[dart-announce] Calling close on dart:io HttpClient is now required

[Søren Gjesse]

In r39542 we changed the dart:io HttpClient shutdown handling. This

enables proper handling of HTTP persistent connections. However this also

adds the requirement for calling HttpClient.close when done using it. Failing

to call HttpClient.close can cause your dart:io programs to hang until the

HttpClient.idleTimeout has expired after all I/O activity has otherwise

completed. The default value for HttpClient.idleTimeout is 15 seconds.

Note that the documentation for dart:io HttpClient have always stated that

calling HttpClient.close was required to close idle persistent connections.

If you are experiencing shutdown issues with your dart:io program which might

be related to this change, you can simulate the behavior from before this

change by lowering client.idleTimeout:

 var client = new HttpClient();

 client.idleTimeout = const Duration(milliseconds: 100);

This should only be used as a short term workaround. Tracking your HttpClient

instances and closing them properly is the right thing to do.

This change will be part of the first 1.7 developer release.

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[tomaszkubacki]

seeing that, I miss from C#

using statement.

e.g

using(some_disposable_resource){

...//do some operations on some_disposable_resource

}

//will be disposed,closed,whatever here....

[Martin Kustermann]

You can potentially implement this yourself. The new await/async syntax will make it significantly easier to implement. The only requirement is that you get a Future which completes once you're done with an HttpClient. For example:

Something like this:

// Usage:

var client = new HttpClient();

using(client, () {

  return await someOperation(client);

});

// Implementation of using

Future using(resource, operation) {

  return operation().whenComplete(() => resource.close());

}

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['Bob Nystrom' via Dart Announcements]

On Tue, Aug 26, 2014 at 5:13 AM, 'Martin Kustermann' via Dart Announcements <anno...@dartlang.org> wrote:

You can potentially implement this yourself. The new await/async syntax will make it significantly easier to implement. The only requirement is that you get a Future which completes once you're done with an HttpClient. For example:

Something like this:

// Usage:

var client = new HttpClient();

using(client, () {

  return await someOperation(client);

});

To use await here, you also have to mark the function async:

using(client, () async {

  return await someOperation(client);

});

But it isn't buying you anything in this case. You can just do:

using(client, () {

  return someOperation(client);

});

or even:

using(client, () => someOperation(client));

- bob

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[Cogman]

Yeah. It would be nice if dart had a resource leak prevention thingy (try with resources in java, using C#, destructors in C++).

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