prompt: 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()
  
  ```
  
golden_diff: 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:
  
verification_info: {"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"}]}