bpo-34410: Fix a crash in the tee iterator when re-enter it. (GH-15625)
RuntimeError is now raised in this case.
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index a3f403a..8d134d4 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -645,6 +645,10 @@
used anywhere else; otherwise, the *iterable* could get advanced without
the tee objects being informed.
+ ``tee`` iterators are not threadsafe. A :exc:`RuntimeError` may be
+ raised when using simultaneously iterators returned by the same :func:`tee`
+ call, even if the original *iterable* is threadsafe.
+
This itertool may require significant auxiliary storage (depending on how
much temporary data needs to be stored). In general, if one iterator uses
most or all of the data before another iterator starts, it is faster to use
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 98b8c83..eaa6197 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -11,6 +11,7 @@
from functools import reduce
import sys
import struct
+import threading
maxsize = support.MAX_Py_ssize_t
minsize = -maxsize-1
@@ -1494,6 +1495,42 @@
del forward, backward
raise
+ def test_tee_reenter(self):
+ class I:
+ first = True
+ def __iter__(self):
+ return self
+ def __next__(self):
+ first = self.first
+ self.first = False
+ if first:
+ return next(b)
+
+ a, b = tee(I())
+ with self.assertRaisesRegex(RuntimeError, "tee"):
+ next(a)
+
+ def test_tee_concurrent(self):
+ start = threading.Event()
+ finish = threading.Event()
+ class I:
+ def __iter__(self):
+ return self
+ def __next__(self):
+ start.set()
+ finish.wait()
+
+ a, b = tee(I())
+ thread = threading.Thread(target=next, args=[a])
+ thread.start()
+ try:
+ start.wait()
+ with self.assertRaisesRegex(RuntimeError, "tee"):
+ next(b)
+ finally:
+ finish.set()
+ thread.join()
+
def test_StopIteration(self):
self.assertRaises(StopIteration, next, zip())
diff --git a/Misc/NEWS.d/next/Library/2019-08-31-01-52-59.bpo-34410.7KbWZQ.rst b/Misc/NEWS.d/next/Library/2019-08-31-01-52-59.bpo-34410.7KbWZQ.rst
new file mode 100644
index 0000000..64e778e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-08-31-01-52-59.bpo-34410.7KbWZQ.rst
@@ -0,0 +1,2 @@
+Fixed a crash in the :func:`tee` iterator when re-enter it. RuntimeError is
+now raised in this case.
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index cf419ad..e60ad5b 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -443,6 +443,7 @@
PyObject_HEAD
PyObject *it;
int numread; /* 0 <= numread <= LINKCELLS */
+ int running;
PyObject *nextlink;
PyObject *(values[LINKCELLS]);
} teedataobject;
@@ -465,6 +466,7 @@
if (tdo == NULL)
return NULL;
+ tdo->running = 0;
tdo->numread = 0;
tdo->nextlink = NULL;
Py_INCREF(it);
@@ -493,7 +495,14 @@
else {
/* this is the lead iterator, so fetch more data */
assert(i == tdo->numread);
+ if (tdo->running) {
+ PyErr_SetString(PyExc_RuntimeError,
+ "cannot re-enter the tee iterator");
+ return NULL;
+ }
+ tdo->running = 1;
value = PyIter_Next(tdo->it);
+ tdo->running = 0;
if (value == NULL)
return NULL;
tdo->numread++;