Zo doen wijdat in oost

devplacepy/services/nodes/circuit.py

@@ -0,0 +1,71 @@
+# retoor <retoor@molodetz.nl>
+
+from __future__ import annotations
+
+import time
+from dataclasses import dataclass
+from typing import Callable, Hashable
+
+from devplacepy.services.nodes.spec import SPEC
+
+LIMITS = SPEC.limits
+
+CLOSED = "closed"
+OPEN = "open"
+HALF_OPEN = "half_open"
+
+
+@dataclass
+class _Circuit:
+    failures: int = 0
+    opened_at: float = 0.0
+    probing: bool = False
+
+
+class CircuitBreaker:
+    def __init__(
+        self,
+        failures: int = LIMITS.breaker_failures,
+        open_seconds: float = LIMITS.breaker_open_seconds,
+        clock: Callable[[], float] = time.monotonic,
+    ) -> None:
+        self.failures = max(1, failures)
+        self.open_seconds = open_seconds
+        self._clock = clock
+        self._circuits: dict[Hashable, _Circuit] = {}
+
+    def state(self, key: Hashable) -> str:
+        circuit = self._circuits.get(key)
+        if circuit is None or circuit.failures < self.failures:
+            return CLOSED
+        if self._clock() - circuit.opened_at < self.open_seconds:
+            return OPEN
+        return HALF_OPEN
+
+    def allows(self, key: Hashable) -> bool:
+        state = self.state(key)
+        if state == CLOSED:
+            return True
+        if state == OPEN:
+            return False
+        return not self._circuits[key].probing
+
+    def begin(self, key: Hashable) -> None:
+        if self.state(key) == HALF_OPEN:
+            self._circuits[key].probing = True
+
+    def success(self, key: Hashable) -> None:
+        self._circuits.pop(key, None)
+
+    def failure(self, key: Hashable) -> None:
+        circuit = self._circuits.setdefault(key, _Circuit())
+        circuit.probing = False
+        circuit.failures += 1
+        if circuit.failures >= self.failures:
+            circuit.opened_at = self._clock()
+
+    def forget(self, key: Hashable) -> None:
+        self._circuits.pop(key, None)
+
+    def open_count(self) -> int:
+        return sum(1 for key in list(self._circuits) if self.state(key) != CLOSED)