Race condition on iOS setActive behavior. Non-explicit documentation

[brianangulo]

Thank you for your open source contributions.

Current behavior

Our users reported the scanner not showing. After looking into it we believe that when updating isActive prop with the same prop to show/hide the scanner camera a race condition seems to occur causing the session to become nil and since setupIfNeeded doesn't seem to get recalled from setting isActive the component gets "stuck" in a state unable to reopen the camera until the app is closed and reopened.

Another issue somewhat related is that the memory is not getting released on unMount automatically, forcing us to do it JS side or not do it at all.

Expected behavior

The component always closes and opens the camera.

How to reproduce?

Very hard to reproduce organically (as its sometimes is with race conditions) but in theory tapping opening and closing really fast on a high refresh rate screen may trigger it.

Preview

What have you tried so far?

Your Environment

software	version
ios	18.5
android	N/A (iOS only)
react-native	v0.76.9
@pushpendersingh/react-native-scanner	v1.5.0
node	v20.19.1
npm or yarn	npm

[brianangulo]

With so many libraries having similar APIs of show/hide similar to the isActive prop for modal type components its easy to get miss use it. So I would recommend either a prop name and Readme update or refactoring isActive to behave as a show/hide prop. I can also help with an upfix if you let me know which approach you'd like to take.

[brianangulo]

Also a few nice update to haves:

• Having an onCameraReady prop callback to run once the camera is mounted since there's a delay and causes custom overlays to get mounted first
• Adding better error handling, if the devices fail to start for example there's no way for the JS side to know and handle that, we should turn the commands into throwable promises
• Opening and closing via commands only

[JerakRus]

Hi @brianangulo! If you have a solution, could you please share it? It seems this is the issue that is causing the app to crash after upgrading to RN 0.80.0 with this log:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[RCTView setIsActive:]: unrecognized selector sent to instance 0x104412b30'
*** First throw call stack:
(0x191da0f20 0x189c4f2b8 0x191eaa480 0x194e7d9ac 0x191d3dfb4 0x191d3d8d0 0x108164884 0x1081652f0 0x108165ac0 0x1081cecbc 0x1081cee68 0x108165950 0x108165e68 0x191d41e54 0x191d41c98 0x108165d38 0x108165b24 0x1084cb600 0x107c25ba0 0x107c23ecc 0x107c23c7c 0x107c2338c 0x107c3ef74 0x107c3eaac 0x107c3ea50 0x107c3e9f8 0x107c3e9c4 0x107c3d84c 0x108523fe4 0x108523264 0x108523098 0x107c3752c 0x107c371fc 0x107c36b6c 0x108249a58 0x103a84b98 0x103a867bc 0x103a96d58 0x103a9690c 0x191d73710 0x191d70914 0x191d6fcd8 0x1d67bd1a8 0x1943a9ae8 0x19445dd98 0x1945d7504 0x1077d133c 0x1077d12ac 0x1077d1c50 0x1b5547154)
libc++abi: terminating due to uncaught exception of type NSException

[brianangulo]

Hi @brianangulo! If you have a solution, could you please share it? It seems this is the issue that is causing the app to crash after upgrading to RN 0.80.0 with this log:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[RCTView setIsActive:]: unrecognized selector sent to instance 0x104412b30'
*** First throw call stack:
(0x191da0f20 0x189c4f2b8 0x191eaa480 0x194e7d9ac 0x191d3dfb4 0x191d3d8d0 0x108164884 0x1081652f0 0x108165ac0 0x1081cecbc 0x1081cee68 0x108165950 0x108165e68 0x191d41e54 0x191d41c98 0x108165d38 0x108165b24 0x1084cb600 0x107c25ba0 0x107c23ecc 0x107c23c7c 0x107c2338c 0x107c3ef74 0x107c3eaac 0x107c3ea50 0x107c3e9f8 0x107c3e9c4 0x107c3d84c 0x108523fe4 0x108523264 0x108523098 0x107c3752c 0x107c371fc 0x107c36b6c 0x108249a58 0x103a84b98 0x103a867bc 0x103a96d58 0x103a9690c 0x191d73710 0x191d70914 0x191d6fcd8 0x1d67bd1a8 0x1943a9ae8 0x19445dd98 0x1945d7504 0x1077d133c 0x1077d12ac 0x1077d1c50 0x1b5547154)
libc++abi: terminating due to uncaught exception of type NSException

Hi @JerakRus, yours may be a different issue but in case it works for you heres what we did. We patched the library's setIsActive method using patch-package library this way:

+    dispatch_async(_sessionQueue, ^{
+        // reading from parent
+        BOOL currentActiveState = self->isActive;
+        
+        if (currentActiveState) {
+            // in case it gets dealloc/unmounted/released
+            [self setupSessionIfNeeded];
+            
+            dispatch_async(dispatch_get_main_queue(), ^{
+                [self resumePreview];
+            });
+            [self resumeScanning];
+        } else {
+            dispatch_async(dispatch_get_main_queue(), ^{
+                [self pausePreview];
+            });
+            [self stopScanning];
+            [self releaseCamera];
+        }
+    });
 }

[JerakRus]

@brianangulo Thank you very much for sharing your solution!

Unfortunately, we checked it and it didn't help us. It turns out that the problem is in something else and I should create a separate issue.

Thanks again!

[pushpender-singh-ap]

Hi @brianangulo - Thank you for sharing the issue details. Unfortunately, I am currently unable to reproduce the problem on my end. I will make another attempt to recreate it, and if I am able to do so, I will update you accordingly. In the meantime, if you are able to consistently reproduce the issue and have a proposed solution, please feel free to raise a PR, as it would be greatly appreciated.

[pushpender-singh-ap]

Hi @brianangulo - Have you tried like that to active the camera again:

Commands.resumeScanning(scannerRef?.current);
setIsActive(true);

reference code:

react-native-scanner/example/App.tsx

Line 135 in 9b1e9b4

onPress={() => {

[pushpender-singh-ap]

@brianangulo @JerakRus This package has been rewritten in Swift and Objective-C++. The issue has now been resolved. Please refer to the latest documentation, as there are some breaking changes. Make sure to install the latest version.