shm_status: implement a robust shm connect method

src/otaclient_common/shm_status.py

@@ -70,6 +70,21 @@ def verify_msg(self, _raw_msg: bytes, _expected_hmac: bytes) -> bool:
         )
 
 
+def _ensure_connect_shm(
+    name: str, *, max_retry: int, retry_interval: int
+) -> mp_shm.SharedMemory:
+    for _idx in range(max_retry):
+        try:
+            return mp_shm.SharedMemory(name=name, create=False)
+        except Exception as e:
+            logger.warning(
+                f"retry #{_idx}: failed to connect to {name=}: {e!r}, keep retrying ..."
+            )
+            time.sleep(retry_interval)
+    else:
+        raise ValueError(f"failed to connect share memory with {name=}")
+
+
 class MPSharedStatusReader(SHA512Verifier, Generic[T]):
 
     def __init__(
@@ -80,18 +95,9 @@ def __init__(
         max_retry: int = 6,
         retry_interval: int = 1,
     ) -> None:
-        for _idx in range(max_retry):
-            try:
-                self._shm = shm = mp_shm.SharedMemory(name=name, create=False)
-                break
-            except Exception as e:
-                logger.warning(
-                    f"retry #{_idx}: failed to connect to {name=}: {e!r}, keep retrying ..."
-                )
-                time.sleep(retry_interval)
-        else:
-            raise ValueError(f"failed to connect share memory with {name=}")
-
+        self._shm = shm = _ensure_connect_shm(
+            name, max_retry=max_retry, retry_interval=retry_interval
+        )
         self.mem_size = size = shm.size
         self.msg_max_size = size - self.MIN_ENCAP_MSG_LEN
         self._key = key
@@ -141,23 +147,30 @@ def __init__(
         *,
         name: str | None = None,
         size: int = 0,
+        key: bytes,
         create: bool = False,
         msg_max_size: int | None = None,
-        key: bytes,
+        max_retry: int = 6,
+        retry_interval: int = 1,
     ) -> None:
         if create:
             _msg_max_size = size - self.MIN_ENCAP_MSG_LEN
             if _msg_max_size < 0:
                 raise ValueError(f"{size=} < {self.MIN_ENCAP_MSG_LEN=}")
             self._shm = shm = mp_shm.SharedMemory(name=name, size=size, create=True)
             self.mem_size = shm.size
-        else:
-            self._shm = shm = mp_shm.SharedMemory(name=name, create=False)
+
+        elif name:
+            self._shm = shm = _ensure_connect_shm(
+                name, max_retry=max_retry, retry_interval=retry_interval
+            )
             self.mem_size = size = shm.size
             _msg_max_size = size - self.MIN_ENCAP_MSG_LEN
             if _msg_max_size < 0:
                 shm.close()
                 raise ValueError(f"{size=} < {self.MIN_ENCAP_MSG_LEN=}")
+        else:
+            raise ValueError("<name> must be specified if <create> is False")
 
         self.name = shm.name
         self._key = key