Merge pull request #231653 from EvanR-Dev/evanroman/thread-logging-docs

Add logging from user created threads documentation

Author: prmerger-automator[bot]

articles/azure-functions/functions-reference-python.md

@@ -517,6 +517,28 @@ More logging methods are available that let you write to the console at differen
 
 To learn more about logging, see [Monitor Azure Functions](functions-monitoring.md).
 
+### Logging from created threads
+
+To see logs coming from your created threads, include the [`context`](/python/api/azure-functions/azure.functions.context) argument in the function's signature. This argument contains an attribute `thread_local_storage` which stores a local `invocation_id`. This can be set to the function's current `invocation_id` to ensure the context is changed.
+
+```python
+import azure.functions as func
+import logging
+import threading
+
+
+def main(req, context):
+    logging.info('Python HTTP trigger function processed a request.')
+    t = threading.Thread(target=log_function, args=(context,))
+    t.start()
+
+
+def log_function(context):
+    context.thread_local_storage.invocation_id = context.invocation_id
+    logging.info('Logging from thread.')
+```
+
+
 ### Log custom telemetry
 
 By default, the Functions runtime collects logs and other telemetry data that are generated by your functions. This telemetry ends up as traces in Application Insights. Request and dependency telemetry for certain Azure services are also collected by default by [triggers and bindings](functions-triggers-bindings.md#supported-bindings). 
@@ -850,6 +872,7 @@ The [`Context`](/python/api/azure-functions/azure.functions.context) class has t
 | `function_directory` | The directory in which the function is running. |
 | `function_name` | The name of the function. |
 | `invocation_id` | The ID of the current function invocation. |
+| `thread_local_storage` | The thread local storage of the function. Contains a local `invocation_id` for [logging from created threads](#logging-from-created-threads). |
 | `trace_context` | The context for distributed tracing. For more information, see  [`Trace Context`](https://www.w3.org/TR/trace-context/). |
 | `retry_context` | The context for retries to the function. For more information, see [`retry-policies`](./functions-bindings-errors.md#retry-policies). |