I'm not sure if this is the right list for this, but then I'm not sure what is
the right list.
I'm seeing a consistent problem disposing of GCD semaphores. For example, if I
create a semaphore like this:
semaphore = dispatch_semaphore_create (10);
and then use if for a while, then try to destroy it (using ARC):
semaphore = nil;
If the semaphore's count is less than the original value (10 in the example), I
get a EXC_BAD_INSTRUCTION crash:
> #0 0x00007fff91fcfb5f in _dispatch_semaphore_dispose ()
> #1 0x00007fff91fcc898 in _dispatch_dispose ()
> #2 0x00007fff91fcc837 in -[OS_dispatch_object _xref_dispose] ()
> 0x00007fff91fcfb3e <+0000> push %rbp
> 0x00007fff91fcfb3f <+0001> mov %rsp,%rbp
> 0x00007fff91fcfb42 <+0004> push %rbx
> 0x00007fff91fcfb43 <+0005> push %rax
> 0x00007fff91fcfb44 <+0006> mov %rdi,%rbx
> 0x00007fff91fcfb47 <+0009> mov 0x38(%rbx),%rax
> 0x00007fff91fcfb4b <+0013> cmp 0x40(%rbx),%rax
> 0x00007fff91fcfb4f <+0017> jge 0x7fff91fcfb61
> <_dispatch_semaphore_dispose+35>
> 0x00007fff91fcfb51 <+0019> lea 0xa8a6(%rip),%rcx # 0x7fff91fda3fe
> 0x00007fff91fcfb58 <+0026> mov %rcx,-0x17cbe317(%rip) #
> 0x7fff7a311848 <gCRAnnotations+8>
> 0x00007fff91fcfb5f <+0033> ud2a << Thread 1: Program received signal:
> 'EXC_BAD_INSTRUCTION'
It's not clear to me why it should matter whether the original count has been
restored. There's nothing waiting on the semaphore -- the operations that
decremented the count have themselves be disposed of already.
If I forcibly increment the count to 10 *or more*, there's no crash.
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