Vendor SwiftNIO NIOLock into the new ConnectionPoolModule target (vapor#416)

The new `ConnectionPoolModule` shall be dependency free. But we need a lock. Let's vendor NIOLock from SwiftNIO.

Author: fabianfett

Diff for: NOTICE.txt

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Vapor open source project
 //
-// Copyright (c) 2017-2021 Vapor project authors
+// Copyright (c) 2017-2023 Vapor project authors
 // Licensed under MIT
 //
 // See LICENSE for license information
@@ -11,3 +11,10 @@
 //
 //===----------------------------------------------------------------------===//
 
+This product contains a derivation of the NIOLock implementation
+from Swift NIO.
+
+  * LICENSE (Apache License 2.0):
+    * https://www.apache.org/licenses/LICENSE-2.0
+  * HOMEPAGE:
+    * https://github.com/apple/swift-nio

Diff for: Sources/ConnectionPoolModule/NIOLock.swift

@@ -0,0 +1,268 @@
+// Implementation vendored from SwiftNIO:
+//   https://github.com/apple/swift-nio
+
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2017-2022 Apple Inc. and the SwiftNIO project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+#if canImport(Darwin)
+import Darwin
+#elseif os(Windows)
+import ucrt
+import WinSDK
+#elseif canImport(Glibc)
+import Glibc
+#elseif canImport(Musl)
+import Musl
+#else
+#error("The concurrency NIOLock module was unable to identify your C library.")
+#endif
+
+#if os(Windows)
+@usableFromInline
+typealias LockPrimitive = SRWLOCK
+#else
+@usableFromInline
+typealias LockPrimitive = pthread_mutex_t
+#endif
+
+@usableFromInline
+enum LockOperations { }
+
+extension LockOperations {
+    @inlinable
+    static func create(_ mutex: UnsafeMutablePointer<LockPrimitive>) {
+        mutex.assertValidAlignment()
+
+#if os(Windows)
+        InitializeSRWLock(mutex)
+#else
+        var attr = pthread_mutexattr_t()
+        pthread_mutexattr_init(&attr)
+        debugOnly {
+            pthread_mutexattr_settype(&attr, .init(PTHREAD_MUTEX_ERRORCHECK))
+        }
+        
+        let err = pthread_mutex_init(mutex, &attr)
+        precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
+#endif
+    }
+    
+    @inlinable
+    static func destroy(_ mutex: UnsafeMutablePointer<LockPrimitive>) {
+        mutex.assertValidAlignment()
+
+#if os(Windows)
+        // SRWLOCK does not need to be free'd
+#else
+        let err = pthread_mutex_destroy(mutex)
+        precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
+#endif
+    }
+    
+    @inlinable
+    static func lock(_ mutex: UnsafeMutablePointer<LockPrimitive>) {
+        mutex.assertValidAlignment()
+
+#if os(Windows)
+        AcquireSRWLockExclusive(mutex)
+#else
+        let err = pthread_mutex_lock(mutex)
+        precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
+#endif
+    }
+    
+    @inlinable
+    static func unlock(_ mutex: UnsafeMutablePointer<LockPrimitive>) {
+        mutex.assertValidAlignment()
+
+#if os(Windows)
+        ReleaseSRWLockExclusive(mutex)
+#else
+        let err = pthread_mutex_unlock(mutex)
+        precondition(err == 0, "\(#function) failed in pthread_mutex with error \(err)")
+#endif
+    }
+}
+
+// Tail allocate both the mutex and a generic value using ManagedBuffer.
+// Both the header pointer and the elements pointer are stable for
+// the class's entire lifetime.
+//
+// However, for safety reasons, we elect to place the lock in the "elements"
+// section of the buffer instead of the head. The reasoning here is subtle,
+// so buckle in.
+//
+// _As a practical matter_, the implementation of ManagedBuffer ensures that
+// the pointer to the header is stable across the lifetime of the class, and so
+// each time you call `withUnsafeMutablePointers` or `withUnsafeMutablePointerToHeader`
+// the value of the header pointer will be the same. This is because ManagedBuffer uses
+// `Builtin.addressOf` to load the value of the header, and that does ~magic~ to ensure
+// that it does not invoke any weird Swift accessors that might copy the value.
+//
+// _However_, the header is also available via the `.header` field on the ManagedBuffer.
+// This presents a problem! The reason there's an issue is that `Builtin.addressOf` and friends
+// do not interact with Swift's exclusivity model. That is, the various `with` functions do not
+// conceptually trigger a mutating access to `.header`. For elements this isn't a concern because
+// there's literally no other way to perform the access, but for `.header` it's entirely possible
+// to accidentally recursively read it.
+//
+// Our implementation is free from these issues, so we don't _really_ need to worry about it.
+// However, out of an abundance of caution, we store the Value in the header, and the LockPrimitive
+// in the trailing elements. We still don't use `.header`, but it's better to be safe than sorry,
+// and future maintainers will be happier that we were cautious.
+//
+// See also: https://github.com/apple/swift/pull/40000
+@usableFromInline
+final class LockStorage<Value>: ManagedBuffer<Value, LockPrimitive> {
+    
+    @inlinable
+    static func create(value: Value) -> Self {
+        let buffer = Self.create(minimumCapacity: 1) { _ in
+            return value
+        }
+        let storage = unsafeDowncast(buffer, to: Self.self)
+        
+        storage.withUnsafeMutablePointers { _, lockPtr in
+            LockOperations.create(lockPtr)
+        }
+        
+        return storage
+    }
+    
+    @inlinable
+    func lock() {
+        self.withUnsafeMutablePointerToElements { lockPtr in
+            LockOperations.lock(lockPtr)
+        }
+    }
+    
+    @inlinable
+    func unlock() {
+        self.withUnsafeMutablePointerToElements { lockPtr in
+            LockOperations.unlock(lockPtr)
+        }
+    }
+    
+    @inlinable
+    deinit {
+        self.withUnsafeMutablePointerToElements { lockPtr in
+            LockOperations.destroy(lockPtr)
+        }
+    }
+    
+    @inlinable
+    func withLockPrimitive<T>(_ body: (UnsafeMutablePointer<LockPrimitive>) throws -> T) rethrows -> T {
+        try self.withUnsafeMutablePointerToElements { lockPtr in
+            return try body(lockPtr)
+        }
+    }
+    
+    @inlinable
+    func withLockedValue<T>(_ mutate: (inout Value) throws -> T) rethrows -> T {
+        try self.withUnsafeMutablePointers { valuePtr, lockPtr in
+            LockOperations.lock(lockPtr)
+            defer { LockOperations.unlock(lockPtr) }
+            return try mutate(&valuePtr.pointee)
+        }
+    }
+}
+
+extension LockStorage: @unchecked Sendable { }
+
+/// A threading lock based on `libpthread` instead of `libdispatch`.
+///
+/// - note: ``NIOLock`` has reference semantics.
+///
+/// This object provides a lock on top of a single `pthread_mutex_t`. This kind
+/// of lock is safe to use with `libpthread`-based threading models, such as the
+/// one used by NIO. On Windows, the lock is based on the substantially similar
+/// `SRWLOCK` type.
+@usableFromInline
+struct NIOLock {
+    @usableFromInline
+    internal let _storage: LockStorage<Void>
+    
+    /// Create a new lock.
+    @inlinable
+    init() {
+        self._storage = .create(value: ())
+    }
+
+    /// Acquire the lock.
+    ///
+    /// Whenever possible, consider using `withLock` instead of this method and
+    /// `unlock`, to simplify lock handling.
+    @inlinable
+    func lock() {
+        self._storage.lock()
+    }
+
+    /// Release the lock.
+    ///
+    /// Whenever possible, consider using `withLock` instead of this method and
+    /// `lock`, to simplify lock handling.
+    @inlinable
+    func unlock() {
+        self._storage.unlock()
+    }
+
+    @inlinable
+    internal func withLockPrimitive<T>(_ body: (UnsafeMutablePointer<LockPrimitive>) throws -> T) rethrows -> T {
+        return try self._storage.withLockPrimitive(body)
+    }
+}
+
+extension NIOLock {
+    /// Acquire the lock for the duration of the given block.
+    ///
+    /// This convenience method should be preferred to `lock` and `unlock` in
+    /// most situations, as it ensures that the lock will be released regardless
+    /// of how `body` exits.
+    ///
+    /// - Parameter body: The block to execute while holding the lock.
+    /// - Returns: The value returned by the block.
+    @inlinable
+    func withLock<T>(_ body: () throws -> T) rethrows -> T {
+        self.lock()
+        defer {
+            self.unlock()
+        }
+        return try body()
+    }
+
+    @inlinable
+    func withLockVoid(_ body: () throws -> Void) rethrows -> Void {
+        try self.withLock(body)
+    }
+}
+
+extension NIOLock: Sendable {}
+
+extension UnsafeMutablePointer {
+    @inlinable
+    func assertValidAlignment() {
+        assert(UInt(bitPattern: self) % UInt(MemoryLayout<Pointee>.alignment) == 0)
+    }
+}
+
+/// A utility function that runs the body code only in debug builds, without
+/// emitting compiler warnings.
+///
+/// This is currently the only way to do this in Swift: see
+/// https://forums.swift.org/t/support-debug-only-code/11037 for a discussion.
+@inlinable
+internal func debugOnly(_ body: () -> Void) {
+    // FIXME: duplicated with NIO.
+    assert({ body(); return true }())
+}