BufferedWriter from Lib/io.py is thread-safe, but... the Python 
instruction "with self._write_lock:" could be interrupted when the 
lock is already acquired. Especially, _lsprof.Profiler() uses ceval 
hook and is called when the lock is acquired. But if the profiler (or 
any other module using the hook) re-use the stream (stdout or stderr), 
we get a deadlock!?

Well, this problem is really not critical since only developers 
profilers (really?).

Solution: use C implementation of Lib/io.py (from Python 2.6) to avoid 
ceval hook?

Example with py3k trunk:
 >>> import _lsprof
 >>> prof=_lsprof.Profiler(42)
 >>> prof.enable()
 # _lsprof calls 42() 
 #   -> 42 is not callable
 #   -> call PyErr_WriteUnraisable(<42 is not callable>)
 #   -> deadlock

Traceback example:

#6  0x080ecb30 in PyThread_acquire_lock (lock=0x820f550, waitflag=1) 
at Python/thread_pthread.h:352
(...)
#8  0x08162521 in PyCFunction_Call (func=0x83abfbc, arg=0xb7dc6034, 
kw=0x0) at Objects/methodobject.c:81
#9  0x080b3659 in call_function (pp_stack=0xbfbf9474, oparg=0) at 
Python/ceval.c:3403
#10 0x080ae7a6 in PyEval_EvalFrameEx (f=0x83b9f94, throwflag=0) at 
Python/ceval.c:2205
#11 0x080b3aae in fast_function (func=0x83a25b4, pp_stack=0xbfbf9724, 
n=2, na=2, nk=0) at Python/ceval.c:3491
#12 0x080b37ef in call_function (pp_stack=0xbfbf9724, oparg=1) at 
Python/ceval.c:3424
#13 0x080ae7a6 in PyEval_EvalFrameEx (f=0x83b981c, throwflag=0) at 
Python/ceval.c:2205
#14 0x080b1aee in PyEval_EvalCodeEx (co=0x838a328, globals=0x8330534, 
locals=0x0, args=0x8373da0, argcount=2, kws=0x0, kwcount=0, defs=0x0,
    defcount=0, kwdefs=0x0, closure=0x0) at Python/ceval.c:2840
#15 0x0814ab2e in function_call (func=0x83a3b8c, arg=0x8373d8c, 
kw=0x0) at Objects/funcobject.c:628
#16 0x08118d19 in PyObject_Call (func=0x83a3b8c, arg=0x8373d8c, 
kw=0x0) at Objects/abstract.c:2181
#17 0x08132eb0 in method_call (func=0x83a3b8c, arg=0x8373d8c, kw=0x0) 
at Objects/classobject.c:323
#18 0x08118d19 in PyObject_Call (func=0x83037dc, arg=0x83141f4, 
kw=0x0) at Objects/abstract.c:2181
#19 0x080b2ed8 in PyEval_CallObjectWithKeywords (func=0x83037dc, 
arg=0x83141f4, kw=0x0) at Python/ceval.c:3283
#20 0x08141779 in PyFile_WriteObject (v=0x8398e28, f=0x83ab0dc, 
flags=1) at Objects/fileobject.c:164
#21 0x08141974 in PyFile_WriteString (s=0x819a2f2 "Exception ", 
f=0x83ab0dc) at Objects/fileobject.c:189
#22 0x080c473c in PyErr_WriteUnraisable (obj=0x81fbd78) at 
Python/errors.c:696
#23 0xb7f9612f in CallExternalTimer (pObj=0x83a7aa8) 
at /home/haypo/prog/py3k/Modules/_lsprof.c:135
#24 0xb7f96984 in Stop (pObj=0x83a7aa8, self=0x826c6d8, 
entry=0x826ec80) at /home/haypo/prog/py3k/Modules/_lsprof.c:337
#25 0xb7f96c60 in ptrace_leave_call (self=0x83a7aa8, key=0x81cb150) 
at /home/haypo/prog/py3k/Modules/_lsprof.c:420
#26 0xb7f96d5c in profiler_callback (self=0x83a7aa8, frame=0x835a0b4, 
what=6, arg=0x83ab92c) at /home/haypo/prog/py3k/Modules/_lsprof.c:471
#27 0x080b28cb in call_trace (func=0xb7f96c85 <profiler_callback>, 
obj=0x83a7aa8, frame=0x835a0b4, what=6, arg=0x83ab92c)
    at Python/ceval.c:3090
#28 0x080b35da in call_function (pp_stack=0xbfbf9d74, oparg=1) at 
Python/ceval.c:3403
#29 0x080ae7a6 in PyEval_EvalFrameEx (f=0x835a0b4, throwflag=0) at 
Python/ceval.c:2205


ceval hook: Python/ceval.3403:
   PCALL(PCALL_CFUNCTION);
   if (flags & (METH_NOARGS | METH_O)) {
      ...
   } else {
      PyObject *callargs;
      callargs = load_args(pp_stack, na);
      READ_TIMESTAMP(*pintr0);
      C_TRACE(x, PyCFunction_Call(func,callargs,NULL)); <= **here**
      READ_TIMESTAMP(*pintr1);
      Py_XDECREF(callargs);
   }