connection updates

DBSyn/DatabaseModel.swift

@@ -683,6 +683,7 @@ final class DatabaseModel: ObservableObject {
         saveActiveQuery()
         if let oldID = selectedID { NativeMySQLRunner.disconnect(profileID: oldID) }
         result = QueryResult()
+        isRunning = false
         selectedID = id
         UserDefaults.standard.set(id.uuidString, forKey: "DBSyn.selectedConnectionID")
         selectedDatabase = profile.database
@@ -887,7 +888,7 @@ final class DatabaseModel: ObservableObject {
                         introspect(database: usedSchema)
                     }
                 }
-                guard selectedID == profile.id else { isRunning = false; return }
+                guard selectedID == profile.id else { return }
                 if listingDatabases {
                     databases = lastResult.rows.compactMap { $0.first }
                     status = "Connected to \(profile.name)"
@@ -914,7 +915,7 @@ final class DatabaseModel: ObservableObject {
             if !listingDatabases {
                 queryDurationText = String(format: "%.3f s", Date().timeIntervalSince(queryStarted))
             }
-            isRunning = false
+            if selectedID == profile.id { isRunning = false }
         }
     }
 

DBSyn/MySQLProtocol.swift

@@ -437,40 +437,78 @@ private final class PersistentMySQLSessions {
         let connection: MySQLWireConnection
     }
 
-    private let queue = DispatchQueue(label: "DBSyn.MySQLSessions")
-    private var connections: [UUID: Entry] = [:]
+    // Each profile has its own serial executor. An unreachable server cannot
+    // block requests to any other saved connection.
+    private final class SessionSlot {
+        let queue: DispatchQueue
+        var entry: Entry?
+        // Only accessed on queue except generation, which is lock protected.
+        private let generationLock = NSLock()
+        private var currentGeneration: UInt64 = 0
+
+        init(id: UUID) {
+            queue = DispatchQueue(label: "DBSyn.MySQLSession.\(id.uuidString)")
+        }
+        func generation() -> UInt64 {
+            generationLock.lock(); defer { generationLock.unlock() }
+            return currentGeneration
+        }
+        func invalidate() {
+            generationLock.lock(); currentGeneration &+= 1; generationLock.unlock()
+        }
+    }
+
+    private let slotsLock = NSLock()
+    private var slots: [UUID: SessionSlot] = [:]
+
+    private func slot(for id: UUID) -> SessionSlot {
+        slotsLock.lock(); defer { slotsLock.unlock() }
+        if let existing = slots[id] { return existing }
+        let created = SessionSlot(id: id)
+        slots[id] = created
+        return created
+    }
 
     func execute(profile: ConnectionProfile, database: String,
                  password: String, sql: String) throws -> QueryResult {
-        try queue.sync {
-            // A changed connection profile or password requires a new session.
-            if let previous = connections[profile.id],
-               (previous.profile != profile || previous.password != password) {
-                connections.removeValue(forKey: profile.id)
+        let session = slot(for: profile.id)
+        let expectedGeneration = session.generation()
+        return try session.queue.sync {
+            guard session.generation() == expectedGeneration else {
+                throw MySQLWireError(message: "Connection request superseded")
             }
-
-            if connections[profile.id] == nil {
+            if let previous = session.entry,
+               (previous.profile != profile || previous.password != password) {
+                session.entry = nil
+                DBSynSSHTunnels.shared.stop(profile.id)
+            }
+            if session.entry == nil {
                 let endpoint = try DBSynSSHTunnels.shared.endpoint(for: profile)
-                let connection = try MySQLWireConnection(host: endpoint.0, port: endpoint.1, requireTLS: !profile.useSSHTunnel && profile.useTLS && !["127.0.0.1", "localhost", "::1"].contains(endpoint.0.lowercased()))
+                let connection = try MySQLWireConnection(
+                    host: endpoint.0, port: endpoint.1,
+                    requireTLS: !profile.useSSHTunnel && profile.useTLS &&
+                        !["127.0.0.1", "localhost", "::1"].contains(endpoint.0.lowercased())
+                )
                 connection.markHost(endpoint.0)
                 try connection.authenticate(user: profile.username,
                                             password: password, database: database)
-                connections[profile.id] = Entry(profile: profile,
-                                                password: password,
-                                                connection: connection)
+                guard session.generation() == expectedGeneration else {
+                    throw MySQLWireError(message: "Connection request superseded")
+                }
+                session.entry = Entry(profile: profile, password: password,
+                                      connection: connection)
             }
-
-            guard let entry = connections[profile.id] else {
+            guard let entry = session.entry else {
                 throw MySQLWireError(message: "MySQL session was not created")
             }
             do {
-                // Crucially, no new authentication takes place here. USE,
-                // session variables and transactions survive between queries.
-                return try entry.connection.query(sql)
+                let result = try entry.connection.query(sql)
+                guard session.generation() == expectedGeneration else {
+                    throw MySQLWireError(message: "Connection request superseded")
+                }
+                return result
             } catch {
-                // The wire protocol can be out of sync after a failed query.
-                // Discard it rather than silently issuing commands on a bad socket.
-                connections.removeValue(forKey: profile.id)
+                session.entry = nil
                 throw error
             }
         }
@@ -479,23 +517,36 @@ private final class PersistentMySQLSessions {
     func stream(profile: ConnectionProfile, database: String,
                 password: String, sql: String,
                 onRow: (String) throws -> Void) throws -> Int64 {
-        try queue.sync {
-            guard let entry = connections[profile.id],
+        let session = slot(for: profile.id)
+        let expectedGeneration = session.generation()
+        return try session.queue.sync {
+            guard session.generation() == expectedGeneration,
+                  let entry = session.entry,
                   entry.profile == profile, entry.password == password else {
                 throw MySQLWireError(message: "Export session is no longer connected")
             }
             do {
-                return try entry.connection.streamFirstColumn(sql, onRow: onRow)
+                return try entry.connection.streamFirstColumn(sql, onRow: { row in
+                    guard session.generation() == expectedGeneration else {
+                        throw MySQLWireError(message: "Export cancelled: connection switched")
+                    }
+                    try onRow(row)
+                })
             } catch {
-                connections.removeValue(forKey: profile.id)
+                session.entry = nil
                 throw error
             }
         }
     }
 
     func disconnect(profileID: UUID) {
-        queue.sync { _ = connections.removeValue(forKey: profileID) }
-        DBSynSSHTunnels.shared.stop(profileID)
+        let session = slot(for: profileID)
+        // Invalidate immediately without waiting for a blocked network read.
+        session.invalidate()
+        session.queue.async {
+            session.entry = nil
+            DBSynSSHTunnels.shared.stop(profileID)
+        }
     }
 }
 
@@ -526,8 +577,6 @@ enum NativeMySQLRunner {
     // Connection shutdown may wait behind a slow network operation on the
     // session's serial queue. Never make the SwiftUI main thread wait for it.
     static func disconnect(profileID: UUID) {
-        Task.detached(priority: .utility) {
-            PersistentMySQLSessions.shared.disconnect(profileID: profileID)
-        }
+        PersistentMySQLSessions.shared.disconnect(profileID: profileID)
     }
 }