docs: Clarify thread safety (#219)

Author: ptiurin

README.md

@@ -29,6 +29,10 @@ Optional parameters
 ## Examples
 See [PEP-249](https://www.python.org/dev/peps/pep-0249) for the DB API reference and specifications. An example [jupyter notebook](https://github.com/firebolt-db/firebolt-sdk/tree/main/examples/dbapi.ipynb) is included to illustrate the use of the Firebolt API.
 
+## Special considerations
+### Cursor objects should not be shared between threads
+Cursor is not thread-safe and should not be shared across threads. In a multi-threaded environment you can share a Connection, but each thread would need to keep its own Cursor. This corresponds to a thread safety 2 in the [DBApi specification](https://peps.python.org/pep-0249/#threadsafety).
+
 ## Optional features
 ### Faster datetime with ciso8601
 By default, firebolt-sdk uses `datetime` module to parse date and datetime values, which might be slow for a large amount of operations. In order to speed up datetime operations, it's possible to use [ciso8601](https://pypi.org/project/ciso8601/) package. In order to install firebolt-sdk with `ciso8601` support, run `pip install "firebolt-sdk[ciso8601]"`

src/firebolt/async_db/__init__.py

@@ -32,5 +32,5 @@
 
 apilevel = "2.0"
 # threads may only share the module and connections, cursors should not be shared
-threadsafety = 1
+threadsafety = 2
 paramstyle = "qmark"

src/firebolt/db/__init__.py

@@ -31,5 +31,6 @@
 )
 
 apilevel = "2.0"
-threadsafety = 3  # threads may share the module, connections and cursors
+# threads may only share the module and connections, cursors should not be shared
+threadsafety = 2
 paramstyle = "qmark"