{"action":"created","comment":{"url":"https://api.github.com/repos/grpc/grpc-java/pulls/comments/92525005","pull_request_review_id":13042123,"id":92525005,"diff_hunk":"@@ -85,13 +87,50 @@\n   @Nullable\n   private SubchannelPicker lastPicker;\n \n-  DelayedClientTransport2(Executor streamCreationExecutor) {\n-    this.streamCreationExecutor = streamCreationExecutor;\n+  @GuardedBy(\"lock\")\n+  private long lastPickerVersion;","path":"core/src/main/java/io/grpc/internal/DelayedClientTransport2.java","position":36,"original_position":36,"commit_id":"bd554fbe2ae3d8bb6dce55d297b6e56d39cd1b75","original_commit_id":"bd554fbe2ae3d8bb6dce55d297b6e56d39cd1b75","user":{"login":"zhangkun83","id":9053690,"avatar_url":"https://avatars.githubusercontent.com/u/9053690?v=3","gravatar_id":"","url":"https://api.github.com/users/zhangkun83","html_url":"https://github.com/zhangkun83","followers_url":"https://api.github.com/users/zhangkun83/followers","following_url":"https://api.github.com/users/zhangkun83/following{/other_user}","gists_url":"https://api.github.com/users/zhangkun83/gists{/gist_id}","starred_url":"https://api.github.com/users/zhangkun83/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/zhangkun83/subscriptions","organizations_url":"https://api.github.com/users/zhangkun83/orgs","repos_url":"https://api.github.com/users/zhangkun83/repos","events_url":"https://api.github.com/users/zhangkun83/events{/privacy}","received_events_url":"https://api.github.com/users/zhangkun83/received_events","type":"User","site_admin":false},"body":"In case of pick-first, there is only one Subchannel, thus the picker may return it in `IDLE`, `CONNECTING` and `READY`. `CONNECTING->READY` must trigger `updatePicker` to get the delayed streams reprocessed. Without this change, the LoadBalancer *must* create a new picker instance, even if it's literally the same, otherwise new streams that race with `updatePicker` may have this failure mode:\r\n1. T1: `DelayedClientTransport.newStream()`, enters the while-loop, gets null transport because it's still CONNECTING, not yet enters the synchronized block.\r\n2. T2: transport CONNECTING->READY, calls `updatePicker()` with the same picker\r\n3. T1:  enters the synchronized block, finds `picker == lastPicker`, even though `lastPicker` was rewritten after `newStream()` started.\r\n4. Outcome: the stream will be buffered, even though the Subchannel is already READY.\r\n\r\nOf course the pick-first LB could work this around by excluding CONNECTING Subchannels, thus returning `withNoResult()` for CONNECTING state, forcing a different picker to be created for the `CONNECTING->READY` transition, but the version number actually **fixes an inconsistency in delayed transport**: `reprocess()` does not ignore identical pickers, but the while-loop in `newStream()`, which is meant to solve the race between `reprocess()` and `newStream(), did ignore identical pickers.","created_at":"2016-12-15T01:00:44Z","updated_at":"2016-12-15T01:07:13Z","html_url":"https://github.com/grpc/grpc-java/pull/2505#discussion_r92525005","pull_request_url":"https://api.github.com/repos/grpc/grpc-java/pulls/2505","_links":{"self":{"href":"https://api.github.com/repos/grpc/grpc-java/pulls/comments/92525005"},"html":{"href":"https://github.com/grpc/grpc-java/pull/2505#discussion_r92525005"},"pull_request":{"href":"https://api.github.com/repos/grpc/grpc-java/pulls/2505"}}},"pull_request":{"url":"https://api.github.com/repos/grpc/grpc-java/pulls/2505","id":97607686,"html_url":"https://github.com/grpc/grpc-java/pull/2505","diff_url":"https://github.com/grpc/grpc-java/pull/2505.diff","patch_url":"https://github.com/grpc/grpc-java/pull/2505.patch","issue_url":"https://api.github.com/repos/grpc/grpc-java/issues/2505","number":2505,"state":"open","locked":false,"title":"core: two changes on DelayedClientTransport2.","user":{"login":"zhangkun83","id":9053690,"avatar_url":"https://avatars.githubusercontent.com/u/9053690?v=3","gravatar_id":"","url":"https://api.github.com/users/zhangkun83","html_url":"https://github.com/zhangkun83","followers_url":"https://api.github.com/users/zhangkun83/followers","following_url":"https://api.github.com/users/zhangkun83/following{/other_user}","gists_url":"https://api.github.com/users/zhangkun83/gists{/gist_id}","starred_url":"https://api.github.com/users/zhangkun83/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/zhangkun83/subscriptions","organizations_url":"https://api.github.com/users/zhangkun83/orgs","repos_url":"https://api.github.com/users/zhangkun83/repos","events_url":"https://api.github.com/users/zhangkun83/events{/privacy}","received_events_url":"https://api.github.com/users/zhangkun83/received_events","type":"User","site_admin":false},"body":"1. 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Rationale: if reprocess() is called again with\r\nthe same picker, all pending streams will be reprocessed by this picker\r\nagain, thus there is no reason to leave out the racing new stream.","created_at":"2016-12-12T18:33:05Z","updated_at":"2016-12-15T01:07:13Z","closed_at":null,"merged_at":null,"merge_commit_sha":"6687f335e273d667ba3a5e25c8134f8ff6f5d320","assignee":{"login":"ejona86","id":2811396,"avatar_url":"https://avatars.githubusercontent.com/u/2811396?v=3","gravatar_id":"","url":"https://api.github.com/users/ejona86","html_url":"https://github.com/ejona86","followers_url":"https://api.github.com/users/ejona86/followers","following_url":"https://api.github.com/users/ejona86/following{/other_user}","gists_url":"https://api.github.com/users/ejona86/gists{/gist_id}","starred_url":"https://api.github.com/users/ejona86/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/ejona86/subscriptions","organizations_url":"https://api.github.com/users/ejona86/orgs","repos_url":"https://api.github.com/users/ejona86/repos","events_url":"https://api.github.com/users/ejona86/events{/privacy}","received_events_url":"https://api.github.com/users/ejona86/received_events","type":"User","site_admin":false},"assignees":[{"login":"ejona86","id":2811396,"avatar_url":"https://avatars.githubusercontent.com/u/2811396?v=3","gravatar_id":"","url":"https://api.github.com/users/ejona86","html_url":"https://github.com/ejona86","followers_url":"https://api.github.com/users/ejona86/followers","following_url":"https://api.github.com/users/ejona86/following{/other_user}","gists_url":"https://api.github.com/users/ejona86/gists{/gist_id}","starred_url":"https://api.github.com/users/ejona86/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/ejona86/subscriptions","organizations_url":"https://api.github.com/users/ejona86/orgs","repos_url":"https://api.github.com/users/ejona86/repos","events_url":"https://api.github.com/users/ejona86/events{/privacy}","received_events_url":"https://api.github.com/users/ejona86/received_events","type":"User","site_admin":false}],"milestone":null,"commits_url":"https://api.github.com/repos/grpc/grpc-java/pulls/2505/commits","review_comments_url":"https://api.github.com/repos/grpc/grpc-java/pulls/2505/comments","review_comment_url":"https://api.github.com/repos/grpc/grpc-java/pulls/comments{/number}","comments_url":"https://api.github.com/repos/grpc/grpc-java/issues/2505/comments","statuses_url":"https://api.github.com/repos/grpc/grpc-java/statuses/bd554fbe2ae3d8bb6dce55d297b6e56d39cd1b75","head":{"label":"zhangkun83:lbv2_delayedtransport_3","ref":"lbv2_delayedtransport_3","sha":"bd554fbe2ae3d8bb6dce55d297b6e56d39cd1b75","user":{"login":"zhangkun83","id":9053690,"avatar_url":"https://avatars.githubusercontent.com/u/9053690?v=3","gravatar_id":"","url":"https://api.github.com/users/zhangkun83","html_url":"https://github.com/zhangkun83","followers_url":"https://api.github.com/users/zhangkun83/followers","following_url":"https://api.github.com/users/zhangkun83/following{/other_user}","gists_url":"https://api.github.com/users/zhangkun83/gists{/gist_id}","starred_url":"https://api.github.com/users/zhangkun83/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/zhangkun83/subscriptions","organizations_url":"https://api.github.com/users/zhangkun83/orgs","repos_url":"https://api.github.com/users/zhangkun83/repos","events_url":"https://api.github.com/users/zhangkun83/events{/privacy}","received_events_url":"https://api.github.com/users/zhangkun83/received_events","type":"User","site_admin":false},"repo":{"id":31399597,"name":"grpc-java","full_name":"zhangkun83/grpc-java","owner":{"login":"zhangkun83","id":9053690,"avatar_url":"https://avatars.githubusercontent.com/u/9053690?v=3","gravatar_id":"","url":"https://api.github.com/users/zhangkun83","html_url":"https://github.com/zhangkun83","followers_url":"https://api.github.com/users/zhangkun83/followers","following_url":"https://api.github.com/users/zhangkun83/following{/other_user}","gists_url":"https://api.github.com/users/zhangkun83/gists{/gist_id}","starred_url":"https://api.github.com/users/zhangkun83/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/zhangkun83/subscriptions","organizations_url":"https://api.github.com/users/zhangkun83/orgs","repos_url":"https://api.github.com/users/zhangkun83/repos","events_url":"https://api.github.com/users/zhangkun83/events{/privacy}","received_events_url":"https://api.github.com/users/zhangkun83/received_events","type":"User","site_admin":false},"private":false,"html_url":"https://github.com/zhangkun83/grpc-java","description":"The Java gRPC implementation. 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