[Python-checkins] r51195 - in python/trunk: Doc/api/init.tex Lib/test/test_threading.py Misc/NEWS Python/pystate.c
tim.peters
python-checkins at python.org
Fri Aug 11 00:45:36 CEST 2006
Author: tim.peters
Date: Fri Aug 11 00:45:34 2006
New Revision: 51195
Modified:
python/trunk/Doc/api/init.tex
python/trunk/Lib/test/test_threading.py
python/trunk/Misc/NEWS
python/trunk/Python/pystate.c
Log:
Followup to bug #1069160.
PyThreadState_SetAsyncExc(): internal correctness changes wrt
refcount safety and deadlock avoidance. Also added a basic test
case (relying on ctypes) and repaired the docs.
Modified: python/trunk/Doc/api/init.tex
==============================================================================
--- python/trunk/Doc/api/init.tex (original)
+++ python/trunk/Doc/api/init.tex Fri Aug 11 00:45:34 2006
@@ -696,15 +696,15 @@
\end{cfuncdesc}
\begin{cfuncdesc}{int}{PyThreadState_SetAsyncExc}{long id, PyObject *exc}
- Asynchronously raise an exception in a thread.
+ Asynchronously raise an exception in a thread.
The \var{id} argument is the thread id of the target thread;
\var{exc} is the exception object to be raised.
This function does not steal any references to \var{exc}.
- To prevent naive misuse, you must write your own C extension
- to call this. Must be called with the GIL held.
- Returns the number of thread states modified; if it returns a number
- greater than one, you're in trouble, and you should call it again
- with \var{exc} set to \constant{NULL} to revert the effect.
+ To prevent naive misuse, you must write your own C extension
+ to call this. Must be called with the GIL held.
+ Returns the number of thread states modified; this is normally one, but
+ will be zero if the thread id isn't found. If \var{exc} is
+ \constant{NULL}, the pending exception (if any) for the thread is cleared.
This raises no exceptions.
\versionadded{2.3}
\end{cfuncdesc}
Modified: python/trunk/Lib/test/test_threading.py
==============================================================================
--- python/trunk/Lib/test/test_threading.py (original)
+++ python/trunk/Lib/test/test_threading.py Fri Aug 11 00:45:34 2006
@@ -131,6 +131,75 @@
threading._DummyThread))
del threading._active[tid]
+ # PyThreadState_SetAsyncExc() is a CPython-only gimmick, not (currently)
+ # exposed at the Python level. This test relies on ctypes to get at it.
+ def test_PyThreadState_SetAsyncExc(self):
+ try:
+ import ctypes
+ except ImportError:
+ if verbose:
+ print "test_PyThreadState_SetAsyncExc can't import ctypes"
+ return # can't do anything
+
+ set_async_exc = ctypes.pythonapi.PyThreadState_SetAsyncExc
+
+ class AsyncExc(Exception):
+ pass
+
+ exception = ctypes.py_object(AsyncExc)
+
+ # `worker_started` is set by the thread when it's inside a try/except
+ # block waiting to catch the asynchronously set AsyncExc exception.
+ # `worker_saw_exception` is set by the thread upon catching that
+ # exception.
+ worker_started = threading.Event()
+ worker_saw_exception = threading.Event()
+
+ class Worker(threading.Thread):
+ def run(self):
+ self.id = thread.get_ident()
+ self.finished = False
+
+ try:
+ while True:
+ worker_started.set()
+ time.sleep(0.1)
+ except AsyncExc:
+ self.finished = True
+ worker_saw_exception.set()
+
+ t = Worker()
+ if verbose:
+ print " started worker thread"
+ t.start()
+
+ # Try a thread id that doesn't make sense.
+ if verbose:
+ print " trying nonsensical thread id"
+ result = set_async_exc(-1, exception)
+ self.assertEqual(result, 0) # no thread states modified
+
+ # Now raise an exception in the worker thread.
+ if verbose:
+ print " waiting for worker thread to get started"
+ worker_started.wait()
+ if verbose:
+ print " verifying worker hasn't exited"
+ self.assert_(not t.finished)
+ if verbose:
+ print " attempting to raise asynch exception in worker"
+ result = set_async_exc(t.id, exception)
+ self.assertEqual(result, 1) # one thread state modified
+ if verbose:
+ print " waiting for worker to say it caught the exception"
+ worker_saw_exception.wait(timeout=10)
+ self.assert_(t.finished)
+ if verbose:
+ print " all OK -- joining worker"
+ if t.finished:
+ t.join()
+ # else the thread is still running, and we have no way to kill it
+
def test_main():
test.test_support.run_unittest(ThreadTests)
Modified: python/trunk/Misc/NEWS
==============================================================================
--- python/trunk/Misc/NEWS (original)
+++ python/trunk/Misc/NEWS Fri Aug 11 00:45:34 2006
@@ -78,6 +78,15 @@
- Bug #1530448, ctypes buld failure on Solaris 10 was fixed.
+C API
+-----
+
+- Bug #1069160. Internal correctness changes were made to
+ ``PyThreadState_SetAsyncExc()``. A test case was added, and
+ the documentation was changed to state that the return value
+ is always 1 (normal) or 0 (if the specified thread wasn't found).
+
+
Mac
---
@@ -148,7 +157,7 @@
- os.urandom no longer masks unrelated exceptions like SystemExit or
KeyboardInterrupt.
-- Bug #1525866: Don't copy directory stat times in
+- Bug #1525866: Don't copy directory stat times in
shutil.copytree on Windows
- Bug #1002398: The documentation for os.path.sameopenfile now correctly
@@ -281,7 +290,7 @@
- Bug #1527397: PythonLauncher now launches scripts with the working directory
set to the directory that contains the script instead of the user home
- directory. That latter was an implementation accident and not what users
+ directory. That latter was an implementation accident and not what users
expect.
Modified: python/trunk/Python/pystate.c
==============================================================================
--- python/trunk/Python/pystate.c (original)
+++ python/trunk/Python/pystate.c Fri Aug 11 00:45:34 2006
@@ -342,28 +342,43 @@
/* Asynchronously raise an exception in a thread.
Requested by Just van Rossum and Alex Martelli.
To prevent naive misuse, you must write your own extension
- to call this. Must be called with the GIL held.
- Returns the number of tstates modified; if it returns a number
- greater than one, you're in trouble, and you should call it again
- with exc=NULL to revert the effect. This raises no exceptions. */
+ to call this, or use ctypes. Must be called with the GIL held.
+ Returns the number of tstates modified (normally 1, but 0 if `id` didn't
+ match any known thread id). Can be called with exc=NULL to clear an
+ existing async exception. This raises no exceptions. */
int
PyThreadState_SetAsyncExc(long id, PyObject *exc) {
PyThreadState *tstate = PyThreadState_GET();
PyInterpreterState *interp = tstate->interp;
PyThreadState *p;
- int count = 0;
+
+ /* Although the GIL is held, a few C API functions can be called
+ * without the GIL held, and in particular some that create and
+ * destroy thread and interpreter states. Those can mutate the
+ * list of thread states we're traversing, so to prevent that we lock
+ * head_mutex for the duration.
+ */
HEAD_LOCK();
for (p = interp->tstate_head; p != NULL; p = p->next) {
- if (p->thread_id != id)
- continue;
- Py_CLEAR(p->async_exc);
- Py_XINCREF(exc);
- p->async_exc = exc;
- count += 1;
+ if (p->thread_id == id) {
+ /* Tricky: we need to decref the current value
+ * (if any) in p->async_exc, but that can in turn
+ * allow arbitrary Python code to run, including
+ * perhaps calls to this function. To prevent
+ * deadlock, we need to release head_mutex before
+ * the decref.
+ */
+ PyObject *old_exc = p->async_exc;
+ Py_XINCREF(exc);
+ p->async_exc = exc;
+ HEAD_UNLOCK();
+ Py_XDECREF(old_exc);
+ return 1;
+ }
}
HEAD_UNLOCK();
- return count;
+ return 0;
}
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