Initial implementation of the package.

.github/workflows/dart.yaml

@@ -34,6 +34,7 @@ jobs:
         run: dart analyze --fatal-infos
 
   test:
+    needs: analyze
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:

.gitignore

@@ -8,3 +8,6 @@ build/
 # Omit committing pubspec.lock for library packages; see
 # https://dart.dev/guides/libraries/private-files#pubspeclock.
 pubspec.lock
+
+# VSCode configuration files
+.vscode/

CHANGELOG.md

@@ -1,3 +1,5 @@
 ## 0.1.0-wip
 
 - Initial version.
+- Expose `Mutex` and `ConditionVariable`
+- Implement `Mailbox`.

README.md

@@ -1,22 +1,22 @@
 [![Dart](https://github.com/dart-lang/native_synchronization/actions/workflows/dart.yaml/badge.svg)](https://github.com/dart-lang/native_synchronization/actions/workflows/dart.yaml)
 
-Low level synchronization primitives built on dart:ffi.
+This package exposes a portable interface for low-level thread
+synchronization primitives like `Mutex` and `ConditionVariable`.
 
-## TODO: Projects docs
-
-TODO: Add a brief project description here.
+It also provides some slightly more high-level synchronization primitives
+like `Mailbox` built on top of low-level primitives.
 
 ## Status: experimental
 
 **NOTE**: This package is currently experimental and published under the
 [labs.dart.dev](https://dart.dev/dart-team-packages) pub publisher in order to
-solicit feedback. 
+solicit feedback.
 
 For packages in the labs.dart.dev publisher we generally plan to either graduate
 the package into a supported publisher (dart.dev, tools.dart.dev) after a period
 of feedback and iteration, or discontinue the package. These packages have a
 much higher expected rate of API and breaking changes.
 
 Your feedback is valuable and will help us evolve this package. For general
-feedback, suggestions, and comments, please file an issue in the 
+feedback, suggestions, and comments, please file an issue in the
 [bug tracker](https://github.com/dart-lang/native_synchronization/issues).

lib/mailbox.dart

@@ -0,0 +1,125 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:ffi';
+import 'dart:typed_data';
+
+import 'package:ffi/ffi.dart';
+
+import 'package:native_synchronization/primitives.dart';
+import 'package:native_synchronization/sendable.dart';
+
+final class _MailboxRepr extends Struct {
+  external Pointer<Uint8> buffer;
+
+  @Int32()
+  external int bufferLength;
+
+  @Int32()
+  external int state;
+}
+
+class _SendableMailbox {
+  final int address;
+  final Sendable<Mutex> mutex;
+  final Sendable<ConditionVariable> condVar;
+
+  _SendableMailbox(
+      {required this.address, required this.mutex, required this.condVar});
+}
+
+/// Mailbox communication primitive.
+///
+/// This synchronization primitive allows a single producer to send messages
+/// to one or more consumers. Producer uses [put] to place a message into
+/// a mailbox which consumers can then [take] out.
+///
+/// [Mailbox] object can not be directly sent to other isolates via a
+/// `SendPort`, but it can be converted to a `Sendable<Mailbox>` via
+/// `asSendable` getter.
+///
+/// [Mailbox] object is owned by an isolate which created them.
+class Mailbox {
+  final Pointer<_MailboxRepr> _mailbox;
+  final Mutex _mutex;
+  final ConditionVariable _condVar;
+
+  static const _stateEmpty = 0;
+  static const _stateFull = 1;
+
+  static final finalizer = Finalizer((Pointer<_MailboxRepr> mailbox) {
+    calloc.free(mailbox.ref.buffer);
+    calloc.free(mailbox);
+  });
+
+  Mailbox()
+      : _mailbox = calloc.allocate(sizeOf<_MailboxRepr>()),
+        _mutex = Mutex(),
+        _condVar = ConditionVariable() {
+    finalizer.attach(this, _mailbox);
+  }
+
+  Mailbox._fromSendable(_SendableMailbox sendable)
+      : _mailbox = Pointer.fromAddress(sendable.address),
+        _mutex = sendable.mutex.materialize(),
+        _condVar = sendable.condVar.materialize();
+
+  /// Place a message into the mailbox if has space for it.
+  ///
+  /// If mailbox already contains a message then [put] will throw.
+  void put(Uint8List message) {
+    final buffer = message.isEmpty ? nullptr : _toBuffer(message);
+    _mutex.runLocked(() {
+      if (_mailbox.ref.state != _stateEmpty) {
+        throw StateError('Mailbox is full');
+      }
+
+      _mailbox.ref.state = _stateFull;
+      _mailbox.ref.buffer = buffer;
+      _mailbox.ref.bufferLength = message.length;
+
+      _condVar.notify();
+    });
+  }
+
+  /// Take a message from the mailbox.
+  ///
+  /// If mailbox is empty this will synchronously block until message
+  /// is available.
+  Uint8List take() => _mutex.runLocked(() {
+        while (_mailbox.ref.state != _stateFull) {
+          _condVar.wait(_mutex);
+        }
+
+        final result = _toList(_mailbox.ref.buffer, _mailbox.ref.bufferLength);
+
+        _mailbox.ref.state = _stateEmpty;
+        _mailbox.ref.buffer = nullptr;
+        _mailbox.ref.bufferLength = 0;
+        return result;
+      });
+
+  static final _emptyResponse = Uint8List(0);
+
+  static Uint8List _toList(Pointer<Uint8> buffer, int length) {
+    return length == 0
+        ? _emptyResponse
+        // We have to ignore sdk_version_since warning due to dartbug.com/53142.
+        // ignore: sdk_version_since
+        : buffer.asTypedList(length, finalizer: malloc.nativeFree);
+  }
+
+  static Pointer<Uint8> _toBuffer(Uint8List list) {
+    final buffer = malloc.allocate<Uint8>(list.length);
+    buffer.asTypedList(list.length).setRange(0, list.length, list);
+    return buffer;
+  }
+
+  Sendable<Mailbox> get asSendable => Sendable.wrap(
+      Mailbox._fromSendable,
+      _SendableMailbox(
+          address: _mailbox.address,
+          mutex: _mutex.asSendable,
+          condVar: _condVar.asSendable));
+}

lib/posix.dart

@@ -0,0 +1,93 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of 'primitives.dart';
+
+class _PosixMutex extends Mutex {
+  /// This is maximum value of `sizeof(pthread_mutex_t)` across all supported
+  /// platforms.
+  static const _sizeInBytes = 64;
+
+  final Pointer<pthread_mutex_t> _impl;
+
+  static final _finalizer = Finalizer<Pointer<pthread_mutex_t>>((ptr) {
+    pthread_mutex_destroy(ptr);
+    malloc.free(ptr);
+  });
+
+  _PosixMutex()
+      : _impl = malloc.allocate(_PosixMutex._sizeInBytes),
+        super._() {
+    if (pthread_mutex_init(_impl, nullptr) != 0) {
+      malloc.free(_impl);
+      throw StateError('Failed to initialize mutex');
+    }
+    _finalizer.attach(this, _impl);
+  }
+
+  _PosixMutex.fromAddress(int address)
+      : _impl = Pointer.fromAddress(address),
+        super._();
+
+  @override
+  void _lock() {
+    if (pthread_mutex_lock(_impl) != 0) {
+      throw StateError('Failed to lock mutex');
+    }
+  }
+
+  @override
+  void _unlock() {
+    if (pthread_mutex_unlock(_impl) != 0) {
+      throw StateError('Failed to unlock mutex');
+    }
+  }
+
+  @override
+  int get _address => _impl.address;
+}
+
+class _PosixConditionVariable extends ConditionVariable {
+  /// This is maximum value of `sizeof(pthread_cond_t)` across all supported
+  /// platforms.
+  static const _sizeInBytes = 64;
+
+  final Pointer<pthread_cond_t> _impl;
+
+  static final _finalizer = Finalizer<Pointer<pthread_cond_t>>((ptr) {
+    pthread_cond_destroy(ptr);
+    malloc.free(ptr);
+  });
+
+  _PosixConditionVariable()
+      : _impl = malloc.allocate(_PosixConditionVariable._sizeInBytes),
+        super._() {
+    if (pthread_cond_init(_impl, nullptr) != 0) {
+      malloc.free(_impl);
+      throw StateError('Failed to initialize condition variable');
+    }
+    _finalizer.attach(this, _impl);
+  }
+
+  _PosixConditionVariable.fromAddress(int address)
+      : _impl = Pointer.fromAddress(address),
+        super._();
+
+  @override
+  void notify() {
+    if (pthread_cond_signal(_impl) != 0) {
+      throw StateError('Failed to signal condition variable');
+    }
+  }
+
+  @override
+  void wait(covariant _PosixMutex mutex) {
+    if (pthread_cond_wait(_impl, mutex._impl) != 0) {
+      throw StateError('Failed to wait on a condition variable');
+    }
+  }
+
+  @override
+  int get _address => _impl.address;
+}

lib/primitives.dart

@@ -0,0 +1,117 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// This library contains native synchronization primitives such as [Mutex]
+/// and [ConditionVariable] implemented on top of low-level primitives
+/// provided by the OS.
+///
+/// See OS specific documentation for more details:
+///
+/// * POSIX man pages (Linux, Android, Mac OS X and iOS X)
+///     * `pthread_mutex_lock` and `pthread_mutex_unlock`,
+///     * `pthread_cond_wait` and `pthread_cond_signal`.
+/// * Windows
+///     * [Slim Reader/Writer (SRW) Locks](https://learn.microsoft.com/en-us/windows/win32/sync/slim-reader-writer--srw--locks),
+///     * [Condition Variables](https://learn.microsoft.com/en-us/windows/win32/sync/condition-variables),
+library;
+
+import 'dart:ffi';
+import 'dart:io';
+
+import 'package:ffi/ffi.dart';
+import 'package:native_synchronization/sendable.dart';
+
+import 'package:native_synchronization/src/bindings/pthread.dart';
+import 'package:native_synchronization/src/bindings/winapi.dart';
+
+part 'posix.dart';
+part 'windows.dart';
+
+/// A *mutex* synchronization primitive.
+///
+/// Mutex can be used to synchronize access to a native resource shared between
+/// multiple threads.
+///
+/// [Mutex] object can not be directly sent to other isolates via a `SendPort`,
+/// but it can be converted to a `Sendable<Mutex>` via `asSendable` getter.
+///
+/// Mutex objects are owned by an isolate which created them.
+sealed class Mutex implements Finalizable {
+  Mutex._();
+
+  factory Mutex() => Platform.isWindows ? _WindowsMutex() : _PosixMutex();
+
+  /// Acquire exclusive ownership of this mutex.
+  ///
+  /// If this mutex is already acquired then an attempt to acquire it
+  /// blocks the current thread until the mutex is released by the
+  /// current owner.
+  ///
+  /// **Warning**: attempting to hold a mutex across asynchronous suspension
+  /// points will lead to undefined behavior and potentially crashes.
+  void _lock();
+
+  /// Release exclusive ownership of this mutex.
+  ///
+  /// It is an error to release ownership of the mutex if it was not
+  /// previously acquired.
+  void _unlock();
+
+  /// Run the given synchronous `action` under a mutex.
+  ///
+  /// This function takes exclusive ownership of the mutex, executes `action`
+  /// and then releases the mutex. It returns the value returned by `action`.
+  ///
+  /// **Warning**: you can't combine `runLocked` with an asynchronous code.
+  R runLocked<R>(R Function() action) {
+    _lock();
+    try {
+      return action();
+    } finally {
+      _unlock();
+    }
+  }
+
+  Sendable<Mutex> get asSendable => Sendable.wrap(
+      Platform.isWindows ? _WindowsMutex.fromAddress : _PosixMutex.fromAddress,
+      _address);
+
+  int get _address;
+}
+
+/// A *condition variable* synchronization primitive.
+///
+/// Condition variable can be used to synchronously wait for a condition to
+/// occur.
+///
+/// [ConditionVariable] object can not be directly sent to other isolates via a
+/// `SendPort`, but it can be converted to a `Sendable<ConditionVariable>`
+/// object via [asSendable] getter.
+///
+/// [ConditionVariable] objects are owned by an isolate which created them.
+sealed class ConditionVariable implements Finalizable {
+  ConditionVariable._();
+
+  factory ConditionVariable() => Platform.isWindows
+      ? _WindowsConditionVariable()
+      : _PosixConditionVariable();
+
+  /// Block and wait until another thread calls [notify].
+  ///
+  /// `mutex` must be a [Mutex] object exclusively held by the current thread.
+  /// It will be released and the thread will block until another thread
+  /// calls [notify].
+  void wait(Mutex mutex);
+
+  /// Wake up at least one thread waiting on this condition variable.
+  void notify();
+
+  Sendable<ConditionVariable> get asSendable => Sendable.wrap(
+      Platform.isWindows
+          ? _WindowsConditionVariable.fromAddress
+          : _PosixConditionVariable.fromAddress,
+      _address);
+
+  int get _address;
+}