Repository: gradio-app/gradio

Issue:
Infinite loop when Progress() is called at the startup with Examples(cache_examples=True)
### Describe the bug

Possible infinite loop occurs when you try to call examples at the startup with `cache_examples=True` option.

### Problem 1: Infinite loop.

- Progress bar `gr.Progress()` iterated within a callback function called by manual interaction -> No problem.
- Progress bar `gr.Progress()`  iterated within a callback function from manually selected and called examples -> No problem.
- Progress bar `gr.Progress()`  iterated within a callback function from automatic caching process at startup with `cache_examples=True` option in `gr.Examples() -> Infinite loop.

### Problem 2: tqdm output error.

Additionally, in case of infinite loop, the value of the iterator is not the iterable element but `<gradio.helpers.Progress object at 0x7f304622e280>`. (It should be integer, list element, etc.)

### Have you searched existing issues?  🔎

- [X] I have searched and found no existing issues

### Reproduction

```python
import time
import gradio as gr


def foo(progress=gr.Progress()):
    for i in progress.tqdm(range(10)):
        print(i)
        time.sleep(0.5)


with gr.Blocks() as demo:
    gr.Examples(
        [[], [], []],
        inputs=[],
        outputs=[],
        fn=foo,
        cache_examples=True,
    )

demo.queue().launch()
```


### Screenshot

![image](https://github.com/gradio-app/gradio/assets/12259041/a7714b1a-0559-4cda-9e1e-e3a9dd0ad05c)


### Logs

_No response_

### System Info

```shell
Gradio Environment Information:
------------------------------
Operating System: Linux
gradio version: 4.8.0
gradio_client version: 0.7.1

------------------------------------------------
gradio dependencies in your environment:

aiofiles: 23.2.1
altair: 5.2.0
fastapi: 0.104.1
ffmpy: 0.3.1
gradio-client==0.7.1 is not installed.
httpx: 0.25.2
huggingface-hub: 0.19.4
importlib-resources: 6.1.1
jinja2: 3.1.2
markupsafe: 2.1.3
matplotlib: 3.8.2
numpy: 1.26.2
orjson: 3.9.10
packaging: 23.2
pandas: 2.1.3
pillow: 10.1.0
pydantic: 2.5.2
pydub: 0.25.1
python-multipart: 0.0.6
pyyaml: 6.0.1
requests: 2.31.0
semantic-version: 2.10.0
tomlkit==0.12.0 is not installed.
typer: 0.9.0
typing-extensions: 4.8.0
uvicorn: 0.24.0.post1
authlib; extra == 'oauth' is not installed.
itsdangerous; extra == 'oauth' is not installed.


gradio_client dependencies in your environment:

fsspec: 2023.10.0
httpx: 0.25.2
huggingface-hub: 0.19.4
packaging: 23.2
requests: 2.31.0
typing-extensions: 4.8.0
websockets: 11.0.3
```


### Severity

Blocking usage of gradio

Hints from issue comments:
@abidlabs: Hi, apologies for the late follow up. We haven't had a chance to look into this issue, but the Gradio codebase has changed quite significantly since this issue was created, particularly with the release of Gradio 5. Could you let us know if this is still an issue in the latest version of Gradio (`pip install --upgrade gradio`)? Thanks!
@abidlabs: Closing the issue for now, but can reopen if the issue continues to persist in the latest version of Gradio@hysts: @abidlabs It seems that this issue still persists in `gradio==5.12.0`.

Solution patch:
diff --git a/.changeset/curly-numbers-kneel.md b/.changeset/curly-numbers-kneel.md
new file mode 100644
index 000000000..f69a5e890
--- /dev/null
+++ b/.changeset/curly-numbers-kneel.md
@@ -0,0 +1,5 @@
+---
+"gradio": patch
+---
+
+fix:Resolve issues around example caching with `gr.Progress`
diff --git a/gradio/chat_interface.py b/gradio/chat_interface.py
index caaa57397..b074c4571 100644
--- a/gradio/chat_interface.py
+++ b/gradio/chat_interface.py
@@ -127,7 +127,7 @@ class ChatInterface(Blocks):
             examples: sample inputs for the function; if provided, appear within the chatbot and can be clicked to populate the chatbot input. Should be a list of strings representing text-only examples, or a list of dictionaries (with keys `text` and `files`) representing multimodal examples. If `additional_inputs` are provided, the examples must be a list of lists, where the first element of each inner list is the string or dictionary example message and the remaining elements are the example values for the additional inputs -- in this case, the examples will appear under the chatbot.
             example_labels: labels for the examples, to be displayed instead of the examples themselves. If provided, should be a list of strings with the same length as the examples list. Only applies when examples are displayed within the chatbot (i.e. when `additional_inputs` is not provided).
             example_icons: icons for the examples, to be displayed above the examples. If provided, should be a list of string URLs or local paths with the same length as the examples list. Only applies when examples are displayed within the chatbot (i.e. when `additional_inputs` is not provided).
-            cache_examples: if True, caches examples in the server for fast runtime in examples. The default option in HuggingFace Spaces is True. The default option elsewhere is False.
+            cache_examples: if True, caches examples in the server for fast runtime in examples. The default option in HuggingFace Spaces is True. The default option elsewhere is False.  Note that examples are cached separately from Gradio's queue() so certain features, such as gr.Progress(), gr.Info(), gr.Warning(), etc. will not be displayed in Gradio's UI for cached examples.
             cache_mode: if "eager", all examples are cached at app launch. If "lazy", examples are cached for all users after the first use by any user of the app. If None, will use the GRADIO_CACHE_MODE environment variable if defined, or default to "eager".
             run_examples_on_click: if True, clicking on an example will run the example through the chatbot fn and the response will be displayed in the chatbot. If False, clicking on an example will only populate the chatbot input with the example message. Has no effect if `cache_examples` is True
             title: a title for the interface; if provided, appears above chatbot in large font. Also used as the tab title when opened in a browser window.
diff --git a/gradio/helpers.py b/gradio/helpers.py
index 45ed3f9d8..dc138c57f 100644
--- a/gradio/helpers.py
+++ b/gradio/helpers.py
@@ -122,7 +122,7 @@ class Examples:
             inputs: the component or list of components corresponding to the examples
             outputs: optionally, provide the component or list of components corresponding to the output of the examples. Required if `cache_examples` is not False.
             fn: optionally, provide the function to run to generate the outputs corresponding to the examples. Required if `cache_examples` is not False. Also required if `run_on_click` is True.
-            cache_examples: If True, caches examples in the server for fast runtime in examples. If "lazy", then examples are cached (for all users of the app) after their first use (by any user of the app). If None, will use the GRADIO_CACHE_EXAMPLES environment variable, which should be either "true" or "false". In HuggingFace Spaces, this parameter is True (as long as `fn` and `outputs` are also provided). The default option otherwise is False.
+            cache_examples: If True, caches examples in the server for fast runtime in examples. If "lazy", then examples are cached (for all users of the app) after their first use (by any user of the app). If None, will use the GRADIO_CACHE_EXAMPLES environment variable, which should be either "true" or "false". In HuggingFace Spaces, this parameter is True (as long as `fn` and `outputs` are also provided). The default option otherwise is False. Note that examples are cached separately from Gradio's queue() so certain features, such as gr.Progress(), gr.Info(), gr.Warning(), etc. will not be displayed in Gradio's UI for cached examples.
             cache_mode: if "lazy", examples are cached after their first use. If "eager", all examples are cached at app launch. If None, will use the GRADIO_CACHE_MODE environment variable if defined, or default to "eager".
             examples_per_page: how many examples to show per page.
             label: the label to use for the examples component (by default, "Examples")
@@ -685,7 +685,6 @@ class Progress(Iterable):
     The Progress class provides a custom progress tracker that is used in a function signature.
     To attach a Progress tracker to a function, simply add a parameter right after the input parameters that has a default value set to a `gradio.Progress()` instance.
     The Progress tracker can then be updated in the function by calling the Progress object or using the `tqdm` method on an Iterable.
-    The Progress tracker is currently only available with `queue()`.
     Example:
         import gradio as gr
         import time
@@ -695,7 +694,7 @@ class Progress(Iterable):
             for i in progress.tqdm(range(100)):
                 time.sleep(0.1)
             return x
-        gr.Interface(my_function, gr.Textbox(), gr.Textbox()).queue().launch()
+        gr.Interface(my_function, gr.Textbox(), gr.Textbox()).launch()
     """
 
     def __init__(
@@ -712,6 +711,8 @@ class Progress(Iterable):
         self.iterables: list[TrackedIterable] = []
 
     def __len__(self):
+        if not self.iterables:
+            return 0
         return self.iterables[-1].length
 
     def __iter__(self):
@@ -798,7 +799,10 @@ class Progress(Iterable):
             self.iterables.append(
                 TrackedIterable(iter(iterable), 0, length, desc, unit, _tqdm)
             )
-        return self
+            return self
+        if iterable is None:
+            return iter([])
+        return iter(iterable)
 
     def update(self, n: int | float = 1):
         """
@@ -850,28 +854,38 @@ def patch_tqdm() -> None:
     ):
         self._progress = LocalContext.progress.get()
         if self._progress is not None:
-            self._progress.tqdm(iterable, desc, total, unit, _tqdm=self)
-            kwargs["file"] = open(os.devnull, "w")  # noqa: SIM115
+            callback = self._progress._progress_callback()
+            if callback is not None:
+                self._progress.tqdm(iterable, desc, total, unit, _tqdm=self)
+                kwargs["file"] = open(os.devnull, "w")  # noqa: SIM115
         self.__init__orig__(iterable, desc, total, *args, unit=unit, **kwargs)
 
     def iter_tqdm(self):
         if self._progress is not None:
-            return self._progress
+            callback = self._progress._progress_callback()
+            if callback is not None:
+                return self._progress
         return self.__iter__orig__()
 
     def update_tqdm(self, n=1):
         if self._progress is not None:
-            self._progress.update(n)
+            callback = self._progress._progress_callback()
+            if callback is not None:
+                self._progress.update(n)
         return self.__update__orig__(n)
 
     def close_tqdm(self):
         if self._progress is not None:
-            self._progress.close(self)
+            callback = self._progress._progress_callback()
+            if callback is not None:
+                self._progress.close(self)
         return self.__close__orig__()
 
     def exit_tqdm(self, exc_type, exc_value, traceback):
         if self._progress is not None:
-            self._progress.close(self)
+            callback = self._progress._progress_callback()
+            if callback is not None:
+                self._progress.close(self)
         return self.__exit__orig__(exc_type, exc_value, traceback)
 
     # Backup
diff --git a/gradio/interface.py b/gradio/interface.py
index 7afe3e295..0301b213e 100644
--- a/gradio/interface.py
+++ b/gradio/interface.py
@@ -156,7 +156,7 @@ class Interface(Blocks):
             inputs: a single Gradio component, or list of Gradio components. Components can either be passed as instantiated objects, or referred to by their string shortcuts. The number of input components should match the number of parameters in fn. If set to None, then only the output components will be displayed.
             outputs: a single Gradio component, or list of Gradio components. Components can either be passed as instantiated objects, or referred to by their string shortcuts. The number of output components should match the number of values returned by fn. If set to None, then only the input components will be displayed.
             examples: sample inputs for the function; if provided, appear below the UI components and can be clicked to populate the interface. Should be nested list, in which the outer list consists of samples and each inner list consists of an input corresponding to each input component. A string path to a directory of examples can also be provided, but it should be within the directory with the python file running the gradio app. If there are multiple input components and a directory is provided, a log.csv file must be present in the directory to link corresponding inputs.
-            cache_examples: If True, caches examples in the server for fast runtime in examples. If "lazy", then examples are cached (for all users of the app) after their first use (by any user of the app). If None, will use the GRADIO_CACHE_EXAMPLES environment variable, which should be either "true" or "false". In HuggingFace Spaces, this parameter defaults to True (as long as `fn` and `outputs` are also provided).
+            cache_examples: If True, caches examples in the server for fast runtime in examples. If "lazy", then examples are cached (for all users of the app) after their first use (by any user of the app). If None, will use the GRADIO_CACHE_EXAMPLES environment variable, which should be either "true" or "false". In HuggingFace Spaces, this parameter defaults to True (as long as `fn` and `outputs` are also provided).  Note that examples are cached separately from Gradio's queue() so certain features, such as gr.Progress(), gr.Info(), gr.Warning(), etc. will not be displayed in Gradio's UI for cached examples.
             cache_mode: if "lazy", examples are cached after their first use. If "eager", all examples are cached at app launch. If None, will use the GRADIO_CACHE_MODE environment variable if defined, or default to "eager". In HuggingFace Spaces, this parameter defaults to "eager" except for ZeroGPU Spaces, in which case it defaults to "lazy".
             examples_per_page: if examples are provided, how many to display per page.
             preload_example: If an integer is provided (and examples are being cached), the example at that index in the examples list will be preloaded when the Gradio app is first loaded. If False, no example will be preloaded.


Test patch:
diff --git a/test/test_helpers.py b/test/test_helpers.py
index fe8f252e2..613976c57 100644
--- a/test/test_helpers.py
+++ b/test/test_helpers.py
@@ -273,9 +273,14 @@ class TestProcessExamples:
             prediction = io.examples_handler.load_from_cache(0)
         assert prediction[0].path.endswith(".webp")
 
-    def test_caching_audio(self, patched_cache_folder, connect):
+    def test_caching_audio_with_progress(self, patched_cache_folder, connect):
+        def audio_identity(x, prog=gr.Progress()):
+            for _ in prog.tqdm(range(5)):
+                pass
+            return x
+
         io = gr.Interface(
-            lambda x: x,
+            audio_identity,
             "audio",
             "audio",
             examples=[["test/test_files/audio_sample.wav"]],