[SPARK-3993] [PySpark] fix bug while reuse worker after take()

After take(), maybe there are some garbage left in the socket, then next task assigned to this worker will hang because of corrupted data.

We should make sure the socket is clean before reuse it, write END_OF_STREAM at the end, and check it after read out all result from python.

Author: Davies Liu <davies.liu@gmail.com>
Author: Davies Liu <davies@databricks.com>

Closes #2838 from davies/fix_reuse and squashes the following commits:

8872914 [Davies Liu] fix tests
660875b [Davies Liu] fix bug while reuse worker after take()
[SPARK-4000][BUILD] Sends archived unit tests logs to Jenkins master

This PR sends archived unit tests logs to the build history directory in Jenkins master, so that we can serve it via HTTP later to help debugging Jenkins build failures.

pwendell JoshRosen Please help review, thanks!

Author: Cheng Lian <lian@databricks.com>

Closes #2845 from liancheng/log-archive and squashes the following commits:

ac8d9d4 [Cheng Lian] Includes build number in messages posted to GitHub
68c7010 [Cheng Lian] Logs backup should be implemented in dev/run-tests-jenkins
4b912f7 [Cheng Lian] Sends archived unit tests logs to Jenkins master
SPARK-3812 Build changes to publish effective pom.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #2921 from ScrapCodes/build-changes-effective-pom and squashes the following commits:

8841491 [Prashant Sharma] Fixed broken maven build.
aa7b91d [Prashant Sharma] used an unused dep.
0300dac [Prashant Sharma] improved comment messages..
28f891e [Prashant Sharma] Added a useless dependency, so that we can shade it. And realized fake shading works for us.
553d96b [Prashant Sharma] Shaded some unused class of an unused dep, to generate effective pom(s)
[SPARK-2652] [PySpark] donot use KyroSerializer as default serializer

KyroSerializer can not serialize customized class without registered explicitly, use it as default serializer in PySpark will introduce some regression in MLlib.

cc mengxr

Author: Davies Liu <davies@databricks.com>

Closes #2916 from davies/revert and squashes the following commits:

43eb6d3 [Davies Liu] donot use KyroSerializer as default serializer
[SPARK-3900][YARN] ApplicationMaster's shutdown hook fails and IllegalStateException is thrown.

ApplicationMaster registers a shutdown hook and it calls ApplicationMaster#cleanupStagingDir.

cleanupStagingDir invokes FileSystem.get(yarnConf) and it invokes FileSystem.getInternal. FileSystem.getInternal also registers shutdown hook.
In FileSystem of hadoop 0.23, the shutdown hook registration does not consider whether shutdown is in progress or not (In 2.2, it's considered).

    // 0.23
    if (map.isEmpty() ) {
      ShutdownHookManager.get().addShutdownHook(clientFinalizer, SHUTDOWN_HOOK_PRIORITY);
    }

    // 2.2
    if (map.isEmpty()
                && !ShutdownHookManager.get().isShutdownInProgress()) {
       ShutdownHookManager.get().addShutdownHook(clientFinalizer, SHUTDOWN_HOOK_PRIORITY);
    }

Thus, in 0.23, another shutdown hook can be registered when ApplicationMaster's shutdown hook run.

This issue cause IllegalStateException as follows.

    java.lang.IllegalStateException: Shutdown in progress, cannot add a shutdownHook
            at org.apache.hadoop.util.ShutdownHookManager.addShutdownHook(ShutdownHookManager.java:152)
            at org.apache.hadoop.fs.FileSystem$Cache.getInternal(FileSystem.java:2306)
            at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:2278)
            at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:316)
            at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:162)
            at org.apache.spark.deploy.yarn.ApplicationMaster.org$apache$spark$deploy$yarn$ApplicationMaster$$cleanupStagingDir(ApplicationMaster.scala:307)
            at org.apache.spark.deploy.yarn.ApplicationMaster$$anon$3.run(ApplicationMaster.scala:118)
            at org.apache.hadoop.util.ShutdownHookManager$1.run(ShutdownHookManager.java:54)

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2924 from sarutak/SPARK-3900-2 and squashes the following commits:

9112817 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3900-2
97018fa [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3900
2c2850e [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3900
ee52db2 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3900
a7d6c9b [Kousuke Saruta] Merge branch 'SPARK-3900' of github.com:sarutak/spark into SPARK-3900
1cdf03c [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3900
a5f6443 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-3900
57b397d [Kousuke Saruta] Fixed IllegalStateException caused by shutdown hook registration in another shutdown hook
[SPARK-4051] [SQL] [PySpark] Convert Row into dictionary

Added a method to Row to turn row into dict:

```
>>> row = Row(a=1)
>>> row.asDict()
{'a': 1}
```

Author: Davies Liu <davies@databricks.com>

Closes #2896 from davies/dict and squashes the following commits:

8d97366 [Davies Liu] convert Row into dict
[SPARK-4050][SQL] Fix caching of temporary tables with projections.

Previously cached data was found by `sameResult` plan matching on optimized plans.  This technique however fails to locate the cached data when a temporary table with a projection is queried with a further reduced projection.  The failure is due to the fact that optimization will collapse the projections, producing a plan that no longer produces the sameResult as the cached data (though the cached data still subsumes the desired data).  For example consider the following previously failing test case.

```scala
sql("CACHE TABLE tempTable AS SELECT key FROM testData")
assertCached(sql("SELECT COUNT(*) FROM tempTable"))
```

In this PR I change the matching to occur after analysis instead of optimization, so that in the case of temporary tables, the plans will always match.  I think this should work generally, however, this error does raise questions about the need to do more thorough subsumption checking when locating cached data.

Another question is what sort of semantics we want to provide when uncaching data from temporary tables.  For example consider the following sequence of commands:

```scala
testData.select('key).registerTempTable("tempTable1")
testData.select('key).registerTempTable("tempTable2")
cacheTable("tempTable1")

// This obviously works.
assertCached(sql("SELECT COUNT(*) FROM tempTable1"))

// It seems good that this works ...
assertCached(sql("SELECT COUNT(*) FROM tempTable2"))

// ... but is this valid?
uncacheTable("tempTable2")

// Should this still be cached?
assertCached(sql("SELECT COUNT(*) FROM tempTable1"), 0)
```

Author: Michael Armbrust <michael@databricks.com>

Closes #2912 from marmbrus/cachingBug and squashes the following commits:

9c822d4 [Michael Armbrust] remove commented out code
5c72fb7 [Michael Armbrust] Add a test case / question about uncaching semantics.
63a23e4 [Michael Armbrust] Perform caching on analyzed instead of optimized plan.
03f1cfe [Michael Armbrust] Clean-up / add tests to SameResult suite.
[SPARK-2706][SQL] Enable Spark to support Hive 0.13

Given that a lot of users are trying to use hive 0.13 in spark, and the incompatibility between hive-0.12 and hive-0.13 on the API level I want to propose following approach, which has no or minimum impact on existing hive-0.12 support, but be able to jumpstart the development of hive-0.13 and future version support.

Approach: Introduce “hive-version” property,  and manipulate pom.xml files to support different hive version at compiling time through shim layer, e.g., hive-0.12.0 and hive-0.13.1. More specifically,

1. For each different hive version, there is a very light layer of shim code to handle API differences, sitting in sql/hive/hive-version, e.g., sql/hive/v0.12.0 or sql/hive/v0.13.1

2. Add a new profile hive-default active by default, which picks up all existing configuration and hive-0.12.0 shim (v0.12.0)  if no hive.version is specified.

3. If user specifies different version (currently only 0.13.1 by -Dhive.version = 0.13.1), hive-versions profile will be activated, which pick up hive-version specific shim layer and configuration, mainly the hive jars and hive-version shim, e.g., v0.13.1.

4. With this approach, nothing is changed with current hive-0.12 support.

No change by default: sbt/sbt -Phive
For example: sbt/sbt -Phive -Pyarn -Phadoop-2.4 -Dhadoop.version=2.4.0 assembly

To enable hive-0.13: sbt/sbt -Dhive.version=0.13.1
For example: sbt/sbt -Dhive.version=0.13.1 -Pyarn -Phadoop-2.4 -Dhadoop.version=2.4.0 assembly

Note that in hive-0.13, hive-thriftserver is not enabled, which should be fixed by other Jira, and we don’t need -Phive with -Dhive.version in building (probably we should use -Phive -Dhive.version=xxx instead after thrift server is also supported in hive-0.13.1).

Author: Zhan Zhang <zhazhan@gmail.com>
Author: zhzhan <zhazhan@gmail.com>
Author: Patrick Wendell <pwendell@gmail.com>

Closes #2241 from zhzhan/spark-2706 and squashes the following commits:

3ece905 [Zhan Zhang] minor fix
410b668 [Zhan Zhang] solve review comments
cbb4691 [Zhan Zhang] change run-test for new options
0d4d2ed [Zhan Zhang] rebase
497b0f4 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
8fad1cf [Zhan Zhang] change the pom file and make hive-0.13.1 as the default
ab028d1 [Zhan Zhang] rebase
4a2e36d [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
4cb1b93 [zhzhan] Merge pull request #1 from pwendell/pr-2241
b0478c0 [Patrick Wendell] Changes to simplify the build of SPARK-2706
2b50502 [Zhan Zhang] rebase
a72c0d4 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
cb22863 [Zhan Zhang] correct the typo
20f6cf7 [Zhan Zhang] solve compatability issue
f7912a9 [Zhan Zhang] rebase and solve review feedback
301eb4a [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
10c3565 [Zhan Zhang] address review comments
6bc9204 [Zhan Zhang] rebase and remove temparory repo
d3aa3f2 [Zhan Zhang] Merge branch 'master' into spark-2706
cedcc6f [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
3ced0d7 [Zhan Zhang] rebase
d9b981d [Zhan Zhang] rebase and fix error due to rollback
adf4924 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
3dd50e8 [Zhan Zhang] solve conflicts and remove unnecessary implicts
d10bf00 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
dc7bdb3 [Zhan Zhang] solve conflicts
7e0cc36 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
d7c3e1e [Zhan Zhang] Merge branch 'master' into spark-2706
68deb11 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
d48bd18 [Zhan Zhang] address review comments
3ee3b2b [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
57ea52e [Zhan Zhang] Merge branch 'master' into spark-2706
2b0d513 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
9412d24 [Zhan Zhang] address review comments
f4af934 [Zhan Zhang] rebase
1ccd7cc [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
128b60b [Zhan Zhang] ignore 0.12.0 test cases for the time being
af9feb9 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
5f5619f [Zhan Zhang] restructure the directory and different hive version support
05d3683 [Zhan Zhang] solve conflicts
e4c1982 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
94b4fdc [Zhan Zhang] Spark-2706: hive-0.13.1 support on spark
87ebf3b [Zhan Zhang] Merge branch 'master' into spark-2706
921e914 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
f896b2a [Zhan Zhang] Merge branch 'master' into spark-2706
789ea21 [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
cb53a2c [Zhan Zhang] Merge branch 'master' of https://github.com/apache/spark
f6a8a40 [Zhan Zhang] revert
ba14f28 [Zhan Zhang] test
dbedff3 [Zhan Zhang] Merge remote-tracking branch 'upstream/master'
70964fe [Zhan Zhang] revert
fe0f379 [Zhan Zhang] Merge branch 'master' of https://github.com/zhzhan/spark
70ffd93 [Zhan Zhang] revert
42585ec [Zhan Zhang] test
7d5fce2 [Zhan Zhang] test
[SPARK-4026][Streaming] Write ahead log management

As part of the effort to avoid data loss on Spark Streaming driver failure, we want to implement a write ahead log that can write received data to HDFS. This allows the received data to be persist across driver failures. So when the streaming driver is restarted, it can find and reprocess all the data that were received but not processed.

This was primarily implemented by @harishreedharan. This is still WIP, as he is going to improve the unitests by using HDFS mini cluster.

Author: Hari Shreedharan <hshreedharan@apache.org>
Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #2882 from tdas/driver-ha-wal and squashes the following commits:

e4bee20 [Tathagata Das] Removed synchronized, Path.getFileSystem is threadsafe
55514e2 [Tathagata Das] Minor changes based on PR comments.
d29fddd [Tathagata Das] Merge pull request #20 from harishreedharan/driver-ha-wal
a317a4d [Hari Shreedharan] Directory deletion should not fail tests
9514dc8 [Tathagata Das] Added unit tests to test reading of corrupted data and other minor edits
3881706 [Tathagata Das] Merge pull request #19 from harishreedharan/driver-ha-wal
4705fff [Hari Shreedharan] Sort listed files by name. Use local files for WAL tests.
eb356ca [Tathagata Das] Merge pull request #18 from harishreedharan/driver-ha-wal
82ce56e [Hari Shreedharan] Fix file ordering issue in WALManager tests
5ff90ee [Hari Shreedharan] Fix tests to not ignore ordering and also assert all data is present
ef8db09 [Tathagata Das] Merge pull request #17 from harishreedharan/driver-ha-wal
7e40e56 [Hari Shreedharan] Restore old build directory after tests
587b876 [Hari Shreedharan] Fix broken test. Call getFileSystem only from synchronized method.
b4be0c1 [Hari Shreedharan] Remove unused method
edcbee1 [Hari Shreedharan] Tests reading and writing data using writers now use Minicluster.
5c70d1f [Hari Shreedharan] Remove underlying stream from the WALWriter.
4ab602a [Tathagata Das] Refactored write ahead stuff from streaming.storage to streaming.util
b06be2b [Tathagata Das] Adding missing license.
5182ffb [Hari Shreedharan] Added documentation
172358d [Tathagata Das] Pulled WriteAheadLog-related stuff from tdas/spark/tree/driver-ha-working
[SPARK-2713] Executors of same application in same host should only download files & jars once

If Spark lunched multiple executors in one host for one application, every executor would download it dependent files and jars (if not using local: url) independently. It maybe result in huge latency. In my case, it result in 20 seconds latency to download dependent jars(size about 17M) when I lunched 32 executors in every host(total 4 hosts).

This patch will cache downloaded files and jars for executors to reduce network throughput and download latency. In my case, the latency was reduced from 20 seconds to less than 1 second.

Author: Li Zhihui <zhihui.li@intel.com>
Author: li-zhihui <zhihui.li@intel.com>

Closes #1616 from li-zhihui/cachefiles and squashes the following commits:

36940df [Li Zhihui] Close cache for local mode
935fed6 [Li Zhihui] Clean code.
f9330d4 [Li Zhihui] Clean code again
7050d46 [Li Zhihui] Clean code
074a422 [Li Zhihui] Fix: deal with spark.files.overwrite
03ed3a8 [li-zhihui] rename cache file name as XXXXXXXXX_cache
2766055 [li-zhihui] Use url.hashCode + timestamp as cachedFileName
76a7b66 [Li Zhihui] Clean code & use applcation work directory as cache directory
3510eb0 [Li Zhihui] Keep fetchFile private
2ffd742 [Li Zhihui] add comment for FileLock
e0ebd48 [Li Zhihui] Try and finally lock.release
7fb7c0b [Li Zhihui] Release lock before copy files
6b997bf [Li Zhihui] Executors of same application in same host should only download files & jars once
[SPARK-4076] Parameter expansion in spark-config is wrong

In sbin/spark-config.sh, parameter expansion is used to extract source root as follows.

    this="${BASH_SOURCE-$0}"

I think, the parameter expansion should be ":" instead of "".
If we use "-" and BASH_SOURCE="", (empty character is set, not unset),
"" (empty character) is set to $this.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2930 from sarutak/SPARK-4076 and squashes the following commits:

32a0370 [Kousuke Saruta] Fixed wrong parameter expansion
[SPARK-4075] [Deploy] Jar url validation is not enough for Jar file

In deploy.ClientArguments.isValidJarUrl, the url is checked as follows.

    def isValidJarUrl(s: String): Boolean = s.matches("(.+):(.+)jar")

So, it allows like 'hdfs:file.jar' (no authority).

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2925 from sarutak/uri-syntax-check-improvement and squashes the following commits:

cf06173 [Kousuke Saruta] Improved URI syntax checking
[SPARK-4013] Do not create multiple actor systems on each executor

In the existing code, each coarse-grained executor has two concurrently running actor systems. This causes many more error messages to be logged than necessary when the executor is lost or killed because we receive a disassociation event for each of these actor systems.

This is blocking #2840.

Author: Andrew Or <andrewor14@gmail.com>

Closes #2863 from andrewor14/executor-actor-system and squashes the following commits:

44ce2e0 [Andrew Or] Avoid starting two actor systems on each executor
[SPARK-4067] refactor ExecutorUncaughtExceptionHandler

https://issues.apache.org/jira/browse/SPARK-4067

currently , we call Utils.tryOrExit everywhere
AppClient
Executor
TaskSchedulerImpl
It makes the name of ExecutorUncaughtExceptionHandler unfit to the real case....

Author: Nan Zhu <nanzhu@Nans-MacBook-Pro.local>
Author: Nan Zhu <nanzhu@nans-mbp.home>

Closes #2913 from CodingCat/SPARK-4067 and squashes the following commits:

035ee3d [Nan Zhu] make RAT happy
e62e416 [Nan Zhu] add some general Exit code
a10b63f [Nan Zhu] refactor
[GraphX] Modify option name according to example doc in SynthBenchmark

Now graphx.SynthBenchmark example has an option of iteration number named as "niter". However, in its document, it is named as "niters". The mismatch between the implementation and document causes certain IllegalArgumentException while trying that example.

Author: Grace <jie.huang@intel.com>

Closes #2888 from GraceH/synthbenchmark and squashes the following commits:

f101ee1 [Grace] Modify option name according to example doc
[HOTFIX][SQL] Remove sleep on reset() failure.

Author: Michael Armbrust <michael@databricks.com>

Closes #2934 from marmbrus/patch-2 and squashes the following commits:

a96dab2 [Michael Armbrust] Remove sleep on reset() failure.
[SPARK-4080] Only throw IOException from [write|read][Object|External]

If classes implementing Serializable or Externalizable interfaces throw
exceptions other than IOException or ClassNotFoundException from their
(de)serialization methods, then this results in an unhelpful
"IOException: unexpected exception type" rather than the actual exception that
produced the (de)serialization error.

This patch fixes this by adding a utility method that re-wraps any uncaught
exceptions in IOException (unless they are already instances of IOException).

Author: Josh Rosen <joshrosen@databricks.com>

Closes #2932 from JoshRosen/SPARK-4080 and squashes the following commits:

cd3a9be [Josh Rosen] [SPARK-4080] Only throw IOException from [write|read][Object|External].
[SPARK-4056] Upgrade snappy-java to 1.1.1.5

This upgrades snappy-java to 1.1.1.5, which improves error messages when attempting to deserialize empty inputs using SnappyInputStream (see https://github.com/xerial/snappy-java/issues/89).

Author: Josh Rosen <rosenville@gmail.com>
Author: Josh Rosen <joshrosen@databricks.com>

Closes #2911 from JoshRosen/upgrade-snappy-java and squashes the following commits:

adec96c [Josh Rosen] Use snappy-java 1.1.1.5
cc953d6 [Josh Rosen] [SPARK-4056] Upgrade snappy-java to 1.1.1.4
[SQL] Update Hive test harness for Hive 12 and 13

As part of the upgrade I also copy the newest version of the query tests, and whitelist a bunch of new ones that are now passing.

Author: Michael Armbrust <michael@databricks.com>

Closes #2936 from marmbrus/fix13tests and squashes the following commits:

d9cbdab [Michael Armbrust] Remove user specific tests
65801cd [Michael Armbrust] style and rat
8f6b09a [Michael Armbrust] Update test harness to work with both Hive 12 and 13.
f044843 [Michael Armbrust] Update Hive query tests and golden files to 0.13
[SPARK-2321] Stable pull-based progress / status API

This pull request is a first step towards the implementation of a stable, pull-based progress / status API for Spark (see [SPARK-2321](https://issues.apache.org/jira/browse/SPARK-2321)).  For now, I'd like to discuss the basic implementation, API names, and overall interface design.  Once we arrive at a good design, I'll go back and add additional methods to expose more information via these API.

#### Design goals:

- Pull-based API
- Usable from Java / Scala / Python (eventually, likely with a wrapper)
- Can be extended to expose more information without introducing binary incompatibilities.
- Returns immutable objects.
- Don't leak any implementation details, preserving our freedom to change the implementation.

#### Implementation:

- Add public methods (`getJobInfo`, `getStageInfo`) to SparkContext to allow status / progress information to be retrieved.
- Add public interfaces (`SparkJobInfo`, `SparkStageInfo`) for our API return values.  These interfaces consist entirely of Java-style getter methods.  The interfaces are currently implemented in Java.  I decided to explicitly separate the interface from its implementation (`SparkJobInfoImpl`, `SparkStageInfoImpl`) in order to prevent users from constructing these responses themselves.
-Allow an existing JobProgressListener to be used when constructing a live SparkUI.  This allows us to re-use this listeners in the implementation of this status API.  There are a few reasons why this listener re-use makes sense:
   - The status API and web UI are guaranteed to show consistent information.
   - These listeners are already well-tested.
   - The same garbage-collection / information retention configurations can apply to both this API and the web UI.
- Extend JobProgressListener to maintain `jobId -> Job` and `stageId -> Stage` mappings.

The progress API methods are implemented in a separate trait that's mixed into SparkContext.  This helps to avoid SparkContext.scala from becoming larger and more difficult to read.

Author: Josh Rosen <joshrosen@databricks.com>
Author: Josh Rosen <joshrosen@apache.org>

Closes #2696 from JoshRosen/progress-reporting-api and squashes the following commits:

e6aa78d [Josh Rosen] Add tests.
b585c16 [Josh Rosen] Accept SparkListenerBus instead of more specific subclasses.
c96402d [Josh Rosen] Address review comments.
2707f98 [Josh Rosen] Expose current stage attempt id
c28ba76 [Josh Rosen] Update demo code:
646ff1d [Josh Rosen] Document spark.ui.retainedJobs.
7f47d6d [Josh Rosen] Clean up SparkUI constructors, per Andrew's feedback.
b77b3d8 [Josh Rosen] Merge remote-tracking branch 'origin/master' into progress-reporting-api
787444c [Josh Rosen] Move status API methods into trait that can be mixed into SparkContext.
f9a9a00 [Josh Rosen] More review comments:
3dc79af [Josh Rosen] Remove creation of unused listeners in SparkContext.
249ca16 [Josh Rosen] Address several review comments:
da5648e [Josh Rosen] Add example of basic progress reporting in Java.
7319ffd [Josh Rosen] Add getJobIdsForGroup() and num*Tasks() methods.
cc568e5 [Josh Rosen] Add note explaining that interfaces should not be implemented outside of Spark.
6e840d4 [Josh Rosen] Remove getter-style names and "consistent snapshot" semantics:
08cbec9 [Josh Rosen] Begin to sketch the interfaces for a stable, public status API.
ac2d13a [Josh Rosen] Add jobId->stage, stageId->stage mappings in JobProgressListener
24de263 [Josh Rosen] Create UI listeners in SparkContext instead of in Tabs: