fix: address CodeQL concurrency warnings

[FrankChen021]

What

• wake every blocked reader when input is added, completed, or failed
• prove terminal stream transitions release multiple waiting readers
• synchronize MapDB check/use sequences on MapDB's own monitor

Why

This addresses all five CodeQL warnings in the concurrency group:

• 4 java/notify-instead-of-notify-all
• 1 java/toctou-race-condition

Impact

Terminal input-stream transitions can no longer leave additional readers blocked. MapDB close and cache disposal cannot interleave between isClosed() and the corresponding state-changing operation.

Root cause

The stream implementations relied on an implicit single-waiter assumption. The MapDB lifecycle method was synchronized on the anonymous handler instance rather than on the database object used by MapDB's own synchronized APIs.

Checks

• affected-module compilation and Checkstyle passed
• processing concurrency tests: 17 passed
• lookup cache lifecycle/concurrency tests: 57 passed
• git diff --check

Created by GPT-5.6-Sol.

[Copilot]

🟡 Not ready to approve

notifyAll() in AppendableByteArrayInputStream.add() can enable concurrent readers to proceed and race on shared read state, and the MapDB manager changes need small follow-ups for lock scope and final field consistency.

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Pull request overview

This PR updates several synchronization points to address CodeQL concurrency warnings (notify vs notifyAll, and a TOCTOU check/use pattern around MapDB lifecycle) in Druid’s processing and lookup-cache components.

Changes:

• Switch monitor signaling from notify() to notifyAll() in stream/channel paths to ensure terminal transitions (and chunk/backpressure transitions) don’t leave additional waiters blocked.
• Add tests proving AppendableByteArrayInputStream terminal transitions (done, exceptionCaught) unblock multiple waiting readers.
• Synchronize MapDB “check then use” sequences (isClosed() + delete/close) on the DB instance monitor.

File summaries

File	Description
processing/src/test/java/org/apache/druid/java/util/http/client/io/AppendableByteArrayInputStreamTest.java	Adds multi-reader blocking/unblock tests for done() and exceptionCaught().
processing/src/main/java/org/apache/druid/java/util/http/client/io/AppendableByteArrayInputStream.java	Changes monitor notification to notifyAll() in producer/terminal methods.
processing/src/main/java/org/apache/druid/frame/channel/ReadableInputStreamFrameChannel.java	Uses notifyAll() when releasing backpressure waiters on readMonitor.
extensions-core/lookups-cached-global/src/main/java/org/apache/druid/server/lookup/namespace/cache/OffHeapNamespaceExtractionCacheManager.java	Synchronizes MapDB check/use sequences on the DB instance and documents the rationale.

Review details

Comments suppressed due to low confidence (1)

extensions-core/lookups-cached-global/src/main/java/org/apache/druid/server/lookup/namespace/cache/OffHeapNamespaceExtractionCacheManager.java:162

• Per the project code style (“Always use final for fields and variables that are not reassigned”, see AGENTS.md:40), these atomic field references should be final since they are never reassigned.

  private final DB mmapDB;
  private final File tmpFile;
  private AtomicLong mapDbKeyCounter = new AtomicLong(0);
  private AtomicInteger cacheCount = new AtomicInteger(0);

• Files reviewed: 4/4 changed files
• Comments generated: 2
• Review effort level: Low

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[Copilot]

🟢 Ready to approve

The concurrency fixes are narrowly scoped, align with the PR’s stated CodeQL goals, and are supported by targeted multi-waiter tests for the terminal stream transitions.

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Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0 new
• Review effort level: Lite

We're testing this review assessment. Please use 👍 or 👎 to tell us if it's correct.