I'm running into a problem with my code that is most easily solved by splitting
up everything into a client server model, where the client is the main thread
of my application, and the server is a background thread that does networking
type stuff. I want the client to update itself as soon as there are any
changes in the server. I have two options; I can fix the server to call
methods in the client when there are updates, and vice-versa, or I can use KVO
and have the client observe changes in the server. The former is fast and
easy, but it means that I can only have one client and one server, which is too
brittle for what is happening. KVO is ideal, but I don't know it works across
threads. My current plan of action is something akin to the following (I
banged all of this out in outlook, so there may be syntax errors, but I hope
this gets the gist across):
--- Server.h ---
@interface server : NSObject
{
NSImage *periodicallyChangingImage;
NSThread *updaterThread;
id <sourceProtocol> imageSource;
}
@property(retain, readonly) NSImage *periodicallyChangingImage;
- (id) initWithSource:(id <sourceProtocol>) source;
@end
--- End of Server.h ---
--- Server.m ---
@interface server()
@property(retain, readwrite) NSImage *periodicallyChangingImage;
@property(retain, readwrite) NSThread *updaterThread;
@property(retain, readwrite) id <sourceProtocol>) imageSource;
- (void) threadSelector:(id)object;
@end
@implementation
@synthesize periodicallyChangingImage;
@synthesize updaterThread;
@synthesize imageSource;
- (id) initWithSource:(id <sourceProtocol>) source
{
self = [super init];
if (self)
{
self.imageSource = source;
self.updaterThread = [NSThread initWithTarget:self
selector:@selector(threadSelector:) object:self];
[self.updaterThread start];
}
return self;
}
- (void) threadSelector:(id)object
{
server *theServer = (server *) object;
NSImage *temp;
while ([self.updaterThread isCancelled] == NO)
{
temp = [self.imageSource getImageBlob]; // This line blocks for
a long time sometimes
// I'm hoping that the compiler is smart about locking &
unlocking, but splitting the lines should
// take care of any long hangs (the line above hangs, but the
line below is fast)
theServer.periodicallyChangingImage = temp;
}
}
@end
--- End of Server.m ---
--- Client.h ---
@interface client : NSObject
{
server *imageServer;
}
- (id) initWithServer:(server *) newServer;
@end
--- End of Client.h ---
--- Client.m ---
@interface client()
@property(retain, readwrite) server *imageServer;
@end
@implementation
@synthesize imageServer;
- (id) initWithServer:(server *) newServer
{
self = [super init];
if (self)
{
self.imageServer = newServer;
[self observeValueForKeyPath:@"periodicallyChangingImage"
ofObject:newServer
change:NSKeyValueObservingOptionsNew
context:NULL];
}
return self;
}
- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void *)context
{
switch (object)
{
case self.imageServer:
if ([keyPath isEqual:@"periodicallyChangingImage"])
{
// Do something with
server.periodicallyChangingImage, probably display it immediately.
}
break;
default:
// No idea what the object is, do something intelligent
to report the error
break;
}
}
@end
--- End of Client.m ---
I know that properties are supposed to default to thread-safe, and I know that
as long as I don’t explicitly specify getter/setter methods, properties should
be KVC/KVO compliant, but I'm not sure if the above is 100% kosher. Is there
anything I should be worried about?
Thanks,
Cem Karan
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