I have a need to play a brief sound 3 seconds or so (like a count down beep) before I perform some other action in an iOS application.
The use case is as follows:
User clicks a button... the beeps play (simple beeps using AudioServicesPlaySystemSound... then the rest of the method is run.
I cannot seem to find out a way to block my method while the tones are playing.
I've tried the following:
[self performSelector:#selector(playConfirmationBeep) onThread:[NSThread currentThread] withObject:nil waitUntilDone:YES];
But the tones play synchronously while the rest of the method is performed.
What am I missing with the above call?
AudioServicesPlaySystemSound is asynchronous so you can't block on it. What you want to do is get the audio services to notify you when playback is finished. You can do that via AudioServicesAddSystemSoundCompletion.
It's a C-level API so things are a bit ugly, but you probably want something like:
// somewhere, a C function like...
void audioServicesSystemSoundCompleted(SystemSoundID ssID, void *clientData)
{
[(MyClass *)clientData systemSoundCompleted:ssID];
}
// meanwhile, in your class' init, probably...
AudioServicesAddSystemSoundCompletion(
soundIDAsYoullPassToAudioServicesPlaySystemSound,
NULL, // i.e. [NSRunloop mainRunLoop]
NULL, // i.e. NSDefaultRunLoopMode
audioServicesSystemSoundCompleted,
self);
// in your dealloc, to avoid a dangling pointer:
AudioServicesRemoveSystemSoundCompletion(
soundIDAsYoullPassToAudioServicesPlaySystemSound);
// somewhere in your class:
- (void)systemSoundCompleted:(SystemSoundID)sound
{
if(sound == soundIDAsYoullPassToAudioServicesPlaySystemSound)
{
NSLog(#"time to do the next thing!");
}
}
If you actually want to block the UI while the sound is playing, and assuming your class is a view controller, you should probably just disable self.view.userInteractionDisable for the relevant period. What you definitely don't want to do is block the main run loop; that'll stop important system events like low memory warnings getting through and hence potentially cause your app to be force quit. You also probably still want to obey things like device rotations.
Related
I am working on an iOS application that, say on a button click, launches several threads, each executing a piece of Open GL code. These threads either have a different EAGLContext set on them, or if they use same EAGLContext, then they are synchronised (i.e. 2 threads don't set same EAGLContext in parallel).
Now suppose the app goes into background. As per Apple's documentation, we should stop all the OpenGL calls in applicationWillResignActive: callback so that by the time applicationDidEnterBackground: is called, no further GL calls are made.
I am using dispatch_queues to create background threads. For e.g.:
__block Byte* renderedData; // some memory already allocated
dispatch_sync(glProcessingQueue, ^{
[EAGLContext setCurrentContext:_eaglContext];
glViewPort(...)
glBindFramebuffer(...)
glClear(...)
glDrawArrays(...)
glReadPixels(...) // read in renderedData
}
use renderedData for something else
My question is - how to handle applicationWillResignActive: so that any such background GL calls can be not just stopped, but also be able to resume on applicationDidBecomeActive:? Should I wait for currently running blocks to finish before returning from applicationWillResignActive:? Or should I just suspend glProcessingQueue and return?
I have also read that similar is the case when app is interrupted in other ways, like displaying an alert, a phone call, etc.
I can have multiple such threads at any point of time, invoked by possibly multiple ViewControllers, so I am looking for some scalable solution or design pattern.
The way I see it you need to either pause a thread or kill it.
If you kill it you need to ensure all resources are released which means again calling openGL most likely. In this case it might actually be better to simply wait for the block to finish execution. This means the block must not take too long to finish which is impossible to guarantee and since you have multiple contexts and threads this may realistically present an issue.
So pausing seems better. I am not sure if there is a direct API to pause a thread but you can make it wait. Maybe a s system similar to this one can help.
The linked example seems to handle exactly what you would want; it already checks the current thread and locks that one. I guess you could pack that into some tool as a static method or a C function and wherever you are confident you can pause the thread you would simply do something like:
dispatch_sync(glProcessingQueue, ^{
[EAGLContext setCurrentContext:_eaglContext];
[ThreadManager pauseCurrentThreadIfNeeded];
glViewPort(...)
glBindFramebuffer(...)
[ThreadManager pauseCurrentThreadIfNeeded];
glClear(...)
glDrawArrays(...)
glReadPixels(...) // read in renderedData
[ThreadManager pauseCurrentThreadIfNeeded];
}
You might still have an issue with main thread if it is used. You might want to skip pause on that one otherwise your system may simply never wake up again (not sure though, try it).
So now you are look at interface of your ThreadManager to be something like:
+ (void)pause {
__threadsPaused = YES;
}
+ (void)resume {
__threadsPaused = NO;
}
+ (void)pauseCurrentThreadIfNeeded {
if(__threadsPaused) {
// TODO: insert code for locking until __threadsPaused becomes false
}
}
Let us know what you find out.
For example:
- (void)someFunc {
[self someFunc1];
[self someFunc2];
[self someFunc3];
}
I call someFunc. As I understand if I interrupt the application then the application doesn't guarantee that all the inner code in someFunc will be performed.
I must call someFunc1, someFunc2 and someFunc3 only once.
The problems I don't know how to solve:
someFunc1, someFunc2 and someFunc3 should be called atomically.
storing info for next launch. For example if we successfully have performed someFunc1 only then at next launch the application should call someFunc2 and someFunc3 only.
I know about method applicationWillTerminate:, but I don't know how to solve the current issue with it.
EDITED
Multitasking is not a solution because Even if the device is running iOS 4 or later, the device may not support multitasking., so it doesn't solve the general problem and makes the final solution more difficult only.
EDITED
For those who spam with off topic answers: read the title first - Save state when user exits an application. Where have you seen here putting the application into background?
This does't make sense. If these functions are running on the main thread, there is no way that the application can terminate normally while your functions are running. This is because the events sent like applicationWillTerminate: are sent on the same thread.
If your function is running on a different thread to the main thread, you will need to save some state information after each function completes, but you still have a race condition.
It might be better to check your application's state before running each function. For example, if you have a three step login/registration process with a server, you should query the server to see if the stage has been completed already before running it.
It's difficult to be more specific without knowing what you are doing in these functions.
You should use background tasks !
Take a look at the documentation here :
Executing a Finite-Length Task in the Background
Put the call of someFunc in the middle of the background task.
If your app goes to the background state, you'll have extra time to finish the execution of the method.
Make your functions to return bool, and when you call them, store the bool value to nsdefaults.
When the app restarts,check the bools from sndefaults, and if they are NO, run the functions and update them.
Nobody wants to help. So my temporary solution:
to save a last state I use a writing to a file because it enables to set its operation as atomic/nonatomic
I have replaced this code with something like this:
typedef enum {
state1,
state2,
state3
} MyState;
#property (assign) MyState state;
-(void)someFunc {
switch (state) {
case state1:
{
[self someFunc1];
state = state2;
[self someFunc];
break;
}
case state2:
{
[self someFunc2];
state = state3;
[self someFunc];
break;
}
default:
break;
}
}
Can you point me to design pattern guides to adapt my style to AVFoundation's asynch approach?
Working an app where you create an image and place audio onto hotspots on it. I'm implementing export to a movie that is the image with effects (glow of hotspot) playing under the audio.
I can reliably create the video and audio tracks and can correctly get audio into an AVMutableComposition and play it back. Problem is with the video. I've narrowed it to my having written a synchronous solution to a problem that requires use of AVFoundation's asynch writing methods.
The current approach and where it fails (each step is own method):
Create array of dictionaries. 2 objects in dictionary. One dictionary object is image representing a keyframe, another object is URL of audio that ends on that keyframe. First dictionary has start keyframe but not audio URL.
For each dictionary in the array, replace the UIImage with an array of start image->animation tween images->end state image, with proper count for FPS and duration of audio.
For each dictionary in the array, convert image array into a soundless mp4 and save using [AVAssetWriter finishWritingWithCompletionHandler], then replace image array in dictionary with URL of mp4. Each dictionary of mp4 & audio URL represents a segment of final movie, where order of dictionaries in array dictates insert order for final movie
-- all of above works, stuff gets made & ordered right, vids and audio playback --
For each dictionary with mp4 & audio URL, load into AVAssets and insert into an AVMutableComposition track, one track for audio & one for video. The audio load & insert works, plays back. But the video fails and appears to fail because step 4 starts before step 3's AVAssetWriter finishWritingWithCompletionHandler finishes for all MP4 tracks.
One approach would be to pause via while loop and wait for status on the AVAssetWriter to say done. This smacks of working against the framework. In practice it is also leading to ugly and sometimes seemingly infinite waits for loops to end.
But simply making step 4 the completion handler for finishWritingWithCompletionHandler is non-trivial because I am writing multiple tracks but I want step 4 to launch only after the last track is written. Because step 3 is basically a for-each processor, I think all completion handlers would need to be the same. I guess I could use bools or counters to change up the completion handler, but it just feels like a kluge.
If any of the above made any sense, can someone give me/point to a primer on design patterns for asynch handling like this? TIA.
You can use GCD dispatch groups for that sort of problem.
From the docs:
Grouping blocks allows for aggregate synchronization. Your application
can submit multiple blocks and track when they all complete, even
though they might run on different queues. This behavior can be
helpful when progress can’t be made until all of the specified tasks
are complete.
The basic idea is, that you call dispatch_group_enter for each of your async tasks. In the completion handler of your tasks, you call dispatch_group_leave.
Dispatch groups work similar to counting semaphores. You increment a counter (using dipsatch_group_wait) when you start a task, and you decrement a counter when a task finishes.
dispatch_group_notify lets you install a completion handler block for your group. This block gets executed when the counter reaches 0.
This blog post provides a good overview and a complete code sample: http://amro.co/post/48248949039/using-gcd-to-wait-on-many-tasks
#weichsel Thank you very much. That seems like it should work. But, I'm using dispatch_group_wait and it seems to not wait. I've been banging against it for several hours since you first replied but now luck. Here's what I've done:
Added property that is a dispatch group, called videoDispatchGroup, and call dispatch_group_create in the init of the class doing the video processing
In the method that creates the video tracks, use dispatch_group_async(videoDispatchGroup, dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ [videoWriter finishWritingWithCompletionHandler:^{
The video track writing method is called from a method chaining together the various steps. In that method, after the call to write the tracks, I call dispatch_group_wait(videoProcessingGroup, DISPATCH_TIME_FOREVER);
In the dealloc, call dispatch_release(videoDispatchGroup)
That's all elided a bit, but essentially the call to dispatch_group_wait doesn't seem to be waiting. My guess is it has something to do with the dispatch_group_asyn call, but I'm not sure exactly what.
I've found another means of handling this, using my own int count/decrement via the async handler on finishWritingWithCompletion handler. But I'd really like to up my skills by understanding GCD better.
Here's the code-- dispatch_group_wait never seems to fire, but the movies themselves are made. Code is elided a bit for brevity, but nothing was removed that doesn't work without the GCD code.
#implementation MovieMaker
// This is the dispatch group
#synthesize videoProcessingGroup = _videoProcessingGroup;
-(id)init {
self = [super init];
if (self) {
_videoProcessingGroup = dispatch_group_create();
}
return self;
}
-(void)dealloc {
dispatch_release(self.videoProcessingGroup);
}
-(id)convert:(MTCanvasElementViewController *)sourceObject {
// code fails in same way with or without this line
dispatch_group_enter(self.videoProcessingGroup);
// This method works its way down to writeImageArrayToMovie
_tracksData = [self collectTracks:sourceObject];
NSString *fileName = #"";
// The following seems to never stop waiting, the movies themselves get made though
// Wait until dispatch group finishes processing temp tracks
dispatch_group_wait(self.videoProcessingGroup, DISPATCH_TIME_FOREVER);
// never gets to here
fileName = [self writeTracksToMovie:_tracksData];
// Wait until dispatch group finishes processing final track
dispatch_group_wait(self.videoProcessingGroup, DISPATCH_TIME_FOREVER);
return fileName;
}
// #param videoFrames should be NSArray of UIImage, all of same size
// #return path to temp file
-(NSString *)writeImageArrayToMovie:(NSArray *)videoFrames usingDispatchGroup:(dispatch_group_t)dispatchGroup {
// elided a bunch of stuff, but it all works
AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:[NSURL fileURLWithPath:result]
fileType:AVFileTypeMPEG4
error:&error];
//elided stuff
//Finish the session:
[writerInput markAsFinished];
dispatch_group_async(dispatchGroup, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[videoWriter finishWritingWithCompletionHandler:^{
dispatch_group_leave(dispatchGroup);
// not sure I ever get here? NSLogs don't write out.
CVPixelBufferPoolRelease(adaptor.pixelBufferPool);
}];
});
return result;
}
Hi !
I'm building a timer using GCD for the purpose of playing a sound at a specific interval, to be more precise, it's a metronome sound. I've been trying for days to solve my issue but nothing. Everything is good but when I set my tempo to a bigger value , let's say 150 bpm or 200 bpm, when the sound starts for the first time, it fires very quickly(almost like two sounds in the same time meaning it does not have the expected interval) and after this , it calibrates. I start the sound the second time , all is good... so this happens only the first time I resume my dispatch source so I'm guessing it has something to do with loading the sound from the disk , like in this post : Slow start for AVAudioPlayer the first time a sound is played . For my sound I used at first an instance of AVAudioPlayer with prepareToPlay and play and also created it in the AppDelegate class, it hasn't work...I have even tried the SoundManager class developed by #NickLockwood,same issue. At present, I'm using a SystemSoundID. As for the timers, this is my first GCD timer , I've already tried the classical NSTimer, CADisplayLink and other timers found on git... all in vain.
Another interesting issue is that with the other timers , everything is perfect on the simulator but on the device the same glitch.
Here's the code, I hope someone will bring me to the light.
-(void)playButtonAction //
{
if (_metronomeIsAnimatingAndPLaying == NO)
{
[self startAnimatingArm]; // I start my animation and create my timer
metronomeTimer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));
dispatch_source_set_timer(metronomeTimer,dispatch_time(DISPATCH_TIME_NOW, duration * NSEC_PER_SEC),duration * NSEC_PER_SEC,duration *NSEC_PER_SEC);
dispatch_source_set_event_handler(metronomeTimer, ^{[self playTick];});
dispatch_resume(metronomeTimer);
_metronomeIsAnimatingAndPLaying = YES;
}
}
-(void)playTick
{
AudioServicesPlaySystemSound(appDeleg.soundID); // soundID is created in appDelegate
}
In my application didFinishLaunching
NSString *path = [[NSBundle mainBundle] pathForResource:#"tick"
ofType:#"caf"];
AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:path]
, &_soundID);
And BPM setter and getter :
- (NSUInteger)bpm
{
return round(60.0 / duration);
}
- (void)setBpm:(NSUInteger)bpm
{
if (bpm >= MaxBPM) {
bpm = MaxBPM;
} else if (bpm <= MinBPM) {
bpm = MinBPM;
}
duration = (60.0 / bpm);
}
This arrangement will fundamentally never work.
GCD is a thread-pool designed to facilitate task-level parallelism. It is usually asynchronous and non real-time. These are almost precisely the opposite characteristics to those required in an audio application.
Each thread servicing a GCD queue is contending with other threads in the system for an opportunity to execute. Furthermore, the queue may be busy at requested time processing something else. If that something else is long-running - and long-running tasks are precisely the kind of thing that GCD is made for - the scheduler may pre-empt the thread before the operation has completed and penalise the queue; it may wait a long time for service.
The Manpage for GCD states the following about timers on GCD queues:
A best effort attempt is made to submit the event handler block to the target queue at the specified time; however, actual invocation may occur at a later time.
NSTimer will not be any better. Its documentation states A timer is not a real-time mechanism. Since you'll probably run this on the application's main run-loop, it will also be very unpredictable.
The solution to this problem is to use lower-level audio APIs - specifically Audio Units. The advantage of doing so is that soft-syth units have an event queue which is serviced by the unit's render handler. This runs on a real-time thread, and offers extremely robust and predictable service. Since you can queue a considerable number of events with timestamps in the future, your timing requirements are now quite loose. You could safely use either GCD or a NSTimer for this.
I've just read the following post and have tried to implement the approach described there:
Writing iOS acceptance tests using Kiwi - Being Agile
All the stuff described there does work perfectly. But! there is one thing that breaks determinism when I am running my acceptance tests.
Here is the repo on Github where author of the post pushed his experiments (it can be found on the bottom of the page in the comments): https://github.com/moredip/2012-Olympics-iOS--iPad-and-iPhone--source-code/tree/kiwi-acceptance-mk1
Consider this code he uses for tapping a view:
- (void) tapViewViaSelector:(NSString *)viewSelector{
[UIAutomationBridge tapView:[self viewViaSelector:viewSelector]];
sleepFor(0.1); //ugh
}
...where sleepFor has the following definition behind itself:
#define sleepFor(interval) (CFRunLoopRunInMode(kCFRunLoopDefaultMode, interval, false))
It is a naive attempt ('naive' is not about the author, but about the fact that it is the first thing that comes into a head) to wait for a tiny period of time until all the animations are processed and soak all the possible events that were(or could be) scheduled to a main run loop (see also this comment).
The problem is that this naive code does not work in a deterministic way. There are a bunches of UI interactions which cause fx next button tap to be pressed before the current edited textfield's keyboard is disappeared and so on...
If I just increase the time from 0.1 to fx 1 all the problems disappear, but this leads to that every single interaction like "fill in textfield with a text..." or "tap button with title..." become to cost One second!
So I don't mean just increasing a wait time here, but rather a way to make such artificial waits guarantee that I do can proceed my test case with a next step.
I hope that it should be a more reliable way to wait enough until all the stuff caused by current action (all the transitions/animations or whatever main run loop stuff) are done.
To summarize it all to be a question:
Is there a way to exhaust/drain/soak all the stuff scheduled to a main thread and its run loop to be sure that main thread is idle and its run loop is "empty"?
This was my initial solution:
// DON'T like it
static inline void runLoopIfNeeded() {
// https://developer.apple.com/library/mac/#documentation/CoreFOundation/Reference/CFRunLoopRef/Reference/reference.html
while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.1, YES) == kCFRunLoopRunHandledSource);
// DON'T like it
if (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.1, YES) == kCFRunLoopRunHandledSource) runLoopIfNeeded();
}
you can try this
while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, true) == kCFRunLoopRunHandledSource);
this will run until no more things in the run loop. you can try to change the time interval to 0.1 if 0 is not working.
To check on the status of a run loop associated with a thread and register callbacks for separate phases, you may use a CFRunLoopObserverRef. This allows for extremely fine grained control over when the callbacks are invoked. Also, you don't have to depend on hacky timeouts and such.
One can be added like so (notice I am adding one to the main run loop)
CFRunLoopObserverRef obs = CFRunLoopObserverCreateWithHandler(kCFAllocatorDefault, kCFRunLoopAllActivities, true, 0 /* order */, handler);
CFRunLoopAddObserver([NSRunLoop mainRunLoop].getCFRunLoop, obs, kCFRunLoopCommonModes);
CFRelease(obs);
Depending on the activities you register for, your handler will get invoked appropriately. In the sample above, the observer listens for all activities. You probably only need kCFRunLoopBeforeWaiting
You handler could look like this
id handler = ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
switch (activity) {
case kCFRunLoopEntry:
// About to enter the processing loop. Happens
// once per `CFRunLoopRun` or `CFRunLoopRunInMode` call
break;
case kCFRunLoopBeforeTimers:
case kCFRunLoopBeforeSources:
// Happens before timers or sources are about to be handled
break;
case kCFRunLoopBeforeWaiting:
// All timers and sources are handled and loop is about to go
// to sleep. This is most likely what you are looking for :)
break;
case kCFRunLoopAfterWaiting:
// About to process a timer or source
break;
case kCFRunLoopExit:
// The `CFRunLoopRun` or `CFRunLoopRunInMode` call is about to
// return
break;
}
};
Here is my current solution, I will add some comments and explanations to the code a bit later, if nobody tell me I am wrong or suggests a better answer first:
// It is much better, than it was, but still unsure
static inline void runLoopIfNeeded() {
// https://developer.apple.com/library/mac/#documentation/CoreFOundation/Reference/CFRunLoopRef/Reference/reference.html
__block BOOL flag = NO;
// http://stackoverflow.com/questions/7356820/specify-to-call-someting-when-main-thread-is-idle
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
dispatch_async(dispatch_get_main_queue(), ^{
flag = YES;
});
});
while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.1, YES) == kCFRunLoopRunHandledSource);
if (flag == NO) runLoopIfNeeded();
}
Right now I don't have any ideas how this could be made more effective.