Re: Deadlock in +initialize with libojbc2

[Tom Davie]

Just a quick heads up – I'm still experiencing this deadlock in version 1.6.1 
of the runtime.  It can still be fixed by locking the runtime before locking 
the initialise lock in objc_send_initialize.

Tom Davie

On 13 Aug 2012, at 11:26, Thomas Davie <address@hidden> wrote:

> 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 <address@hidden> 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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