iOS Error::Report function crash

[huanghe810229530]

The language of WCDB

Objective-C

The version of WCDB

v1.0.6

The platform of WCDB

iOS

The installation of WCDB

Cocoapods

What's the issue?

As follow: When the query table exists, application in WCDB: : Error: Report function crashed（accidentally）. how should solve?

// when app go background, I call this method
- (void)getMembersWithGroupId:(int)groupId resultBlock:(void (^)(NSArray *results))block {
     // otherQueue is a synac queue
    dispatch_async(self.otherQueue, ^{
        NSString *tableName = [NSString stringWithFormat:@"%@_%ld", kTableGroupMember, (long)groupId];
        WCTTable *table = [self.db getTableOfName:tableName withClass:Member.class];
        
        NSArray *res = [table getAllObjects];
        block(res);
    });
}

// Crash info
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x00020001013aa660
VM Region Info: 0x20001013aa660 is not in any region. Bytes after previous region: 562946215945825
REGION TYPE START - END [ VSIZE] PRT/MAX SHRMOD REGION DETAIL
MALLOC_NANO (reserved) 00000001d8000000-00000001e0000000 [128.0M] rw-/rwx SM=NUL ...(unallocated)
--->
UNUSED SPACE AT END

[huanghe810229530]

@RingoD Help to look at，thanks！

[RingoD]

Did you register your own report function?

[huanghe810229530]

I just do this:

+(DBManager*)sharedDBMagnger {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedDBMagnger = [[DBManager alloc]init];
        sharedDBMagnger.messageQueue = dispatch_queue_create("db_message_queue", NULL);
        sharedDBMagnger.otherQueue = dispatch_queue_create("db_other_queue", NULL);
        [WCTStatistics SetGlobalErrorReport:^(WCTError *error) {
            DEBUGLog(@"[WCDB]%@", error);
        }];
    });
    
    return sharedDBMagnger;
}

Is there a problem with this?

[RingoD]

It seems like nothing wrong. Can you provide a reproducible project for this issue?

[huanghe810229530]

The probability of this problem is very low. Development have not seen, but the online version appeared several times.

[RingoD]

Em... I have no idea about this. There is no same crash for us. Maybe we should wait for more information.

[huanghe810229530]

Ok, I will collect the new information, if have I will tell you.

[highlystuff]

I met this issue,too... any solution?

[liufengdev]

The same for me, any solution?

[liufengdev]

After a very thorough review, i have found that where there is a crash like this, there is also a [db close] operation (the reason for [db close] is trying to reduce size of wal file, maybe i was wrong), about 99%. So i review the document, remove all [db close] operation, and use journal_size_limit instead to reach my purpose.

[liufengdev]

In wcdb, default value for journal_size_limit is -1, which means NO LIMIT (https://www.sqlite.org/pragma.html#pragma_journal_size_limit).

[RingoD]

@liufengdev Hi. I read your comment and confuse that why do you think this crash is related to close? Did you have any evidence?

[liufengdev]

@RingoD

1. Just a try without evidence and actually this crash has NO matter with close.
2. Today, we find a way to reproduce it, just deliberately kill you app via double click home button and swap up. While you doing this, Main Thread will clean all static shared_ptr, and deconstruct them, the question is, at this time , some other thread may be accessing data from shared_ptr. Moreover, this is the evidence for Thread Safety with some parts in WCDB, see https://pastebin.com/NQxBUbrE

What happens when we deliberately kill our app?

` thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 7.1

frame #0: 0x000000010ea28d20 msgInHouse`WCDB::Error::ReportMethodObj::~ReportMethodObj(this=0x0000600000c21560) at error.cpp:75:9
frame #1: 0x000000010ea28d85 msgInHouse`WCDB::Error::ReportMethodObj::~ReportMethodObj(this=0x0000600000c21560) at error.cpp:74:48
frame #2: 0x000000010ea31feb msgInHouse`std::__1::default_delete<WCDB::Error::ReportMethodObj>::operator(this=0x00006000002210b8, __ptr=0x0000600000c21560)(WCDB::Error::ReportMethodObj*) const at memory:2335:5
frame #3: 0x000000010ea31c80 msgInHouse`std::__1::__shared_ptr_pointer<WCDB::Error::ReportMethodObj*, std::__1::default_delete<WCDB::Error::ReportMethodObj>, std::__1::allocator<WCDB::Error::ReportMethodObj> >::__on_zero_shared(this=0x00006000002210a0) at memory:3636:5
frame #4: 0x000000010ea2e9da msgInHouse`std::__1::__shared_count::__release_shared(this=0x00006000002210a0) at memory:3540:9
frame #5: 0x000000010ea2e97f msgInHouse`std::__1::__shared_weak_count::__release_shared(this=0x00006000002210a0) at memory:3582:27
frame #6: 0x000000010ea2e94c msgInHouse`std::__1::shared_ptr<WCDB::Error::ReportMethodObj>::~shared_ptr(this=0x00000001124a5ab8) at memory:4518:19
frame #7: 0x000000010ea28c45 msgInHouse`std::__1::shared_ptr<WCDB::Error::ReportMethodObj>::~shared_ptr(this=0x00000001124a5ab8) at memory:4516:1
frame #8: 0x000000011f6a5d35 libsystem_c.dylib`__cxa_finalize_ranges + 319
frame #9: 0x000000011f6a6068 libsystem_c.dylib`exit + 48
frame #10: 0x0000000128103b57 UIKitCore`-[UIApplication _terminateWithStatus:] + 276
frame #11: 0x000000012794229a UIKitCore`__98-[__UICanvasLifecycleMonitor_Compatability deactivateEventsOnly:withContext:forceExit:completion:]_block_invoke.261 + 330
frame #12: 0x0000000128107cc9 UIKitCore`_runAfterCACommitDeferredBlocks + 318
frame #13: 0x00000001280f7199 UIKitCore`_cleanUpAfterCAFlushAndRunDeferredBlocks + 358
frame #14: 0x000000012812432b UIKitCore`_afterCACommitHandler + 124
frame #15: 0x0000000117ab00f7 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
frame #16: 0x0000000117aaa5be CoreFoundation`__CFRunLoopDoObservers + 430
frame #17: 0x0000000117aaac31 CoreFoundation`__CFRunLoopRun + 1505
frame #18: 0x0000000117aaa302 CoreFoundation`CFRunLoopRunSpecific + 626
frame #19: 0x00000001201b72fe GraphicsServices`GSEventRunModal + 65
frame #20: 0x00000001280fcba2 UIKitCore`UIApplicationMain + 140
frame #21: 0x000000010c3469f0 msgInHouse`main(argc=1, argv=0x00007ffee38ba018) at main.m:14:16
frame #22: 0x000000011f5be541 libdyld.dylib`start + 1
frame #23: 0x000000011f5be541 libdyld.dylib`start + 1`

Wish all above will help.

ReportMethodObj is just a wrapper for ReportMethod, only used for debug.

class ReportMethodObj { public: ReportMethod func; ReportMethodObj(ReportMethod func); ~ReportMethodObj(); };

[liufengdev]

Moreover, on June 17,2019

https://developer.apple.com/documentation/xcode_release_notes/xcode_11_beta_2_release_notes,
Clang now provides a mechanism for controlling exit-time destructor registration

[liufengdev]

@huanghe810229530 The compiler flag -fno-c++-static-destructors works [Xcode 10.2].

[RingoD]

@liufengdev Yes, -fno-c++-static-destructors will be added to the compiler options. But I didn't know that it's already supported since Xcode 10.2. Thanks.