이 아닐 때까지 해당 스레드를 차단해야합니다.예기치 않은 세마포어 동작, sem_wait()를 넘어서 실행되는 스레드
내 문제는 다음과 같습니다. 몇 가지 매우 빠른 예제 코드 (아래), 그리고 왜 모르겠지만 일단 스레드가 만들어지면 semawait() 값이 0 인 것처럼 보일지라도 sem_wait() 이상의 코드를 실행하는 것 같습니다. 이것은있을 것입니다.
편집 : Perception의 조언에 따라 sem_wait()의 반환 값을 확인했으며 errno를 "Operation Timed Out"으로 설정 한 것 같습니다. 지금까지 내가 말할 수있는 한, sem_timedwait()를 사용하지 않는다면 이런 일이 일어나서는 안된다. 아직 파고 ...
편집 2 : Oop. 내 출력을 더 자세히 읽어야합니다. 실제로 "구현되지 않은 기능"으로 설정되어 있습니다.
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <errno.h>
// vars
int jobsInQueue, currentJob;
sem_t *semaphore;
pthread_t threads[10];
int runningThreads = 0;
// prototypes
void *do_work(void *arg);
void add_job();
int main()
{
// i for the for loop used to create the threads
int i;
// counter for jobs in the queue
jobsInQueue = 0;
// indicator for the current job
currentJob = 0;
// indicator for whether we have reached the limit imposed in the while loop used for adding jobs
int reachedlimit = 0;
// create the semaphore
semaphore = sem_open("semaphore", O_CREAT, 0600, 0);
// get the value of the semaphore and temporarily store it in reachedlimit
sem_getvalue(semaphore, &reachedlimit);
// print off the value of the semaphore. I think I'm crazy because the threads are executing code
// before the semaphore is posted to, but this appears to be zero...
fprintf(stderr, "semaphore: %d", reachedlimit);
fflush(stderr);
// set reachedlimit back to zero because we expect it to be zero below
reachedlimit = 0;
for(i = 0; i < 10; ++i)
{
// create a pthread
pthread_create(&threads[i], NULL, &do_work, (void *)i);
// increment the number of running threads
runningThreads++;
}
// sleep for a couple of seconds just as separator space
sleep(2);
// while there are threads running
while(runningThreads > 0)
{
// sleep for a tenth of a second
usleep(100000);
// after that, if there are 1000 or more jobs in the queue, we've reached the number of total jobs we want
if(jobsInQueue >= 1000) reachedlimit = 1;
// if we haven't reached that, then add another job
if(reachedlimit == 0) add_job();
// print that we're still sleeping and the number of jobs in the queue.
fprintf(stderr, "Still sleeping. Jobs in queue: %d\n", jobsInQueue);
fflush(stderr);
}
}
void *do_work(void *arg)
{
// when the thread is created, print this thread's number to the console
fprintf(stderr, "I am thread %d.\n", (int)arg);
fflush(stderr);
// then loop infinitely doing the following...
while(1)
{
// wait until the semaphore's value is no longer zero <-- doesn't seem to do this
sem_wait(semaphore);
// if we are on the 1000th job, terminate the thread
if (currentJob >= 1000) {
runningThreads--;
fprintf(stderr, "Thread %d terminated", (int)arg);
fflush(stderr);
pthread_exit((void *)1);
}
// otherwise, increment the current job counter
currentJob++;
// tell the console that this thread took a job
fprintf(stderr, "Thread %d: I took a job.: %d\n", (int)arg, currentJob);
fflush(stderr);
// subtract one from the count of jobs in the queue
jobsInQueue--;
// sleep for at least one second before taking another job
sleep(1);
}
// this will never happen because the while loop will never be broken
runningThreads--;
return NULL;
}
void add_job()
{
// increment the count of jobs in the queue
jobsInQueue++;
// print that a job has been added
fprintf(stderr, "Job added\n");
fflush(stderr);
// post to the semaphore, which should essentially release the job for "processing" if I understand correctly.
sem_post(semaphore);
}
일부 샘플 출력 : 특별히 연결을 해제하지 않는 한
semaphore: 0
I am thread 0.
I am thread 1.
Thread 0: I took a job.: 1
I am thread 2.
I am thread 3.
Thread 1: I took a job.: 2
I am thread 4.
I am thread 5.
I am thread 6.
Thread 2: I took a job.: 3
I am thread 7.
I am thread 8.
Thread 3: I took a job.: 4
I am thread 9.
Thread 4: I took a job.: 5
Thread 5: I took a job.: 6
Thread 6: I took a job.: 7
Thread 7: I took a job.: 8
Thread 8: I took a job.: 9
Thread 9: I took a job.: 10
Thread 0: I took a job.: 12
Thread 4: I took a job.: 11
Thread 5: I took a job.: 13
Thread 6: I took a job.: 14
Thread 1: I took a job.: 15
Thread 8: I took a job.: 17
Thread 3: I took a job.: 16
Thread 7: I took a job.: 18
Thread 2: I took a job.: 19
Thread 9: I took a job.: 20
Thread 0: I took a job.: 21
Thread 1: I took a job.: 22
Thread 8: I took a job.: 23
Thread 3: I took a job.: 24
Thread 5: I took a job.: 25
Thread 7: I took a job.: 26
Thread 6: I took a job.: 27
Thread 2: I took a job.: 29
Thread 4: I took a job.: 28
Thread 9: I took a job.: 30
Job added
Still sleeping. Jobs in queue: -29
Job added
Still sleeping. Jobs in queue: -28
Job added
Still sleeping. Jobs in queue: -27
Job added
Still sleeping. Jobs in queue: -26
Job added
Still sleeping. Jobs in queue: -25
Job added
Still sleeping. Jobs in queue: -24
Job added
Still sleeping. Jobs in queue: -23
Job added
Still sleeping. Jobs in queue: -22
Job added
Still sleeping. Jobs in queue: -21
Thread 3: I took a job.: 31
Thread 0: I took a job.: 32
Thread 5: I took a job.: 33
Thread 2: I took a job.: 34
Thread 1: I took a job.: 35
Thread 7: I took a job.: 36
Thread 9: I took a job.: 37
Thread 8: I took a job.: 38
Thread 6: I took a job.: 39
Thread 4: I took a job.: 40
Job added
Still sleeping. Jobs in queue: -30
Job added
Still sleeping. Jobs in queue: -29
Job added
Still sleeping. Jobs in queue: -28
Job added
Still sleeping. Jobs in queue: -27
Job added
Still sleeping. Jobs in queue: -26
Job added
Still sleeping. Jobs in queue: -25
'sem_wait'의 반환 값을 테스트하여 호출이 실제로 성공했는지 확인해야합니다. – Perception
또한'sem_open()'의 반환 값을 테스트해야합니다. – caf