prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Document hydra.callbacks api.
  - [ ]  Document API
  - [ ]  Add news fragment if missing
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `hydra/experimental/callback.py`
  Content:
  ```
  1 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
  2 import logging
  3 from typing import Any
  4 
  5 from omegaconf import DictConfig
  6 
  7 from hydra.core.utils import JobReturn
  8 
  9 logger = logging.getLogger(__name__)
  10 
  11 
  12 class Callback:
  13     def on_run_start(self, config: DictConfig, **kwargs: Any) -> None:
  14         """
  15         Called in RUN mode before job starts.
  16         """
  17         ...
  18 
  19     def on_run_end(self, config: DictConfig, **kwargs: Any) -> None:
  20         """
  21         Called in RUN mode after job ends.
  22         """
  23         ...
  24 
  25     def on_multirun_start(self, config: DictConfig, **kwargs: Any) -> None:
  26         """
  27         Called in MULTIRUN mode before any job starts.
  28         """
  29         ...
  30 
  31     def on_multirun_end(self, config: DictConfig, **kwargs: Any) -> None:
  32         """
  33         Called in MULTIRUN mode after all job end.
  34         """
  35         ...
  36 
  37     def on_job_start(self, config: DictConfig, **kwargs: Any) -> None:
  38         """
  39         Called in both RUN and MULTIRUN modes inside a Hydra job; before running
  40         application code.
  41         """
  42         ...
  43 
  44     def on_job_end(
  45         self, config: DictConfig, job_return: JobReturn, **kwargs: Any
  46     ) -> None:
  47         """
  48         Called in both RUN and MULTIRUN modes inside a Hydra job; after running
  49         application code.
  50         """
  51         ...
  52
  ```
  --- 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/hydra/experimental/callback.py b/hydra/experimental/callback.py
  --- a/hydra/experimental/callback.py
  +++ b/hydra/experimental/callback.py
  @@ -30,14 +30,14 @@
   
       def on_multirun_end(self, config: DictConfig, **kwargs: Any) -> None:
           """
  -        Called in MULTIRUN mode after all job end.
  +        Called in MULTIRUN mode after all jobs end.
           """
           ...
   
       def on_job_start(self, config: DictConfig, **kwargs: Any) -> None:
           """
  -        Called in both RUN and MULTIRUN modes inside a Hydra job; before running
  -        application code.
  +        Called in both RUN and MULTIRUN modes, once for each Hydra job (before running
  +        application code).
           """
           ...
   
  @@ -45,7 +45,7 @@
           self, config: DictConfig, job_return: JobReturn, **kwargs: Any
       ) -> None:
           """
  -        Called in both RUN and MULTIRUN modes inside a Hydra job; after running
  -        application code.
  +        Called in both RUN and MULTIRUN modes, once for each Hydra job (after running
  +        application code).
           """
           ...
  
verification_info: {"golden_diff": "diff --git a/hydra/experimental/callback.py b/hydra/experimental/callback.py\n--- a/hydra/experimental/callback.py\n+++ b/hydra/experimental/callback.py\n@@ -30,14 +30,14 @@\n \n     def on_multirun_end(self, config: DictConfig, **kwargs: Any) -> None:\n         \"\"\"\n-        Called in MULTIRUN mode after all job end.\n+        Called in MULTIRUN mode after all jobs end.\n         \"\"\"\n         ...\n \n     def on_job_start(self, config: DictConfig, **kwargs: Any) -> None:\n         \"\"\"\n-        Called in both RUN and MULTIRUN modes inside a Hydra job; before running\n-        application code.\n+        Called in both RUN and MULTIRUN modes, once for each Hydra job (before running\n+        application code).\n         \"\"\"\n         ...\n \n@@ -45,7 +45,7 @@\n         self, config: DictConfig, job_return: JobReturn, **kwargs: Any\n     ) -> None:\n         \"\"\"\n-        Called in both RUN and MULTIRUN modes inside a Hydra job; after running\n-        application code.\n+        Called in both RUN and MULTIRUN modes, once for each Hydra job (after running\n+        application code).\n         \"\"\"\n         ...\n", "issue": "Document hydra.callbacks api.\n- [ ]  Document API\r\n- [ ]  Add news fragment if missing\n", "before_files": [{"content": "# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved\nimport logging\nfrom typing import Any\n\nfrom omegaconf import DictConfig\n\nfrom hydra.core.utils import JobReturn\n\nlogger = logging.getLogger(__name__)\n\n\nclass Callback:\n    def on_run_start(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in RUN mode before job starts.\n        \"\"\"\n        ...\n\n    def on_run_end(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in RUN mode after job ends.\n        \"\"\"\n        ...\n\n    def on_multirun_start(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in MULTIRUN mode before any job starts.\n        \"\"\"\n        ...\n\n    def on_multirun_end(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in MULTIRUN mode after all job end.\n        \"\"\"\n        ...\n\n    def on_job_start(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in both RUN and MULTIRUN modes inside a Hydra job; before running\n        application code.\n        \"\"\"\n        ...\n\n    def on_job_end(\n        self, config: DictConfig, job_return: JobReturn, **kwargs: Any\n    ) -> None:\n        \"\"\"\n        Called in both RUN and MULTIRUN modes inside a Hydra job; after running\n        application code.\n        \"\"\"\n        ...\n", "path": "hydra/experimental/callback.py"}], "after_files": [{"content": "# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved\nimport logging\nfrom typing import Any\n\nfrom omegaconf import DictConfig\n\nfrom hydra.core.utils import JobReturn\n\nlogger = logging.getLogger(__name__)\n\n\nclass Callback:\n    def on_run_start(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in RUN mode before job starts.\n        \"\"\"\n        ...\n\n    def on_run_end(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in RUN mode after job ends.\n        \"\"\"\n        ...\n\n    def on_multirun_start(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in MULTIRUN mode before any job starts.\n        \"\"\"\n        ...\n\n    def on_multirun_end(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in MULTIRUN mode after all jobs end.\n        \"\"\"\n        ...\n\n    def on_job_start(self, config: DictConfig, **kwargs: Any) -> None:\n        \"\"\"\n        Called in both RUN and MULTIRUN modes, once for each Hydra job (before running\n        application code).\n        \"\"\"\n        ...\n\n    def on_job_end(\n        self, config: DictConfig, job_return: JobReturn, **kwargs: Any\n    ) -> None:\n        \"\"\"\n        Called in both RUN and MULTIRUN modes, once for each Hydra job (after running\n        application code).\n        \"\"\"\n        ...\n", "path": "hydra/experimental/callback.py"}]}