1 files changed, 30 insertions, 0 deletions
diff --git a/docs/examples/userguide/buffer/view_count.py b/docs/examples/userguide/buffer/view_count.py
new file mode 100644
index 000000000..6a0554abc
--- /dev/null
+++ b/docs/examples/userguide/buffer/view_count.py
@@ -0,0 +1,30 @@
+# distutils: language = c++
+
+from cython.cimports.cpython import Py_buffer
+from cython.cimports.libcpp.vector import vector
+
+@cython.cclass
+class Matrix:
+
+    view_count: cython.int
+
+    ncols: cython.Py_ssize_t
+    v: vector[cython.float]
+    # ...
+
+    def __cinit__(self, ncols: cython.Py_ssize_t):
+        self.ncols = ncols
+        self.view_count = 0
+
+    def add_row(self):
+        if self.view_count > 0:
+            raise ValueError("can't add row while being viewed")
+        self.v.resize(self.v.size() + self.ncols)
+
+    def __getbuffer__(self, buffer: cython.pointer(Py_buffer), flags: cython.int):
+        # ... as before
+
+        self.view_count += 1
+
+    def __releasebuffer__(self, buffer: cython.pointer(Py_buffer)):
+        self.view_count -= 1