More comments on the ticket lock code

include/ucore/ticket_lock.h

@@ -3,7 +3,9 @@
 
 #include <pthread.h>
 
-/** An fair alternative to a bare pthread_mutex_t to prevent starvation*/
+/** An fair alternative to a bare pthread_mutex_t to prevent starvation.
+ * The members of UCTicketLock must never be accessed directly.
+ */
 struct UCTicketLock {
     pthread_cond_t cond;
     pthread_mutex_t mutex;

src/ticket_lock.c

@@ -1,6 +1,13 @@
 #include <assert.h>
 #include "ucore/ticket_lock.h"
 
+//pthread implementation of http://en.wikipedia.org/wiki/Ticket_lock
+//The underlying phtread mutex is not held while the lock is acquired.
+//This will allow other threads to enqueue itself. 
+//
+//The condition variable is needed to wake up threads waiting to acquire 
+//the lock instead of letting the system block on the pthread mutex while waiting.
+
 int uc_ticket_lock_init(struct UCTicketLock *lock)
 {
     return uc_ticket_lock_init_ex(lock, NULL, NULL);