Add connectionCreationFailing and circuitBreak states to ConnectionPool (#610)

Author: adam-fowler

Sources/ConnectionPoolModule/ConnectionPool.swift

@@ -116,6 +116,10 @@ public struct ConnectionPoolConfiguration: Sendable {
     /// become idle.
     public var maximumConnectionHardLimit: Int
 
+    /// The amount of time to pass between the first failed connection
+    /// before triggering the circuit breaker.
+    public var circuitBreakerTripAfter: Duration
+
     /// The time that a _preserved_ idle connection stays in the
     /// pool before it is closed.
     public var idleTimeout: Duration
@@ -125,6 +129,7 @@ public struct ConnectionPoolConfiguration: Sendable {
         self.minimumConnectionCount = 0
         self.maximumConnectionSoftLimit = 16
         self.maximumConnectionHardLimit = 16
+        self.circuitBreakerTripAfter = .seconds(60)
         self.idleTimeout = .seconds(60)
     }
 }
@@ -151,7 +156,7 @@ public final class ConnectionPool<
     public typealias ConnectionFactory = @Sendable (ConnectionID, ConnectionPool<Connection, ConnectionID, ConnectionIDGenerator, Request, RequestID, KeepAliveBehavior, ObservabilityDelegate, Clock>) async throws -> ConnectionAndMetadata<Connection>
 
     @usableFromInline
-    typealias StateMachine = PoolStateMachine<Connection, ConnectionIDGenerator, ConnectionID, Request, Request.ID, CheckedContinuation<Void, Never>>
+    typealias StateMachine = PoolStateMachine<Connection, ConnectionIDGenerator, ConnectionID, Request, Request.ID, CheckedContinuation<Void, Never>, Clock, Clock.Instant>
 
     @usableFromInline
     let factory: ConnectionFactory
@@ -203,7 +208,8 @@ public final class ConnectionPool<
         var stateMachine = StateMachine(
             configuration: .init(configuration, keepAliveBehavior: keepAliveBehavior),
             generator: idGenerator,
-            timerCancellationTokenType: CheckedContinuation<Void, Never>.self
+            timerCancellationTokenType: CheckedContinuation<Void, Never>.self,
+            clock: clock
         )
 
         let (stream, continuation) = AsyncStream.makeStream(of: NewPoolActions.self)
@@ -574,6 +580,7 @@ extension PoolConfiguration {
         self.maximumConnectionHardLimit = configuration.maximumConnectionHardLimit
         self.keepAliveDuration = keepAliveBehavior.keepAliveFrequency
         self.idleTimeoutDuration = configuration.idleTimeout
+        self.circuitBreakerTripAfter = configuration.circuitBreakerTripAfter
     }
 }
 

Sources/ConnectionPoolModule/ConnectionPoolError.swift

@@ -4,6 +4,7 @@ public struct ConnectionPoolError: Error, Hashable {
     enum Base: Error, Hashable, Sendable {
         case requestCancelled
         case poolShutdown
+        case connectionCreationCircuitBreakerTripped
     }
 
     @usableFromInline
@@ -22,4 +23,9 @@ public struct ConnectionPoolError: Error, Hashable {
     public static var poolShutdown: Self {
         ConnectionPoolError(.poolShutdown)
     }
+    /// The connection pool has failed to make a connection after a defined time
+    @inlinable
+    public static var connectionCreationCircuitBreakerTripped: Self {
+        ConnectionPoolError(.connectionCreationCircuitBreakerTripped)
+    }
 }