WebSVN – HelenOS-historic – Diff – /kernel/trunk/generic/src/synch/rwlock.c



 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
 
/** Reader/Writer locks
 *
 * A reader/writer lock can be held by multiple readers at a time.
 * Or it can be exclusively held by a sole writer at a time.
 */
 
/*
 * These locks are not recursive.
 * Neither readers nor writers will suffer starvation.

 * Initialize reader/writer lock.
 *
 * @param rwl Reader/Writer lock.
 */
void rwlock_initialize(rwlock_t *rwl) {
    spinlock_initialize(&rwl->lock, "rwlock_t");
    mutex_initialize(&rwl->exclusive);
    rwl->readers_in = 0;
}
 
/** Acquire reader/writer lock for reading

                 * rwl->lock is held.)
                 */
                interrupts_restore(ipl);
                break;
            case ESYNCH_OK_ATOMIC:
                panic("_mutex_lock_timeout()==ESYNCH_OK_ATOMIC\n");
                break;
            dafault:
                panic("invalid ESYNCH\n");
                break;
        }
        return rc;
    }
 

    spinlock_unlock(&rwl->lock);
    interrupts_restore(ipl);
}
 
 
/** Direct handoff of reader/writer lock ownership.
 *
 * Direct handoff of reader/writer lock ownership
 * to waiting readers or a writer.
 *
 * Must be called with rwl->lock locked.

 */
void let_others_in(rwlock_t *rwl, int readers_only)
{
    rwlock_type_t type = RWLOCK_NONE;
    thread_t *t = NULL;
    bool one_more = true;
   
    spinlock_lock(&rwl->exclusive.sem.wq.lock);
 
    if (!list_empty(&rwl->exclusive.sem.wq.head))
        t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link);

        if (!list_empty(&rwl->exclusive.sem.wq.head)) {
            t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link);
            if (t) {
                spinlock_lock(&t->lock);
                if (t->rwlock_holder_type != RWLOCK_READER)
                    one_more = false;
                spinlock_unlock(&t->lock); 
            }
        }
    } while ((type == RWLOCK_READER) && t && one_more);
 

Rev 552	Rev 557
Line 24...	Line 24...
24	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT	24	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF	25	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.	26	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27	*/	27	*/
28		28
29		-
-		29	/** Reader/Writer locks
30	/*	30	*
31	* Reader/Writer locks	31	* A reader/writer lock can be held by multiple readers at a time.
-		32	* Or it can be exclusively held by a sole writer at a time.
32	*/	33	*/
33		34
34	/*	35	/*
35	* These locks are not recursive.	36	* These locks are not recursive.
36	* Neither readers nor writers will suffer starvation.	37	* Neither readers nor writers will suffer starvation.
Line 73...	Line 74...
73	* Initialize reader/writer lock.	74	* Initialize reader/writer lock.
74	*	75	*
75	* @param rwl Reader/Writer lock.	76	* @param rwl Reader/Writer lock.
76	*/	77	*/
77	void rwlock_initialize(rwlock_t *rwl) {	78	void rwlock_initialize(rwlock_t *rwl) {
78	spinlock_initialize(&rwl->lock, "rwlock");	79	spinlock_initialize(&rwl->lock, "rwlock_t");
79	mutex_initialize(&rwl->exclusive);	80	mutex_initialize(&rwl->exclusive);
80	rwl->readers_in = 0;	81	rwl->readers_in = 0;
81	}	82	}
82		83
83	/** Acquire reader/writer lock for reading	84	/** Acquire reader/writer lock for reading
Line 216...	Line 217...
216	* rwl->lock is held.)	217	* rwl->lock is held.)
217	*/	218	*/
218	interrupts_restore(ipl);	219	interrupts_restore(ipl);
219	break;	220	break;
220	case ESYNCH_OK_ATOMIC:	221	case ESYNCH_OK_ATOMIC:
221	panic("_mutex_lock_timeout()==ESYNCH_OK_ATOMIC");	222	panic("_mutex_lock_timeout()==ESYNCH_OK_ATOMIC\n");
222	break;	223	break;
223	dafault:	224	dafault:
224	panic("invalid ESYNCH");	225	panic("invalid ESYNCH\n");
225	break;	226	break;
226	}	227	}
227	return rc;	228	return rc;
228	}	229	}
229		230
Line 281...	Line 282...
281	spinlock_unlock(&rwl->lock);	282	spinlock_unlock(&rwl->lock);
282	interrupts_restore(ipl);	283	interrupts_restore(ipl);
283	}	284	}
284		285
285		286
286	/** Direct handoff	287	/** Direct handoff of reader/writer lock ownership.
287	*	288	*
288	* Direct handoff of reader/writer lock ownership	289	* Direct handoff of reader/writer lock ownership
289	* to waiting readers or a writer.	290	* to waiting readers or a writer.
290	*	291	*
291	* Must be called with rwl->lock locked.	292	* Must be called with rwl->lock locked.
Line 304...	Line 305...
304	*/	305	*/
305	void let_others_in(rwlock_t *rwl, int readers_only)	306	void let_others_in(rwlock_t *rwl, int readers_only)
306	{	307	{
307	rwlock_type_t type = RWLOCK_NONE;	308	rwlock_type_t type = RWLOCK_NONE;
308	thread_t *t = NULL;	309	thread_t *t = NULL;
309	int one_more = 1;	310	bool one_more = true;
310		311
311	spinlock_lock(&rwl->exclusive.sem.wq.lock);	312	spinlock_lock(&rwl->exclusive.sem.wq.lock);
312		313
313	if (!list_empty(&rwl->exclusive.sem.wq.head))	314	if (!list_empty(&rwl->exclusive.sem.wq.head))
314	t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link);	315	t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link);
Line 350...	Line 351...
350	if (!list_empty(&rwl->exclusive.sem.wq.head)) {	351	if (!list_empty(&rwl->exclusive.sem.wq.head)) {
351	t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link);	352	t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link);
352	if (t) {	353	if (t) {
353	spinlock_lock(&t->lock);	354	spinlock_lock(&t->lock);
354	if (t->rwlock_holder_type != RWLOCK_READER)	355	if (t->rwlock_holder_type != RWLOCK_READER)
355	one_more = 0;	356	one_more = false;
356	spinlock_unlock(&t->lock);	357	spinlock_unlock(&t->lock);
357	}	358	}
358	}	359	}
359	} while ((type == RWLOCK_READER) && t && one_more);	360	} while ((type == RWLOCK_READER) && t && one_more);
360		361

Subversion Repositories HelenOS-historic

(root)/kernel/trunk/generic/src/synch/rwlock.c – Rev 552 → 557