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iOS objc_retain crash troubleshooting

iOS objc_retain crash troubleshooting
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Crashes involving objc_retain typically occur due to memory management issues in Objective-C, such as over-releasing an object that has already been deallocated. Here’s a step-by-step plan to diagnose and potentially fix such crashes:

Sample crash from obj_retain:

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x0000000509def8f0
Exception Codes: 0x0000000000000001, 0x0000000509def8f0
VM Region Info: 0x509def8f0 is not in any region.  Bytes after previous region: 8218671345  Bytes before following region: 46005290768
      REGION TYPE                 START - END      [ VSIZE] PRT/MAX SHRMOD  REGION DETAIL
      MALLOC_NANO              300000000-320000000 [512.0M] rw-/rwx SM=PRV
--->  GAP OF 0xca0000000 BYTES
      commpage (reserved)      fc0000000-1000000000 [  1.0G] ---/--- SM=NUL  reserved VM address space (unallocated)
Termination Reason: SIGNAL 11 Segmentation fault: 11
Terminating Process: exc handler [56545]

Triggered by Thread:  1


Kernel Triage:
VM - (arg = 0x3) mach_vm_allocate_kernel failed within call to vm_map_enter

...

Thread 1 Crashed:
0   libobjc.A.dylib               	0x00000001853f5468 objc_retain + 16 (:-1)

...

Thread 3:
0   libsystem_kernel.dylib        	0x00000001d660c338 fsync + 8 (:-1)
1   libsqlite3.dylib              	0x00000001b73d5aa0 unixSync + 212 (sqlite3.c:44599)
2   libsqlite3.dylib              	0x00000001b73deb54 syncJournal + 496 (sqlite3.c:68073)
3   libsqlite3.dylib              	0x00000001b73d5660 sqlite3PagerCommitPhaseOne + 392 (sqlite3.c:70356)
4   libsqlite3.dylib              	0x00000001b73c5d68 sqlite3BtreeCommitPhaseOne + 172 (sqlite3.c:80934)
5   libsqlite3.dylib              	0x00000001b73c5930 vdbeCommit + 1136 (sqlite3.c:93952)
6   libsqlite3.dylib              	0x00000001b739ec60 sqlite3VdbeHalt + 1352 (sqlite3.c:94362)
7   libsqlite3.dylib              	0x00000001b73bfb50 sqlite3VdbeExec + 42536 (sqlite3.c:101084)
8   libsqlite3.dylib              	0x00000001b73b4c6c sqlite3_step + 964 (sqlite3.c:97699)

...

How to troubleshooting objc_retain crash issue?

Enable Zombies in Xcode

  1. Go to Product > Scheme > Edit Scheme.
  2. Select the “Run” scheme on the left, then go to the “Diagnostics” tab.
  3. Check the “Enable Zombie Objects” option.

This will help identify messages sent to deallocated instances.

Analyze Stack Trace

  • Look at the crash stack trace to identify where the crash is happening.
  • Pay attention to your own code rather than system libraries.

Review Object Lifecycle

  • Examine the lifecycle of the object that is being accessed when the crash occurs.
  • Ensure that it is not being over-released or accessed after being deallocated.

Use Instruments

  • Use the Instruments tool in Xcode to track down memory leaks and reference cycles.
  • Specifically, the Leaks and Allocations instruments can be very helpful.

Audit Your Code

  • Manually audit your code for proper memory management.
  • Ensure that every retain has a corresponding release or autorelease.
  • Look for patterns that might lead to premature deallocation.

ARC vs. Manual Memory Management

  • If you’re not using Automatic Reference Counting (ARC), consider converting to ARC if possible, as it can manage memory more safely.
  • If converting to ARC is not feasible, review your manual memory management practices.

Weak References

  • Ensure that delegates and other references that could create retain cycles are marked as weak or assign to prevent them from retaining each other indefinitely.

Thread Safety

  • Make sure that objects are accessed in a thread-safe manner.
  • Use synchronization mechanisms if necessary to prevent concurrent access issues.
  • If your app uses concurrency, ensure that shared resources are properly synchronized. Accessing mutable shared resources from multiple threads without proper synchronization can lead to undefined behavior, including segmentation faults.

In this crash, a “Segmentation fault: 11” error in iOS development typically indicates that your application is trying to access memory that it shouldn’t be. This can happen for a variety of reasons, such as dereferencing a null pointer, accessing memory beyond the bounds of an array, or using an object after it has been deallocated. It may also due to thread safety caused memory corruption, enable Zombie Objects in Xcode. This can help identify where your code is accessing objects that have already been released.

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