From 2bf8ce84cfa548ec51702e693b0bb997241c989d Mon Sep 17 00:00:00 2001
From: Guillermo Rodriguez <guillermo@telos.net>
Date: Sun, 6 Apr 2025 21:04:18 -0300
Subject: [PATCH] Add trio resource semantics to eventfd

---
 tests/test_eventfd.py    | 42 ++++++++++++++++++++++++++++++++++++----
 tractor/linux/eventfd.py | 39 +++++++++++++++++++++++++++----------
 2 files changed, 67 insertions(+), 14 deletions(-)

diff --git a/tests/test_eventfd.py b/tests/test_eventfd.py
index 3d757169..3432048b 100644
--- a/tests/test_eventfd.py
+++ b/tests/test_eventfd.py
@@ -1,13 +1,13 @@
 import trio
 import pytest
-from tractor.ipc import (
+from tractor.linux.eventfd import (
     open_eventfd,
     EFDReadCancelled,
     EventFD
 )
 
 
-def test_eventfd_read_cancellation():
+def test_read_cancellation():
     '''
     Ensure EventFD.read raises EFDReadCancelled if EventFD.close()
     is called.
@@ -15,7 +15,7 @@ def test_eventfd_read_cancellation():
     '''
     fd = open_eventfd()
 
-    async def _read(event: EventFD):
+    async def bg_read(event: EventFD):
         with pytest.raises(EFDReadCancelled):
             await event.read()
 
@@ -25,8 +25,42 @@ def test_eventfd_read_cancellation():
                 EventFD(fd, 'w') as event,
                 trio.fail_after(3)
             ):
-                n.start_soon(_read, event)
+                n.start_soon(bg_read, event)
                 await trio.sleep(0.2)
                 event.close()
 
     trio.run(main)
+
+
+def test_read_trio_semantics():
+    '''
+    Ensure EventFD.read raises trio.ClosedResourceError and
+    trio.BusyResourceError.
+
+    '''
+
+    fd = open_eventfd()
+
+    async def bg_read(event: EventFD):
+        try:
+            await event.read()
+
+        except EFDReadCancelled:
+            ...
+
+    async def main():
+        async with trio.open_nursery() as n:
+
+            # start background read and attempt
+            # foreground read, should be busy
+            with EventFD(fd, 'w') as event:
+                n.start_soon(bg_read, event)
+                await trio.sleep(0.2)
+                with pytest.raises(trio.BusyResourceError):
+                    await event.read()
+
+            # attempt read after close
+            with pytest.raises(trio.ClosedResourceError):
+                await event.read()
+
+    trio.run(main)
diff --git a/tractor/linux/eventfd.py b/tractor/linux/eventfd.py
index f262c051..8ddf3669 100644
--- a/tractor/linux/eventfd.py
+++ b/tractor/linux/eventfd.py
@@ -129,12 +129,21 @@ class EventFD:
         self._omode: str = omode
         self._fobj = None
         self._cscope: trio.CancelScope | None = None
+        self._is_closed: bool = True
+        self._read_lock = trio.StrictFIFOLock()
+
+    @property
+    def closed(self) -> bool:
+        return self._is_closed
 
     @property
     def fd(self) -> int | None:
         return self._fd
 
     def write(self, value: int) -> int:
+        if self.closed:
+            raise trio.ClosedResourceError
+
         return write_eventfd(self._fd, value)
 
     async def read(self) -> int:
@@ -145,19 +154,26 @@ class EventFD:
         in order to make it cancellable when `self.close()` is called.
 
         '''
-        self._cscope = trio.CancelScope()
-        with self._cscope:
-            return await trio.to_thread.run_sync(
-                read_eventfd, self._fd,
-                abandon_on_cancel=True
-            )
+        if self.closed:
+            raise trio.ClosedResourceError
 
-        if self._cscope.cancelled_caught:
-            raise EFDReadCancelled
+        if self._read_lock.locked():
+            raise trio.BusyResourceError
 
-        self._cscope = None
+        async with self._read_lock:
+            self._cscope = trio.CancelScope()
+            with self._cscope:
+                return await trio.to_thread.run_sync(
+                    read_eventfd, self._fd,
+                    abandon_on_cancel=True
+                )
 
-    def read_direct(self) -> int:
+            if self._cscope.cancelled_caught:
+                raise EFDReadCancelled
+
+            self._cscope = None
+
+    def read_nowait(self) -> int:
         '''
         Direct call to `read_eventfd(self.fd)`, unless `eventfd` was
         opened with `EFD_NONBLOCK` its gonna block the thread.
@@ -167,6 +183,7 @@ class EventFD:
 
     def open(self):
         self._fobj = os.fdopen(self._fd, self._omode)
+        self._is_closed = False
 
     def close(self):
         if self._fobj:
@@ -179,6 +196,8 @@ class EventFD:
         if self._cscope:
             self._cscope.cancel()
 
+        self._is_closed = True
+
     def __enter__(self):
         self.open()
         return self