Class

NSDistributedLock

A lock that multiple applications on multiple hosts can use to restrict access to some shared resource, such as a file.

Declaration

@interface NSDistributedLock : NSObject

Overview

The lock is implemented by an entry (such as a file or directory) in the file system. For multiple applications to use an NSDistributedLock object to coordinate their activities, the lock must be writable on a file system accessible to all hosts on which the applications might be running.

Use the tryLock method to attempt to acquire a lock. You should generally use the unlock method to release the lock rather than breakLock.

NSDistributedLock doesn’t conform to the NSLocking protocol, nor does it have a lock method. The protocol’s lock method is intended to block the execution of the thread until successful. For an NSDistributedLock object, this could mean polling the file system at some predetermined rate. A better solution is to provide the tryLock method and let you determine the polling frequency that makes sense for your application.

Topics

Creating an NSDistributedLock

+ lockWithPath:

Returns an NSDistributedLock object initialized to use as the locking object the file-system entry specified by a given path.

- initWithPath:

Initializes an NSDistributedLock object to use as the lock the file-system entry specified by a given path.

Acquiring a Lock

- tryLock

Attempts to acquire the receiver and immediately returns a Boolean value that indicates whether the attempt was successful.

Relinquishing a Lock

- breakLock

Forces the lock to be relinquished.

- unlock

Relinquishes the receiver.

Getting Lock Information

lockDate

Returns the time the receiver was acquired by any of the NSDistributedLock objects using the same path.

Relationships

Inherits From

See Also

Threads and Locking

NSThread

A thread of execution.

NSLocking

The elementary methods adopted by classes that define lock objects.

NSLock

An object that coordinates the operation of multiple threads of execution within the same application.

NSRecursiveLock

A lock that may be acquired multiple times by the same thread without causing a deadlock.

NSConditionLock

A lock that can be associated with specific, user-defined conditions.

NSCondition

A condition variable whose semantics follow those used for POSIX-style conditions.