I want to run certain background tasks.
Scenario: I would like a button to activate a thread or timer, and then have the thread/timer to start repeating every second returning a NSRunInformationalAlertPanel to the user with data.
This is what I have for my timer:
-(void)workerThread:(NSTimer*) theTimer {
if(intNumberOfTicks > 0)
{
NSRunInformationalAlertPanel(#"The Serial", [NSString stringWithFormat:#"%d", intNumberOfTicks], #"OK", nil, nil);
//[txtTimeMinutes setStringValue:[NSString stringWithFormat:#"%d", intNumberOfTicks]];
intNumberOfTicks--;
}
else {
[timer invalidate];
}
}
And for starting the method...
intNumberOfTicks = 5;
timer = [[NSTimer scheduledTimerWithTimeInterval:1 target: self selector:#selector(workerThread:) userInfo:self repeats:true] retain];
// Or for threading...
///[NSThread detachNewThreadSelector:#selector(workerThread) toTarget:self withObject:nil];
Can anyone help me implement what I need, maybe providing the most basic examples for a NSThread or NSTimer. I have looked at the Apple Dev Refrences but no luck.
Using NSTimer will execute the selector in the same thread as the one which instantiated and invoked it.
If your task must be carried out in a background thread try calling performSelectorInBackground:withObject:
https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/nsobject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/performSelectorInBackground:withObject:
From that background thread you can use a scheduled timer the way that you described above.
Related
Suppose I have a method that does some asynchronous tasks. Let's say it refreshes user's access permission and it may take several minutes depending on the internet connection speed or whatever.
I have to call this method periodically (i.e. scheduled call using NSTimer's method scheduledTimerWithTimeInterval: target: selector: userInfo: repeats:)
-(void)refreshPermission {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// do something that takes a few minutes
});
}
Now I call this method as timer = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:#selector(refreshPermission) userInfo:nil repeats:YES];. That is, this call is fired every 10 seconds.
What I need to do is, I need to somehow skip one (or, more than one)
scheduled call to this method if something is happening inside that
asynchronous block (Let's say, user's access permission hasn't been
updated).
But once the block is done (that is, user's access permission has been updated), scheduled call with timer should resume.
Any idea or any sample on how to accomplish this??
I think you can do it by using a Bool variable. You can declare Bool variable globally and by using its state you can manage your task in function call.
In method refreshPermission
-(void)refreshPermission {
if(!isExecuting){
isExecuting = YES;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Perform your tasks
isExecuting = NO;
}
}
}
I've come up with this approach. Got the idea from #Sunny's answer.
It worked for me. But any suggestion regarding this implementation is appreciated.
-(void)refresh {
NSLog(#"Refresh called");
NSLock *theLock = [[NSLock alloc] init];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSLog(#"Async task assigned");
if(!isExecuting){
[theLock lock];
isExecuting = YES;
[theLock unlock];
// Perform your tasks
NSLog(#"Async task started");
[NSThread sleepForTimeInterval: 13.0]; // for testing purpose
NSLog(#"Async task completed");
[theLock lock];
isExecuting = NO;
[theLock unlock];
}
});
}
Here isExecuting is an instance variable of the containing class. And it was set to isExecuting = NO; before setting the actual scheduled timer for calling the method periodically.
Here I used NSLock for the assurance that no other thread can change the value of isExecuting while a thread is in execution of it's task. I added this locking because every time -(void)refresh method is invoked, there is a possibility that multiple threads become eligible for the execution and changing value of isExecuting. So it's better to make it thread save when changing value of shared variable.
Here's my scenario....
I have a Core MIDI app that detects Note On and Note Off messages which is working nicely.
I have have some midiSend methods that send messages back to the controller to illuminate LEDs - also working fine.
What I want to do now is on the Note Off message have the LED blink on and off. This is my code:
[midiListener performSelectorOnMainThread:#selector(startTimer:) withObject:midiMsgParts waitUntilDone:YES];
-(void)startTimer:(NSDictionary *)dict {
ledIntervalCount = 0;
ledIntervalTimer = [NSTimer scheduledTimerWithTimeInterval:0.3
target:self
selector:#selector(ledIntervalLoop:)
userInfo:dict
repeats:YES];
}
-(void)ledIntervalLoop:(NSTimer *)inboundTimer{
NSDictionary *userInfo = [NSDictionary dictionaryWithDictionary:[inboundTimer userInfo]];
NSLog(#"%#", userInfo);
UInt32 onCommand = [[userInfo objectForKey:#"noteOn"] intValue];
//UInt32 offCommand = [[userInfo objectForKey:#"noteOff"] intValue];
UInt32 theNote = [[userInfo objectForKey:#"note"] intValue];
ledIntervalCount++;
if (ledIntervalCount > 3) {
[ledIntervalTimer invalidate];
ledIntervalTimer = nil;
} else {
if(ledIntervalCount %2){
[self sendNoteOnIlluminate:onCommand midiNote:theNote];
}else{
[self sendNoteOnCommand:onCommand midiNote:theNote];
}
}
}
So I'm using an NSTimer to alternate the LED on/off commands. It works fine when I press a single button but not when I press multiple ones at the same time. It seems like it only picks on the last call to the startTimer method.
This is where I think I need to implement a dispatch queue with GCD. So that each NSTimer will execute in full without being interrupted by the method calls that follow.
Am I correct? Will GCD allow me to have the NSTimer run concurrently?
GCD is a new concept to me so some guidance on how I might implement it would help. I've read through some of the reference guides but need to see some example code in the context of my scenario. I guess what I'm asking here is, what part of my code would go in the block?
AH you invalidate the timers anyway... after 3 tries. ALL -- you need X counters for X timers, you have 1 counter for X timer
instead of one long ledIntervalCount, have a NSMutableArray with ledIntervalCounts! One per timer
then in the userInfo for the timer, provide the index to the counter that is to be used
The problem was that I was calling the class from within a method wrapped in an autorelease. I now run this on the main thread and it works fine.
In other words, if I have a process that continuously runs, but users can change parameters on the GUI that effect the process operation characteristics, where is a better place to put the process, in a NSThread or NSTimer?
While NSThread and NSTimer are two separate things for different needs, lets compare the two functions:
Using NSThread:
-(void) doSomethingEverySecond {
__block int cumValue = 0; // cumulative value
__block void(^execBlock)() = ^{
while (1)
{
#try
{
// some code here that might either A: call continue to continue the loop,
// or B: throw an exception.
cumValue++;
NSLog(#"Cumulative Value is: %i", cumValue);
if (cumValue == 5)
return;
}
#finally
{
[NSThread sleepForTimeInterval:1];
}
}
};
[NSThread detachNewThreadSelector:#selector(invoke) toTarget:[execBlock copy] withObject:nil];
}
Using NSTimer:
-(void) doSomethingEverySecond {
__block NSTimer *timer = nil;
__block int cumValue = 0;
__block void (^execBlock)() = ^{
cumValue++;
NSLog(#"Cumulative Value is: %i", cumValue);
if (cumValue == 5)
[timer invalidate];
};
timer = [NSTimer scheduledTimerWithTimeInterval:1 target:[execBlock copy] selector:#selector(invoke) userInfo:nil repeats:YES];
}
Now, if we want to something only once, NSThread is the way to go, as shown in the following:
-(void) doSomethingOnce {
__block void (^execBlock)() = ^{
NSLog(#"Doing something that could take a LONG time!");
};
[NSThread detachNewThreadSelector:#selector(invoke) toTarget:[execBlock copy] withObject:nil];
}
Now, for the NSTimer variant:
-(void) doSomethingOnce {
__block void (^execBlock)() = ^{
NSLog(#"Doing something that could take a LONG time!");
};
[NSTimer scheduledTimerWithTimeInterval:0 target:[execBlock copy] selector:#selector(invoke) userInfo:nil repeats:NO];
}
The reason for this is that we have complete control over the thread while using a NSThread, but if using a NSTimer, than we are executing inside a NSRunLoop which may freeze the UI if any heavy lifting is done inside. THAT is the advantage of a NSThread over a NSTimer.
You are also guaranteed that a NSThread that is detached is executed immediately, with a NSTimer, which is based on NSRunLoop, cannot, as it may or may not be able to execute immediately.
There is a 3rd alternative (well technically a fourth too, pthreads, but I will ignore that for now), GCD, but I would suggest you RTFM on that, as it's too broad of a topic to cover in this post.
NSThread and NSTimer are not mutually exclusive or replacements for one another. NSThread allows you to control a thread of execution and NSTimer is just that, a timer.
I assume you mean running an NSTimer on a background thread rather than on the main thread? That is generally a good idea so that the timer has less potential to be delayed by things occurring on your main thread (such as user interaction with the application).
You should read Apple's Threading Programming Guide.
I have an app that calls a sometimes-fast, sometimes-slow method. I know an upper bound for how long it will take (2 seconds). I'd like to set a timer to start when the method is called, run the code, but then not produce the output until 2 seconds has passed, no matter how long it actually takes. That way the user perceives the action as always taking the same amount of time. How can I implement this?
What I would like is something along the lines of this:
-(IBAction)doStuff {
// START A TIMER, LOOK BUSY
[activityIndicator startAnimating];
... real work happens here ...
... NSString *coolString gets assigned ...
// WHEN TIMER == 2 SECONDS, REVEAL COOLNESS
[activityIndicator stopAnimating];
[textField setText:coolString];
}
There are a couple of ways to delay an action in Cocoa. The easiest may be to use performSelector:withObject:afterDelay:. This method sets up a timer for you and calls the specified method when the time comes. It's an NSObject method, so your objects all get it for free.
The tricky part here is that the first method will block the main thread, so you need get it onto a background thread, and then get back to the main thread in order to update the UI. Here's a stab at it:
// Put the method which will take a while onto another thread
[self performSelectorInBackground:#selector(doWorkForUnknownTime)
withObject:nil];
// Delay the display for exactly two seconds, on the main thread
[self performSelector:#selector(displayResults)
withObject:nil
afterDelay:2.0];
- (void)doWorkForUnknownTime {
// results is an ivar
results = ...; // Perform calculations
}
- (void)displayResults {
if( !results ){
// Make sure that we really got results
[self performSelector:#selector(displayResults:)
withObject:nil
afterDelay:0.5];
return;
}
// Do the display!
}
The only other thing I can think of is to store the time that the "work" method is called in an NSDate, and check how long it took when you get the results. If it isn't two seconds yet, sleep the background thread, then call back to the main thread when you're done.
[self performSelectorInBackground:#selector(doWorkForUnknownTime:)
withObject:[NSDate date]];
- (void)doWorkForUnknownTime:(NSDate *)startTime {
// All threads must have an autorelease pool in place for Cocoa.
#autoreleasepool{
// This will take some time
NSString * results = ...; // Perform calculations
NSTimeInterval elapsedTime = [[NSDate date] timeIntervalSinceDate:startTime];
if( elapsedTime < 2.0 ){
// Okay to do this to wait since we're on a background thread,
// although not ideal; sleeping threads are kind of wasteful.
// Try not to do this a lot.
sleep(2.0 - elapsedTime);
}
// Don't forget to retain results on the main thread!
[self performSelectorOnMainThread:#selector(displayResults:)
withObject:results
waitUntilDone:YES];
// [results release]; // if necessary
}
}
[self performSelector:#selector(myfunc) withObject: afterDelay:];
should help.
-(IBAction)doStuff {
// START A TIMER, LOOK BUSY
[activityIndicator startAnimating];
... real work happens here ...
... NSString *coolString gets assigned ...
// WHEN TIMER == 2 SECONDS, REVEAL COOLNESS
[self performSelector:#selector(revealCoolnessWithString:) withObject:coolString afterDelay:2];
}
- (void)revealCoolnessWithString:(NSString *)coolString
{
[activityIndicator stopAnimating];
[textField setText:coolString];
}
Hope this helps
I've been searching for and attempting to program for myself, an answer to this question.
I've got a secondary thread running inside my mainView controller which is then running a timer which counts down to 0.
Whilst this timer is running the secondary thread which initiated the timer should be paused/blocked whatever.
When the timer reaches 0 the secondary thread should continue.
I've Experimented with both NSCondition and NSConditionLock with no avail, so id ideally like solutions that solve my problem with code, or point me to a guide on how to solve this. Not ones that simply state "Use X".
- (void)bettingInit {
bettingThread = [[NSThread alloc] initWithTarget:self selector:#selector(betting) object:nil];
[bettingThread start];
}
- (void)betting {
NSLog(#"betting Started");
for (int x = 0; x < [dealerNormalise count]; x++){
NSNumber *currSeat = [dealerNormalise objectAtIndex:x];
int currSeatint = [currSeat intValue];
NSString *currPlayerAction = [self getSeatInfo:currSeatint objectName:#"PlayerAction"];
if (currPlayerAction != #"FOLD"){
if (currPlayerAction == #"NULL"){
[inactivitySeconds removeAllObjects];
NSNumber *inactivitySecondsNumber = [NSNumber numberWithInt:10];
runLoop = [NSRunLoop currentRunLoop];
betLooper = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(betLoop) userInfo:nil repeats:YES];
[runLoop addTimer:[betLooper retain] forMode:NSDefaultRunLoopMode];
[runLoop run];
// This Thread needs to pause here, and wait for some input from the other thread, then continue on through the for loop
NSLog(#"Test");
}
}
}
}
- (void)threadKiller {
[betLooper invalidate];
//The input telling the thread to continue can alternatively come from here
return;
}
- (void)betLoop {
NSLog(#"BetLoop Started");
NSNumber *currentSeconds = [inactivitySeconds objectAtIndex:0];
int currentSecondsint = [currentSeconds intValue];
int newSecondsint = currentSecondsint - 1;
NSNumber *newSeconds = [NSNumber numberWithInt:newSecondsint];
[inactivitySeconds replaceObjectAtIndex:0 withObject:newSeconds];
inacTimer.text = [NSString stringWithFormat:#"Time: %d",newSecondsint];
if (newSecondsint == 0){
[self performSelector:#selector(threadKiller) onThread:bettingThread withObject:nil waitUntilDone:NO];
// The input going to the thread to continue should ideally come from here, or within the threadKiller void above
}
}
You can't run a timer on a thread and sleep the thread at the same time. You may want to reconsider whether you need a thread at all.
There's a few things that need to be pointed out here. First, when you schedule your timer:
betLooper = [NSTimer scheduledTimerWithTimeInterval:1
target:self
selector:#selector(betLoop:)
userInfo:nil
repeats:YES];
it's added to and retained by the current run loop by that method, so you don't need to do that manually. Just [myRunLoop run]. Your timer's selector argument is also invalid -- a timer's "target method" needs to look like this:
- (void)timerFireMethod:(NSTimer *)tim;
This also means that you don't need to retain the timer if all you want to do is invalidate it, since you will have a reference to it from inside that method.
Second, it's not clear what you mean by "this thread needs to sleep to wait for input". When you schedule that timer, the method (betLoop) is called on the same thread. If you were to sleep the thread, the timer would stop too.
You seem to be a little mixed up regarding methods/threads. The method betting is running on your thread. It is not itself a thread, and it's possible to call other methods from betting that will also be on that thread. If you want a method to wait until another method has completed, you simply call the second method inside the first:
- (void)doSomethingThenWaitForAnotherMethodBeforeDoingOtherStuff {
// Do stuff...
[self methodWhichINeedToWaitFor];
// Continue...
}
I think you just want to let betting return; the run loop will keep the thread running, and as I said, the other methods you call from methods on the thread are also on the thread. Then, when you've done the countdown, call another method to do whatever work needs to be done (you can also invalidate the timer inside betLoop:), and finalize the thread:
- (void)takeCareOfBusiness {
// Do the things you were going to do in `betting`
// Make sure the run loop stops; invalidating the timer doesn't guarantee this
CFRunLoopStop(CFRunLoopGetCurrent());
return; // Thread ends now because it's not doing anything.
}
Finally, since the timer's method is on the same thread, you don't need to use performSelector:onThread:...; just call the method normally.
You should take a look at the Threading Programming Guide.
Also, don't forget to release the bettingThread object that you created.
NSThread has a class method + (void)sleepForTimeInterval:(NSTimeInterval)ti. Have a look at this :).
NSThread Class Reference