---
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.

## Version 5.0.0-alpha.7

_2022-04-26_

**This release introduces new Kotlin-friendly APIs.** When we migrated OkHttp from Java to Kotlin in
OkHttp 4.0, we kept our Java-first APIs. With 5.0 we're continuing to support Java and adding
additional improvements for Kotlin users. In this alpha we're excited to skip-the-builder for

  final Policy policy;

  private CycleDetectingLockFactory(Policy policy) {
    this.policy = checkNotNull(policy);
  }

  /**
   * Tracks the currently acquired locks for each Thread, kept up to date by calls to {@link
   * #aboutToAcquire(CycleDetectingLock)} and {@link #lockStateChanged(CycleDetectingLock)}.
   */
  // This is logically a Set, but an ArrayList is used to minimize the amount

   * concurrently readable hash table. The map supports non-blocking reads and concurrent writes
   * across different segments.
   *
   * The page replacement algorithm's data structures are kept casually consistent with the map. The
   * ordering of writes to a segment is sequentially consistent. An update to the map and recording
   * of reads may not be immediately reflected on the algorithm's data structures. These structures

   * once after loading completes). Much internal cache management is performed at the segment
   * granularity. For example, access queues and write queues are kept per segment when they are
   * required by the selected eviction algorithm. As such, when writing unit tests it is not
   * uncommon to specify {@code concurrencyLevel(1)} in order to achieve more deterministic eviction

	lastUpdate time.Time

	// updateCurrentPath should be called whenever a new path is scanned.
	updateCurrentPath func(string)
}

// Cache structure and compaction:
//
// A cache structure will be kept with a tree of usages.
// The cache is a tree structure where each keeps track of its children.
//
// An uncompacted branch contains a count of the files only directly at the

		}
		newMeta[k] = v
	}
	return newMeta
}

// Extracts etag value from the metadata.
func extractETag(metadata map[string]string) string {
	etag, ok := metadata["etag"]
	if !ok {
		// md5Sum tag is kept for backward compatibility.
		etag = metadata["md5Sum"]
	}
	// Success.
	return etag
}

// HasPrefix - Prefix matcher string matches prefix in a platform specific way.

 *     .writeTimeout(1000, TimeUnit.MILLISECONDS)
 *     .build();
 * ```
 *
 * This example shows a call with a short 500 millisecond read timeout and a 1000 millisecond
 * write timeout. Original configuration is kept, but can be overriden.
 *
 * ```java
 * OkHttpClient eagerClient = client.newBuilder()
 *     .readTimeout(500, TimeUnit.MILLISECONDS)
 *     .build();
 * Response response = eagerClient.newCall(request).execute();

// Return a new execution session with the associated graph, or NULL on
// error. Does not take ownership of any input parameters.
//
// *`graph` must be a valid graph (not deleted or nullptr). `graph` will be
// kept alive for the lifetime of the returned TF_Session. New nodes can still
// be added to `graph` after this call.
TF_CAPI_EXPORT extern TF_Session* TF_NewSession(TF_Graph* graph,

pseudo-instruction <code>NO_LOCAL_POINTERS</code>.
Because stack resizing is implemented by moving the stack,
the stack pointer may change during any function call:
even pointers to stack data must not be kept in local variables.
</p>

<p>
Assembly functions should always be given Go prototypes,
both to provide pointer information for the arguments and results
and to let <code>go</code> <code>vet</code> check that