Crash when looping through RLMResults

[MV-EricDeHaan]

Goals

Looping through objects in RLMResults

Expected Results

Enumeration of realm objects

Actual Results

Sometimes it does enumerate but sometimes it crashes...

* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x10)
    frame #0: 0x0000000188f9ef0c libsystem_pthread.dylib`pthread_mutex_lock$VARIANT$mp
    frame #1: 0x000000010135f510 MVAnalyticsSDK`realm::SharedGroup::do_open(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, bool, bool, realm::SharedGroupOptions) + 2804
  * frame #2: 0x000000010128cd9c MVAnalyticsSDK`realm::SharedGroup::open(this=0x000000010496fc00, repl=<unavailable>, options=const realm::SharedGroupOptions @ 0x000000016f52e8f0) at group_shared.hpp:863:5 [opt]
    frame #3: 0x000000010128ca38 MVAnalyticsSDK`realm::SharedGroup::SharedGroup(this=0x000000010496fc00, repl=0x000000028392ae80, options=const realm::SharedGroupOptions @ 0x000000016f52eaf0) at group_shared.hpp:836:5 [opt]
    frame #4: 0x00000001012860f8 MVAnalyticsSDK`realm::Realm::open_with_config(realm::Realm::Config const&, std::__1::unique_ptr<realm::Replication, std::__1::default_delete<realm::Replication> >&, std::__1::unique_ptr<realm::SharedGroup, std::__1::default_delete<realm::SharedGroup> >&, std::__1::unique_ptr<realm::Group, std::__1::default_delete<realm::Group> >&, realm::Realm*) [inlined] realm::SharedGroup::SharedGroup(this=<unavailable>, repl=<unavailable>) at group_shared.hpp:835:1 [opt]
    frame #5: 0x00000001012860e8 MVAnalyticsSDK`realm::Realm::open_with_config(realm::Realm::Config const&, std::__1::unique_ptr<realm::Replication, std::__1::default_delete<realm::Replication> >&, std::__1::unique_ptr<realm::SharedGroup, std::__1::default_delete<realm::SharedGroup> >&, std::__1::unique_ptr<realm::Group, std::__1::default_delete<realm::Group> >&, realm::Realm*) [inlined] std::__1::__unique_if<realm::SharedGroup>::__unique_single std::__1::make_unique<realm::SharedGroup, realm::Replication&, realm::SharedGroupOptions&>(__args=0x000000028392ae80) at memory:3128 [opt]
    frame #6: 0x00000001012860a4 MVAnalyticsSDK`realm::Realm::open_with_config(config=<unavailable>, history=<unavailable>, shared_group=<unavailable>, read_only_group=<unavailable>, realm=<unavailable>) at shared_realm.cpp:196 [opt]
    frame #7: 0x00000001011bfc54 MVAnalyticsSDK`realm::_impl::RealmCoordinator::pin_version(this=<unavailable>, versionid=<unavailable>) at realm_coordinator.cpp:458:13 [opt]
    frame #8: 0x00000001011bfd40 MVAnalyticsSDK`realm::_impl::RealmCoordinator::register_notifier(notifier=std::__1::shared_ptr<realm::_impl::CollectionNotifier>::element_type @ 0x00000001099932c8 strong=2 weak=1) at realm_coordinator.cpp:490:14 [opt]
    frame #9: 0x00000001011c8d6c MVAnalyticsSDK`realm::Results::prepare_async(this=0x000000010997bd28, force=<unavailable>) at results.cpp:732:5 [opt]
    frame #10: 0x00000001011c5954 MVAnalyticsSDK`realm::Results::evaluate_query_if_needed(this=0x000000010997bd28, wants_notifications=true) at results.cpp:268:17 [opt]
    frame #11: 0x00000001011c568c MVAnalyticsSDK`realm::util::Optional<realm::BasicRowExpr<realm::Table> > realm::Results::try_get<realm::BasicRowExpr<realm::Table> >(this=0x000000010997bd28, row_ndx=0) at results.cpp:203:13 [opt]
    frame #12: 0x00000001011c5564 MVAnalyticsSDK`realm::BasicRowExpr<realm::Table> realm::Results::get<realm::BasicRowExpr<realm::Table> >(this=0x000000010997bd28, row_ndx=0) at results.cpp:216:20 [opt]
    frame #13: 0x0000000101a941dc VerusSDK`RLMAccessorContext auto realm::Results::get<RLMAccessorContext>(this=0x000000016f52f080, t=0x0000000000000000)::'lambda'(RLMAccessorContext&)::operator()<realm::BasicRowExpr<realm::Table>*>(RLMAccessorContext&) const at results.hpp:306:56
    frame #14: 0x0000000101a93c28 VerusSDK`RLMAccessorContext realm::switch_on_type<auto realm::Results::get<RLMAccessorContext>(RLMAccessorContext&, unsigned long)::'lambda'(RLMAccessorContext&)>(type=Object, fn=0x000000016f52f080) at property.hpp:171:33
    frame #15: 0x0000000101a93794 VerusSDK`RLMAccessorContext realm::Results::dispatch<auto realm::Results::get<RLMAccessorContext>(RLMAccessorContext&, unsigned long)::'lambda'(RLMAccessorContext&)>(this=0x000000010997bd28, fn=0x000000016f52f080) const at results.hpp:300:12
    frame #16: 0x0000000101a8f338 VerusSDK`auto realm::Results::get<RLMAccessorContext>(this=0x000000010997bd28, ctx=0x000000016f52f370, row_ndx=0) at results.hpp:306:12
    frame #17: 0x0000000101a8f0d8 VerusSDK`::-[RLMFastEnumerator countByEnumeratingWithState:count:](self=0x000000010995aab0, _cmd="countByEnumeratingWithState:count:", state=0x000000016f52f528, len=16) at RLMCollection.mm:129:51
    frame #18: 0x0000000101a8f584 VerusSDK`RLMFastEnumerate(state=0x000000016f52f528, len=16, collection=0x000000010997bd20) at RLMCollection.mm:167:12
    frame #19: 0x0000000101bc7054 VerusSDK`::-[RLMResults countByEnumeratingWithState:objects:count:](self=0x000000010997bd20, _cmd="countByEnumeratingWithState:objects:count:", state=0x000000016f52f528, buffer=0x000000016f52f598, len=16) at RLMResults.mm:181:12
    frame #20: 0x0000000101912b28 VerusSDK`-[ApiManager getScannedProducts](self=0x00000002819c8880, _cmd="getScannedProducts") at ApiManager.m:1154:5
    frame #21: 0x00000001019220e0 VerusSDK`-[VerusManager getScannedProducts](self=0x0000000283049600, _cmd="getScannedProducts") at VerusManager.m:893:12
    frame #22: 0x00000001008e7e54 Verus (int)`ScansTableViewController.showData(self=0x000000010449e430) at ScansTableViewController.swift:176:47
    frame #23: 0x00000001008de63c Verus (int)`MVViewController.viewWillAppear(animated=true, self=0x000000010449e430) at MVViewController.swift:39:9
    frame #24: 0x00000001008de69c Verus (int)`@objc MVViewController.viewWillAppear(_:) at <compiler-generated>:0
    frame #25: 0x00000001008e0ff0 Verus (int)`ScansTableViewController.viewWillAppear(animated=true, self=0x000000010449e430) at ScansTableViewController.swift:39:15
    frame #26: 0x00000001008e10bc Verus (int)`@objc ScansTableViewController.viewWillAppear(_:) at <compiler-generated>:0
    frame #27: 0x00000001b56ed940 UIKitCore`-[UIViewController _setViewAppearState:isAnimating:] + 584
    frame #28: 0x00000001b56ee00c UIKitCore`-[UIViewController __viewWillAppear:] + 140
    frame #29: 0x00000001b56457d4 UIKitCore`-[UINavigationController _startCustomTransition:] + 1248
    frame #30: 0x00000001b5659714 UIKitCore`-[UINavigationController _startDeferredTransitionIfNeeded:] + 708
    frame #31: 0x00000001b565ab3c UIKitCore`-[UINavigationController __viewWillLayoutSubviews] + 164
    frame #32: 0x00000001b563dd4c UIKitCore`-[UILayoutContainerView layoutSubviews] + 224
    frame #33: 0x00000001b6129170 UIKitCore`-[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1292
    frame #34: 0x000000018d8c3c60 QuartzCore`-[CALayer layoutSublayers] + 184
    frame #35: 0x000000018d8c8c08 QuartzCore`CA::Layer::layout_if_needed(CA::Transaction*) + 332
    frame #36: 0x000000018d82b3e4 QuartzCore`CA::Context::commit_transaction(CA::Transaction*) + 348
    frame #37: 0x000000018d859620 QuartzCore`CA::Transaction::commit() + 640
    frame #38: 0x000000018d85a15c QuartzCore`CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) + 92
    frame #39: 0x0000000189317d08 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32
    frame #40: 0x0000000189312a30 CoreFoundation`__CFRunLoopDoObservers + 412
    frame #41: 0x0000000189312fac CoreFoundation`__CFRunLoopRun + 1228
    frame #42: 0x00000001893127c0 CoreFoundation`CFRunLoopRunSpecific + 436
    frame #43: 0x000000018b51379c GraphicsServices`GSEventRunModal + 104
    frame #44: 0x00000001b5c91c38 UIKitCore`UIApplicationMain + 212
    frame #45: 0x000000010091e864 Verus (int)`main at AppDelegate.swift:15:7
    frame #46: 0x0000000188dd68e0 libdyld.dylib`start + 4

Steps to Reproduce

Code Sample

    RLMRealm *realm = [RLMRealm realmWithConfiguration:sharedInstance.realmConfiguration error:NULL];
    RLMResults<ScannedProduct *> *rlmScanned = [[ScannedProduct allObjectsInRealm:realm] sortedResultsUsingKeyPath:@"scannedAt" ascending:NO];
    NSLog(@"#scanned: %lu", (unsigned long)rlmScanned.count);
    
    NSMutableArray *result = [[NSMutableArray alloc] init];
    for (ScannedProduct *rlmScannedProduct in rlmScanned) {
        MVScannedProduct *scannedProduct = [sharedInstance getMVScannedProduct:rlmScannedProduct];
        
        [result addObject:scannedProduct];
    }
    return result;

Version of Realm and Tooling

Realm framework version: 3.14.1

Realm Object Server version: ?

Xcode version: 10.3

iOS/OSX version: 12.3

Dependency manager + version: ?

[bmunkholm]

Can you reproduce it (perhaps unreliable)? How and where do you do that? How frequently does it happen?

[MV-EricDeHaan]

In my app I can reproduce it. I have a ViewController with a tableview that shows data I retrieve from a Realm. That viewcontroller is one of the first I show. When I navigate from that viewcontroller to another viewcontroller and navigate back than in the viewWillAppear I try to retrieve the data (again) that is the moment the crash appears. I can get the count from the RLMResults and ik gives me the correct number of objects, but the moment I enter the for loop it results in a crash.

[bmunkholm]

So you can reliably reproduce this - is it every single time?
Is it on a device, or the emulator?
Can you try to reduce the issue down to a self contained minimal repro project? (often that helps to debug it)

[MV-EricDeHaan]

(Un)fortunately I can reliably reproduce this. It is on a device.
I have a, for me, complex situation. I build a framework that uses Realm. When I use that framework in the mentioned app the crash happens. When I add a target in my framework project that uses the framework, I sometimes can reproduce the issue. But that is not reliable, it occurs occasionally...

[bmunkholm]

Well, "if we can reproduce it we can fix it" :-).
Does the same happen in a simulator?
Would it be possible to share the app and framework with us?

[MV-EricDeHaan]

I second your first statement ;-)
The app uses the camera for scanning (Vuforia and Digimarc) so the simulator does not work.
I can share my project, but my manager and CEO are a bit more reserved…

What is the best way to share? A zip over WeTransfer and a password via email?

[bmunkholm]

@MV-EricDeHaan You can create a private issue at support.realm.io and share the password there. Reference this github issue.
Ideally try to reduce the scope/dependencies of the app.
Also include full instructions on how to reproduce.

@tgoyne Can you see anything obvious here?

[bmunkholm]

For internal reference to the app sent in to support: https://support.realm.io/a/tickets/4694.