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  1. 52048d3 allow the 2.12 prerelease sdks (#44) by Jacob MacDonald · 8 days ago master 1.5.0-nullsafety.2
  2. 5633543 Prepare for the 2.11 dev SDKs (#43) by Nate Bosch · 6 weeks ago 1.5.0-nullsafety.1
  3. 8d7b580 Fixes for Dart 2.10 (#42) by Kevin Moore · 3 months ago 1.5.0-nullsafety
  4. eedbd5f update for the 2.10 dev sdk (#41) by Jacob MacDonald · 3 months ago
  5. e33cec8 Merge the null_safety branch into master (#40) by Jacob MacDonald · 4 months ago

The pool package exposes a Pool class which makes it easy to manage a limited pool of resources.

The easiest way to use a pool is by calling withResource. This runs a callback and returns its result, but only once there aren't too many other callbacks currently running.

// Create a Pool that will only allocate 10 resources at once. After 30 seconds
// of inactivity with all resources checked out, the pool will throw an error.
final pool = new Pool(10, timeout: new Duration(seconds: 30));

Future<String> readFile(String path) {
  // Since the call to [File.readAsString] is within [withResource], no more
  // than ten files will be open at once.
  return pool.withResource(() => new File(path).readAsString());

For more fine-grained control, the user can also explicitly request generic PoolResource objects that can later be released back into the pool. This is what withResource does under the covers: requests a resource, then releases it once the callback completes.

Pool ensures that only a limited number of resources are allocated at once. It‘s the caller’s responsibility to ensure that the corresponding physical resource is only consumed when a PoolResource is allocated.

class PooledFile implements RandomAccessFile {
  final RandomAccessFile _file;
  final PoolResource _resource;

  static Future<PooledFile> open(String path) {
    return pool.request().then((resource) {
      return new File(path).open().then((file) {
        return new PooledFile._(file, resource);

  PooledFile(this._file, this._resource);

  // ...

  Future<RandomAccessFile> close() {
    return _file.close.then((_) {
      return this;