Re: Deadlock in +initialize with libojbc2

[Thomas Davie]

I've done some reading through the source for libobjc2, and added a quick and 
dirty hack to lock the runtime in objc_send_initialize, as thread 1 was locking 
initialize lock then runtime lock while thread 2 was locking runtime lock then 
initialize lock... I though do not understand in any way how the threading 
model of libojbc2 works, so I probably did something pretty dumb in doing that.

I'd appreciate it if someone with knowledge of how threading is meant to work 
here could take a look at that and see if what I did was sane.

Thanks

Tom Davie

On 13 Aug 2012, at 10:11, Thomas Davie <tom.davie@gmail.com> wrote:

> Hi all,
> 
> I'm hitting an issue with deadlocks in +initialize.  I'm using the latest 
> (svn 35399) libobjc2.  Gdb tells me this:
> 
> (gdb) info threads
>  Id   Target Id         Frame 
> * 2    Thread 0x7fffe2612700 (LWP 8878) "bds" 0x00007ffff65f9be4 in 
> __lll_lock_wait () from /lib/x86_64-linux-gnu/libpthread.so.0
>  1    Thread 0x7ffff7fe6000 (LWP 8875) "bds" 0x00007ffff65f9be4 in 
> __lll_lock_wait () from /lib/x86_64-linux-gnu/libpthread.so.0
> (gdb) thread 1
> [Switching to thread 1 (Thread 0x7ffff7fe6000 (LWP 8875))]
> #0  0x00007ffff65f9be4 in __lll_lock_wait () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> (gdb) bt
> #0  0x00007ffff65f9be4 in __lll_lock_wait () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #1  0x00007ffff65f5200 in _L_lock_928 () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #2  0x00007ffff65f5099 in pthread_mutex_lock () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #3  0x00007ffff6a96919 in create_dtable_for_class (class=0x7fffdc862900, 
> root_dtable=0xae4ab0) at dtable.c:498
> #4  0x00007ffff6a964b9 in objc_send_initialize (object=<optimized out>) at 
> dtable.c:693
> #5  0x00007ffff6a9e776 in objc_msg_lookup_internal (receiver=<optimized out>, 
> selector=<optimized out>, sender=<optimized out>) at sendmsg2.c:73
> #6  objc_msg_lookup_sender (receiver=<optimized out>, selector=<optimized 
> out>, sender=<optimized out>) at sendmsg2.c:171
> #7  0x00000000005a4678 in -[Move 
> initWithAttack:withSoldier:againstTile:rolls:preAttackHP:preAttackPositions:preAttackBuffs:defenders:]
>  (self=0x7fffdc862878, _cmd=0x9b5770, a=0x28e5908, s=0x2e0e478, 
> #8  A bunch of my code all the way down to main.
> (gdb) thread 2
> [Switching to thread 2 (Thread 0x7fffe2612700 (LWP 8878))]
> #0  0x00007ffff65f9be4 in __lll_lock_wait () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> (gdb) bt
> #0  0x00007ffff65f9be4 in __lll_lock_wait () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #1  0x00007ffff65f5200 in _L_lock_928 () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #2  0x00007ffff65f5099 in pthread_mutex_lock () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #3  0x00007ffff6a95fb8 in dtable_for_class (cls=<optimized out>, 
> cls=<optimized out>, cls=<optimized out>) at ./dtable.h:66
> #4  classHasDtable (cls=<optimized out>, cls=<optimized out>, cls=<optimized 
> out>) at ./dtable.h:110
> #5  mergeMethodsFromSuperclass (super=0x7ffff7d1a8e0, cls=<optimized out>, 
> methods=0x65ea8f0) at dtable.c:444
> #6  0x00007ffff6a9628d in add_method_list_to_class (cls=0x7ffff7d1a8e0, 
> list=<optimized out>) at dtable.c:488
> #7  0x00007ffff6a9aaa6 in class_addMethod (cls=0x7ffff7d1a8e0, 
> name=<optimized out>, imp=0x7ffff77eac30 <-[NSGDate timeIntervalSince1970]>, 
> types=<optimized out>) at runtime.c:191
> #8  0x00007ffff794ec4f in GSObjCAddMethods (cls=0x7ffff7d1a8e0, 
> list=0x65ea7a0, replace=0 '\000') at GSObjCRuntime.m:559
> #9  0x00007ffff794f566 in GSObjCAddClassBehavior (receiver=0x7ffff7d1a8e0, 
> behavior=0x7ffff7d1a810) at GSObjCRuntime.m:902
> #10 0x00007ffff77eb116 in +[GSDateSingle initialize] (self=0x7ffff7d1a8e0, 
> _cmd=<optimized out>) at NSDate.m:1517
> #11 0x00007ffff6a965c6 in objc_send_initialize (object=<optimized out>) at 
> dtable.c:733
> #12 0x00007ffff6a96427 in objc_send_initialize (object=<optimized out>) at 
> dtable.c:666
> #13 0x00007ffff6a9e776 in objc_msg_lookup_internal (receiver=<optimized out>, 
> selector=<optimized out>, sender=<optimized out>) at sendmsg2.c:73
> #14 objc_msg_lookup_sender (receiver=<optimized out>, selector=<optimized 
> out>, sender=<optimized out>) at sendmsg2.c:171
> #15 0x00007ffff77e975b in +[NSDate distantFuture] (self=0x7ffff7d1a740, 
> _cmd=<optimized out>) at NSDate.m:985
> #16 0x00007ffff78af10d in +[NSRunLoop initialize] (self=0x7ffff7d5fc40, 
> _cmd=<optimized out>) at NSRunLoop.m:697
> #17 0x00007ffff6a965c6 in objc_send_initialize (object=<optimized out>) at 
> dtable.c:733
> #18 0x00007ffff6a9e776 in objc_msg_lookup_internal (receiver=<optimized out>, 
> selector=<optimized out>, sender=<optimized out>) at sendmsg2.c:73
> #19 objc_msg_lookup_sender (receiver=<optimized out>, selector=<optimized 
> out>, sender=<optimized out>) at sendmsg2.c:171
> #20 0x00000000004aa888 in -[DatabaseConnection runPingThread] 
> (self=0x2a06698, _cmd=0x9b76b0) at Classes/Database/DatabaseConnection.m:120
> #21 0x00007ffff786a655 in -[NSObject performSelector:withObject:] 
> (self=<optimized out>, _cmd=<optimized out>, aSelector=0x9b76b0, 
> anObject=0x7fffe2610500) at NSObject.m:2001
> #22 0x00007ffff78e336e in -[NSThread main] (self=0x2a1c5b8, _cmd=<optimized 
> out>) at NSThread.m:741
> #23 0x00007ffff78e3b05 in nsthreadLauncher (thread=0x2a1c5b8) at 
> NSThread.m:807
> #24 0x00007ffff65f2efc in start_thread () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #25 0x00007ffff632d59d in clone () from /lib/x86_64-linux-gnu/libc.so.6
> #26 0x0000000000000000 in ?? ()
> 
> Does anyone have any idea why this might be happening?
> 
> Thanks
> 
> Tom Davie
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