openzipkin/zipkin · error · IllegalArgumentException

concurrency < 1

Error message

concurrency < 1

What it means

ActiveMQCollector.Builder.concurrency(int) requires at least 1 concurrent message listener; 0 or negative values throw IllegalArgumentException. Concurrency controls how many JMS MessageListeners process spans from the queue in parallel.

Source

Thrown at zipkin-collector/activemq/src/main/java/zipkin2/collector/activemq/ActiveMQCollector.java:64

      return this;
    }

    public Builder connectionFactory(ActiveMQConnectionFactory connectionFactory) {
      if (connectionFactory == null) throw new NullPointerException("connectionFactory == null");
      this.connectionFactory = connectionFactory;
      return this;
    }

    /** Queue zipkin spans will be consumed from. Defaults to "zipkin". */
    public Builder queue(String queue) {
      if (queue == null) throw new NullPointerException("queue == null");
      this.queue = queue;
      return this;
    }

    /** Count of concurrent message listeners on the queue. Defaults to 1 */
    public Builder concurrency(int concurrency) {
      if (concurrency < 1) throw new IllegalArgumentException("concurrency < 1");
      this.concurrency = concurrency;
      return this;
    }

    @Override public ActiveMQCollector build() {
      if (connectionFactory == null) throw new NullPointerException("connectionFactory == null");
      return new ActiveMQCollector(this);
    }
  }

  final String queue;
  final LazyInit lazyInit;

  ActiveMQCollector(Builder builder) {
    this.queue = builder.queue;
    this.lazyInit = new LazyInit(builder);
  }

View on GitHub (pinned to 878ce2a1fa)

Solutions

1. Set concurrency to 1 or higher; 1 is the default and is fine for low volume.
2. Validate/normalize parsed config before the builder: if (c < 1) c = 1 or fail with a clear config error.
3. Check the raw property value (empty string, whitespace, wrong key) if it parses to 0.

Example fix

// before
int c = Integer.parseInt(props.getProperty("concurrency", "0"));
builder.concurrency(c); // throws 'concurrency < 1'

// after
int c = Integer.parseInt(props.getProperty("concurrency", "1"));
builder.concurrency(Math.max(1, c));

java
int c = Integer.parseInt(props.getProperty("concurrency", "1"));
if (c < 1) throw new IllegalArgumentException("concurrency must be >= 1: " + c);
builder.concurrency(c);

When it happens

Trigger: Calling .concurrency(0) or a negative number — commonly a parsed config value (ACTIVEMQ_CONCURRENCY) that defaulted to 0 or was misparsed (e.g. empty string parsed as 0).

Common situations: Numeric env property unset and defaulting to 0 in a properties loader; a "disable" flag misused as concurrency; config typos producing non-numeric parses.

Related errors

• metrics == null
• connectionFactory == null
• queue == null
• rate should be between 0 and 1: was {}
• storage == null

AI-assisted analysis of openzipkin/zipkin@878ce2a1fa (2026-08-14). Data as JSON: /api/errors/6a2f5f1a9116d4a4. Report an issue: GitHub.