eclipse-vertx/vert.x · info · IllegalStateException

Result is already complete

Error message

Result is already complete

What it means

SC_GATEWAY_TIMEOUT is an HttpResponseExpectation constant asserting an HTTP 504 status. When used as a client expectation it fails any response whose status is not exactly 504, reporting '504 Gateway Timeout'.

Source

Thrown at vertx-core/src/main/java/io/vertx/core/Promise.java:76

  default void complete(T result, Throwable failure) {
    if (failure == null) {
      succeed(result);
    } else {
      fail(failure);
    }
  }

  /**
   * Set the result. Any handler will be called, if there is one, and the promise will be marked as completed.
   * <p/>
   * Any handler set on the associated promise will be called.
   *
   * @param result  the result
   * @throws IllegalStateException when the promise is already completed
   */
  default void complete(T result) {
    if (!tryComplete(result)) {
      throw new IllegalStateException("Result is already complete");
    }
  }

  /**
   * Calls {@code complete(null)}
   *
   * @throws IllegalStateException when the promise is already completed
   */
  default void complete() {
    if (!tryComplete(null)) {
      throw new IllegalStateException("Promise already completed");
    }
  }

  default void succeed(T result) {
    if (!tryComplete(result)) {
      throw new IllegalStateException("Promise already completed");
    }

View on GitHub (pinned to fb308bd8c3)

Solutions

1. Increase upstream processing performance or gateway/proxy timeout settings so requests complete in time.
2. Add client-side timeouts and retries with backoff for idempotent requests.
3. If 504 is the intended contract (timeout tests), keep SC_GATEWAY_TIMEOUT and ensure the proxy timeout is shorter than the client timeout.

Example fix

// before
request.expect(HttpResponseExpectation.SC_GATEWAY_TIMEOUT).send();
// after
request.expect(HttpResponseExpectation.status(200)).send();

long started = System.nanoTime();
if (response.statusCode() == 504) { /* upstream timeout: back off and retry idempotent ops */ }

When it happens

Trigger: Applying request.expect(HttpResponseExpectation.SC_GATEWAY_TIMEOUT) to a response with a different status; matching responses where an upstream gateway/proxy timed out.

Common situations: Upstream service latency exceeded the proxy timeout in production; load tests deliberately provoking gateway timeouts; asserting timeout semantics in proxy integration tests.

Understand the failure class

Background: Request timed out: what client-side request timeouts mean across libraries (Request timed out, TIMED_OUT, APITimeoutError) — this error's family across 39 libraries.

Related errors

• maxExecuteTime must be > 0
• size must be > 0
• Promise already completed
• eventLoopPoolSize must be > 0
• 408 Request Timeout

AI-assisted analysis of eclipse-vertx/vert.x@fb308bd8c3 (2026-09-06). Data as JSON: /api/errors/db2123e41d050cfb. Report an issue: GitHub.