freezes with multi-threading ?

Hi

I'm using sqlobjects with webware for python on my website in production
since 2007.
Since about one year ago (maybe more...), from time to time (about every
week/month), the python process completely freezes under high load.

I upgraded to sqlobject 1.3.2 with latest mysqlDB, and still have the
problem.

All signals are ignored.  it can only be killed with a kill -9.
strace show the python process is stuck in a futex kernel call.

Recently, I tried to gdb the frozen python process: All threads are waiting
for a semaphore, except one, that is waiting probably for a mysql response,
in the _mysql.so object of python-mysql.

unfortunately, the gdb pystack macro doesn't work for me. So I can't get
the python stack. It seems that gdb cpu gets all cpu dureing a very very
long time. I haven't waited enough...

All threads waiting for a semaphore. I don't know if it is the python GIL
or another mysql or sqlobject related lock. The GIL would explain that
signals are ineffective.


#0  0x00110416 in __kernel_vsyscall ()
#1  0x005a8865 in sem_wait@@GLIBC_2.1 () from /lib/libpthread.so.0


#2  0x0067eafb in PyThread_acquire_lock (lock=0x8dc7028, waitflag=1) at
Python/thread_pthread.h:349
#3  0x00682eb8 in lock_PyThread_acquire_lock (self=0x854c430,
args=0xb7f3102c) at Modules/threadmodule.c:46

#4  0x0060d7ed in PyCFunction_Call (func=0x8eeb0ec, arg=0xb7f3102c, kw=0x0)
at Objects/methodobject.c:108
#5  0x0065ac72 in PyEval_EvalFrameEx (f=0x93d7ff4, throwflag=0) at
Python/ceval.c:3564

#6  0x00659fcd in PyEval_EvalFrameEx (f=0x8e2e53c, throwflag=0) at
Python/ceval.c:3650
#7  0x0065b6bf in PyEval_EvalCodeEx (co=0x8922410, globals=0x891e3e4,
locals=0x0, args=0x9cfa2dc, argcount=1, kws=0x9cfa2e0,

    kwcount=0, defs=0x891af18, defcount=1, closure=0x0) at
Python/ceval.c:2831
#8  0x00659844 in PyEval_EvalFrameEx (f=0x9cfa12c, throwflag=0) at
Python/ceval.c:3660

#9  0x00659fcd in PyEval_EvalFrameEx (f=0x8dccfa4, throwflag=0) at
Python/ceval.c:3650
#10 0x0065b6bf in PyEval_EvalCodeEx (co=0x87ad848, globals=0x87a924c,
locals=0x0, args=0x8d43818, argcount=2, kws=0x0,
....

except one thread: ( I still have to check all 25 threads...)
#0  0x00110416 in __kernel_vsyscall ()
#1  0x005a952b in read () from /lib/libpthread.so.0


#2  0x00295338 in vio_read () from /usr/lib/mysql/libmysqlclient_r.so.15
#3  0x002953ae in vio_read_buff () from
/usr/lib/mysql/libmysqlclient_r.so.15


#4  0x002967ab in ?? () from /usr/lib/mysql/libmysqlclient_r.so.15
#5  0x00296b9b in my_net_read () from /usr/lib/mysql/libmysqlclient_r.so.15


#6  0x0028fe39 in cli_safe_read () from
/usr/lib/mysql/libmysqlclient_r.so.15
#7  0x00290c35 in ?? () from /usr/lib/mysql/libmysqlclient_r.so.15


#8  0x0028f1e4 in mysql_real_query () from
/usr/lib/mysql/libmysqlclient_r.so.15
#9  0x00243f53 in _mysql_ConnectionObject_query (self=0x941160c,
args=0x978138c) at _mysql.c:2008

#10 0x0060d7ed in PyCFunction_Call (func=0x9c300cc, arg=0x978138c, kw=0x0)
at Objects/methodobject.c:108
#11 0x0065ac72 in PyEval_EvalFrameEx (f=0x940d924, throwflag=0) at
Python/ceval.c:3564

#12 0x00659fcd in PyEval_EvalFrameEx (f=0x9b12c64, throwflag=0) at
Python/ceval.c:3650
#13 0x00659fcd in PyEval_EvalFrameEx (f=0x9b7cdf4, throwflag=0) at
Python/ceval.c:3650

#14 0x0065b6bf in PyEval_EvalCodeEx (co=0x8d2ead0, globals=0x8d304f4,
locals=0x0, args=0x9240fec, argcount=2, kws=0x9240ff4,
    kwcount=0, defs=0x8d37358, defcount=1, closure=0x0) at
Python/ceval.c:2831
...

Note: I also get some "ProgrammingError: Commands out of sync; you can't
run this command now" errors from time to time.

This is why I'm suspecting a wrong connection management between my threads.

Could it be related to the fact that I'm using the sqlHub.processConnection
feature of SqlObject?
Reading the code, I don't understand the call path from dbConnection to the
SqlHub.

How is the connection pool managed?
Is it thread safe?

Thanks in advance for your support

Best regards

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