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paperh18648 margl-907 margr0 margt0 margb0 fi0 ri0 ql sb0 f1 fs24 Copyright f3 'e3f1 1994 by NeXT Computer, Inc. All Rights Reserved.
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fs36 NSConditionLock
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fs28 f0 b fs24 Inherits From:tab b0 fs28 f1 NSObject
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fs28 s6 f0 b fs24 Conforms To:tab b0 fs28 f1 NSLocking
fi0 NSObject (NSObject)
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fs28 s7 fi-2771 f0 b fs24 Declared In:tab b0 fs28 f1 Foundation/NSLock.h
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fs28 Class Description
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fs28 NSConditionLock objects are used to lock and unlock threads when specified conditions occur.
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fs28 The user of an NSConditionLock object can lock when a process enters a particular state and can set the state to something else when releasing the lock. The states are defined by the lock'27s user. NSConditionLock is well suited to synchronizing different modules such as a producer and a consumer where the two modules must share data, but the consumer must sleep until a condition is met such as more data being available.
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fs28 The NSConditionLock class provides four ways of locking its objects (b lockb0 ,b lockWhenCondition:b0 ,b tryLockb0 , and b tryLockWhenConditionb0 ) and two ways of unlocking (b unlock b0 andb unlockWithCondition:b0 ). Any combination of locking method and unlocking method is legal.
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fs28 The following example shows how the producer-consumer problem might be handled using condition locks. The producer need not wait for a condition, but must wait for the lock to be made available so it can safely create shared data. For example, a producer could use a lock this way:
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fs28 pard s5 li1231 fi0 ri1007 ql f2 fs20 /* create the lock only once */
id condLock = [NSConditionLock new];
[condLock lock];
/* Manipulate global data... */
[condLock unlockWithCondition:HAS_DATA];
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fs28 Multiple consumer threads can then lock until there'27s data available and everyone is out of locked critical sections. In the following code sample, the consumer sleeps until the producer invokes b unlockWithCondition:b0 with the parameter HAS_DATA:
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fs28 pard s5 li1231 fi0 ri1007 ql f2 fs20 [condLock lockWhenCondition:HAS_DATA];
/* Manipulate global data if necessary... */
[condLock unlockWithCondition:(moreData ? HAS_DATA : NO_DATA)];
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fs28 An NSConditionLock object doesn'27t busy-wait, so it can be used to lock time-consuming operations without degrading system performance.
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fs28 The NSConditionLock, NSLock, and NSRecursiveLock classes all implement the NSLocking protocol with various features and performance characteristics; see the other class descriptions for more information.
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fs28 Initializing an NSConditionLock
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fs28 fi-6552 {f3 -} (id)b initWithCondition:b0 (int)i conditioni0 tab Initializes a newly created NSConditionLock and sets its condition to i conditioni0 .
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fs28 Returning the Condition
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fs28 fi-6552 {f3 -} (int)b conditionb0 tab Returns the receiver'27s condition, the state that must be achieved before a conditional lock can be acquired or released.
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fs28 Acquiring and Releasing a Lock
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fs28 fi-6552 {f3 -} (void)b lockWhenCondition:b0 (int)i conditioni0 tab Attempts to acquire a lock when i conditioni0 is met. Blocks until i conditioni0 is met.
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fs28 fi-6552 {f3 -} (void)b unlockWithCondition:b0 (int)i conditioni0 tab Releases the lock and sets lock state to i conditioni0 .
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fs28 fi-6552 {f3 -} (BOOL)b tryLockb0 tab Attempts to acquire a lock. Returns YES if successful and NO otherwise.
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fs28 fi-6552 {f3 -} (BOOL)b tryLockWhenCondition:b0 (int)i conditioni0 tab Attempts to acquire a lock when i conditioni0 is met. Returns YES if successful and NO otherwise.
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