MyCATApache/Mycat-Server · error · IllegalArgumentException

n must be > 0

Error message

n must be > 0

What it means

SingleProducerSequencer.next(n) is the blocking claim of n slots for the single publisher thread. It rejects n < 1 with IllegalArgumentException before computing the wrap point and waiting for consumers to free capacity.

Solutions

1. Skip the claim when the batch is empty instead of calling next(0)
2. Use next(1) for single-event publishes
3. Validate/chunk sizes so n is always >= 1

Example fix

// before
long seq = ringBuffer.next(events.size()); // 0 for empty list
// after
if (events.isEmpty()) return;
long seq = ringBuffer.next(events.size());

if (n >= 1) { long seq = ringBuffer.next(n); }

boolean canClaim(int n) { return n >= 1; }

try { long seq = ringBuffer.next(n); } catch (IllegalArgumentException e) { log.error("invalid claim count", e); }

When it happens

Trigger: Calling next(0) or next(-1) (or RingBuffer.next(0)) on a single-producer ring buffer, typically from batch-publishing code whose chunk size computed to zero or negative.

Common situations: Publishing loops like while(remaining>0){ n=min(CHUNK,remaining); ... remaining-=n; } where rounding lets n become 0; empty event lists passed to a batch publisher.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• bufferSize must not be less than 1
• bufferSize must be a power of 2
• n must be > 0
• bufferSize must not be less than 1
• bufferSize must be a power of 2

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/07a66ad72c30ab83. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/memory/unsafe/ringbuffer/producer/SingleProducerSequencer.java:101

    @Override
    public long remainingCapacity() {
        //使用的 = 生产的 - 已经消费的
        //剩余容量 = 容量 - 使用的
        long nextValue = this.nextValue;
        long consumed = Util.getMinimumSequence(gatingSequences, nextValue);
        long produced = nextValue;
        return getBufferSize() - (produced - consumed);
    }

    @Override
    public long next() {
        return next(1);
    }

    @Override
    public long next(int n) {
        if (n < 1) {
            throw new IllegalArgumentException("n must be > 0");
        }

        long nextValue = this.nextValue;
        //next方法和之前的hasAvailableCapacity同理，只不过这里是相当于阻塞的
        long nextSequence = nextValue + n;
        long wrapPoint = nextSequence - bufferSize;
        long cachedGatingSequence = this.cachedValue;

        if (wrapPoint > cachedGatingSequence || cachedGatingSequence > nextValue) {
            long minSequence;
            //只要wrapPoint大于最小的gatingSequences，那么不断唤醒消费者去消费，并利用LockSupport让出CPU，直到wrapPoint不大于最小的gatingSequences
            while (wrapPoint > (minSequence = Util.getMinimumSequence(gatingSequences, nextValue))) {
                waitStrategy.signalAllWhenBlocking();
                LockSupport.parkNanos(1L); // TODO: Use waitStrategy to spin?
            }
            //同理，缓存最小的gatingSequences
            this.cachedValue = minSequence;
        }

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