Fix ReAwaitable to support concurrent await calls (#2108)

CHANGELOG.md

@@ -6,6 +6,13 @@ incremental in minor, bugfixes only are patches.
 See [0Ver](https://0ver.org/).
 
 
+## Unreleased
+
+### Bugfixes
+
+- Fixes that `ReAwaitable` does not support concurrent await calls. Issue #2108
+
+
 ## 0.25.0
 
 ### Features

docs/pages/future.rst

@@ -69,6 +69,17 @@ its result to ``IO``-based containers.
 This helps a lot when separating pure and impure
 (async functions are impure) code inside your app.
 
+.. note::
+  ``Future`` containers can be awaited multiple times and support concurrent
+  awaits from multiple async tasks. This is achieved through an internal
+  caching mechanism that ensures the underlying coroutine is only executed
+  once, while all subsequent or concurrent awaits receive the cached result.
+  This makes ``Future`` containers safe to use in complex async workflows
+  where the same future might be awaited from different parts of your code.
+
+  The implementation supports multiple async frameworks including asyncio,
+  trio, and anyio, with automatic framework detection and fallback support.
+
 
 FutureResult
 ------------

pyproject.toml

@@ -73,6 +73,7 @@ pytest-mypy-plugins = "^3.1"
 pytest-subtests = "^0.14"
 pytest-shard = "^0.1"
 covdefaults = "^2.3"
+pytest-asyncio = "^1.0.0"
 
 [tool.poetry.group.docs]
 optional = true

returns/contrib/mypy/_features/kind.py

@@ -69,7 +69,7 @@ def attribute_access(ctx: AttributeContext) -> MypyType:
         is_lvalue=False,
         is_super=False,
         is_operator=False,
-        msg=ctx.api.msg,
+        msg=exprchecker.msg,
         original_type=instance,
         chk=ctx.api,  # type: ignore
         in_literal_context=exprchecker.is_literal_context(),

returns/primitives/reawaitable.py

@@ -1,6 +1,9 @@
+import asyncio
+import logging
+import threading
 from collections.abc import Awaitable, Callable, Generator
 from functools import wraps
-from typing import NewType, ParamSpec, TypeVar, cast, final
+from typing import Any, NewType, ParamSpec, TypeVar, cast, final
 
 _ValueType = TypeVar('_ValueType')
 _AwaitableT = TypeVar('_AwaitableT', bound=Awaitable)
@@ -19,6 +22,23 @@ class ReAwaitable:
     So, in reality we still ``await`` once,
     but pretending to do it multiple times.
 
+    This class is thread-safe and supports concurrent awaits from multiple
+    async tasks. When multiple tasks await the same instance simultaneously,
+    only one will execute the underlying coroutine while others will wait
+    and receive the cached result.
+
+    **Async Framework Support and Lock Selection:**
+
+    The lock selection follows a strict priority order with automatic fallback:
+
+    1. **asyncio.Lock()** - Primary choice when asyncio event loop available
+    2. **trio.Lock()** - Used when asyncio fails and trio available
+    3. **anyio.Lock()** - Used when asyncio/trio fail, anyio available
+    4. **threading.Lock()** - Final fallback for unsupported frameworks
+
+    Lock selection happens lazily on first await and is logged at DEBUG level
+    for troubleshooting. The framework detection is automatic and transparent.
+
     Why is that required? Because otherwise,
     ``Future`` containers would be unusable:
 
@@ -48,12 +68,13 @@ class ReAwaitable:
 
     """
 
-    __slots__ = ('_cache', '_coro')
+    __slots__ = ('_cache', '_coro', '_lock')
 
     def __init__(self, coro: Awaitable[_ValueType]) -> None:
         """We need just an awaitable to work with."""
         self._coro = coro
         self._cache: _ValueType | _Sentinel = _sentinel
+        self._lock: Any | None = None
 
     def __await__(self) -> Generator[None, None, _ValueType]:
         """
@@ -99,10 +120,95 @@ def __repr__(self) -> str:
         """
         return repr(self._coro)
 
+    def _try_asyncio_lock(self, logger: logging.Logger) -> Any:
+        """Try to create an asyncio lock."""
+        try:
+            asyncio_lock = asyncio.Lock()
+        except RuntimeError:
+            return None
+        logger.debug('ReAwaitable: Using asyncio.Lock for concurrency control')
+        return asyncio_lock
+
+    def _try_trio_lock(self, logger: logging.Logger) -> Any:
+        """Try to create a trio lock."""
+        try:
+            import trio  # noqa: PLC0415
+        except ImportError:
+            return None
+        trio_lock = trio.Lock()
+        logger.debug('ReAwaitable: Using trio.Lock for concurrency control')
+        return trio_lock
+
+    def _try_anyio_lock(self, logger: logging.Logger) -> Any:
+        """Try to create an anyio lock."""
+        try:
+            import anyio  # noqa: PLC0415
+        except ImportError:
+            return None
+        anyio_lock = anyio.Lock()
+        logger.debug('ReAwaitable: Using anyio.Lock for concurrency control')
+        return anyio_lock
+
+    def _create_lock(self) -> Any:  # noqa: WPS320
+        """Create appropriate lock for the current async framework.
+
+        Attempts framework detection: asyncio -> trio -> anyio -> threading.
+        Logs the selected framework at DEBUG level for troubleshooting.
+        """
+        logger = logging.getLogger(__name__)
+
+        # Try asyncio first (most common)
+        asyncio_lock = self._try_asyncio_lock(logger)
+        if asyncio_lock is not None:
+            return asyncio_lock
+
+        logger.debug('ReAwaitable: asyncio.Lock unavailable, trying trio')
+
+        # Try trio
+        trio_lock = self._try_trio_lock(logger)
+        if trio_lock is not None:
+            return trio_lock
+
+        logger.debug('ReAwaitable: trio.Lock unavailable, trying anyio')
+
+        # Try anyio
+        anyio_lock = self._try_anyio_lock(logger)
+        if anyio_lock is not None:
+            return anyio_lock
+
+        logger.debug(
+            'ReAwaitable: anyio.Lock unavailable, '
+            'falling back to threading.Lock'
+        )
+
+        # Fallback to threading lock
+        threading_lock = threading.Lock()
+        logger.debug(
+            'ReAwaitable: Using threading.Lock fallback for concurrency control'
+        )
+        return threading_lock
+
     async def _awaitable(self) -> _ValueType:
         """Caches the once awaited value forever."""
-        if self._cache is _sentinel:
-            self._cache = await self._coro
+        if self._cache is not _sentinel:
+            return self._cache  # type: ignore
+
+        # Create lock on first use to detect the async framework
+        if self._lock is None:
+            self._lock = self._create_lock()
+
+        # Handle different lock types
+        if hasattr(self._lock, '__aenter__'):
+            # Async lock (asyncio, trio, anyio)
+            async with self._lock:
+                if self._cache is _sentinel:
+                    self._cache = await self._coro
+        else:
+            # Threading lock fallback for unsupported frameworks
+            with self._lock:
+                if self._cache is _sentinel:
+                    self._cache = await self._coro
+
         return self._cache  # type: ignore
 
 

setup.cfg

@@ -105,6 +105,12 @@ addopts =
   --cov-fail-under=100
   # pytest-mypy-plugin:
   --mypy-ini-file=setup.cfg
+  # pytest-asyncio:
+  --asyncio-mode=auto
+
+# Registered markers:
+markers =
+  asyncio: mark test as asynchronous
 
 # Ignores some warnings inside:
 filterwarnings =

tests/test_contrib/test_hypothesis/test_laws/__init__.py

@@ -0,0 +1 @@
+# Empty init file for test module

tests/test_contrib/test_hypothesis/test_laws/test_user_specified_strategy.py

@@ -1,11 +1,14 @@
+from hypothesis import HealthCheck
 from hypothesis import strategies as st
-from test_hypothesis.test_laws import test_custom_type_applicative
 
 from returns.contrib.hypothesis.laws import check_all_laws
 
+from . import test_custom_type_applicative  # noqa: WPS300
+
 container_type = test_custom_type_applicative._Wrapper  # noqa: SLF001
 
 check_all_laws(
     container_type,
     container_strategy=st.builds(container_type, st.integers()),
+    settings_kwargs={'suppress_health_check': [HealthCheck.too_slow]},
 )

tests/test_primitives/test_reawaitable/__init__.py

@@ -0,0 +1 @@
+# Empty init file for test module