groue · groue · Aug 25, 2024 · Feb 11, 2024
diff --git a/GRDB.xcodeproj/project.pbxproj b/GRDB.xcodeproj/project.pbxproj
@@ -105,6 +105,7 @@
 		563C67B324628BEA00E94EDC /* DatabasePoolTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 563C67B224628BEA00E94EDC /* DatabasePoolTests.swift */; };
 		563CBBE12A595131008905CE /* SQLIndexGenerator.swift in Sources */ = {isa = PBXBuildFile; fileRef = 563CBBE02A595131008905CE /* SQLIndexGenerator.swift */; };
 		563DE4F3231A91E2005081B7 /* DatabaseConfigurationTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 563DE4EC231A91E2005081B7 /* DatabaseConfigurationTests.swift */; };
+		563EA3E12C7B3A22001BE0D4 /* Mutex.swift in Sources */ = {isa = PBXBuildFile; fileRef = 563EA3E02C7B3A22001BE0D4 /* Mutex.swift */; };
 		563EF415215F87EB007DAACD /* OrderedDictionary.swift in Sources */ = {isa = PBXBuildFile; fileRef = 563EF414215F87EB007DAACD /* OrderedDictionary.swift */; };
 		563EF42D2161180D007DAACD /* AssociationAggregate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 563EF42C2161180D007DAACD /* AssociationAggregate.swift */; };
 		563EF43F216131D1007DAACD /* AssociationAggregateTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 563EF43E216131D1007DAACD /* AssociationAggregateTests.swift */; };
@@ -186,7 +187,7 @@
 		566B912B1FA4D0CC0012D5B0 /* StatementAuthorizer.swift in Sources */ = {isa = PBXBuildFile; fileRef = 566B912A1FA4D0CC0012D5B0 /* StatementAuthorizer.swift */; };
 		566B91331FA4D3810012D5B0 /* TransactionObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = 566B91321FA4D3810012D5B0 /* TransactionObserver.swift */; };
 		566B9C2025C6CC24004542CF /* RowDecodingError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 566B9C1F25C6CC24004542CF /* RowDecodingError.swift */; };
-		566BE71E2342542F00A8254B /* LockedBox.swift in Sources */ = {isa = PBXBuildFile; fileRef = 566BE7172342542F00A8254B /* LockedBox.swift */; };
+		566BE71E2342542F00A8254B /* Mutex.swift in Sources */ = {isa = PBXBuildFile; fileRef = 566BE7172342542F00A8254B /* Mutex.swift */; };
 		566DDE0D288D763C0000DCFB /* Fixits.swift in Sources */ = {isa = PBXBuildFile; fileRef = 566DDE0C288D763C0000DCFB /* Fixits.swift */; };
 		56703297212B5450007D270F /* DatabaseUUIDEncodingStrategyTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56703290212B544F007D270F /* DatabaseUUIDEncodingStrategyTests.swift */; };
 		56713FDD2691F409006153C3 /* JSONRequiredEncoder.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56713FDC2691F409006153C3 /* JSONRequiredEncoder.swift */; };
@@ -534,6 +535,7 @@
 		563C67B224628BEA00E94EDC /* DatabasePoolTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DatabasePoolTests.swift; sourceTree = "<group>"; };
 		563CBBE02A595131008905CE /* SQLIndexGenerator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SQLIndexGenerator.swift; sourceTree = "<group>"; };
 		563DE4EC231A91E2005081B7 /* DatabaseConfigurationTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DatabaseConfigurationTests.swift; sourceTree = "<group>"; };
+		563EA3E02C7B3A22001BE0D4 /* Mutex.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Mutex.swift; sourceTree = "<group>"; };
 		563EF414215F87EB007DAACD /* OrderedDictionary.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OrderedDictionary.swift; sourceTree = "<group>"; };
 		563EF42C2161180D007DAACD /* AssociationAggregate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AssociationAggregate.swift; sourceTree = "<group>"; };
 		563EF43E216131D1007DAACD /* AssociationAggregateTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AssociationAggregateTests.swift; sourceTree = "<group>"; };
@@ -628,7 +630,7 @@
 		566B912A1FA4D0CC0012D5B0 /* StatementAuthorizer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StatementAuthorizer.swift; sourceTree = "<group>"; };
 		566B91321FA4D3810012D5B0 /* TransactionObserver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TransactionObserver.swift; sourceTree = "<group>"; };
 		566B9C1F25C6CC24004542CF /* RowDecodingError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RowDecodingError.swift; sourceTree = "<group>"; };
-		566BE7172342542F00A8254B /* LockedBox.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = LockedBox.swift; sourceTree = "<group>"; };
+		566BE7172342542F00A8254B /* Mutex.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Mutex.swift; sourceTree = "<group>"; };
 		566DDE0C288D763C0000DCFB /* Fixits.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Fixits.swift; sourceTree = "<group>"; };
 		56703290212B544F007D270F /* DatabaseUUIDEncodingStrategyTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DatabaseUUIDEncodingStrategyTests.swift; sourceTree = "<group>"; };
 		56713FDC2691F409006153C3 /* JSONRequiredEncoder.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = JSONRequiredEncoder.swift; sourceTree = "<group>"; };
@@ -1010,6 +1012,7 @@
 			children = (
 				56677C14241D14450050755D /* FailureTestCase.swift */,
 				5623E0901B4AFACC00B20B7F /* GRDBTestCase.swift */,
+				563EA3E02C7B3A22001BE0D4 /* Mutex.swift */,
 				562EA81E1F17B26F00FA528C /* Compilation */,
 				56A238111B9C74A90082EB20 /* Core */,
 				567B5BDA2AD3281B00629622 /* Dump */,
@@ -1318,7 +1321,7 @@
 				56717270261C68E900423B6F /* CaseInsensitiveIdentifier.swift */,
 				563EF4492161F179007DAACD /* Inflections.swift */,
 				569BBA482291707D00478429 /* Inflections+English.swift */,
-				566BE7172342542F00A8254B /* LockedBox.swift */,
+				566BE7172342542F00A8254B /* Mutex.swift */,
 				563B8FC424A1D3B9007A48C9 /* OnDemandFuture.swift */,
 				563EF414215F87EB007DAACD /* OrderedDictionary.swift */,
 				5659F4971EA8D989004A4992 /* Pool.swift */,
@@ -2058,6 +2061,7 @@
 				5615B275222B107900061C1C /* AssociationHasOneThroughFetchableRecordTests.swift in Sources */,
 				56D4966F1D81309E008276D7 /* RecordPrimaryKeyNoneTests.swift in Sources */,
 				56D496621D81304E008276D7 /* StatementArguments+FoundationTests.swift in Sources */,
+				563EA3E12C7B3A22001BE0D4 /* Mutex.swift in Sources */,
 				56176C5D1EACCCC7000F3F2B /* FTS5TokenizerTests.swift in Sources */,
 				56D496B21D8133CE008276D7 /* DatabaseQueueInMemoryTests.swift in Sources */,
 				562393601DEE06D300A6B01F /* CursorTests.swift in Sources */,
@@ -2265,7 +2269,7 @@
 				5690C3401D23E82A00E59934 /* Data.swift in Sources */,
 				5659F4881EA8D94E004A4992 /* Utils.swift in Sources */,
 				567B5BE82AD3284100629622 /* DumpFormat.swift in Sources */,
-				566BE71E2342542F00A8254B /* LockedBox.swift in Sources */,
+				566BE71E2342542F00A8254B /* Mutex.swift in Sources */,
 				56A238931B9C750B0082EB20 /* DatabaseMigrator.swift in Sources */,
 				5603CEBB2AC862EC00CF097D /* SQLJSONExpressible.swift in Sources */,
 				56F89DF72A57EAA9002FE2AA /* ColumnDefinition.swift in Sources */,

diff --git a/GRDB/Core/Database.swift b/GRDB/Core/Database.swift
@@ -292,7 +292,7 @@ public final class Database: CustomStringConvertible, CustomDebugStringConvertib
     var isInsideTransactionBlock = false
 
     /// Support for `checkForSuspensionViolation(from:)`
-    @LockedBox var isSuspended = false
+    let isSuspendedMutex = Mutex(false)
 
     /// Support for `checkForSuspensionViolation(from:)`
     /// This cache is never cleared: we assume journal mode never changes.
@@ -1125,22 +1125,25 @@ public final class Database: CustomStringConvertible, CustomDebugStringConvertib
     ///
     /// Suspension ends with `resume()`.
     func suspend() {
-        $isSuspended.update { isSuspended in
+        let needsInterrupt = isSuspendedMutex.withLock { isSuspended in
             if isSuspended {
-                return
+                return false
             }
 
-            // Prevent future lock acquisition
             isSuspended = true
-
-            // Interrupt the database because this may trigger an
-            // SQLITE_INTERRUPT error which may itself abort a transaction and
-            // release a lock. See <https://www.sqlite.org/c3ref/interrupt.html>
+            return true
+        }
+
+        if needsInterrupt {
+            // Interrupting the database can trigger an SQLITE_INTERRUPT
+            // error which may itself abort a transaction and
+            // release a database lock, which is our goal.
+            // See <https://www.sqlite.org/c3ref/interrupt.html>
+            //
+            // Maybe interrupt will not release any lock. To address this,
+            // we'll issue a rollback on next database access which requires
+            // a lock. See `checkForSuspensionViolation(from:).`
             interrupt()
-
-            // Now what about the eventual remaining lock? We'll issue a
-            // rollback on next database access which requires a lock, in
-            // checkForSuspensionViolation(from:).
         }
     }
 
@@ -1152,7 +1155,7 @@ public final class Database: CustomStringConvertible, CustomDebugStringConvertib
     ///
     /// See suspend().
     func resume() {
-        isSuspended = false
+        isSuspendedMutex.store(false)
     }
 
     /// Support for `checkForSuspensionViolation(from:)`
@@ -1182,9 +1185,9 @@ public final class Database: CustomStringConvertible, CustomDebugStringConvertib
     ///
     /// See `suspend()` and ``Configuration/observesSuspensionNotifications``.
     func checkForSuspensionViolation(from statement: Statement) throws {
-        try $isSuspended.read { isSuspended in
+        let needsAbort = try isSuspendedMutex.withLock { isSuspended in
             guard isSuspended else {
-                return
+                return false
             }
 
             if try journalMode() == "wal" && statement.isReadonly {
@@ -1195,7 +1198,7 @@ public final class Database: CustomStringConvertible, CustomDebugStringConvertib
                 // Those are not read-only:
                 // - INSERT ...
                 // - BEGIN IMMEDIATE TRANSACTION
-                return
+                return false
             }
 
             if statement.releasesDatabaseLock {
@@ -1204,9 +1207,14 @@ public final class Database: CustomStringConvertible, CustomDebugStringConvertib
                 // - ROLLBACK
                 // - ROLLBACK TRANSACTION TO SAVEPOINT
                 // - RELEASE SAVEPOINT
-                return
+                return false
             }
 
+            // Assume statement can acquire a write lock: abort.
+            return true
+        }
+
+        if needsAbort {
             // Attempt at releasing an eventual lock with ROLLBACk,
             // as explained in Database.suspend().
             //

diff --git a/GRDB/Core/DatabasePool.swift b/GRDB/Core/DatabasePool.swift
@@ -11,7 +11,7 @@ public final class DatabasePool {
     /// It is constant, until close() sets it to nil.
     private var readerPool: Pool<SerializedDatabase>?
 
-    @LockedBox var databaseSnapshotCount = 0
+    let databaseSnapshotCountMutex = Mutex(0)
 
     /// If Database Suspension is enabled, this array contains the necessary `NotificationCenter` observers.
     private var suspensionObservers: [NSObjectProtocol] = []
@@ -144,7 +144,7 @@ public final class DatabasePool {
     }
 }
 
-// @unchecked because of databaseSnapshotCount, readerPool and suspensionObservers
+// @unchecked because of readerPool and suspensionObservers
 extension DatabasePool: @unchecked Sendable { }
 
 extension DatabasePool {
@@ -845,7 +845,7 @@ extension DatabasePool {
             path: path,
             configuration: DatabasePool.readerConfiguration(writer.configuration),
             defaultLabel: "GRDB.DatabasePool",
-            purpose: "snapshot.\($databaseSnapshotCount.increment())")
+            purpose: "snapshot.\(databaseSnapshotCountMutex.increment())")
     }
 
 #if SQLITE_ENABLE_SNAPSHOT || (!GRDBCUSTOMSQLITE && !GRDBCIPHER)

diff --git a/GRDB/Core/DatabaseRegionObservation.swift b/GRDB/Core/DatabaseRegionObservation.swift
@@ -89,16 +89,16 @@ extension DatabaseRegionObservation {
         onChange: @escaping (Database) -> Void)
     -> AnyDatabaseCancellable
     {
-        @LockedBox var state = ObservationState.pending
+        let stateMutex = Mutex(ObservationState.pending)
 
         // Use unsafeReentrantWrite so that observation can start from any
         // dispatch queue.
         writer.unsafeReentrantWrite { db in
             do {
                 let region = try observedRegion(db).observableRegion(db)
-                $state.update {
+                stateMutex.withLock { state in
                     let observer = DatabaseRegionObserver(region: region, onChange: {
-                        if case .cancelled = state {
+                        if case .cancelled = stateMutex.load() {
                             return
                         }
                         onChange($0)
@@ -111,7 +111,7 @@ extension DatabaseRegionObservation {
                     // the observer.
                     db.add(transactionObserver: observer, extent: .observerLifetime)
 
-                    $0 = .started(observer)
+                    state = .started(observer)
                 }
             } catch {
                 onError(error)
@@ -122,7 +122,7 @@ extension DatabaseRegionObservation {
             // Deallocates the transaction observer. This makes sure that the
             // `onChange` callback will never be called again, because the
             // observation was started with the `.observerLifetime` extent.
-            state = .cancelled
+            stateMutex.store(.cancelled)
         }
     }
 }

diff --git a/GRDB/Utils/LockedBox.swift b/GRDB/Utils/LockedBox.swift
diff --git a/GRDB/Utils/Mutex.swift b/GRDB/Utils/Mutex.swift
@@ -0,0 +1,54 @@
+import Foundation
+
+/// A Mutex protects a value with an NSLock.
+///
+/// We'll replace it with the SE-0433 Mutex when it is available.
+/// <https://github.com/apple/swift-evolution/blob/main/proposals/0433-mutex.md>
+final class Mutex<T> {
+    private var _value: T
+    private var lock = NSLock()
+
+    init(_ value: T) {
+        _value = value
+    }
+
+    /// Runs the provided closure while holding a lock on the value.
+    ///
+    /// - parameter body: A closure that can modify the value.
+    func withLock<U>(_ body: (inout T) throws -> U) rethrows -> U {
+        lock.lock()
+        defer { lock.unlock() }
+        return try body(&_value)
+    }
+}
+
+// Inspired by <https://forums.swift.org/t/se-0433-synchronous-mutual-exclusion-lock/71174/58>
+extension Mutex {
+    func load() -> T {
+        withLock { $0 }
+    }
+
+    func store(_ value: T) {
+        withLock { $0 = value }
+    }
+}
+
+extension Mutex where T: Numeric {
+    @discardableResult
+    func increment() -> T {
+        withLock { n in
+            n += 1
+            return n
+        }
+    }
+
+    @discardableResult
+    func decrement() -> T {
+        withLock { n in
+            n -= 1
+            return n
+        }
+    }
+}
+
+extension Mutex: @unchecked Sendable where T: Sendable { }
diff --git a/GRDB/ValueObservation/Observers/ValueConcurrentObserver.swift b/GRDB/ValueObservation/Observers/ValueConcurrentObserver.swift
@@ -146,7 +146,7 @@ final class ValueConcurrentObserver<Reducer: ValueReducer, Scheduler: ValueObser
     private var notificationCallbacks: NotificationCallbacks?
 
     /// The fetching state for observation of constant regions.
-    @LockedBox private var fetchingState = FetchingState.idle
+    private let fetchingStateMutex = Mutex(FetchingState.idle)
 
     /// Support for `TransactionObserver`, protected by the serialized writer
     /// dispatch queue.
@@ -780,7 +780,7 @@ extension ValueConcurrentObserver: TransactionObserver {
     }
 
     private func setNeedsFetching(databaseAccess: DatabaseAccess) {
-        $fetchingState.update { state in
+        fetchingStateMutex.withLock { state in
             switch state {
             case .idle:
                 state = .fetching
@@ -806,7 +806,7 @@ extension ValueConcurrentObserver: TransactionObserver {
 
             self.reduce(fetchResult)
 
-            $fetchingState.update { state in
+            fetchingStateMutex.withLock { state in
                 switch state {
                 case .idle:
                     // GRDB bug