Make ring buf api use pickle-able RBToken

tests/test_ringbuf.py

@@ -92,8 +92,10 @@ def test_ringbuf(
     buf_size: int
 ):
     async def main():
-
-        with open_ringbuf('test_ringbuf') as token:
+        with open_ringbuf(
+            'test_ringbuf',
+            buf_size=buf_size
+        ) as token:
             proc_kwargs = {
                 'pass_fds': (token.write_eventfd, token.wrap_eventfd)
             }

tractor/ipc/_ringbuf.py

@@ -58,15 +58,22 @@ class RBToken(Struct, frozen=True):
 @cm
 def open_ringbuf(
     shm_name: str,
+    buf_size: int = 10 * 1024,
     write_efd_flags: int = 0,
     wrap_efd_flags: int = 0
 ) -> RBToken:
+    shm = SharedMemory(
+        name=shm_name,
+        size=buf_size,
+        create=True
+    )
     token = RBToken(
         shm_name=shm_name,
         write_eventfd=open_eventfd(flags=write_efd_flags),
         wrap_eventfd=open_eventfd(flags=wrap_efd_flags)
     )
     yield token
+    shm.close()
 
 
 class RingBuffSender(trio.abc.SendStream):
@@ -82,18 +89,16 @@ class RingBuffSender(trio.abc.SendStream):
         token: RBToken,
         start_ptr: int = 0,
         buf_size: int = 10 * 1024,
-        unlink_on_exit: bool = False
     ):
         token = RBToken.from_msg(token)
         self._shm = SharedMemory(
             name=token.shm_name,
             size=buf_size,
-            create=True
+            create=False
         )
         self._write_event = EventFD(token.write_eventfd, 'w')
         self._wrap_event = EventFD(token.wrap_eventfd, 'r')
         self._ptr = start_ptr
-        self.unlink_on_exit = unlink_on_exit
 
     @property
     def key(self) -> str:
@@ -142,11 +147,7 @@ class RingBuffSender(trio.abc.SendStream):
     async def aclose(self):
         self._write_event.close()
         self._wrap_event.close()
-        if self.unlink_on_exit:
-            self._shm.unlink()
-
-        else:
-            self._shm.close()
+        self._shm.close()
 
     async def __aenter__(self):
         self._write_event.open()