1 files changed, 77 insertions, 0 deletions
diff --git a/nixos/lib/test-driver/test_driver/polling_condition.py b/nixos/lib/test-driver/test_driver/polling_condition.py
new file mode 100644
index 00000000000..459845452fa
--- /dev/null
+++ b/nixos/lib/test-driver/test_driver/polling_condition.py
@@ -0,0 +1,77 @@
+from typing import Callable, Optional
+import time
+
+from .logger import rootlog
+
+
+class PollingConditionFailed(Exception):
+    pass
+
+
+class PollingCondition:
+    condition: Callable[[], bool]
+    seconds_interval: float
+    description: Optional[str]
+
+    last_called: float
+    entered: bool
+
+    def __init__(
+        self,
+        condition: Callable[[], Optional[bool]],
+        seconds_interval: float = 2.0,
+        description: Optional[str] = None,
+    ):
+        self.condition = condition  # type: ignore
+        self.seconds_interval = seconds_interval
+
+        if description is None:
+            if condition.__doc__:
+                self.description = condition.__doc__
+            else:
+                self.description = condition.__name__
+        else:
+            self.description = str(description)
+
+        self.last_called = float("-inf")
+        self.entered = False
+
+    def check(self) -> bool:
+        if self.entered or not self.overdue:
+            return True
+
+        with self, rootlog.nested(self.nested_message):
+            rootlog.info(f"Time since last: {time.monotonic() - self.last_called:.2f}s")
+            try:
+                res = self.condition()  # type: ignore
+            except Exception:
+                res = False
+            res = res is None or res
+            rootlog.info(self.status_message(res))
+            return res
+
+    def maybe_raise(self) -> None:
+        if not self.check():
+            raise PollingConditionFailed(self.status_message(False))
+
+    def status_message(self, status: bool) -> str:
+        return f"Polling condition {'succeeded' if status else 'failed'}: {self.description}"
+
+    @property
+    def nested_message(self) -> str:
+        nested_message = ["Checking polling condition"]
+        if self.description is not None:
+            nested_message.append(repr(self.description))
+
+        return " ".join(nested_message)
+
+    @property
+    def overdue(self) -> bool:
+        return self.last_called + self.seconds_interval < time.monotonic()
+
+    def __enter__(self) -> None:
+        self.entered = True
+
+    def __exit__(self, exc_type, exc_value, traceback) -> None:  # type: ignore
+        self.entered = False
+        self.last_called = time.monotonic()