fix(s3stream): reduce CPU overhead in AsyncNetworkBandwidthLimiter when traffic hits limit

[JUSTMEETPATEL]

Motivation

Resolves #2052

When network traffic reaches the configured bandwidth limit, AsyncNetworkBandwidthLimiter consumes excessive CPU due to wasteful wake-up cycles in its consumer thread. The flame graphs in the issue show this overhead clearly.

Root Cause

Two problems in the signaling logic create a hot wake-up loop under sustained load:

1. consume() calls condition.signalAll() on every enqueue (even when availableTokens <= 0). This wakes the run() thread, which acquires the lock, checks ableToConsume() (returns false since tokens are exhausted), and immediately blocks again. Under sustained traffic at the limit, every incoming request triggers this wasteful cycle: wake -> lock -> check -> sleep -> wake -> lock -> check -> sleep.

2. refillToken() uses signalAll() instead of signal(). Only the single run() thread ever waits on this condition variable, so signalAll() is unnecessary overhead.

Changes

AsyncNetworkBandwidthLimiter.java (1 file changed, 1 insertion, 2 deletions):

• consume(): Removed condition.signalAll() after enqueueing a BucketItem. The run() thread cannot drain the queue without available tokens, so waking it serves no purpose. When tokens are available and the queue is empty, consume() takes the fast-path and completes the future inline without queuing, so run() never needs a signal in that path either.

• refillToken(): Replaced signalAll() with signal(). Only one thread (run()) waits on this condition, making signalAll() unnecessary.

Verification

All 10 existing tests in AsyncNetworkBandwidthLimiterTest pass:

• testByPassConsume / testByPassConsume2
• testThrottleConsume / testThrottleConsume2 / testThrottleConsume3 / testThrottleConsume4 / testThrottleConsume5
• testThrottleConsumeWithPriority / testThrottleConsumeWithPriority1
• testThrottleConsumeWithLargeChunk

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[Copilot]

Pull request overview

This PR addresses excessive CPU usage in AsyncNetworkBandwidthLimiter when bandwidth is saturated by reducing unnecessary wake-ups of the consumer (run()) thread.

Changes:

• Replace condition.signalAll() with condition.signal() in refillToken() since only the run() thread waits on the condition.
• Remove condition.signalAll() from consume() after enqueueing, avoiding a hot wake/sleep loop when availableTokens <= 0.

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