Documentation Archive Developer


Inherits From:

Conforms To:
NSObject (NSObject)

Declared In:

Class Description

An NSThread object controls a thread of execution. Use NSThread when you want to have an Objective-C message run in its own thread of execution or if you need to terminate or delay the current thread.

A thread is an executable unit. A task is made up of one or more threads. Each thread has its own execution stack and is capable of independent input/output. All threads share the virtual memory address space and communication rights of their task. When a thread is started, it is detached from its initiating thread. The new thread runs independently. That is, the initiating thread does not know the new thread's state.

To have an Objective-C message run in its own thread of execution, send the message detachNewThreadSelector:toTarget:withObject: to the NSThread class object. This method detaches a new thread from the current thread, and the specified target executes the specified method in that thread. When the target has finished executing the method, the thread exits.

When you use detachNewThreadSelector:toTarget:withObject:, your application becomes multithreaded. At any time you can send isMultiThreaded to find out if the application is multithreaded, that is, if a thread was ever detached from the main thread. isMultiThreaded returns YES even if the detached thread has completed execution.

Note: Do not interchange the use of the cthreads functions and NSThread objects within an application. In particular, do not use cthread_fork() to create a thread that executes an Objective-C message. isMultiThreaded returns YES only if detachNewThreadSelector:toTarget:withObject: was used to create the thread. If you need to terminate the current thread, send the exit message to the NSThread class object. Similarly, you send the sleepUntilDate: message to the NSThread class object to block the current thread for a period of time.

Method Types

Querying an NSThread
+ isMultiThreaded
+ currentThread
- threadDictionary
Detaching a thread
+ detachNewThreadSelector:toTarget:withObject:
Stopping the Current Thread
+ sleepUntilDate:
+ exit

Class Methods


+ (NSThread *)currentThread

Returns an object representing the current thread of execution.

See also: + detachNewThreadSelector:toTarget:withObject:


+ (void)detachNewThreadSelector:(SEL)aSelector

Detaches a new thread for the message [aTarget aSelector:anArgument]. The method aSelector must take only one argument and must not have a return value. The objects aTarget and anArgument are retained during the execution of the detached thread, then released. The detached thread is exited (using the exit class method) as soon as aTarget has completed executing the aSelector method.

Most OpenStep kits are not capable of being used by several threads simultaneously. In particular, the Application Kit cannot be used by more than one thread at a time.

If this is the first thread detached from the current thread, this method posts the NSWillBecomeMultiThreadedNotification with nil to the default notification center.

See also: + currentThread, + isMultiThreaded


+ (void)exit

Terminates the current thread, using the currentThread class method to access that thread. Before exiting the thread, this method posts the NSThreadWillExitNotification with the thread being exited to the default notification center.

See also: + currentThread, + sleepUntilDate:


+ (BOOL)isMultiThreaded

Returns YES if the application is multithreaded. An application is considered to be multithreaded if a thread was ever detached from the main thread using detachNewThreadSelector:toTarget:withObject:. If you detach a thread using the cthread_fork() function, this method returns NO. The detached thread does not have to be running for an application to be considered multithreaded; it may have already exited.

See also: + detachNewThreadSelector:toTarget:withObject:


+ (void)sleepUntilDate:(NSDate *)aDate

Blocks the current thread until the time specified by aDate. No run loop processing occurs while the thread is blocked.

See also: + currentThread, + exit

Instance Methods


- (NSMutableDictionary *)threadDictionary

Returns the NSThread's dictionary, to which you can add data specific to the receiving NSThread. The thread dictionary is not used during any manipulations of the NSThread; it is simply a place where you can store any interesting attributes of a thread. For example, Foundation uses it to store the thread's NSRunLoop instance. You may define your own keys for the dictionary. Accessing the thread dictionary may be slower than it usually is to access an NSMutableDictionary.



This notification does not contain a notification object or userInfo dictionary.

Posted when the first thread is detached from the current thread. NSThread posts this notification at most once-the first time a thread is detached using detachNewThreadSelector:toTarget:withObject:. Any subsequent invocations of detachNewThreadSelector:toTarget:withObject: do not post this notification.


This notification contains a notification object but no userInfo dictionary. The notification object is the existing NSThread.

Posted when a thread exits. NSThread posts this notification whenever it receives the exit message. The notification is posted to the current thread's default notification center. (The current thread is the thread being exited.)

Copyright © 1997, Apple Computer, Inc. All rights reserved.