I'm using a series of AVAudioPlayers concurrent with the main thread using dispatch_async. Before playing each one I must query, whether it is playing using its isPlaying method.
I am generally unfamiliar with multithreading, so how would I go about calling the isPlaying method on the thread that the AVAudioPlayer is currently working on?
You can access the property playing directly on main thread because the operation is read, so it is safe I think :)
But you can't use it to judge if playback has completed as document says : Important: Do not poll this property to determine when playback has completed, instead implement the specified delegate method
You should use delegate and implement the method - (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag, if the method is called, it means the player stop.
Related
I have got an API I can’t impact on. API has a lot of methods with delegate callbacks like -getInfo, -apiDidGetInfo: . There are some limitations, you can only call these methods sequentially and delegate callback might not be called after request. Two methods never should be called at once. I want to convert this API to something like -getInfoWithCompletion: and use some kind of queue inside + some type of watchdog timer to finish current stalled task. How would you do that?
I'm using SndPlaySound(pchar('wav.wav'), snd_ASync); function and it is works but I want to know when selected wav is still playing or already played. How to get a return value?
SND_ASYNC does not provide the information you are looking for. Use SND_SYNC instead. To avoid blocking your main thread, call sndPlaySound() in a worker thread.
Alternatively, have a look at Delphi's TMediaPlayer component. It can run asynchronously (set its Wait property to false), and you can use its OnNotify event (set its Notify property to true) to be told when its Play() method finishes playback.
I'm learning about blocks from a Stanford video. I'm now at the part which explains core data. The teachers mentions something about:
- (void)openWithCompletionHandler:(void (^)(BOOL success))completionHandler;
He said that completionhandler block will be called in the thread which called the method. So basically the method runs async but the blocks get called on the thread, lets assume main.
So my question is do all blocks run on the thread from where the method call was made. To illustrate why I ask this question, I have a Async class which does request to a server.
The format of all these methods is like this:
- (void) getSomething:(id <delegateWhatever> const)delegate{
goto background thread using GCD..
Got result from server...
Go back to main thread and call the delegate method...
}
When I use blocks I do not need to worry about going back to main thread if they will be called where the call was made?
Hope this is clear,
Thanks in advance
If something runs asynchronously, you should read a documentation to know on which thread, e.g. the completion block will be executed. If it is your code, you are in charge here, you can use global GCD queues, you can create your own queue and execute it there or whatever...
In general, blocks behaves like a function or a method call, it is executed on thread, which calls it. It is even possible that the same block will be executed from 2 different threads at the same time.
And just to be clear: Even if you are using blocks, you need to care about going back to main thread, of course if it is necessary
Nothing forces blocks to be called on a particular thread, so it depends on the specific method whether or not you need to worry about its callback being on the main thread. (In practice I don't remember ever seeing a library where a method called on the main thread would not call its completion handler also on the main thread. But you still need to read the documentation of the specific library and method you are using, as always.)
I am making a turnbased game for iOS with game center, 2 participants per match. I would like to implement a time limit on every turn, so that a player don't have to wait forever for the other player to finish its turn. I have tried:
currentMatch endTurnWithNextParticipants:[[NSArray alloc] initWithObjects:nextParticipant,nil] turnTimeout:GKTurnTimeoutDefault matchData:data completionHandler:^(NSError *error)
but nothing happens, the player still has forever to do their turn, so I am obviously missing something here.
What happens when the time limit is reached? How does gamecenter handle this, and where should I handle this?
That method updates the data stored on Game Center for the current match.
According to Apple Docs:
If the next player to act does not take their turn in the specified interval, the next player in the array receives a notification to act. This process continues until a player takes a turn or the last player in the list is notified.
When this method is called, it creates a new background task to handle the request. The method then returns control to your game. Later, when the task is complete, Game Kit calls your completion handler. Keep in mind that the completion handler may be called on a thread other than the one originally used to invoke the method. This means that the code in your block needs to be thread-safe.
I think you need to also end the players go on their end programatically.
2 part question but related so will keep in the same thread:
I'm adding NSOperations to a NSOperationQueue. I need to know when the operation will start and when it ends in order to update the UI.
I thought about adding a "start handler" block to run in the nsoperation as well as a "completion handler" in the NSOperation
Something like
-(id)initOperationWithStartBlock:(StartBlock)startblock completionBlock:(CompletionBlock)completionBlock
but believe that there is a better way to get this from the queue itself.
How can this be done?
I would also like to know the index of the job sent by the NSOperationQueue.
I've tried doing
[[self.myQueue operations] indexForObject:operation]
but the index is always the zeroth index - because the completed jobs were removed from the nsoperationqueue array before I could check the jobs index.
Any way to preserve them?
You need to use Key-Value-Observing pattern in IOS. So for this you need to setup observers in your controller to look for changes to isFinished and isExecuting to catch start and finish hooks.
It depends if you want to perform something from within your object upon starting or elsewhere in your code. From what you are saying (you want to update the UI), this sounds like you want to act outside of your object, but I don't know your program. You have two options:
1) If you want to act in your object upon starting the operation from within the same object, use key-value observation and observe isExecuting with self as the observer and the observed. Don't forget that you will get called whether it goes from NO to YES (starting) or YES to NO (done).
2) If you want to perform an action outside of the object, I would rather recommend to use the very general NSNotification with NSNotificationCenter and within your main, post a notification such as #"willStart" and #"didComplete". In any other object, register as an observer for your notifications.
Either way, don't forget that notifications are sent in the current threads but the UI must be updated on the main thread. You don't know on what thread observe:keyPath: is called. You may need to call performSelectorOnMainThread to update the UI or you can even use the convenient and useful nsoperationqueue mainqueue with a addOperationWithBlock with your UI code. If you use the NotificationCenter, then you can simply yourself post on the main thread with nsobject performSelectorOnMainThread