---
title: "Go, Backwards Compatibility, and GODEBUG"
layout: article
---

<!--
This document is kept in the Go repo, not x/website,
because it documents the full list of known GODEBUG settings,
which are tied to a specific release.
-->

## Introduction {#intro}

Go's emphasis on backwards compatibility is one of its key strengths.
There are, however, times when we cannot maintain complete compatibility.

    server.processNextFrame() // Ping.
    client.processNextFrame() // Pong.

    // After 1000ms the client will attempt a ping 2, but we don't process it. That'll cause the
    // client to fail at 1500ms when it's time to send ping 3 because pong 2 hasn't been received.
    taskFaker.advanceUntil(ns(1000L))
    taskFaker.advanceUntil(ns(1500L))
    client.listener.assertFailure(
      SocketTimeoutException::class.java,

    }

    @Override
    byte[] getBytesInternal() {
      return bytes;
    }

    @Override
    boolean equalsSameBits(HashCode that) {
      // We don't use MessageDigest.isEqual() here because its contract does not guarantee
      // constant-time evaluation (no short-circuiting).
      if (this.bytes.length != that.getBytesInternal().length) {
        return false;
      }

      boolean areEqual = true;

		if n < 0 {
			panic(errNegativeRead)
		}
		if n == 0 {
			return 0, b.readErr()
		}
		b.w += n
	}

	// copy as much as we can
	// Note: if the slice panics here, it is probably because
	// the underlying reader returned a bad count. See issue 49795.
	n = copy(p, b.buf[b.r:b.w])
	b.r += n
	b.lastByte = int(b.buf[b.r-1])
	b.lastRuneSize = -1
	return n, nil
}

   * {@code a == b} (identity equality). There is no meaning whatsoever to the order imposed, but it
   * is constant for the life of the VM.
   *
   * <p>Because the ordering is identity-based, it is not "consistent with {@link
   * Object#equals(Object)}" as defined by {@link Comparator}. Use caution when building a {@link

    Monitor monitor = this.monitor;
    monitor.enter();
    try {
      return q.size();
    } finally {
      monitor.leave();
    }
  }

  /**
   * Always returns {@code Integer.MAX_VALUE} because a {@code MonitorBasedPriorityBlockingQueue} is
   * not capacity constrained.
   *
   * @return {@code Integer.MAX_VALUE}
   */
  @CanIgnoreReturnValue // pushed down from class to method
  @Override

   * permits? As explained above, there is no unique answer. If we are primarily interested to deal
   * with underutilization, then we want stored permits to be given out /faster/ than fresh ones,
   * because underutilization = free resources for the taking. If we are primarily interested to
   * deal with overflow, then stored permits could be given out /slower/ than fresh ones. Thus, we

    * Me seguir para ver quando eu publicar algo novo.

## Tweet sobre o **FastAPI** { #tweet-about-fastapi }

<a href="https://x.com/compose/tweet?text=I'm loving @fastapi because... https://github.com/fastapi/fastapi" class="external-link" target="_blank">Tweet sobre o **FastAPI**</a> e conte para mim e para outras pessoas por que você gosta dele. 🎉

  /*
   * If we make these calls inline inside toImmutableSortedMultiset, we get an Animal Sniffer error,
   * despite the @IgnoreJRERequirement annotation there. My assumption is that, because javac
   * generates a synthetic method for the body of the lambda, the actual method calls that Animal
   * Sniffer is flagging don't appear inside toImmutableSortedMultiset but rather inside that

This button will cause a Javascript alert dialog to appear asking you to type a reason for accepting the changes, e.g. "Added new API for Gradle 8.x".

Clicking okay on the dialog will cause a copy of the `accepted-public-api-changes.json` containing your (properly sorted) addition to be downloaded.