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venv/lib/python3.12/site-packages/redis/multidb/failure_detector.py

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+import math
+import threading
+from abc import ABC, abstractmethod
+from datetime import datetime, timedelta
+from typing import List, Optional, Type
+
+from redis.multidb.circuit import State as CBState
+
+DEFAULT_MIN_NUM_FAILURES = 1000
+DEFAULT_FAILURE_RATE_THRESHOLD = 0.1
+DEFAULT_FAILURES_DETECTION_WINDOW = 2
+
+
+class FailureDetector(ABC):
+    @abstractmethod
+    def register_failure(self, exception: Exception, cmd: tuple) -> None:
+        """Register a failure that occurred during command execution."""
+        pass
+
+    @abstractmethod
+    def register_command_execution(self, cmd: tuple) -> None:
+        """Register a command execution."""
+        pass
+
+    @abstractmethod
+    def set_command_executor(self, command_executor) -> None:
+        """Set the command executor for this failure."""
+        pass
+
+
+class CommandFailureDetector(FailureDetector):
+    """
+    Detects a failure based on a threshold of failed commands during a specific period of time.
+    """
+
+    def __init__(
+        self,
+        min_num_failures: int = DEFAULT_MIN_NUM_FAILURES,
+        failure_rate_threshold: float = DEFAULT_FAILURE_RATE_THRESHOLD,
+        failure_detection_window: float = DEFAULT_FAILURES_DETECTION_WINDOW,
+        error_types: Optional[List[Type[Exception]]] = None,
+    ) -> None:
+        """
+        Initialize a new CommandFailureDetector instance.
+
+        Args:
+            min_num_failures: Minimal count of failures required for failover
+            failure_rate_threshold: Percentage of failures required for failover
+            failure_detection_window: Time interval for executing health checks.
+            error_types: Optional list of exception types to trigger failover. If None, all exceptions are counted.
+
+        The detector tracks command failures within a sliding time window. When the number of failures
+        exceeds the threshold within the specified duration, it triggers failure detection.
+        """
+        self._command_executor = None
+        self._min_num_failures = min_num_failures
+        self._failure_rate_threshold = failure_rate_threshold
+        self._failure_detection_window = failure_detection_window
+        self._error_types = error_types
+        self._commands_executed: int = 0
+        self._start_time: datetime = datetime.now()
+        self._end_time: datetime = self._start_time + timedelta(
+            seconds=self._failure_detection_window
+        )
+        self._failures_count: int = 0
+        self._lock = threading.RLock()
+
+    def register_failure(self, exception: Exception, cmd: tuple) -> None:
+        with self._lock:
+            if self._error_types:
+                if type(exception) in self._error_types:
+                    self._failures_count += 1
+            else:
+                self._failures_count += 1
+
+            self._check_threshold()
+
+    def set_command_executor(self, command_executor) -> None:
+        self._command_executor = command_executor
+
+    def register_command_execution(self, cmd: tuple) -> None:
+        with self._lock:
+            if not self._start_time < datetime.now() < self._end_time:
+                self._reset()
+
+            self._commands_executed += 1
+
+    def _check_threshold(self):
+        if self._failures_count >= self._min_num_failures and self._failures_count >= (
+            math.ceil(self._commands_executed * self._failure_rate_threshold)
+        ):
+            self._command_executor.active_database.circuit.state = CBState.OPEN
+            self._reset()
+
+    def _reset(self) -> None:
+        with self._lock:
+            self._start_time = datetime.now()
+            self._end_time = self._start_time + timedelta(
+                seconds=self._failure_detection_window
+            )
+            self._failures_count = 0
+            self._commands_executed = 0