We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Remove cupyx.allow_synchronize?
`cupyx.allow_synchronize` (#2808) was introduced originally for both unit tests and users who want to notice device synchronization in their own code.

Application in uint tests was dissmissed (#2893) because much more tests were synchronous than I had expected. 

Now I doubt the usefulness of this feature for users as well.
It's fundamentally impossible to eliminate false positives and/or false negatives.

If we took a policy for zero false positives, there would be too many false negatives which I think would make this feature useless.
For example, the documentation of [cudaMemcpy](https://docs.nvidia.com/cuda/cuda-runtime-api/group__CUDART__MEMORY.html#group__CUDART__MEMORY_1gc263dbe6574220cc776b45438fc351e8) says *"This function exhibits synchronous behavior for most use cases"*. If we took this policy, we wouldn't be able to consider this function synchronous, because no condition is mentioned that would make this function asynchronous.

If we took a policy to allow some false positives, this feature wouldn't be used to detect unexpected synchronization in users' code.

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `cupy/_core/syncdetect.py`
Content:
```
1 import contextlib
2 import threading
3 
4 from cupy import _util
5 
6 
7 _thread_local = threading.local()
8 
9 
10 class DeviceSynchronized(RuntimeError):
11     """Raised when device synchronization is detected while disallowed.
12 
13     .. seealso:: :func:`cupyx.allow_synchronize`
14 
15     """
16 
17     def __init__(self, message=None):
18         if message is None:
19             message = 'Device synchronization was detected while disallowed.'
20         super().__init__(message)
21 
22 
23 def _is_allowed():
24     # Returns whether device synchronization is allowed in the current thread.
25     try:
26         return _thread_local.allowed
27     except AttributeError:
28         _thread_local.allowed = True
29         return True
30 
31 
32 def _declare_synchronize():
33     # Raises DeviceSynchronized if device synchronization is disallowed in
34     # the current thread.
35     if not _is_allowed():
36         raise DeviceSynchronized()
37 
38 
39 @contextlib.contextmanager
40 def allow_synchronize(allow):
41     """Allows or disallows device synchronization temporarily in the current \
42 thread.
43 
44     If device synchronization is detected, :class:`cupyx.DeviceSynchronized`
45     will be raised.
46 
47     Note that there can be false negatives and positives.
48     Device synchronization outside CuPy will not be detected.
49     """
50     _util.experimental('cupyx.allow_synchronize')
51     old = _is_allowed()
52     _thread_local.allowed = allow
53     try:
54         yield
55     finally:
56         _thread_local.allowed = old
57
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/cupy/_core/syncdetect.py b/cupy/_core/syncdetect.py
--- a/cupy/_core/syncdetect.py
+++ b/cupy/_core/syncdetect.py
@@ -1,7 +1,6 @@
 import contextlib
 import threading
-
-from cupy import _util
+import warnings
 
 
 _thread_local = threading.local()
@@ -10,6 +9,11 @@
 class DeviceSynchronized(RuntimeError):
     """Raised when device synchronization is detected while disallowed.
 
+    .. warning::
+
+       This API has been deprecated in CuPy v10 and will be removed in future
+       releases.
+
     .. seealso:: :func:`cupyx.allow_synchronize`
 
     """
@@ -41,13 +45,21 @@
     """Allows or disallows device synchronization temporarily in the current \
 thread.
 
+    .. warning::
+
+       This API has been deprecated in CuPy v10 and will be removed in future
+       releases.
+
     If device synchronization is detected, :class:`cupyx.DeviceSynchronized`
     will be raised.
 
     Note that there can be false negatives and positives.
     Device synchronization outside CuPy will not be detected.
     """
-    _util.experimental('cupyx.allow_synchronize')
+    warnings.warn(
+        'cupyx.allow_synchronize will be removed in future releases as it '
+        'is not possible to reliably detect synchronizations.')
+
     old = _is_allowed()
     _thread_local.allowed = allow
     try:

{"golden_diff": "diff --git a/cupy/_core/syncdetect.py b/cupy/_core/syncdetect.py\n--- a/cupy/_core/syncdetect.py\n+++ b/cupy/_core/syncdetect.py\n@@ -1,7 +1,6 @@\n import contextlib\n import threading\n-\n-from cupy import _util\n+import warnings\n \n \n _thread_local = threading.local()\n@@ -10,6 +9,11 @@\n class DeviceSynchronized(RuntimeError):\n     \"\"\"Raised when device synchronization is detected while disallowed.\n \n+    .. warning::\n+\n+       This API has been deprecated in CuPy v10 and will be removed in future\n+       releases.\n+\n     .. seealso:: :func:`cupyx.allow_synchronize`\n \n     \"\"\"\n@@ -41,13 +45,21 @@\n     \"\"\"Allows or disallows device synchronization temporarily in the current \\\n thread.\n \n+    .. warning::\n+\n+       This API has been deprecated in CuPy v10 and will be removed in future\n+       releases.\n+\n     If device synchronization is detected, :class:`cupyx.DeviceSynchronized`\n     will be raised.\n \n     Note that there can be false negatives and positives.\n     Device synchronization outside CuPy will not be detected.\n     \"\"\"\n-    _util.experimental('cupyx.allow_synchronize')\n+    warnings.warn(\n+        'cupyx.allow_synchronize will be removed in future releases as it '\n+        'is not possible to reliably detect synchronizations.')\n+\n     old = _is_allowed()\n     _thread_local.allowed = allow\n     try:\n", "issue": "Remove cupyx.allow_synchronize?\n`cupyx.allow_synchronize` (#2808) was introduced originally for both unit tests and users who want to notice device synchronization in their own code.\r\n\r\nApplication in uint tests was dissmissed (#2893) because much more tests were synchronous than I had expected. \r\n\r\nNow I doubt the usefulness of this feature for users as well.\r\nIt's fundamentally impossible to eliminate false positives and/or false negatives.\r\n\r\nIf we took a policy for zero false positives, there would be too many false negatives which I think would make this feature useless.\r\nFor example, the documentation of [cudaMemcpy](https://docs.nvidia.com/cuda/cuda-runtime-api/group__CUDART__MEMORY.html#group__CUDART__MEMORY_1gc263dbe6574220cc776b45438fc351e8) says *\"This function exhibits synchronous behavior for most use cases\"*. If we took this policy, we wouldn't be able to consider this function synchronous, because no condition is mentioned that would make this function asynchronous.\r\n\r\nIf we took a policy to allow some false positives, this feature wouldn't be used to detect unexpected synchronization in users' code.\n", "before_files": [{"content": "import contextlib\nimport threading\n\nfrom cupy import _util\n\n\n_thread_local = threading.local()\n\n\nclass DeviceSynchronized(RuntimeError):\n    \"\"\"Raised when device synchronization is detected while disallowed.\n\n    .. seealso:: :func:`cupyx.allow_synchronize`\n\n    \"\"\"\n\n    def __init__(self, message=None):\n        if message is None:\n            message = 'Device synchronization was detected while disallowed.'\n        super().__init__(message)\n\n\ndef _is_allowed():\n    # Returns whether device synchronization is allowed in the current thread.\n    try:\n        return _thread_local.allowed\n    except AttributeError:\n        _thread_local.allowed = True\n        return True\n\n\ndef _declare_synchronize():\n    # Raises DeviceSynchronized if device synchronization is disallowed in\n    # the current thread.\n    if not _is_allowed():\n        raise DeviceSynchronized()\n\n\n@contextlib.contextmanager\ndef allow_synchronize(allow):\n    \"\"\"Allows or disallows device synchronization temporarily in the current \\\nthread.\n\n    If device synchronization is detected, :class:`cupyx.DeviceSynchronized`\n    will be raised.\n\n    Note that there can be false negatives and positives.\n    Device synchronization outside CuPy will not be detected.\n    \"\"\"\n    _util.experimental('cupyx.allow_synchronize')\n    old = _is_allowed()\n    _thread_local.allowed = allow\n    try:\n        yield\n    finally:\n        _thread_local.allowed = old\n", "path": "cupy/_core/syncdetect.py"}], "after_files": [{"content": "import contextlib\nimport threading\nimport warnings\n\n\n_thread_local = threading.local()\n\n\nclass DeviceSynchronized(RuntimeError):\n    \"\"\"Raised when device synchronization is detected while disallowed.\n\n    .. warning::\n\n       This API has been deprecated in CuPy v10 and will be removed in future\n       releases.\n\n    .. seealso:: :func:`cupyx.allow_synchronize`\n\n    \"\"\"\n\n    def __init__(self, message=None):\n        if message is None:\n            message = 'Device synchronization was detected while disallowed.'\n        super().__init__(message)\n\n\ndef _is_allowed():\n    # Returns whether device synchronization is allowed in the current thread.\n    try:\n        return _thread_local.allowed\n    except AttributeError:\n        _thread_local.allowed = True\n        return True\n\n\ndef _declare_synchronize():\n    # Raises DeviceSynchronized if device synchronization is disallowed in\n    # the current thread.\n    if not _is_allowed():\n        raise DeviceSynchronized()\n\n\n@contextlib.contextmanager\ndef allow_synchronize(allow):\n    \"\"\"Allows or disallows device synchronization temporarily in the current \\\nthread.\n\n    .. warning::\n\n       This API has been deprecated in CuPy v10 and will be removed in future\n       releases.\n\n    If device synchronization is detected, :class:`cupyx.DeviceSynchronized`\n    will be raised.\n\n    Note that there can be false negatives and positives.\n    Device synchronization outside CuPy will not be detected.\n    \"\"\"\n    warnings.warn(\n        'cupyx.allow_synchronize will be removed in future releases as it '\n        'is not possible to reliably detect synchronizations.')\n\n    old = _is_allowed()\n    _thread_local.allowed = allow\n    try:\n        yield\n    finally:\n        _thread_local.allowed = old\n", "path": "cupy/_core/syncdetect.py"}]}