[vm/ffi] Migrate samples(_2)/ffi to CallocAllocator

This CL does not yet roll `package:ffi` to use `Allocator`, because that
breaks the checked in Dart in Flutter in g3. Instead, this copies
`_CallocAllocator` from `package:ffi` into the samples.

New API landed in: https://dart-review.googlesource.com/c/sdk/+/177705

Issue: #44621
Issue: #38721

Change-Id: I83da349c2e52d7f079aa1569b4726318fee24c9d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/177706
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>

samples/ffi/calloc.dart

@@ -0,0 +1,109 @@
+// Copyright (c) 2021, 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.
+
+// TODO(https://dartbug.com/44621): Remove this copy when package:ffi can be
+// rolled. We need to wait until the `Allocator` interface has rolled into
+// Flutter.
+
+import 'dart:ffi';
+import 'dart:io';
+
+final DynamicLibrary stdlib = Platform.isWindows
+    ? DynamicLibrary.open('kernel32.dll')
+    : DynamicLibrary.process();
+
+typedef PosixCallocNative = Pointer Function(IntPtr num, IntPtr size);
+typedef PosixCalloc = Pointer Function(int num, int size);
+final PosixCalloc posixCalloc =
+    stdlib.lookupFunction<PosixCallocNative, PosixCalloc>('calloc');
+
+typedef PosixFreeNative = Void Function(Pointer);
+typedef PosixFree = void Function(Pointer);
+final PosixFree posixFree =
+    stdlib.lookupFunction<PosixFreeNative, PosixFree>('free');
+
+typedef WinGetProcessHeapFn = Pointer Function();
+final WinGetProcessHeapFn winGetProcessHeap = stdlib
+    .lookupFunction<WinGetProcessHeapFn, WinGetProcessHeapFn>('GetProcessHeap');
+final Pointer processHeap = winGetProcessHeap();
+
+typedef WinHeapAllocNative = Pointer Function(Pointer, Uint32, IntPtr);
+typedef WinHeapAlloc = Pointer Function(Pointer, int, int);
+final WinHeapAlloc winHeapAlloc =
+    stdlib.lookupFunction<WinHeapAllocNative, WinHeapAlloc>('HeapAlloc');
+
+typedef WinHeapFreeNative = Int32 Function(
+    Pointer heap, Uint32 flags, Pointer memory);
+typedef WinHeapFree = int Function(Pointer heap, int flags, Pointer memory);
+final WinHeapFree winHeapFree =
+    stdlib.lookupFunction<WinHeapFreeNative, WinHeapFree>('HeapFree');
+
+const int HEAP_ZERO_MEMORY = 8;
+
+/// Manages memory on the native heap.
+///
+/// Initializes newly allocated memory to zero.
+///
+/// For POSIX-based systems, this uses `calloc` and `free`. On Windows, it uses
+/// `HeapAlloc` with [HEAP_ZERO_MEMORY] and `HeapFree` against the default
+/// public heap.
+class _CallocAllocator implements Allocator {
+  const _CallocAllocator();
+
+  /// Allocates [byteCount] bytes of zero-initialized of memory on the native
+  /// heap.
+  ///
+  /// For POSIX-based systems, this uses `calloc`. On Windows, it uses
+  /// `HeapAlloc` against the default public heap.
+  ///
+  /// Throws an [ArgumentError] if the number of bytes or alignment cannot be
+  /// satisfied.
+  // TODO: Stop ignoring alignment if it's large, for example for SSE data.
+  @override
+  Pointer<T> allocate<T extends NativeType>(int byteCount, {int? alignment}) {
+    Pointer<T> result;
+    if (Platform.isWindows) {
+      result = winHeapAlloc(processHeap, /*flags=*/ HEAP_ZERO_MEMORY, byteCount)
+          .cast();
+    } else {
+      result = posixCalloc(byteCount, 1).cast();
+    }
+    if (result.address == 0) {
+      throw ArgumentError('Could not allocate $byteCount bytes.');
+    }
+    return result;
+  }
+
+  /// Releases memory allocated on the native heap.
+  ///
+  /// For POSIX-based systems, this uses `free`. On Windows, it uses `HeapFree`
+  /// against the default public heap. It may only be used against pointers
+  /// allocated in a manner equivalent to [allocate].
+  ///
+  /// Throws an [ArgumentError] if the memory pointed to by [pointer] cannot be
+  /// freed.
+  ///
+  // TODO(dartbug.com/36855): Once we have a ffi.Bool type we can use it instead
+  // of testing the return integer to be non-zero.
+  @override
+  void free(Pointer pointer) {
+    if (Platform.isWindows) {
+      if (winHeapFree(processHeap, /*flags=*/ 0, pointer) == 0) {
+        throw ArgumentError('Could not free $pointer.');
+      }
+    } else {
+      posixFree(pointer);
+    }
+  }
+}
+
+/// Manages memory on the native heap.
+///
+/// Initializes newly allocated memory to zero. Use [malloc] for unintialized
+/// memory allocation.
+///
+/// For POSIX-based systems, this uses `calloc` and `free`. On Windows, it uses
+/// `HeapAlloc` with [HEAP_ZERO_MEMORY] and `HeapFree` against the default
+/// public heap.
+const Allocator calloc = _CallocAllocator();

samples/ffi/coordinate.dart

@@ -16,8 +16,9 @@ class Coordinate extends Struct {
 
   external Pointer<Coordinate> next;
 
-  factory Coordinate.allocate(double x, double y, Pointer<Coordinate> next) {
-    return allocate<Coordinate>().ref
+  factory Coordinate.allocate(
+      Allocator allocator, double x, double y, Pointer<Coordinate> next) {
+    return allocator<Coordinate>().ref
       ..x = x
       ..y = y
       ..next = next;

samples/ffi/resource_management/pool.dart

@@ -5,48 +5,36 @@
 // Explicit pool used for managing resources.
 
 import "dart:async";
-import 'dart:convert';
 import 'dart:ffi';
-import 'dart:typed_data';
 
-import 'package:ffi/ffi.dart' as packageFfi;
-import 'package:ffi/ffi.dart' show Utf8;
+import 'package:ffi/ffi.dart';
 
-/// Manages native resources.
+import '../calloc.dart';
+
+/// Keeps track of all allocated memory and frees all allocated memory on
+/// [releaseAll].
 ///
-/// Primary implementations are [Pool] and [Unmanaged].
-abstract class ResourceManager {
-  /// Allocates memory on the native heap.
-  ///
-  /// The native memory is under management by this [ResourceManager].
-  ///
-  /// For POSIX-based systems, this uses malloc. On Windows, it uses HeapAlloc
-  /// against the default public heap. Allocation of either element size or count
-  /// of 0 is undefined.
-  ///
-  /// Throws an ArgumentError on failure to allocate.
-  Pointer<T> allocate<T extends NativeType>({int count: 1});
-}
+/// Wraps an [Allocator] to do the actual allocation and freeing.
+class Pool implements Allocator {
+  /// The [Allocator] used for allocation and freeing.
+  final Allocator _wrappedAllocator;
+
+  Pool(this._wrappedAllocator);
 
-/// Manages native resources.
-class Pool implements ResourceManager {
   /// Native memory under management by this [Pool].
   final List<Pointer<NativeType>> _managedMemoryPointers = [];
 
   /// Callbacks for releasing native resources under management by this [Pool].
   final List<Function()> _managedResourceReleaseCallbacks = [];
 
-  /// Allocates memory on the native heap.
-  ///
-  /// The native memory is under management by this [Pool].
-  ///
-  /// For POSIX-based systems, this uses malloc. On Windows, it uses HeapAlloc
-  /// against the default public heap. Allocation of either element size or count
-  /// of 0 is undefined.
+  /// Allocates memory on the native heap by using the allocator supplied to
+  /// the constructor.
   ///
-  /// Throws an ArgumentError on failure to allocate.
-  Pointer<T> allocate<T extends NativeType>({int count: 1}) {
-    final p = Unmanaged().allocate<T>(count: count);
+  /// Throws an [ArgumentError] if the number of bytes or alignment cannot be
+  /// satisfied.
+  @override
+  Pointer<T> allocate<T extends NativeType>(int numBytes, {int? alignment}) {
+    final p = _wrappedAllocator.allocate<T>(numBytes, alignment: alignment);
     _managedMemoryPointers.add(p);
     return p;
   }
@@ -71,17 +59,21 @@ class Pool implements ResourceManager {
     }
     _managedResourceReleaseCallbacks.clear();
     for (final p in _managedMemoryPointers) {
-      Unmanaged().free(p);
+      _wrappedAllocator.free(p);
     }
     _managedMemoryPointers.clear();
   }
+
+  @override
+  void free(Pointer<NativeType> pointer) => throw UnsupportedError(
+      "Individually freeing Pool allocated memory is not allowed");
 }
 
 /// Creates a [Pool] to manage native resources.
 ///
 /// If the isolate is shut down, through `Isolate.kill()`, resources are _not_ cleaned up.
-R using<R>(R Function(Pool) f) {
-  final p = Pool();
+R using<R>(R Function(Pool) f, [Allocator wrappedAllocator = calloc]) {
+  final p = Pool(wrappedAllocator);
   try {
     return f(p);
   } finally {
@@ -96,8 +88,8 @@ R using<R>(R Function(Pool) f) {
 /// Please note that all throws are caught and packaged in [RethrownError].
 ///
 /// If the isolate is shut down, through `Isolate.kill()`, resources are _not_ cleaned up.
-R usePool<R>(R Function() f) {
-  final p = Pool();
+R usePool<R>(R Function() f, [Allocator wrappedAllocator = calloc]) {
+  final p = Pool(wrappedAllocator);
   try {
     return runZoned(() => f(),
         zoneValues: {#_pool: p},
@@ -117,78 +109,3 @@ class RethrownError {
   toString() => """RethrownError(${original})
 ${originalStackTrace}""";
 }
-
-/// Does not manage it's resources.
-class Unmanaged implements ResourceManager {
-  /// Allocates memory on the native heap.
-  ///
-  /// For POSIX-based systems, this uses malloc. On Windows, it uses HeapAlloc
-  /// against the default public heap. Allocation of either element size or count
-  /// of 0 is undefined.
-  ///
-  /// Throws an ArgumentError on failure to allocate.
-  Pointer<T> allocate<T extends NativeType>({int count = 1}) =>
-      packageFfi.allocate(count: count);
-
-  /// Releases memory on the native heap.
-  ///
-  /// For POSIX-based systems, this uses free. On Windows, it uses HeapFree
-  /// against the default public heap. It may only be used against pointers
-  /// allocated in a manner equivalent to [allocate].
-  ///
-  /// Throws an ArgumentError on failure to free.
-  ///
-  void free(Pointer pointer) => packageFfi.free(pointer);
-}
-
-/// Does not manage it's resources.
-final Unmanaged unmanaged = Unmanaged();
-
-extension Utf8InPool on String {
-  /// Convert a [String] to a Utf8-encoded null-terminated C string.
-  ///
-  /// If 'string' contains NULL bytes, the converted string will be truncated
-  /// prematurely. Unpaired surrogate code points in [string] will be preserved
-  /// in the UTF-8 encoded result. See [Utf8Encoder] for details on encoding.
-  ///
-  /// Returns a malloc-allocated pointer to the result.
-  ///
-  /// The memory is managed by the [Pool] passed in as [pool].
-  Pointer<Utf8> toUtf8(ResourceManager pool) {
-    final units = utf8.encode(this);
-    final Pointer<Uint8> result = pool.allocate<Uint8>(count: units.length + 1);
-    final Uint8List nativeString = result.asTypedList(units.length + 1);
-    nativeString.setAll(0, units);
-    nativeString[units.length] = 0;
-    return result.cast();
-  }
-}
-
-extension Utf8Helpers on Pointer<Utf8> {
-  /// Returns the length of a null-terminated string -- the number of (one-byte)
-  /// characters before the first null byte.
-  int strlen() {
-    final Pointer<Uint8> array = this.cast<Uint8>();
-    final Uint8List nativeString = array.asTypedList(_maxSize);
-    return nativeString.indexWhere((char) => char == 0);
-  }
-
-  /// Creates a [String] containing the characters UTF-8 encoded in [this].
-  ///
-  /// [this] must be a zero-terminated byte sequence of valid UTF-8
-  /// encodings of Unicode code points. It may also contain UTF-8 encodings of
-  /// unpaired surrogate code points, which is not otherwise valid UTF-8, but
-  /// which may be created when encoding a Dart string containing an unpaired
-  /// surrogate. See [Utf8Decoder] for details on decoding.
-  ///
-  /// Returns a Dart string containing the decoded code points.
-  String contents() {
-    final int length = strlen();
-    return utf8.decode(Uint8List.view(
-        this.cast<Uint8>().asTypedList(length).buffer, 0, length));
-  }
-}
-
-const int _kMaxSmi64 = (1 << 62) - 1;
-const int _kMaxSmi32 = (1 << 30) - 1;
-final int _maxSize = sizeOf<IntPtr>() == 8 ? _kMaxSmi64 : _kMaxSmi32;

samples/ffi/resource_management/pool_sample.dart

@@ -9,6 +9,7 @@ import 'dart:ffi';
 import 'package:expect/expect.dart';
 
 import 'pool.dart';
+import 'utf8_helpers.dart';
 import '../dylib_utils.dart';
 
 main() {
@@ -21,7 +22,7 @@ main() {
 
   // To ensure resources are freed, wrap them in a [using] call.
   using((Pool pool) {
-    final p = pool.allocate<Int64>(count: 2);
+    final p = pool<Int64>(2);
     p[0] = 24;
     MemMove(p.elementAt(1).cast<Void>(), p.cast<Void>(), sizeOf<Int64>());
     print(p[1]);
@@ -31,23 +32,23 @@ main() {
   // Resources are freed also when abnormal control flow occurs.
   try {
     using((Pool pool) {
-      final p = pool.allocate<Int64>(count: 2);
+      final p = pool<Int64>(2);
       p[0] = 25;
       MemMove(p.elementAt(1).cast<Void>(), p.cast<Void>(), 8);
       print(p[1]);
       Expect.equals(25, p[1]);
       throw Exception("Some random exception");
     });
-    // `free(p)` has been called.
+    // `calloc.free(p)` has been called.
   } on Exception catch (e) {
     print("Caught exception: $e");
   }
 
   // In a pool multiple resources can be allocated, which will all be freed
   // at the end of the scope.
   using((Pool pool) {
-    final p = pool.allocate<Int64>(count: 2);
-    final p2 = pool.allocate<Int64>(count: 2);
+    final p = pool<Int64>(2);
+    final p2 = pool<Int64>(2);
     p[0] = 1;
     p[1] = 2;
     MemMove(p2.cast<Void>(), p.cast<Void>(), 2 * sizeOf<Int64>());
@@ -58,7 +59,7 @@ main() {
   // If the resource allocation happens in a different scope, then one either
   // needs to pass the pool to that scope.
   f1(Pool pool) {
-    return pool.allocate<Int64>(count: 2);
+    return pool<Int64>(2);
   }
 
   using((Pool pool) {