intermittent extaudiofileread exc_bad_access

I have what at the moment seems like an unsolvable EXC_BAD_ACCESS problem. I've tried enabling NSZombie, as seems to be the advice in many posts but I'm dealing with c pointers and not obj c objects so I'm not getting any useful debugging information.

The way my code works is that in advance of it needing some audio from disk I detach a new posix thread passing it a pointer to information about the audio I want. Then I read some samples. The reason I chose posix over NSThread or NSOperation is because it seemed to perform quicker. My audio is quite cpu intensive so I need to read audio as quick as possible.

How can I fix this bad access error? It doesnt occur all of the time. Sometimes it seems to happen when the application is very busy. Very occasionally it doesnt happen at all.

Is there anyway I could just throw a try catch around this as a quick fix? How else can I investigate causes of this is happening?

Edit This is a link to a seperate question I asked but it is related to the same problem

[Threading for intense io][1]

//detachnewthread gets called from remoteio callback

void detachnewthread(AudioSourceOBJ str)
{

    //..... code removed for brevity
    if(str)
    {

        int rc;

        rc = pthread_create(&str->thread, NULL, FetchAudio, (void *)str);
        if (rc){
            printf("ERROR; return code from pthread_create() is %d\n", rc);
            exit(-1);
        }

    }

}


void *FetchAudio(void *threadid)

{ AudioSourceOBJ soundptr=threadid;

AudioUnitSampleType *outSamplesChannelLeft;
AudioUnitSampleType *outSamplesChannelRight;

outSamplesChannelLeft                 = (AudioUnitSampleType *) soundptr->queuebuffer->ABL->mBuffers[0].mData;
outSamplesChannelRight  = (AudioUnitSampleType *)soundptr->queuebuffer->ABL->mBuffers[0].mData;
// ExtAudioFileRef audioFileRef;



// result=  ExtAudioFileOpenURL(str->path, &str->audioFileObject);

AudioStreamBasicDescription importFormat = {0};

size_t bytesPerSample = sizeof (AudioUnitSampleType);

// Fill the application audio format struct's fields to define a linear PCM, 
//        stereo, noninterleaved stream at the hardware sample rate.
importFormat.mFormatID          = kAudioFormatLinearPCM;
importFormat.mFormatFlags       = kAudioFormatFlagsAudioUnitCanonical;
importFormat.mBytesPerPacket    = bytesPerSample;
importFormat.mFramesPerPacket   = 1;
importFormat.mBytesPerFrame     = bytesPerSample;
importFormat.mChannelsPerFrame  = 2;                    // 2 indicates stereo
importFormat.mBitsPerChannel    = 8 * bytesPerSample;
importFormat.mSampleRate        = 44100;


ExtAudioFileSetProperty (
                                     engineDescribtion.audiofilerefs[soundptr->audioindex],
                                     kExtAudioFileProperty_ClientDataFormat,
                                     sizeof (importFormat),
                                     &importFormat
                                     );

UInt32 numberofframestoread=(soundptr->amounttoread);
AudioBufferList *bufferList;

bufferList = (AudioBufferList *) malloc (
                                         sizeof (AudioBufferList) + sizeof (AudioBuffer) * (1)
                                         );


// initialize the mNumberBuffers member
bufferList->mNumberBuffers = 2;

// initialize the mBuffers member to 0
AudioBuffer emptyBuffer = {0};
size_t arrayIndex;
for (arrayIndex = 0; arrayIndex < 2; arrayIndex++) {
    bufferList->mBuffers[arrayIndex] = emptyBuffer;
}

// set up the AudioBuffer structs in the buffer list
bufferList->mBuffers[0].mNumberChannels  = 1;
bufferList->mBuffers[0].mDataByteSize    = numberofframestoread * sizeof (AudioUnitSampleType);
bufferList->mBuffers[0].mData            = (AudioUnitSampleType*)calloc(numberofframestoread, sizeof(AudioUnitSampleType));

    bufferList->mBuffers[1].mNumberChannels  = 1;
    bufferList->mBuffers[1].mDataByteSize    = numberofframestoread * sizeof (AudioUnitSampleType);
    bufferList->mBuffers[1].mData            = (AudioUnitSampleType*)calloc(numberofframestoread, sizeof(AudioUnitSampleType));




AudioUnitSampleType *inSamplesChannelLeft=bufferList->mBuffers[0].mData;
AudioUnitSampleType *inSamplesChannelRight=bufferList->mBuffers[1].mData;



// UInt32 read=(UInt32)soundptr->fetchsample;
UInt32 read_plus_half_buffer=soundptr->fetchsample;

UInt32 readdestination= read_plus_half_buffer+numberofframestoread;
UInt32 actualsamplesread=0;

actualsamplesread=numberofframestoread;


if (readdestination>soundptr->perfectframecount) {


    UInt32 readinpt1=0;
    UInt32 readoutpt1=0;
    UInt32 readinpt2=0;
    UInt32 readoutpt2=0;
    Float32 readtillendamount=0;

    readinpt1=read_plus_half_buffer;
    readoutpt1=soundptr->perfectframecount;
    readinpt2=0;



    if(read_plus_half_buffer>soundptr->perfectframecount)
    {
        readtillendamount=numberofframestoread;
        readinpt1=read_plus_half_buffer-soundptr->perfectframecount;

    }else
    {

        readtillendamount=soundptr->perfectframecount - readinpt1;
        readoutpt2=numberofframestoread-readtillendamount;




    }
    actualsamplesread= readtillendamount;
    ExtAudioFileSeek(engineDescribtion.audiofilerefs[soundptr->audioindex], readinpt1);
    ExtAudioFileRead(engineDescribtion.audiofilerefs[soundptr->audioindex],&actualsamplesread , bufferList);

    int writeposition=soundptr->queuebuffer->position;

    for (int i=0; i<actualsamplesread; i++) {


        outSamplesChannelLeft[writeposition]=inSamplesChannelLeft[i];
        outSamplesChannelRight[writeposition]=inSamplesChannelRight[i];



        writeposition++;

    }

    if (actualsamplesread!=readtillendamount) {

        UInt32 newzeroamount= readtillendamount-actualsamplesread;

        for (int j=0; j<newzeroamount; j++) {

            outSamplesChannelLeft[writeposition]=0;
            outSamplesChannelRight[writeposition]=0;
            writeposition++;

        }

    }       
    bufferList->mBuffers[1].mDataByteSize    = readoutpt2 * sizeof (AudioUnitSampleType);
    bufferList->mBuffers[0].mDataByteSize    = readoutpt2 * sizeof (AudioUnitSampleType);


    ExtAudioFileSeek(engineDescribtion.audiofilerefs[soundptr->audioindex], 0);
    ExtAudioFileRead(engineDescribtion.audiofilerefs[soundptr->audioindex],&readoutpt2 , bufferList);


    for (int k=0; k<readoutpt2; k++) {

        outSamplesChannelLeft[writeposition]=inSamplesChannelLeft[k];
        outSamplesChannelRight[writeposition]=inSamplesChannelRight[k];
        writeposition++;

    }


}else if(readdestination<=soundptr->perfectframecount){

    ExtAudioFileSeek(engineDescribtion.audiofilerefs[soundptr->audioindex], read_plus_half_buffer);

    bufferList->mBuffers[1].mDataByteSize    = actualsamplesread * sizeof (AudioUnitSampleType);
    bufferList->mBuffers[0].mDataByteSize    = actualsamplesread * sizeof (AudioUnitSampleType);
    // crash happens here

    if(bufferList)
    {
   assert( ExtAudioFileRead(engineDescribtion.audiofilerefs[soundptr->audioindex],&actualsamplesread , bufferList));
    }else

    {
        printf("NO BUFFER");
    }



    int writeposition=soundptr->queuebuffer->position;
    for (int i=0; i<actualsamplesread; i++) {

        outSamplesChannelLeft[writeposition]=inSamplesChannelLeft[i];
        outSamplesChannelRight[writeposition]=inSamplesChannelRight[i];
        writeposition++;

    }

    if (actualsamplesread!=numberofframestoread) {
        int zerosamples=0;

        zerosamples=numberofframestoread-actualsamplesread;

        for (int j=0; j<zerosamples; j++) {
            outSamplesChannelLeft[writeposition]=0;
            outSamplesChannelRight[writeposition]=0;
            writeposition++;


        }

    }                

}else
{
    printf("unknown condition");

}





free(bufferList->mBuffers[0].mData); 
free(bufferList->mBuffers[1].mData); 
free(bufferList);
bufferList=nil;

soundptr->queuebuffer->isreading=NO;

// pthread_detach(soundptr->thread);  
// free(&soundptr->m_lock);
return 0;
// pthread_exit(NULL);

}

Edit 2

O.K I've figured out how to use malloc history. I have a big trace statement. This is the first time I've ever seen anything like this before & I don't know how to use it to help myself.

    ALLOC 0x6c67000-0x6c67fd7 [size=4056]: thread_a019c540 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __CFRunLoopRun | __CFRunLoopDoSource1 | __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ | migHelperRecievePortCallout | _XReceivedStatusBarDataAndActions | _UIStatusBarReceivedStatusBarDataAndActions | -[UIStatusBarServer _receivedStatusBarData:actions:] | -[UIStatusBarForegroundView setStatusBarData:actions:animated:] | -[UIStatusBarLayoutManager updateItemsWithData:actions:animated:] | -[UIStatusBarLayoutManager _updateItemView:withData:actions:animated:] | -[UIStatusBarItemView updateContentsAndWidth] | -[UIStatusBarTimeItemView contentsImageForStyle:] | -[UIStatusBarItemView drawText:forStyle:] | -[UIStatusBarItemView drawText:forStyle:forWidth:lineBreakMode:letterSpacing:] | -[NSString(UIStringDrawing) drawAtPoint:forWidth:withFont:lineBreakMode:letterSpacing:] | -[NSString(UIStringDrawing) drawAtPoint:forWidth:withFont:lineBreakMode:letterSpacing:includeEmoji:] | -[NSString(WebStringDrawing) _web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:] | -[NSString(WebStringDrawing) __web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:measureOnly:] | -[NSString(WebStringDrawing) __web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:measureOnly:renderedStringOut:] | drawAtPoint(unsigned short const*, int, WebCore::FloatPoint const&, WebCore::Font const&, WebCore::GraphicsContext*, WebCore::BidiStatus*, int) | WebCore::Font::drawSimpleText(WebCore::GraphicsContext*, WebCore::TextRun const&, WebCore::FloatPoint const&, int, int) const | WebCore::Font::drawGlyphBuffer(WebCore::GraphicsContext*, WebCore::GlyphBuffer const&, WebCore::TextRun const&, WebCore::FloatPoint&) const | WebCore::Font::drawGlyphs(WebCore::GraphicsContext*, WebCore::SimpleFontData const*, WebCore::GlyphBuffer const&, int, int, WebCore::FloatPoint const&, bool) const | WebCore::showGlyphsWithAdvances(WebCore::FontPlatformData const&, CGContext*, unsigned short const*, CGSize const*, unsigned long) | CGContextShowGlyphsWithAdvances | draw_glyphs | ripc_DrawGlyphs | ripc_RenderGlyphs | CGGlyphLockLockGlyphBitmaps | create_missing_bitmaps | CGFontCreateGlyphBitmap8 | aa_create | malloc | malloc_zone_malloc 
----
FREE  0x6c67000-0x6c67fd7 [size=4056]: thread_a019c540 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __CFRunLoopRun | __CFRunLoopDoSource1 | __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ | migHelperRecievePortCallout | _XReceivedStatusBarDataAndActions | _UIStatusBarReceivedStatusBarDataAndActions | -[UIStatusBarServer _receivedStatusBarData:actions:] | -[UIStatusBarForegroundView setStatusBarData:actions:animated:] | -[UIStatusBarLayoutManager updateItemsWithData:actions:animated:] | -[UIStatusBarLayoutManager _updateItemView:withData:actions:animated:] | -[UIStatusBarItemView updateContentsAndWidth] | -[UIStatusBarTimeItemView contentsImageForStyle:] | -[UIStatusBarItemView drawText:forStyle:] | -[UIStatusBarItemView drawText:forStyle:forWidth:lineBreakMode:letterSpacing:] | -[NSString(UIStringDrawing) drawAtPoint:forWidth:withFont:lineBreakMode:letterSpacing:] | -[NSString(UIStringDrawing) drawAtPoint:forWidth:withFont:lineBreakMode:letterSpacing:includeEmoji:] | -[NSString(WebStringDrawing) _web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:] | -[NSString(WebStringDrawing) __web开发者_StackOverflow_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:measureOnly:] | -[NSString(WebStringDrawing) __web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:measureOnly:renderedStringOut:] | drawAtPoint(unsigned short const*, int, WebCore::FloatPoint const&, WebCore::Font const&, WebCore::GraphicsContext*, WebCore::BidiStatus*, int) | WebCore::Font::drawSimpleText(WebCore::GraphicsContext*, WebCore::TextRun const&, WebCore::FloatPoint const&, int, int) const | WebCore::Font::drawGlyphBuffer(WebCore::GraphicsContext*, WebCore::GlyphBuffer const&, WebCore::TextRun const&, WebCore::FloatPoint&) const | WebCore::Font::drawGlyphs(WebCore::GraphicsContext*, WebCore::SimpleFontData const*, WebCore::GlyphBuffer const&, int, int, WebCore::FloatPoint const&, bool) const | WebCore::showGlyphsWithAdvances(WebCore::FontPlatformData const&, CGContext*, unsigned short const*, CGSize const*, unsigned long) | CGContextShowGlyphsWithAdvances | draw_glyphs | ripc_DrawGlyphs | ripc_RenderGlyphs | CGGlyphLockLockGlyphBitmaps | create_missing_bitmaps | CGFontCreateGlyphBitmap8 | aa_destroy | free 

ALLOC 0x6c67000-0x6c67fff [size=4096]: thread_b024f000 |thread_start | _pthread_start | __NSThread__main__ | -[NSThread main] | -[FirstViewController checkstate:] | CALayer_setter_kCAValueFloat | CALayer_setter | CA::Transaction::ensure_compat() | CA::Transaction::create() | malloc | malloc_zone_malloc 
----
FREE  0x6c67000-0x6c67fff [size=4096]: thread_b024f000 |thread_start | _pthread_start | __NSThread__main__ | -[NSString compare:options:] | _pthread_exit | _pthread_tsd_cleanup | free 

ALLOC 0x6c67000-0x6c67fff [size=4096]: thread_b0353000 |thread_start | _pthread_start | __NSThread__main__ | -[NSThread main] | -[FirstViewController checkstate:] | CALayer_setter_kCAValueFloat | CALayer_setter | CA::Transaction::ensure_compat() | CA::Transaction::create() | malloc | malloc_zone_malloc 
----
FREE  0x6c67000-0x6c67fff [size=4096]: thread_b0353000 |thread_start | _pthread_start | __NSThread__main__ | -[NSString compare:options:] | _pthread_exit | _pthread_tsd_cleanup | free 

ALLOC 0x6c67000-0x6c67fff [size=4096]: thread_b0763000 |thread_start | _pthread_start | FetchAudio | ExtAudioFileRead | ExtAudioFile::Read(unsigned long, unsigned long&, AudioBufferList*) | AudioConverterFillComplexBuffer | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | AudioConverterChain::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | CBRConverter::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::GetInputBytes(unsigned long, unsigned long&, CABufferList const*&) | CABufferList::AllocateBuffers(unsigned long) | operator new[](unsigned long) | operator new(unsigned long) | malloc | malloc_zone_malloc 
----
FREE  0x6c67000-0x6c67fff [size=4096]: thread_b0763000 |thread_start | _pthread_start | FetchAudio | ExtAudioFileRead | ExtAudioFile::Read(unsigned long, unsigned long&, AudioBufferList*) | AudioConverterFillComplexBuffer | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | AudioConverterChain::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | CBRConverter::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::GetInputBytes(unsigned long, unsigned long&, CABufferList const*&) | free 

ALLOC 0x6c67000-0x6c67fff [size=4096]: thread_b0a6f000 |thread_start | _pthread_start | FetchAudio | ExtAudioFileRead | ExtAudioFile::Read(unsigned long, unsigned long&, AudioBufferList*) | AudioConverterFillComplexBuffer | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | AudioConverterChain::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | CBRConverter::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::GetInputBytes(unsigned long, unsigned long&, CABufferList const*&) | CABufferList::AllocateBuffers(unsigned long) | operator new[](unsigned long) | operator new(unsigned long) | malloc | malloc_zone_malloc 
----
FREE  0x6c67000-0x6c67fff [size=4096]: thread_b0a6f000 |thread_start | _pthread_start | FetchAudio | ExtAudioFileRead | ExtAudioFile::Read(unsigned long, unsigned long&, AudioBufferList*) | AudioConverterFillComplexBuffer | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | AudioConverterChain::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::FillBuffer(unsigned long&, AudioBufferList&, AudioStreamPacketDescription*) | CBRConverter::RenderOutput(CABufferList*, unsigned long, unsigned long&, AudioStreamPacketDescription*) | BufferedAudioConverter::GetInputBytes(unsigned long, unsigned long&, CABufferList const*&) | free 

ALLOC 0x6c67000-0x6c67fff [size=4096]: thread_b0081000 |thread_start | _pthread_start | __NSThread__main__ | -[NSThread main] | -[FirstViewController checkstate:] | CALayer_setter_kCAValueFloat | CALayer_setter | CA::Transaction::ensure_compat() | CA::Transaction::create() | malloc | malloc_zone_malloc 
----
FREE  0x6c67000-0x6c67fff [size=4096]: thread_b0081000 |thread_start | _pthread_start | __NSThread__main__ | -[NSString compare:options:] | _pthread_exit | _pthread_tsd_cleanup | free 

---

I notice the following lines in your code:

bufferList = (AudioBufferList *) malloc (
                                         sizeof (AudioBufferList) + sizeof (AudioBuffer) * (1)
                                         );
// initialize the mNumberBuffers member
bufferList->mNumberBuffers = 2;

You are malloc'ing an AudioBufferList to have the capacity of one AudioBuffer, but then indicating that it actually has two. Try changing that "* (1)" to "* (2)".

In addition to this, you shouldn't perform malloc's or ExtAudioFileOpen's in the thread, as those will take up time. If you can manage to pre-perform the malloc's and ExtAudioFileOpen's and just keep them in a struct array for your files, you may find a increase in performance / stability.

I may not have read the code completely properly as it looks like the formatting got a little messed up, but I hope this helps.

---

You fix this by locating it and figuring out why it is wrong, not by a try/catch.

Guard Malloc can help you identify many issues in your program. It is a diagnostic option which you can enable in Xcode. The intent of the option is to fail when you attempt to read or write memory you do not own, making it clearer than usual which part of your program is causing issues. full details: man guardmalloc. The first step is to correct all issues guardmalloc points out. You should be able to run your app for hours without these issues.

If you want exceptions and runtime checks to help you identify these issues earlier on (which is worth your consideration), consider C++ rather than C for your implementations.

Update

if it's a heap allocation that is the allocation in question, then malloc logging will likely help you. when malloc logging is enabled and the debugger pauses execution, just use malloc_history to view the callstack for the allocation. malloc_history will lookup the address in the log and dump the callstack of the alloc's creation. from there, you just follow the allocation's flow through your program to find what you are getting wrong.

---

I eventually found the solution to this problem. Every time I needed audio I created a new thread to fetch the audio. On occassion while a thread was fetching audio for a particular the buffer the same buffer would request data again resulting in the same buffer be accessed at the same time, thus the exc_bad_access.

I solved this by having just one thread waiting and being signalled to get data using posix condition.

All of the answers here were useful and have helped me learn a lot about debugging. Thanks guys..

---

The problem is almost certainly happening because your reading memory that you shouldn't be. Hence the EXC_BAD_ACCESS. What's essential is that the sizes of your buffers, and the amount of memory that you are reading is all correct. For example if you try to read more than a buffer's worth, you'll receive an error.

In ExtAudioFileRead, the value at &readoutpt2 should specify the number of frames. Are you sure this value is correct? Is bufferList big enough to store that number of frames? Are you advancing a pointer through bufferList as you read data, and is the amount you advance correct?

Are you correctly allocating memory based upon the underlying type? For example is your audio data integer or floating point format?

Basically, everything needs to add up correctly otherwise you will blow a buffer somewhere!

One other tool to try for tracking down memory issues is guard malloc. You can find more info here Enabling the Malloc Debugging Features