[fix][broker] Guard AsyncTokenBucket against long overflow

[codelipenghui]

Main Issue: N/A

PIP: N/A

Motivation

The async dispatch rate limiter (AsyncTokenBucket) performs multiply-then-divide arithmetic using long. With large rates and longer rate periods (for example, 980,000,000 tokens per 10s), the multiplication can overflow and produce incorrect negative/intermediate values. In dispatch throttling this can keep available tokens at invalid values and effectively stall consumption.

Modifications

• Added overflow-safe floor multiply/divide helper in AsyncTokenBucket:
  • Fast path for non-overflowing long multiplication.
  • Fallback to BigInteger for overflow cases.
  • Clamp large results to Long.MAX_VALUE.
• Replaced overflow-prone arithmetic in token refill path:
  • calculateNewTokensSinceLastUpdate now uses safe multiply/divide.
  • Remainder-nanos back-calculation now uses safe multiply/divide as well.
• Hardened throttling duration calculation:
  • calculateThrottlingDuration(long requiredTokens) now handles subtraction overflow and uses safe multiply/divide.
• Added regression tests in AsyncTokenBucketTest:
  • shouldRefillTokensWithoutOverflowForLargeRateAnd10sPeriod
  • shouldCalculateThrottlingDurationWithoutOverflowForLargeNeedTokens

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Ran unit/regression tests:
  • ./mvnw -pl pulsar-broker -Dtest=AsyncTokenBucketTest -Dsurefire.failIfNoSpecifiedTests=false test
• Ran dispatch-throttling integration tests:
  • ./mvnw -pl pulsar-broker -Dtest=SubscriptionMessageDispatchThrottlingTest -Dsurefire.failIfNoSpecifiedTests=false -DargLine='-Djdk.attach.allowAttachSelf=true -XX:+EnableDynamicAgentLoading' test

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: N/A