NSConditionLock is a class that implements the NSLocking protocol and is used to perform thread locks that are associated with specific, user-defined conditions. The idea behind NSConditionLock is that a thread can acquire a lock only if some arbitrary condition has been satisfied. See Chapter 2.

@interface NSConditionLock : NSObject <NSLocking>
// Initializers
- (id)initWithCondition:(int)condition;
// Instance Methods
- (int)condition;
- (BOOL)lockBeforeDate:(NSDate *)limit;
- (void)lockWhenCondition:(int)condition;
- (BOOL)lockWhenCondition:(int)condition beforeDate:(NSDate *)limit;
- (BOOL)tryLock;
- (BOOL)tryLockWhenCondition:(int)condition;
- (void)unlockWithCondition:(int)condition;
// Methods Implementing NSLocking
- (void)lock;
- (void)unlock;