Add Event Loop pattern

Author: everysoftware

src/behavioral/generator.py

@@ -11,7 +11,6 @@
 
 from __future__ import annotations
 
-import io
 from abc import ABC, abstractmethod
 from sqlite3 import Connection
 from types import TracebackType
@@ -20,22 +19,6 @@
 from src.behavioral.iterator import Iterator
 
 
-class Generator[YieldT, SendT, ReturnT](Iterator[YieldT], ABC):
-    @abstractmethod
-    def send(self, value: SendT) -> YieldT: ...
-
-    @abstractmethod
-    def throw(
-        self,
-        exc_type: type[BaseException],
-        exc_val: BaseException | None = None,
-        tb: TracebackType | None = None,
-    ) -> Self: ...
-
-    @abstractmethod
-    def close(self) -> None: ...
-
-
 # Basic usage
 
 
@@ -72,9 +55,50 @@ def gen_sum() -> PythonGenerator[int, int, int]:
             return total
 
 
+class CommitException(Exception):
+    pass
+
+
+class AbortException(Exception):
+    pass
+
+
+def db_session(
+    db: Connection, sql: str
+) -> PythonGenerator[None, tuple[Any, ...], None]:
+    cursor = db.cursor()
+    try:
+        while True:
+            try:
+                row = yield
+                cursor.execute(sql, row)
+            except CommitException:
+                db.commit()
+            except AbortException:
+                db.rollback()
+    finally:
+        db.rollback()
+
+
 # Class-based generator
 
 
+class Generator[YieldT, SendT, ReturnT](Iterator[YieldT], ABC):
+    @abstractmethod
+    def send(self, value: SendT) -> YieldT: ...
+
+    @abstractmethod
+    def throw(
+        self,
+        exc_type: type[BaseException],
+        exc_val: BaseException | None = None,
+        tb: TracebackType | None = None,
+    ) -> Self: ...
+
+    @abstractmethod
+    def close(self) -> None: ...
+
+
 class SumGenerator(Generator[int, int, int]):
     def __init__(self) -> None:
         self._total = 0
@@ -102,43 +126,3 @@ def __iter__(self) -> SumGenerator:
 
     def __next__(self) -> int:
         return self.send(0)
-
-
-def gen_line(
-    output: io.StringIO, state: dict[str, Any]
-) -> PythonGenerator[str, None, None]:
-    # lines
-    try:
-        while True:
-            line = output.readline().rstrip()
-            if not line:
-                break
-            yield line
-    finally:
-        state["closed"] = True
-        output.close()
-
-
-class CommitException(Exception):
-    pass
-
-
-class AbortException(Exception):
-    pass
-
-
-def db_session(
-    db: Connection, sql: str
-) -> PythonGenerator[None, tuple[Any, ...], None]:
-    cursor = db.cursor()
-    try:
-        while True:
-            try:
-                row = yield
-                cursor.execute(sql, row)
-            except CommitException:
-                db.commit()
-            except AbortException:
-                db.rollback()
-    finally:
-        db.rollback()

src/concurrency/patterns/active_object.py renamed to src/concurrency/examples/coroutines_sleep.py

@@ -0,0 +1 @@
+# @coroutine decorator as asyncio.run

src/concurrency/examples/generators_sleep.py

@@ -0,0 +1,17 @@
+from abc import abstractmethod, ABC
+from typing import Any, Generator
+
+
+GeneratorCoroutine = Generator
+
+
+class Awaitable[T](ABC):
+    @abstractmethod
+    def __await__(self) -> Generator[Any, Any, T]: ...
+
+
+class AwaitableCoroutine[YieldT, SendT, ReturnT](
+    Awaitable[ReturnT], Generator[YieldT, SendT, ReturnT], ABC
+):
+    @abstractmethod
+    def __await__(self) -> Generator[YieldT, SendT, ReturnT]: ...

src/concurrency/patterns/asyncio.py

@@ -1 +1,99 @@
-# https://medium.com/@pekelny/fake-event-loop-python3-7498761af5e0
+"""
+Event Loop is a concurrency design pattern that is used to handle asynchronous events in a program. It is a loop that
+listens for events and then triggers the appropriate event handlers. The Event Loop pattern is commonly used in GUI
+applications, web servers, and other programs that need to handle multiple events simultaneously.
+
+A Task is a subclass of Future that represents a coroutine that is running in the event loop. It is used to
+manage the execution of the coroutine and handle its result.
+"""
+
+from __future__ import annotations
+
+import logging
+from queue import Queue
+from typing import Any
+
+from src.concurrency.patterns.coroutine import GeneratorCoroutine
+from src.concurrency.patterns.future import Future
+
+logger = logging.getLogger(__name__)
+
+
+class Task[T](Future[T]):
+    def __init__(
+        self, gen: GeneratorCoroutine[Any, Any, T], loop: EventLoop
+    ) -> None:
+        super().__init__()
+        self.gen: GeneratorCoroutine[Any, Any, T] = gen
+        self.loop: EventLoop = loop
+        loop.put(self)
+
+    def step(self, value: Any = None) -> None:
+        # Resume the coroutine
+        try:
+            yielded = self.gen.send(value)
+            # If the coroutine yielded a Future, add a callback to resume the coroutine when the Future is done
+            if isinstance(yielded, Future):
+                yielded.add_done_callback(lambda fut: self.step(fut.result()))
+            else:
+                self.loop.put(self)
+        # Coroutine has finished
+        except StopIteration as e:
+            self.set_result(e.value)
+        # Coroutine raised an exception
+        except Exception as e:
+            self.set_exception(e)
+
+
+class EventLoop:
+    def __init__(self) -> None:
+        self.q: Queue[Task[Any]] = Queue()
+
+    def put(self, task: Task[Any]) -> None:
+        self.q.put(task)
+
+    def run_until_complete[T](
+        self, coro: GeneratorCoroutine[Any, Any, T]
+    ) -> T:
+        task = create_task(coro)
+        while not task.done():
+            if not self.q.empty():
+                next_task = self.q.get()
+                next_task.step()
+        return task.result()
+
+    def close(self) -> None:
+        self.q.queue.clear()
+
+
+running_loop: EventLoop | None = None
+
+
+def new_event_loop() -> EventLoop:
+    return EventLoop()
+
+
+def get_running_loop() -> EventLoop | None:
+    return running_loop
+
+
+def get_event_loop() -> EventLoop:
+    loop = get_running_loop()
+    if loop is not None:
+        return loop
+    return new_event_loop()
+
+
+def create_task[T](coro: GeneratorCoroutine[Any, Any, T]) -> Task[T]:
+    return Task(coro, get_event_loop())
+
+
+def run[T](coro: GeneratorCoroutine[Any, Any, T]) -> T:
+    global running_loop
+    loop = get_event_loop()
+    running_loop = loop
+    try:
+        return loop.run_until_complete(coro)
+    finally:
+        running_loop = None
+        loop.close()

src/concurrency/patterns/coroutine.py

@@ -0,0 +1,53 @@
+"""
+A Future is an object that represents the result of an asynchronous operation. It is used to store the result
+    of the operation and notify the caller when the operation is complete.
+"""
+
+from __future__ import annotations
+
+from typing import Callable, Generator
+from src.concurrency.patterns.coroutine import Awaitable
+
+
+class Future[T](Awaitable[T]):
+    def __init__(self) -> None:
+        self._done: bool = False
+        self._result: T | None = None
+        self._exception: BaseException | None = None
+        self._callbacks: list[Callable[[Future[T]], None]] = []
+
+    def done(self) -> bool:
+        return self._done
+
+    def result(self) -> T:
+        if not self._done:
+            raise RuntimeError("Future is not done yet")
+        if self._exception:
+            raise self._exception
+        return self._result  # type: ignore
+
+    def set_result(self, result: T) -> None:
+        self._result = result
+        self._done = True
+        self._schedule_callbacks()
+
+    def set_exception(self, exception: BaseException) -> None:
+        self._exception = exception
+        self._done = True
+        self._schedule_callbacks()
+
+    def add_done_callback(self, callback: Callable[[Future[T]], None]) -> None:
+        self._callbacks.append(callback)
+        if self._done:
+            self._schedule_callbacks()
+
+    def _schedule_callbacks(self) -> None:
+        for callback in self._callbacks:
+            callback(self)
+
+    def __await__(self) -> Generator[Future[T], None, T]:
+        if not self._done:
+            yield self
+        return self.result()
+
+    __iter__ = __await__