Issue #1856: Avoid crashes and lockups when daemon threads run while the

interpreter is shutting down; instead, these threads are now killed when
they try to take the GIL.

3 files changed, 19 insertions, 6 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 50d5aac..5627e83 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -440,6 +440,12 @@ PyEval_RestoreThread(PyThreadState *tstate)
     if (gil_created()) {
         int err = errno;
         take_gil(tstate);
+        /* _Py_Finalizing is protected by the GIL */
+        if (_Py_Finalizing && tstate != _Py_Finalizing) {
+            drop_gil(tstate);
+            PyThread_exit_thread();
+            assert(0);  /* unreachable */
+        }
         errno = err;
     }
 #endif
diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index ad31613..ebc4f1c 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -93,6 +93,8 @@ int Py_IgnoreEnvironmentFlag; /* e.g. PYTHONPATH, PYTHONHOME */
 int Py_NoUserSiteDirectory = 0; /* for -s and site.py */
 int Py_UnbufferedStdioFlag = 0; /* Unbuffered binary std{in,out,err} */
 
+PyThreadState *_Py_Finalizing = NULL;
+
 /* PyModule_GetWarningsModule is no longer necessary as of 2.6
 since _warnings is builtin.  This API should not be used. */
 PyObject *
@@ -191,6 +193,7 @@ Py_InitializeEx(int install_sigs)
     if (initialized)
         return;
     initialized = 1;
+    _Py_Finalizing = NULL;
 
 #if defined(HAVE_LANGINFO_H) && defined(HAVE_SETLOCALE)
     /* Set up the LC_CTYPE locale, so we can obtain
@@ -395,15 +398,19 @@ Py_Finalize(void)
      * the threads created via Threading.
      */
     call_py_exitfuncs();
-    initialized = 0;
-
-    /* Flush stdout+stderr */
-    flush_std_files();
 
     /* Get current thread state and interpreter pointer */
     tstate = PyThreadState_GET();
     interp = tstate->interp;
 
+    /* Remaining threads (e.g. daemon threads) will automatically exit
+       after taking the GIL (in PyEval_RestoreThread()). */
+    _Py_Finalizing = tstate;
+    initialized = 0;
+
+    /* Flush stdout+stderr */
+    flush_std_files();
+
     /* Disable signal handling */
     PyOS_FiniInterrupts();
 
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index 7d36b92..40ebaf6 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -244,9 +244,9 @@ void
 PyThread_exit_thread(void)
 {
     dprintf(("PyThread_exit_thread called\n"));
-    if (!initialized) {
+    if (!initialized)
         exit(0);
-    }
+    pthread_exit(0);
 }
 
 #ifdef USE_SEMAPHORES