Implement request group and pause/resume support #665

lucasr · 2014-09-22T14:47:30Z

Ok, here's an initial take on the whole pause/resume support for Picasso.

This PR adds a new API to RequestCreator that allows you set a group tag/marker to specific requests:

Picasso.with(context)
       .load("http://example.com/image.jpg")
       .group("mygroup")
       .into(someImageView)

By default, all requests are associated with the default group defined as Picasso.DEFAULT_GROUP. This tag can be used to cancel, pause, and resume requests in the same group. To do so, you can use the following new APIs in Picasso:

cancelRequestGroup(String group)
pauseRequestGroup(String group)
resumeRequestGroup(String group)

Here are a few general notes on how this new API behaves:

When you pause a group, any new request for the paused group will not be attached to any BitmapHunter until the group gets resumed. In this case, the requests for a paused group will be queued in the Dispatcher (see pausedActions member).
If a request group is paused while there are already on-going requests for it (i.e. BitmapHunter is either running or waiting for its turn), the requests in the now paused group will get detached from any pending BitmapHunter immediately. If the affected BitmapHunter ends up with no pending actions, it will get canceled (see performPauseGroup).
If a request is canceled while its group is paused, it will be removed from the queue of paused requests accordingly (see performCancel). This might happen, for example, if a new request is initiated for the same target than a paused request.
A BitmapHunter might contain Actions from multiple groups at any given time. Not likely to happen in practice, but it's something we have to handle. This is why there's no 1-to-1 mapping between BitmapHunter and requests groups.

I should probably add some more tests for the new APIs. But I wanted to get some early feedback before spending more time on them. I've added a super simple scroll listener based on the new API. Works like a charm ;-)

closes #561

JakeWharton · 2014-09-22T14:48:57Z

picasso-sample/src/main/java/com/example/picasso/SampleScrollListener.java

+  @Override
+  public void onScrollStateChanged(AbsListView absListView, int scrollState) {
+    final Picasso picasso = Picasso.with(context);
+    if (scrollState == SCROLL_STATE_IDLE || scrollState == SCROLL_STATE_TOUCH_SCROLL) {


No settling state :( Damn you, AbsListView.

lucasr · 2014-09-22T17:59:34Z

Updated the branch:

Changed group identifier to be an Object instead of String. Also added a thorough cautionary note on the group(Object) documentation.
Cleaner loop when pausing a group.

cypressious · 2014-09-22T18:06:29Z

picasso/src/main/java/com/squareup/picasso/RequestCreator.java

@@ -156,6 +157,35 @@ public RequestCreator error(Drawable errorDrawable) {
  }

  /**
+   * Assign this request to a group. Request groups are an easy way to logically
+   * associate related requests that must managed (paused, resumed, or canceled)


Small nitpick: Should be "that must be managed"

Fixed, thanks.

dnkoutso · 2014-09-22T19:29:28Z

This is awesome and a great example why I love OSS.

I am curious about the performance gains from this change. I've always thought the sample app had good performance and near 60fps but everynow and then it would skip a frame. I think this will eliminate this.

JakeWharton · 2014-09-22T19:52:30Z

What do you think about naming this "tag" for parity with OkHttp and Volley (and eventually maybe Retrofit)?

lucasr · 2014-09-22T20:15:05Z

@JakeWharton I'm fine with "tag". I started with it but thought the notion of "request groups" sounded cooler :-) Method names looked a bit verbose though e.g. cancelRequestsWithTag, resumeRequestsWithTag, pauseRequestsWithTag. Any suggestions for the method names?

lucasr · 2014-09-22T20:18:30Z

Maybe just cancelRequests, pauseRequests, and resumeRequests?

lucasr · 2014-09-22T20:48:02Z

Updated branch:

Renamed "group" terminology to "tag" throughout:
- cancelRequestGroup(Object) → cancelRequests(Object)
- pauseRequestGroup(Object) → pauseRequests(Object)
- resumeRequestGroup(Object) → resumeRequests(Object)

JakeWharton · 2014-09-22T21:44:52Z

I was going to say we could just do cancelTag, resumeTag, etc. Requests are the only public-facing unit of work we have and we don't emphasize it anywhere in the public API's method names. Plus it's strange to call .tag(Object) on the builder and another method without "tag" in its name.

lucasr · 2014-09-22T21:49:17Z

@JakeWharton Good point. Done.

lucasr · 2014-09-22T23:05:52Z

Updated branch:

cancelRequests(Object) → cancelTag(Object)
pauseRequests(Object) → pauseTag(Object)
resumeRequests(Object) → resumeTag(Object)
Removed Picasso.DEFAULT_TAG. When tag is null, the Action instance uses itself as its tag—idea borrowed from OkHttp.
Moar tests on new API
Updated sample app to use an Activity as request tag. Ensures there are no pending requests in the activity by calling cancelTag(this) in onDestroy().
Documentation fixes and other small tweaks.

FWIW, I'm happy with the state of the branch now. The only open question I can think of is whether or not we want to have APIs to cancel/pause/resume all requests. We can do this in a follow-up ticket after merging this PR though. Thoughts?

lucasr · 2014-09-22T23:09:11Z

Also, maybe add this PR to the 2.4 milestone and close #561?

JakeWharton · 2014-09-23T02:58:50Z

We don't really use milestones much. Just when were planning issues for the
future, and only about half.
On Sep 22, 2014 7:09 PM, "Lucas Rocha" notifications@github.com wrote:

Also, maybe add this PR to the 2.4 milestone and close #561
#561?

—
Reply to this email directly or view it on GitHub
#665 (comment).

JakeWharton · 2014-09-23T03:04:52Z

picasso/src/main/java/com/squareup/picasso/RequestCreator.java

+   * associate related requests that can be managed (paused, resumed, or canceled)
+   * as a tag.
+   * <p>
+   * Most of the time, you'll be using {@link String} tags but you can also use objects


I will never use strings so let's not say most.

JakeWharton · 2014-09-23T03:17:49Z

This looks fantastic. Beers will reign down upon you the next time you come to SF. Thanks for putting up with our sometimes ridiculous nit picking.

lucasr · 2014-09-23T09:00:20Z

Branch updated with all suggested changes.

JakeWharton · 2014-09-23T13:23:58Z

picasso/src/main/java/com/squareup/picasso/Dispatcher.java

+    if (pausedTags.contains(action.getTag())) {
+      pausedActions.put(action.getTarget(), action);
+      if (action.getPicasso().loggingEnabled) {
+        log(OWNER_DISPATCHER, VERB_IGNORED, action.request.logId(),


I think we want to reuse the "Paused" verb here. "Ignored" makes it seem like we aren't deferring the request.

JakeWharton · 2014-09-23T13:27:40Z

Sorry one more tiny, tiny thing. LGTM otherwise!

lucasr · 2014-09-23T13:39:48Z

@JakeWharton Branch updated.

JakeWharton · 2014-09-23T13:40:10Z

You need to rebase, but only because I merged your other awesome PR.

lucasr · 2014-09-23T13:59:49Z

Rebased.

Implement request group and pause/resume support

JakeWharton · 2014-09-23T14:15:34Z

Thanks!

lucasr · 2014-09-23T14:18:30Z

\o/

cypressious · 2014-09-23T15:20:28Z

When can we expect a release?

JakeWharton · 2014-09-23T15:28:06Z

We don't provide ETAs. We'll release when we feel that it's been thoroughly tested and stable.

felipecsl · 2014-09-24T14:19:37Z

This is awesome. Big kudos!

lucasr mentioned this pull request Sep 22, 2014

ScrollListener to improve performance #561

Closed

JakeWharton reviewed Sep 22, 2014
View reviewed changes

cypressious reviewed Sep 22, 2014
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dnkoutso added this to the Picasso 2.4 milestone Sep 23, 2014

JakeWharton reviewed Sep 23, 2014
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lucasr added 2 commits September 23, 2014 14:57

Implement request tagging and pause/resume support

38ecd59

Use new pause/resume support in sample app

1582094

JakeWharton added a commit that referenced this pull request Sep 23, 2014

Merge pull request #665 from lucasr/request-group

547ebdb

Implement request group and pause/resume support

JakeWharton merged commit 547ebdb into square:master Sep 23, 2014

This was referenced Sep 23, 2014

heavy performance issue #507

Closed

Provide ScrollListener support #433

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This was referenced Sep 23, 2014

prioritise image downloads #344

Closed

How to pause any ongoing background work? #248

Closed

lucasr mentioned this pull request Sep 25, 2014

Implement a Bitmap pool for Picasso #672

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Implement request group and pause/resume support #665

Implement request group and pause/resume support #665

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Implement request group and pause/resume support #665

Implement request group and pause/resume support #665

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