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JAVA-3055 CqlPrepareAsyncProcessor must handle cancellations of the returned Future #2003

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absurdfarce
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@absurdfarce absurdfarce commented Jan 13, 2025

My goal here is to completely decouple the CompletableFuture returned by CqlPrepareAsyncProcessor from the CompletableFuture that retrieves the PreparedStatement. The current implementation merges these two concerns in ways that don't behave nicely with each other.

Note that this approach is functionally very similar to the suggestion offered by @lucboutier in #1757 ... this PR just goes a bit further in explicitly decoupling the elements involved.

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Ideally we wouldn't need to go to all this length to handle such a case. Ideally we'd just slap a whenComplete() op onto the end of the CompletableFuture that loads the value and have it do the right thing in the cancellation case. I think that was my second try, and in that case I could not get such a whenComplete() to fire in obvious cancellation cases. Not sure if there's some kind of JVM issue there or if something else in our code base was somehow blocking the corresponding CancellationException from progressing... but testing made it very clear that when cancel() was called the stage added via whenComplete() wasn't being called correctly.

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DataStax CI is green as of this commit

Comment on lines +63 to +72
private CompletableFuture<PreparedStatement> result;
private Set<CompletableFuture<PreparedStatement>> futures;
private AtomicBoolean lock;

public CacheEntry() {

result = new CompletableFuture<>();
futures = Sets.newHashSet(result);
lock = new AtomicBoolean(false);
}
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Small nit: could probably simplify this by initializing all of these in the variable declaration and then getting rid of the constructor. Should also make these fields all final.

});

// We don't know whether we're dealing with a newly-created entry or one that was
// already cached so try the future insert again. We wind up duoing an extra hash op
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duoing -> doing

public CacheEntry() {

result = new CompletableFuture<>();
futures = Sets.newHashSet(result);
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One observation, HashSet is not thread safe, and futures get added to it in the threads calling prepare|Async (main thread in tests) concurrently.

From what I can tell, Set is used here because in process we want to ensure the future gets added before starting when creating the initial cache entry, and then it's added after the entry is created to ensure it's accounted for, right?

Can probably resolve this by using ConcurrentHashMap or Collections.synchronizedSet

}
}
return result;
CompletableFuture<PreparedStatement> rv = new CompletableFuture<>();
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Since we're creating a brand new future, If the CacheEntry already exists and is completed, won't we return a CompletableFuture that never completes?

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Wrote a test that reproduces this, so it does seem to be a problem:

  @Test
  public void should_complete_if_already_prepared() throws Exception {
    CqlSession session = SessionUtils.newSession(ccmRule, sessionRule.keyspace());
    CqlPrepareAsyncProcessor processor = findProcessor(session);
    Cache<?, ?> cache = processor.getCache();
    assertThat(cache.size()).isEqualTo(0);

    // Prepare a statement and then wait for it to complete
    String cql = "select v from test_table_1 where k = ?";
    CompletableFuture<PreparedStatement> cf1 = toCompletableFuture(session, cql);
    assertThat(cache.size()).isEqualTo(1);

    CqlPrepareAsyncProcessor.CacheEntry entry =
        (CqlPrepareAsyncProcessor.CacheEntry) Iterables.get(cache.asMap().values(), 0);
    PreparedStatement stmt = entry.waitForResult();
    assertThat(cf1.isDone()).isTrue();
    assertThat(cf1.join()).isEqualTo(stmt);

    // Prepare the same prepared statement, which should be completed immediately since it was previously prepared.
    CompletableFuture<PreparedStatement> cf2 = toCompletableFuture(session, cql);
    // cache should not grow
    assertThat(cache.size()).isEqualTo(1);
    CqlPrepareAsyncProcessor.CacheEntry newEntry =
        (CqlPrepareAsyncProcessor.CacheEntry) Iterables.get(cache.asMap().values(), 0);
    // Strictly the same entry in the cache.
    assertThat(entry).isSameAs(newEntry);
    // Note: made futures public just to test this, not necessary, just for demonstrating CacheEntry has this future
    assertThat(newEntry.futures).contains(cf2);
    // Future should be complete (where the test fails)
    assertThat(cf2.isDone()).isTrue();
    assertThat(cf2.join()).isEqualTo(stmt);
  }

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Another possible concern here: Futures get added in process which will be handled in the application threads, while whenComplete gets handled in an io thread. I think even fixing the issue above, technically without additional coordination/synchronization you could have a race where a new Future gets added in process but never gets marked completed in whenComplete.

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Agree with both points. This impl won't work as it stands... I'm wondering if there's anything that can be salvaged here or if this is just an outright dumpster fire and it's time to move on. 😞

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Closing this in favor of #1757. Will bring in the tests in this PR (as well as the introduction of a cache decorator in favor of an outright cache replacement) in a follow-on PR.

@absurdfarce absurdfarce closed this Feb 3, 2025
absurdfarce added a commit to absurdfarce/cassandra-java-driver that referenced this pull request Feb 4, 2025
with a few minor changes due to this implementation
absurdfarce added a commit to absurdfarce/cassandra-java-driver that referenced this pull request Feb 4, 2025
… ability to specify an

arbitrary cache from scratch.

Also bringing tests from apache#2003 forward
with a few minor changes due to this implementation

patch by Bret McGuire; reviewed by Bret McGuire and Andy Tolbert
reference: apache#2008
absurdfarce added a commit that referenced this pull request Feb 4, 2025
… ability to specify an

arbitrary cache from scratch.

Also bringing tests from #2003 forward
with a few minor changes due to this implementation

patch by Bret McGuire; reviewed by Bret McGuire and Andy Tolbert
reference: #2008
dkropachev added a commit to scylladb/java-driver that referenced this pull request Mar 19, 2025
* CASSANDRA-19635: Run integration tests with C* 5.x

patch by Lukasz Antoniak; reviewed by Andy Tolbert, and Bret McGuire for CASSANDRA-19635

* CASSANDRA-19635: Configure Jenkins to run integration tests with C* 5.x

patch by Lukasz Antoniak; reviewed by Bret McGuire for CASSANDRA-19635

* update badge URL to org.apache.cassandra/java-driver-core

* Limit calls to Conversions.resolveExecutionProfile

Those repeated calls account for a non-negligible portion of my application
CPU (0.6%) and can definitly be a final field so that it gets resolved only
once per CqlRequestHandler.

patch by Benoit Tellier; reviewed by Andy Tolbert, and Bret McGuire
reference: apache#1623

* autolink JIRA tickets in commit messages

patch by Stefan Miklosovic; reviewed by Michael Semb Wever for CASSANDRA-19854

* Don't return empty routing key when partition key is unbound

DefaultBoundStatement#getRoutingKey has logic to infer the
routing key when no one has explicitly called setRoutingKey
or otherwise set the routing key on the statement.
It however doesn't check for cases where nothing has been
bound yet on the statement.
This causes more problems if the user decides to get a
BoundStatementBuilder from the PreparedStatement, set some
fields on it, and then copy it by constructing new
BoundStatementBuilder objects with the BoundStatement as a
parameter, since the empty ByteBuffer gets copied to all
bound statements, resulting in all requests being targeted
to the same Cassandra node in a token-aware load balancing
policy.

patch by Ammar Khaku; reviewed by Andy Tolbert, and Bret McGuire
reference: apache#1620

* JAVA-3167: CompletableFutures.allSuccessful() may return never completed future

patch by Lukasz Antoniak; reviewed by Andy Tolbert, and Bret McGuire for JAVA-3167

* ninja-fix Various test fixes

* Run integration tests with DSE 6.9.0

patch by Lukasz Antoniak; reviewed by Bret McGuire
reference: apache#1955

* JAVA-3117: Call CcmCustomRule#after if CcmCustomRule#before fails to allow subsequent tests to run

patch by Henry Hughes; reviewed by Alexandre Dutra and Andy Tolbert for JAVA-3117

* JAVA-3149: Support request cancellation in request throttler
patch by Lukasz Antoniak; reviewed by Andy Tolbert and Chris Lohfink for JAVA-3149

* Fix C* 3.0 tests failing on Jenkins
patch by Lukasz Antoniak; reviewed by Bret McGuire
reference: apache#1939

* Reduce lock held duration in ConcurrencyLimitingRequestThrottler

It might take some (small) time for callback handling when the
throttler request proceeds to submission.

Before this change, the throttler proceed request will happen while
holding the lock, preventing other tasks from proceeding when there is
spare capacity and even preventing tasks from enqueuing until the
callback completes.

By tracking the expected outcome, we can perform the callback outside
of the lock. This means that request registration and submission can
proceed even when a long callback is being processed.

patch by Jason Koch; Reviewed by Andy Tolbert and Chris Lohfink for CASSANDRA-19922

* Annotate BatchStatement, Statement, SimpleStatement methods with CheckReturnValue

Since the driver's default implementation is for
BatchStatement and SimpleStatement methods to be immutable,
we should annotate those methods with @CheckReturnValue.
Statement#setNowInSeconds implementations are immutable so
annotate that too.

patch by Ammar Khaku; reviewed by Andy Tolbert and Bret McGuire
reference: apache#1607

* Remove "beta" support for Java17 from docs

patch by Bret McGuire; reviewed by Andy Tolbert and Alexandre Dutra
reference: apache#1962

* Fix uncaught exception during graceful channel shutdown

after exceeding max orphan ids

patch by Christian Aistleitner; reviewed by Andy Tolbert, and Bret McGuire for apache#1938

* Build a public CI for Apache Cassandra Java Driver

 patch by Siyao (Jane) He; reviewed by Mick Semb Wever for CASSANDRA-19832

* CASSANDRA-19932: Allow to define extensions while creating table
patch by Lukasz Antoniak; reviewed by Bret McGuire and Chris Lohfink

* Fix DefaultSslEngineFactory missing null check on close

patch by Abe Ratnofsky; reviewed by Andy Tolbert and Chris Lohfink for CASSANDRA-20001

* Query builder support for NOT CQL syntax

patch by Bret McGuire; reviewed by Bret McGuire and Andy Tolbert for CASSANDRA-19930

* Fix CustomCcmRule to drop `CURRENT` flag no matter what

If super.after() throws an Exception `CURRENT` flag is never dropped
which leads next tests to fail with IllegalStateException("Attempting to use a Ccm rule while another is in use.  This is disallowed")

Patch by Dmitry Kropachev; reviewed by Andy Tolbert and Bret McGuire for JAVA-3117

* JAVA-3051: Memory leak

patch by Jane He; reviewed by Alexandre Dutra and Bret McGuire for JAVA-3051

* Automate latest Cassandra versions when running CI

 patch by Siyao (Jane) He; reviewed by Mick Semb Wever for CASSJAVA-25

* Refactor integration tests to support multiple C* distributions. Test with DataStax HCD 1.0.0

patch by Lukasz Antoniak; reviewed by Bret McGuire
reference: apache#1958

* Fix TableMetadata.describe() when containing a vector column

patch by Stefan Miklosovic; reviewed by Bret McGuire for CASSJAVA-2

* Move Apache Cassandra 5.x off of beta1 and remove some older Apache Cassandra versions.

patch by Bret McGuire; reviewed by Bret McGuire for CASSJAVA-54

* Update link to Jira to be CASSJAVA

Updating the link to Jira.

Previously we had a component in the CASSANDRA Jira project but now we have a project for each driver - in the case of Java, it's CASSJAVA.

Added CASSJAVA to .asf.yaml

patch by Jeremy Hanna; reviewed by Bret McGuire for CASSJAVA-61

* Move DataStax shaded Guava module into Java driver

patch by Lukasz Antoniak; reviewed by Alexandre Dutra and Bret McGuire for CASSJAVA-52

* JAVA-3057 Allow decoding a UDT that has more fields than expected

patch by Ammar Khaku; reviewed by Andy Tolbert and Bret McGuire
reference: apache#1635

* CASSJAVA-55 Remove setting "Host" header for metadata requests.

With some sysprops enabled this will actually be respected which completely borks Astra routing.

patch by Bret McGuire; reviewed by Alexandre Dutra and Bret McGuire for CASSJAVA-55

* JAVA-3118: Add support for vector data type in Schema Builder, QueryBuilder
patch by Jane He; reviewed by Mick Semb Wever and Bret McGuire for JAVA-3118
reference: apache#1931

* Upgrade Guava to 33.3.1-jre

patch by Lukasz Antoniak; reviewed by Alexandre Dutra and Bret McGuire for CASSJAVA-53

* Do not always cleanup Guava shaded module before packaging

* Revert "Do not always cleanup Guava shaded module before packaging"

This reverts commit 5be52ec.

* Conditionally compile shaded Guava module

* JAVA-3143: Extend driver vector support to arbitrary subtypes and fix handling of variable length types (OSS C* 5.0)

patch by Jane He; reviewed by Bret McGuire and João Reis
reference: apache#1952

* JAVA-3168 Copy node info for contact points on initial node refresh only from first match by endpoint

patch by Alex Sasnouskikh; reviewed by Andy Tolbert and Alexandre Dura for JAVA-3168

* JAVA-3055: Prevent PreparedStatement cache to be polluted if a request is cancelled.

There was a critical issue when the external code cancels a request, indeed the cached CompletableFuture will then always throw a CancellationException.
This may happens, for example, when used by reactive like Mono.zip or Mono.firstWithValue.

patch by Luc Boutier; reviewed by Alexandre Dutra and Bret McGuire
reference: apache#1757

* Expose a decorator for CqlPrepareAsyncProcessor cache rather than the ability to specify an
arbitrary cache from scratch.

Also bringing tests from apache#2003 forward
with a few minor changes due to this implementation

patch by Bret McGuire; reviewed by Bret McGuire and Andy Tolbert
reference: apache#2008

* ninja-fix Using shaded Guava classes for import in order to make OSGi class paths happy.

Major hat tip to Dmitry Konstantinov for the find here!

* Changelog updates for 4.19.0

* [maven-release-plugin] prepare release 4.19.0

* [maven-release-plugin] prepare for next development iteration

* Specify maven-clean-plugin version

Sets the version to 3.4.1 in parent pom.
Having it unspecified causes the following warning:
```
[WARNING] Some problems were encountered while building the effective model for com.scylladb:java-driver-guava-shaded:jar:4.19.0.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-clean-plugin is missing. @ line 97, column 15
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]
```

* Install guava-shaded before running core's compile in CI

Without this module available "Build" and "Unit tests" job fail with
"package <x> does not exist" or "cannot find symbol" pointing to
`[...].shaded.guava.[...]` packages.

* Remove exception catch in `prepared_stmt_metadata_update_loopholes_test`

Since incorporating "JAVA-3057 Allow decoding a UDT that has more fields than
expected" the asuumptions of removed check are no longer valid.

* Switch shaded guava's groupId in osgi-tests

Switches from `org.apache.cassandra` to `com.scylladb`
in `BundleOptions#commonBundles()`.

* Typo: increase line's loglevel in CcmBridge

---------

Co-authored-by: Lukasz Antoniak <[email protected]>
Co-authored-by: Brad Schoening <[email protected]>
Co-authored-by: Benoit Tellier <[email protected]>
Co-authored-by: Stefan Miklosovic <[email protected]>
Co-authored-by: Ammar Khaku <[email protected]>
Co-authored-by: absurdfarce <[email protected]>
Co-authored-by: Henry Hughes <[email protected]>
Co-authored-by: Jason Koch <[email protected]>
Co-authored-by: Christian Aistleitner <[email protected]>
Co-authored-by: janehe <[email protected]>
Co-authored-by: Abe Ratnofsky <[email protected]>
Co-authored-by: absurdfarce <[email protected]>
Co-authored-by: Dmitry Kropachev <[email protected]>
Co-authored-by: janehe <[email protected]>
Co-authored-by: Jeremy Hanna <[email protected]>
Co-authored-by: SiyaoIsHiding <[email protected]>
Co-authored-by: Alex Sasnouskikh <[email protected]>
Co-authored-by: Luc Boutier <[email protected]>
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