[issue17978] Python crashes if Py_Initialize/Py_Finalize are called multiple times

[STINNER Victor]

STINNER Victor  added the comment:

Program described in msg189250 does not crash on the master branch of Python. 
The PEP 587 deeply reworked Python initialization code. There is now a 
preinitialization phase, for example.

Moreover, Programs/_testembed.c has a test calling 
Py_Initialize()+Py_Finalize() multiple times, and this test calls 
Py_SetProgramName() as well.

Upgrade to Python 3.8 to get the fix. (I didn't check if Python 3.7 is also 
fixed.)

--
nosy: +vstinner
resolution:  -> fixed
stage:  -> resolved
status: open -> closed

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[issue17978] Python crashes if Py_Initialize/Py_Finalize are called multiple times

[Marc-Andre Lemburg]

Marc-Andre Lemburg added the comment:

On 15.05.2013 01:28, Amaury Forgeot d'Arc wrote:
> 
> Amaury Forgeot d'Arc added the comment:
> 
> The official way to build without unicode is
>   ./configure --enable-unicode=no
> But see issue17979.

The official way to build without Unicode is:

./configure --disable-unicode

See http://bugs.python.org/issue8767 for the most recent set of fixes that
were supplied to make it work again in Python 2.7.4.

--
nosy: +lemburg

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[issue17978] Python crashes if Py_Initialize/Py_Finalize are called multiple times

[Romulo A. Ceccon]

Romulo A. Ceccon added the comment:

I've made some further investigation on this issue. Here's the output and the 
stack trace using --with-pydebug (and the attached patch applied):

run no. 0
[8766 refs]
free_list[0]->ob_refcnt before XDECREF: 2
run no. 1
[8844 refs]
free_list[0]->ob_refcnt before XDECREF: 1
Fatal Python error: PyThreadState_Get: no current thread
Aborted (core dumped)

Thread 1 (Thread 0x77fed700 (LWP 32572)):
#0  0x77131425 in raise () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x77134b8b in abort () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x004086f4 in Py_FatalError (
msg=0x5a0378 "PyThreadState_Get: no current thread")
at Python/pythonrun.c:1631
#3  0x0054120c in PyThreadState_Get () at Python/pystate.c:330
#4  0x0049a13b in tupledealloc (op=0x84e3a0)
at Objects/tupleobject.c:218
#5  0x0047adf1 in _Py_Dealloc (op=0x84e3a0) at Objects/object.c:2262
#6  0x0049bba9 in PyTuple_Fini () at Objects/tupleobject.c:933
#7  0x0040519b in Py_Finalize () at Python/pythonrun.c:466
#8  0x004047b6 in main ()

A build of Python 2.7.3 using the same steps *does not* crash, although it 
shows the same curious behavior for free_list[0]->ob_refcnt:

[8676 refs]
free_list[0]->ob_refcnt before XDECREF: 2
run no. 1
[8754 refs]
free_list[0]->ob_refcnt before XDECREF: 1
run no. 2
[8832 refs]
free_list[0]->ob_refcnt before XDECREF: 1

I have no idea why it behaves like that, but it seems that the default 
configuration with Unicode enabled is covering some bug (because of the 
additional references held).

Regarding the official way to disable Unicode, I cannot build Python using 
--enable-unicode=no on Ubuntu 13.04. In 2.7.4, 2.7.3, 2.7.2 and 2.6.8 
./configure aborts with:

checking what type to use for unicode... configure: error:
invalid value for --enable-unicode. Use either ucs2 or ucs4
(lowercase).

I'm afraid I'm missing something really obvious. With 2.5.6 I'm able to get 
past the configure part but then it fails when building the modules.

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[issue17978] Python crashes if Py_Initialize/Py_Finalize are called multiple times

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc added the comment:

The official way to build without unicode is
  ./configure --enable-unicode=no
But see issue17979.

--
nosy: +amaury.forgeotdarc

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[issue17978] Python crashes if Py_Initialize/Py_Finalize are called multiple times

[Romulo A. Ceccon]

New submission from Romulo A. Ceccon:

I have patched (see attachment) Python 2.7.4 (as available for download at 
python.org/download) to disable initialization of Unicode (an embeded system 
requirement) and now it segfaults with the following program:

#include 

int main(int argc, char** argv)
{
  int i;
  Py_NoSiteFlag = 1;

  Py_SetProgramName(argv[0]);

  for (i = 0; i < 3; i++)
  {
printf("run no. %d\n", i);

Py_Initialize();
Py_Finalize();
  }

  return 0;
}

The problem appears to be related with the reference count of the empty tuple. 
I've also applied the following patch in Objects/tupleobject.c to help diagnose 
the problem:

@@ -928,6 +928,8 @@ PyTuple_Fini(void)
 #if PyTuple_MAXSAVESIZE > 0
 /* empty tuples are used all over the place and applications may
  * rely on the fact that an empty tuple is a singleton. */
+printf("free_list[0]->ob_refcnt before XDECREF: %d\n",
+free_list[0]->ob_refcnt);
 Py_XDECREF(free_list[0]);
 free_list[0] = NULL;

*Without* the patch for Python/pythonrun.c the program produces the following 
results under Ubuntu 13.04 x64:

run no. 0
free_list[0]->ob_refcnt before XDECREF: 58
run no. 1
free_list[0]->ob_refcnt before XDECREF: 57
run no. 2
free_list[0]->ob_refcnt before XDECREF: 57

Note the strange ref count of the empty tuple (free_list[0]). Now, *with* the 
patch, the application will not hold so many references to the empty tuple and 
the finalization code ends up trying to deallocate it (what, from my limited 
understading of the code, is not supposed to happen):

run no. 0
free_list[0]->ob_refcnt before XDECREF: 2
run no. 1
free_list[0]->ob_refcnt before XDECREF: 1
Segmentation fault (core dumped)

The actual patch I'm using is much more complicated. This is just the minimal 
patch able to reproduce the problem. I tried undefining Py_USING_UNICODE but 
then the build doesn't succeed.

--
components: Interpreter Core
files: pythonrun.c.patch
keywords: patch
messages: 189250
nosy: Romulo A. Ceccon
priority: normal
severity: normal
status: open
title: Python crashes if Py_Initialize/Py_Finalize are called multiple times
type: crash
versions: Python 2.7
Added file: http://bugs.python.org/file30261/pythonrun.c.patch

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