Eucalyptus分析三 lock

Eucalyptus的封锁没有级别，没有类型，只有一种，就是互斥锁，就是把互斥量，条件变量封装到一起了，来实现操作系统中的PV操作，

直接看下面的函数，可直接看懂

 

typedef struct sem_struct {
    int sysv;
    sem_t * posix;
    pthread_mutex_t mutex;
    pthread_cond_t cond;
    int usemutex, mutwaiters, mutcount;
    char * name;
} sem;

 

 

sem * sem_alloc (const int val, const char * name)
{
    DECLARE_ARG;

    sem * s = malloc (sizeof (sem));
    if (s==NULL) return NULL;
    bzero (s, sizeof (sem));
    s->sysv = -1;

    if (name && !strcmp(name, "mutex")) { /* use pthread mutex */
      s->usemutex = 1;
      s->mutcount = val;
      s->mutwaiters = 0;
      pthread_mutex_init(&(s->mutex), NULL);
      pthread_cond_init(&(s->cond), NULL);
    } else if (name) { /* named semaphores */
        if ( sem_unlink (name) == 0) { /* clean up in case previous sem holder crashed */
            logprintfl (EUCAINFO, "sem_alloc(): cleaning up old semaphore %s/n", name);
        }
        if ((s->posix = sem_open (name, O_CREAT | O_EXCL, 0644, val))==SEM_FAILED) {
            free (s);
            return NULL;
        }
        s->name = strdup (name);

    } else { /* SYS V IPC semaphores */
        s->sysv = semget (IPC_PRIVATE, /* private to process & children */
                        1, /* only need one */
                        IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR /* user-only */);
        if (s->sysv<0) {
            free (s);
            return NULL;
        }
       
        /* set the value */
        arg.val = val;
        if (semctl(s->sysv, 0, SETVAL, arg) == -1) {
            free (s);
            return NULL;
        }
    }
   
    return s;
}

int sem_p (sem * s)
{
    int rc;
    if (s && s->usemutex) {
        rc = pthread_mutex_lock(&(s->mutex));
 s->mutwaiters++;
 while(s->mutcount == 0) {
   pthread_cond_wait(&(s->cond), &(s->mutex));
 }
 s->mutwaiters--;
 s->mutcount--;
 rc = pthread_mutex_unlock(&(s->mutex));
 return(rc);
    }

    if (s && s->posix) {
        return sem_wait(s->posix);
    }

    if (s && s->sysv > 0) {
        struct sembuf sb = {0, -1, 0};
        return semop (s->sysv, &sb, 1);
    }

    return -1;
}

int sem_v (sem * s)
{
    int rc;
    if (s && s->usemutex) {
        rc = pthread_mutex_lock(&(s->mutex));
        if (s->mutwaiters > 0) {
   rc = pthread_cond_signal(&(s->cond));
 }
 s->mutcount++;
        rc = pthread_mutex_unlock(&(s->mutex));
 return(rc);
    }

    if (s && s->posix) {
        return sem_post(s->posix);
    }

    if (s && s->sysv > 0) {
        struct sembuf sb = {0, 1, 0};
        return semop (s->sysv, &sb, 1);
    }
   
    return -1;
}

void sem_free (sem * s)
{
    DECLARE_ARG;
   
    if (s && s->posix) {
        sem_close (s->posix);
        sem_unlink (s->name);
        free (s->name);
    }
   
    if (s && s->sysv > 0) {
        semctl (s->sysv, 0, IPC_RMID, arg); /* TODO: check return */
    }
   
    free (s);
}