iPhone app crashes on WebThread MPVolumeSlider

Question

It seems like very broad to ask a question, but this is very annoying and difficult to fix the bug.

Here's the crash log for WebThread which I got from Crashlytics.

Thread : Crashed: WebThread
0  libobjc.A.dylib                0x0000000193e97bd0 objc_msgSend + 16
1  UIKit                          0x0000000187f65dd8 +[UIViewAnimationState  popAnimationState] + 332
2  MediaPlayer                    0x0000000185953358 -[MPVolumeSlider volumeController:volumeValueDidChange:] + 92
3  MediaPlayer                    0x00000001859c5fc4 -[MPVolumeController updateVolumeValue] + 260
4  MediaPlayer                    0x0000000185952cb0 -[MPVolumeSlider didMoveToSuperview] + 144
5  UIKit                          0x0000000187f2c1dc -[UIView(Hierarchy) _postMovedFromSuperview:] + 484
6  UIKit                          0x0000000187f37cbc -[UIView(Internal) _addSubview:positioned:relativeTo:] + 1764
7  MediaPlayer                    0x0000000185955f54 -[MPVolumeView _createSubviews] + 264
8  MediaPlayer                    0x00000001859549d4 -[MPVolumeView _initWithStyle:] + 240
9  MediaPlayer                    0x0000000185954a60 -[MPVolumeView initWithFrame:style:] + 88
10 WebCore                        0x0000000191ba4684 -[WebMediaSessionHelper initWithCallback:] + 132
11 WebCore                        0x0000000191ba3db8 WebCore::MediaSessionManageriOS::MediaSessionManageriOS() + 96
12 WebCore                        0x0000000191ba3d28 WebCore::MediaSessionManager::sharedManager() + 56
13 WebCore                        0x0000000191ba2890 WebCore::MediaSession::MediaSession(WebCore::MediaSessionClient&) + 44
14 WebCore                        0x00000001916e8604 WebCore::HTMLMediaSession::create(WebCore::MediaSessionClient&) + 36
15 WebCore                        0x00000001916d0fb0 WebCore::HTMLMediaElement::HTMLMediaElement(WebCore::QualifiedName const&, WebCore::Document&, bool) + 1100
16 WebCore                        0x000000019170a2b4 WebCore::HTMLVideoElement::create(WebCore::QualifiedName const&, WebCore::Document&, bool) + 68
17 WebCore                        0x00000001916bdd9c WebCore::videoConstructor(WebCore::QualifiedName const&, WebCore::Document&, WebCore::HTMLFormElement*, bool) + 92

I never seen this kind of crash during development(I would be very happy when I can catch it with breakpoint and console log), but only appears to users when it is on live.

Can be only reported by crashlytics.

Possible reason;

App uses MagicalRecord and get data from server in background when start up. This uses multi-thread, and when webkit is using UIKit part and locking, another main thread seems like access it. So I have tried to remove all dispatch_sync and changed it to dispatch_async but the crashes happens again after proceeding a few functional calls.

What I want to know is, why WebCore is running, and I never requested MPVolumeController on UIWebView.

Even they can run on background for some reason, why it crashes? It is happening frequently and users complaint.

Any others have same problem?

Answer 1

This bug occurred since iOS 8.

UIWebView that loads HTML containing audio or video elements will crash randomly.

I fixed it like this:

@interface H5WebKitBugsManager : NSObject

+ (void)fixAllBugs;

@end


#import "H5WebKitBugsManager.h"
#import <objc/runtime.h>

void H5Swizzle(Class c, SEL orig, SEL new)
{
    Method origMethod = class_getInstanceMethod(c, orig);
    Method newMethod = class_getInstanceMethod(c, new);
    if(class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod))) {
        class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    } else {
        method_exchangeImplementations(origMethod, newMethod);
    }
}

@implementation H5WebKitBugsManager

+ (void)fixAllBugs
{
    [self fixBug_MediaPlayerVolumeView];
}

+ (void)fixBug_MediaPlayerVolumeView
{
    CGFloat systemVersion = [UIDevice currentDevice].systemVersion.floatValue;

    if (systemVersion < 8.0f || systemVersion > 9.1) {
    // below ios version 8.0 has no VolumeView
        return;
    }

    Class cls = NSClassFromString(@"WebMediaSessionHelper");
    NSString *allocateVolumeView = @"allocateVolumeView";
    SEL orig = NSSelectorFromString(allocateVolumeView);
    SEL new = @selector(H5WKBMAllocateVolumeView);
    Method newMethod = class_getInstanceMethod(self, new);

    if(class_addMethod(cls, new, method_getImplementation(newMethod), method_getTypeEncoding(newMethod))) {
        H5Swizzle(cls, orig, new);
    }
}

- (void)H5WKBMAllocateVolumeView
{
    // WebKit's MediaSessionManageriOS is a singleton，in MediaSessionManageriOS.m. svn version181,859.
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
            // must be dispatch in background thread
            [self H5WKBMAllocateVolumeView];
        });
    });
}

@end