py/malloc: Add mutex for tracked allocations.

Fixes thread safety issue that could cause memory corruption on ports
with (MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL) - currently only rp2 and
unix have this configuration.

Adds unit test for TLS sockets that exercises this code path.  I wasn't
able to make this fail on rp2, the race condition window is pretty narrow
and may not have a direct impact on a quiet system.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

1 files changed, 57 insertions, 0 deletions

diff --git a/tests/extmod/ssl_threads.py b/tests/extmod/ssl_threads.py
new file mode 100644
index 0000000000..4564abd3d8
--- /dev/null
+++ b/tests/extmod/ssl_threads.py
@@ -0,0 +1,57 @@
+# Ensure that SSL sockets can be allocated from multiple
+# threads without thread safety issues
+import unittest
+
+try:
+    import _thread
+    import io
+    import tls
+    import time
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+class TestSocket(io.IOBase):
+    def write(self, buf):
+        return len(buf)
+
+    def readinto(self, buf):
+        return 0
+
+    def ioctl(self, cmd, arg):
+        return 0
+
+    def setblocking(self, value):
+        pass
+
+
+ITERS = 256
+
+
+class TLSThreads(unittest.TestCase):
+    def test_sslsocket_threaded(self):
+        self.done = False
+        # only run in two threads: too much RAM demand otherwise, and rp2 only
+        # supports two anyhow
+        _thread.start_new_thread(self._alloc_many_sockets, (True,))
+        self._alloc_many_sockets(False)
+        while not self.done:
+            time.sleep(0.1)
+        print("done")
+
+    def _alloc_many_sockets(self, set_done_flag):
+        print("start", _thread.get_ident())
+        ctx = tls.SSLContext(tls.PROTOCOL_TLS_CLIENT)
+        ctx.verify_mode = tls.CERT_NONE
+        for n in range(ITERS):
+            s = TestSocket()
+            s = ctx.wrap_socket(s, do_handshake_on_connect=False)
+            s.close()  # Free associated resources now from thread, not in a GC pass
+        print("done", _thread.get_ident())
+        if set_done_flag:
+            self.done = True
+
+
+if __name__ == "__main__":
+    unittest.main()