1 files changed, 109 insertions, 0 deletions
diff --git a/Lib/test/test_free_threading/test_io.py b/Lib/test/test_free_threading/test_io.py
new file mode 100644
index 00000000000..f9bec740ddf
--- /dev/null
+++ b/Lib/test/test_free_threading/test_io.py
@@ -0,0 +1,109 @@
+import threading
+from unittest import TestCase
+from test.support import threading_helper
+from random import randint
+from io import BytesIO
+from sys import getsizeof
+
+
+class TestBytesIO(TestCase):
+    # Test pretty much everything that can break under free-threading.
+    # Non-deterministic, but at least one of these things will fail if
+    # BytesIO object is not free-thread safe.
+
+    def check(self, funcs, *args):
+        barrier = threading.Barrier(len(funcs))
+        threads = []
+
+        for func in funcs:
+            thread = threading.Thread(target=func, args=(barrier, *args))
+
+            threads.append(thread)
+
+        with threading_helper.start_threads(threads):
+            pass
+
+    @threading_helper.requires_working_threading()
+    @threading_helper.reap_threads
+    def test_free_threading(self):
+        """Test for segfaults and aborts."""
+
+        def write(barrier, b, *ignore):
+            barrier.wait()
+            try: b.write(b'0' * randint(100, 1000))
+            except ValueError: pass  # ignore write fail to closed file
+
+        def writelines(barrier, b, *ignore):
+            barrier.wait()
+            b.write(b'0\n' * randint(100, 1000))
+
+        def truncate(barrier, b, *ignore):
+            barrier.wait()
+            try: b.truncate(0)
+            except: BufferError  # ignore exported buffer
+
+        def read(barrier, b, *ignore):
+            barrier.wait()
+            b.read()
+
+        def read1(barrier, b, *ignore):
+            barrier.wait()
+            b.read1()
+
+        def readline(barrier, b, *ignore):
+            barrier.wait()
+            b.readline()
+
+        def readlines(barrier, b, *ignore):
+            barrier.wait()
+            b.readlines()
+
+        def readinto(barrier, b, into, *ignore):
+            barrier.wait()
+            b.readinto(into)
+
+        def close(barrier, b, *ignore):
+            barrier.wait()
+            b.close()
+
+        def getvalue(barrier, b, *ignore):
+            barrier.wait()
+            b.getvalue()
+
+        def getbuffer(barrier, b, *ignore):
+            barrier.wait()
+            b.getbuffer()
+
+        def iter(barrier, b, *ignore):
+            barrier.wait()
+            list(b)
+
+        def getstate(barrier, b, *ignore):
+            barrier.wait()
+            b.__getstate__()
+
+        def setstate(barrier, b, st, *ignore):
+            barrier.wait()
+            b.__setstate__(st)
+
+        def sizeof(barrier, b, *ignore):
+            barrier.wait()
+            getsizeof(b)
+
+        self.check([write] * 10, BytesIO())
+        self.check([writelines] * 10, BytesIO())
+        self.check([write] * 10 + [truncate] * 10, BytesIO())
+        self.check([truncate] + [read] * 10, BytesIO(b'0\n'*204800))
+        self.check([truncate] + [read1] * 10, BytesIO(b'0\n'*204800))
+        self.check([truncate] + [readline] * 10, BytesIO(b'0\n'*20480))
+        self.check([truncate] + [readlines] * 10, BytesIO(b'0\n'*20480))
+        self.check([truncate] + [readinto] * 10, BytesIO(b'0\n'*204800), bytearray(b'0\n'*204800))
+        self.check([close] + [write] * 10, BytesIO())
+        self.check([truncate] + [getvalue] * 10, BytesIO(b'0\n'*204800))
+        self.check([truncate] + [getbuffer] * 10, BytesIO(b'0\n'*204800))
+        self.check([truncate] + [iter] * 10, BytesIO(b'0\n'*20480))
+        self.check([truncate] + [getstate] * 10, BytesIO(b'0\n'*204800))
+        self.check([truncate] + [setstate] * 10, BytesIO(b'0\n'*204800), (b'123', 0, None))
+        self.check([truncate] + [sizeof] * 10, BytesIO(b'0\n'*204800))
+
+        # no tests for seek or tell because they don't break anything