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NSThread class reference

Authors

Scott Christley (scottc@net-community.com)
Andrew Kachites McCallum (mccallum@gnu.ai.mit.edu)
Richard Frith-Macdonald (richard@brainstorm.co.uk)
Nicola Pero (n.pero@mi.flashnet.it)

Version: 1.81

Date: 2004/09/27 10:24:02

Copyright: (C) 1996-2000 Free Software Foundation, Inc.


Contents -

  1. Software documentation for the NSThread class
  2. Software documentation for the NSObject(NSMainThreadPerformAdditions) category

Software documentation for the NSThread class

NSThread : NSObject

Declared in:
Foundation/NSThread.h
Standards:

This class encapsulates OpenStep threading. See NSLock and its subclasses for handling synchronisation between threads.
Each process begins with a main thread and additional threads can be created using NSThread. The GNUstep implementation of OpenStep has been carefully designed so that the internals of the base library do not use threading (except for methods which explicitly deal with threads of course) so that you can write applications without threading. Non-threaded applications are more efficient (no locking is required) and are easier to debug during development.


Instance Variables

Method summary

currentThread 

+ (NSThread*) currentThread;

Returns the NSThread object corresponding to the current thread.

NB. In GNUstep the library internals use the GSCurrentThread() function as a more efficient mechanism for doing this job - so you cannot use a category to override this method and expect the library internals to use your implementation.


detachNewThreadSelector: toTarget: withObject: 

+ (void) detachNewThreadSelector: (SEL)aSelector toTarget: (id)aTarget withObject: (id)anArgument;

Create a new thread - use this method rather than alloc-init. The new thread will begin executing the message given by aSelector, aTarget, and anArgument. This should have no return value, and must set up an autorelease pool if retain/release memory management is used. It should free this pool before it finishes execution.

Note, unlike in Cocoa (and perhaps OpenStep), the thread will not exit when the method finishes execution. You must call [Thread +exit] yourself (from the thread) to terminate it.


exit 

+ (void) exit;

Terminating a thread What happens if the thread doesn't call +exit - it doesn't terminate!


isMultiThreaded 

+ (BOOL) isMultiThreaded;

Returns a flag to say whether the application is multi-threaded or not.
An application is considered to be multi-threaded if any thread other than the main thread has been started, irrespective of whether that thread has since terminated.
NB. This method returns YES if called within a handler processing NSWillBecomeMultiThreadedNotification


setThreadPriority: 

+ (void) setThreadPriority: (double)pri;

Set the priority of the current thread. This is a value in the range 0.0 (lowest) to 1.0 (highest) which is mapped to the underlying system priorities. The current gnu objc runtime supports three priority levels which you can obtain using values of 0.0, 0.5, and 1.0


sleepUntilDate: 

+ (void) sleepUntilDate: (NSDate*)date;

Delaying a thread... pause until the specified date.


threadPriority 

+ (double) threadPriority;

Return the priority of the current thread.


threadDictionary 

- (NSMutableDictionary*) threadDictionary;

Return the thread dictionary. This dictionary can be used to store arbitrary thread specific data.
NB. This cannot be autoreleased, since we cannot be sure that the autorelease pool for the thread will continue to exist for the entire life of the thread!




Instance Variables for NSThread Class

_active

@protected BOOL _active;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.


_arg

@protected id _arg;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.


_autorelease_vars

@public struct autorelease_thread_vars _autorelease_vars;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.


_exception_handler

@public NSHandler* _exception_handler;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.


_gcontext

@public id _gcontext;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.


_selector

@protected SEL _selector;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.


_target

@protected id _target;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.


_thread_dictionary

@public NSMutableDictionary* _thread_dictionary;

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.





Software documentation for the NSObject(NSMainThreadPerformAdditions) category

NSObject(NSMainThreadPerformAdditions)

Declared in:
Foundation/NSThread.h
Standards:

Extra methods to permit messages to be sent to an object such that they are executed in the main thread.
The main thread is the thread in which the GNUstep system is started, and where the GNUstep gui is used, it is the thread in which gui drawing operations must be performed.

Method summary

performSelectorOnMainThread: withObject: waitUntilDone: 

- (void) performSelectorOnMainThread: (SEL)aSelector withObject: (id)anObject waitUntilDone: (BOOL)aFlag;

Invokes -performSelectorOnMainThread:withObject:waitUntilDone:modes: using the supplied arguments and an array containing common modes.
These modes consist of NSRunLoopMode, NSConnectionreplyMode, and if in an application, the NSApplication modes.


performSelectorOnMainThread: withObject: waitUntilDone: modes: 

- (void) performSelectorOnMainThread: (SEL)aSelector withObject: (id)anObject waitUntilDone: (BOOL)aFlag modes: (NSArray*)anArray;

This method performs aSelector on the receiver, passing anObject as an argument, but does so in the main thread of the program. The receiver and anObject are both retained until the method is performed.

The selector is performed when the runloop of the main thread next runs in one of the modes specified in anArray.
Where this method has been called more than once before the runloop of the main thread runs in the required mode, the order in which the operations in the main thread is done is the same as that in which they were added using this method.

If there are no modes in anArray, the method has no effect and simply returns immediately.

The argument aFlag specifies whether the method should wait until the selector has been performed before returning.
NB. This method does not cause the runloop of the main thread to be run... so if the runloop is not executed by some code in the main thread, the thread waiting for the perform to complete will block forever.

As a special case, if aFlag == YES and the current thread is the main thread, the modes array is ignored and the selector is performed immediately. This behavior is necessary to avoid the main thread being blocked by waiting for a perform which will never happen because the runloop is not executing.



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