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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 NSRecursiveLock
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fs28 f0 b fs24 Inherits From:tab b0 fs28 f1 NSObject
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fs28 s12 f0 b fs24 Conforms To:tab b0 fs28 f1 NSLocking
fi0 NSObject (NSObject)
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fs28 s13 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 NSRecursiveLock is used for locks that need to be reacquired by the same thread.
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fs28 An NSRecursiveLock locks a critical section of code such that a single thread can reaquire the lock multiple times without deadlocking, while preventing access by other threads. (Note that this implies that a recursive lock will not protect a critical section from a signal handler interrupting the thread holding the lock.) Here is an example where a recursive lock functions properly but other lock types would deadlock:
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fs28 pard s10 li1231 fi0 ri1007 ql f2 fs20 // create the lock only once!
NSRecursiveLock *theLock = [NSRecursiveLock new];
/* ...other code... */
[theLock lock];
/* ... possibly a long time of fussing with global data... */
[theLock lock]; /* possibly invoked in a subroutine */
[theLock unlock];
[theLock unlock];
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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 Acquiring a Lock
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fs28 fi-6552 {f3 -} (BOOL)b tryLockb0 tab Attempts to acquire a lock. Returns YES if successful and NO otherwise. This method can be called repeatedly to produce nested locks.
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