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........
  r74841 | thomas.wouters | 2009-09-16 14:55:54 -0500 (Wed, 16 Sep 2009) | 23 lines


  Fix issue #1590864, multiple threads and fork() can cause deadlocks, by
  acquiring the import lock around fork() calls. This prevents other threads
  from having that lock while the fork happens, and is the recommended way of
  dealing with such issues. There are two other locks we care about, the GIL
  and the Thread Local Storage lock. The GIL is obviously held when calling
  Python functions like os.fork(), and the TLS lock is explicitly reallocated
  instead, while also deleting now-orphaned TLS data.

  This only fixes calls to os.fork(), not extension modules or embedding
  programs calling C's fork() directly. Solving that requires a new set of API
  functions, and possibly a rewrite of the Python/thread_*.c mess. Add a
  warning explaining the problem to the documentation in the mean time.

  This also changes behaviour a little on AIX. Before, AIX (but only AIX) was
  getting the import lock reallocated, seemingly to avoid this very same
  problem. This is not the right approach, because the import lock is a
  re-entrant one, and reallocating would do the wrong thing when forking while
  holding the import lock.

  Will backport to 2.6, minus the tiny AIX behaviour change.
........
This commit is contained in:
Benjamin Peterson 2009-10-04 20:32:25 +00:00
parent 60e4cae06a
commit 0df35a93a2
5 changed files with 108 additions and 22 deletions
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31
Python/import.c
View file

@ -262,8 +262,8 @@ static PyThread_type_lock import_lock = 0;
static long import_lock_thread = -1;
static int import_lock_level = 0;
static void
lock_import(void)
void
_PyImport_AcquireLock(void)
{
long me = PyThread_get_thread_ident();
if (me == -1)
@ -287,8 +287,8 @@ lock_import(void)
import_lock_level = 1;
}
static int
unlock_import(void)
int
_PyImport_ReleaseLock(void)
{
long me = PyThread_get_thread_ident();
if (me == -1 || import_lock == NULL)
@ -303,23 +303,16 @@ unlock_import(void)
return 1;
}
/* This function is called from PyOS_AfterFork to ensure that newly
created child processes do not share locks with the parent. */
/* This function used to be called from PyOS_AfterFork to ensure that newly
created child processes do not share locks with the parent, but for some
reason only on AIX systems. Instead of re-initializing the lock, we now
acquire the import lock around fork() calls. */
void
_PyImport_ReInitLock(void)
{
#ifdef _AIX
if (import_lock != NULL)
import_lock = PyThread_allocate_lock();
#endif
}
#else
#define lock_import()
#define unlock_import() 0
#endif
static PyObject *
@ -336,7 +329,7 @@ static PyObject *
imp_acquire_lock(PyObject *self, PyObject *noargs)
{
#ifdef WITH_THREAD
lock_import();
_PyImport_AcquireLock();
#endif
Py_INCREF(Py_None);
return Py_None;
@ -346,7 +339,7 @@ static PyObject *
imp_release_lock(PyObject *self, PyObject *noargs)
{
#ifdef WITH_THREAD
if (unlock_import() < 0) {
if (_PyImport_ReleaseLock() < 0) {
PyErr_SetString(PyExc_RuntimeError,
"not holding the import lock");
return NULL;
@ -2201,9 +2194,9 @@ PyImport_ImportModuleLevel(char *name, PyObject *globals, PyObject *locals,
PyObject *fromlist, int level)
{
PyObject *result;
lock_import();
_PyImport_AcquireLock();
result = import_module_level(name, globals, locals, fromlist, level);
if (unlock_import() < 0) {
if (_PyImport_ReleaseLock() < 0) {
Py_XDECREF(result);
PyErr_SetString(PyExc_RuntimeError,
"not holding the import lock");