Low-memory warning not dispatched on iOS 7 and AudioUnit - memory

Question

I made an example project that first create an Audio Unit render callback, then it allocates memory every 1/20 second and deallocate it as soon as the view controller receive a low-memory warning. The notification is dispatched just once, the second time the view controller doesn't receive any notification and crash due to memory pressure.
This happens only on iOs 7, before everything was working fine.
Here is the code:
#import <AudioUnit/AudioUnit.h>
#import <AudioToolbox/AudioToolbox.h>
#import <AVFoundation/AVFoundation.h>
AudioUnit audioUnit;
#interface ViewController ()
#property (atomic,strong) NSMutableData *data;
#end
#implementation ViewController
- (void)viewDidLoad{
[super viewDidLoad];
self.data=[NSMutableData dataWithLength:1];
[NSTimer scheduledTimerWithTimeInterval:1/20.0
target:self
selector: #selector(increaseMemory)
userInfo:nil repeats:YES];
//Comment setupAudio for testing without Audio
[self setupAudio];
}
-(void)increaseMemory{
[_data appendData:[NSMutableData dataWithLength:10000000]];
NSLog( #"Allocating %i Bytes",[_data length]);
}
OSStatus renderCallback(void *userData, AudioUnitRenderActionFlags *actionFlags,
const AudioTimeStamp *audioTimeStamp, UInt32 busNumber,
UInt32 numFrames, AudioBufferList *buffers) {
OSStatus status = AudioUnitRender(audioUnit, actionFlags, audioTimeStamp,1, numFrames, buffers);
if(status != noErr) {
NSLog(#"Render callback error");
return status;
}
return noErr;
}
-(void)setupAudio{
int sampleRate=44100;
int bufferSize=512;
if(AudioSessionInitialize(NULL, NULL, NULL, NULL) != noErr) {
return;
}
if(AudioSessionSetActive(true) != noErr) {
return;
}
Float32 bufferSizeInSec =bufferSize*1.0f/sampleRate;
if(AudioSessionSetProperty(kAudioSessionProperty_PreferredHardwareIOBufferDuration,
sizeof(Float32), &bufferSizeInSec) != noErr) {
return;
}
UInt32 overrideCategory = 1;
UInt32 audioCategory = kAudioSessionCategory_PlayAndRecord;
if(AudioSessionSetProperty(kAudioSessionProperty_AudioCategory,
sizeof(UInt32), &audioCategory) != noErr) {
return;
}
if(AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryDefaultToSpeaker,
sizeof(UInt32), &overrideCategory) != noErr) {
// Less serious error, but you may want to handle it and bail here
}
AudioComponentDescription componentDescription;
componentDescription.componentType = kAudioUnitType_Output;
componentDescription.componentSubType = kAudioUnitSubType_RemoteIO;
componentDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
componentDescription.componentFlags = 0;
componentDescription.componentFlagsMask = 0;
AudioComponent component = AudioComponentFindNext(NULL, &componentDescription);
if(AudioComponentInstanceNew(component,&audioUnit) != noErr) {
return;
}
UInt32 enable = 1;
if(AudioUnitSetProperty(audioUnit, kAudioOutputUnitProperty_EnableIO,
kAudioUnitScope_Input, 1, &enable, sizeof(UInt32)) != noErr) {
return;
}
AURenderCallbackStruct callbackStruct;
callbackStruct.inputProc = renderCallback; // Render function
callbackStruct.inputProcRefCon = NULL;
if(AudioUnitSetProperty(audioUnit, kAudioUnitProperty_SetRenderCallback,
kAudioUnitScope_Input, 0, &callbackStruct,
sizeof(AURenderCallbackStruct)) != noErr) {
return;
}
AudioStreamBasicDescription streamDescription;
streamDescription.mSampleRate = sampleRate;
streamDescription.mFormatID = kAudioFormatLinearPCM;
streamDescription.mFormatFlags = kAudioFormatFlagIsFloat |
kAudioFormatFlagsNativeEndian |
kAudioFormatFlagIsPacked;
streamDescription.mBitsPerChannel = 32;
streamDescription.mBytesPerFrame = 4;
streamDescription.mChannelsPerFrame = 1;
streamDescription.mBytesPerPacket = streamDescription.mBytesPerFrame *
streamDescription.mChannelsPerFrame;
streamDescription.mFramesPerPacket = 1;
streamDescription.mReserved = 0;
if(AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Input, 0, &streamDescription, sizeof(streamDescription)) != noErr) {
return;
}
if(AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Output, 1, &streamDescription, sizeof(streamDescription)) != noErr) {
return;
}
if(AudioUnitInitialize(audioUnit) != noErr) {
return;
}
if(AudioOutputUnitStart(audioUnit) != noErr) {
return;
}
NSLog(#"Audio Unit setup Complete");
}
- (void)didReceiveMemoryWarning{
[super didReceiveMemoryWarning];
self.data=[NSMutableData dataWithLength:1];
NSLog(#"MEMORY WARNING EVENT -> CLEARING DATA");
}
#end

Answer 1

I've got the same problem. My take, on iOS7, is to use that first memory warning notification to prepare a more final solution. Such as terminating the scheduled timer, and giving the user an alert that memory is low and audio has been shut down, and to free up some memory.