NSData.dataWithBytesNoCopy_length_ is crashing #1107

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1. liamappelbe

   added

   package:objective_c

   on Apr 29, 2024
2. liamappelbe

   assigned

   brianquinlan

   on Apr 29, 2024
3. brianquinlan commented on Apr 29, 2024

   

   brianquinlan

   on Apr 29, 2024

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   @dcharkes

   NSData dataWithBytesNoCopy:length:freeWhenDone: takes ownership of a block of memory that was allocated with malloc.

   Is the package:ffi malloc the (presumably) libc malloc that NSData expects?
4. dcharkes commented on May 1, 2024

   

   dcharkes

   on May 1, 2024

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   I haven't been able to get GDB working on my macbook

   LLDB is the Mac variant.

   Is the package:ffi malloc the (presumably) libc malloc that NSData expects?

   native/pkgs/ffi/lib/src/allocation.dart

   Lines 15 to 16 in 6a9282c

   	final PosixMalloc posixMalloc =
   	stdlib.lookupFunction<PosixMallocNative, PosixMalloc>('malloc');

   Yep, it's malloc in the current process.
5. brianquinlan commented on May 1, 2024

   

   brianquinlan

   on May 1, 2024

   Last edited by brianquinlan

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   I haven't been able to get GDB working on my macbook

   LLDB is the Mac variant.

   Is the package:ffi malloc the (presumably) libc malloc that NSData expects?

   native/pkgs/ffi/lib/src/allocation.dart

   Lines 15 to 16 in 6a9282c

   	final PosixMalloc posixMalloc =
   	stdlib.lookupFunction<PosixMallocNative, PosixMalloc>('malloc');

   Yep, it's malloc in the current process.

   I'm not sure how this fits together. Presumably the malloc of the current process could mean tcmalloc or jemalloc, depending on how the application is linked? But I'd guess that NSData uses whatever the standard deallocator is? Or maybe not ;-)

   Apple's documentation isn't very clear on this. I also notice that we don't use NSData dataWithBytesNoCopy:length:freeWhenDone: at Google at all.

   I think that this code is probably OK how it is now. If people complain about the performance when using large blocks of memory, we could use initWithBytesNoCopy:length:deallocator:

   👍React with 👍1Reacted by Liam Appelbe
6. brianquinlan

   removed their assignment

   on May 1, 2024
7. liamappelbe

   added this to ObjC/Swift interopon May 7, 2024
8. liamappelbe

   moved this to Backlog in ObjC/Swift interopon May 7, 2024
9. vaind commented on Jul 2, 2024

   

   vaind

   on Jul 2, 2024

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   Presumably the malloc of the current process could mean tcmalloc or jemalloc, depending on how the application is linked

   From the docs:

   A buffer containing data for the new object. If freeWhenDone is YES, bytes must point to a memory block allocated with malloc.
10. brianquinlan commented on Jun 26, 2025

    

    brianquinlan

    on Jun 26, 2025

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    I think that we can close this?
11. liamappelbe

    closed this as completedon Jun 27, 2025
12. github-project-automation

    moved this from Backlog to Done in ObjC/Swift interopon Jun 27, 2025