---
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.

_cgo_main.c:

	int main() { return 0; }
	void crosscall2(void(*fn)(void*), void *a, int c, uintptr_t ctxt) { }
	uintptr_t _cgo_wait_runtime_init_done(void) { return 0; }
	void _cgo_release_context(uintptr_t ctxt) { }
	char* _cgo_topofstack(void) { return (char*)0; }
	void _cgo_allocate(void *a, int c) { }
	void _cgo_panic(void *a, int c) { }
	void _cgo_reginit(void) { }

		log.Fatal(err)
	}
	s := string(bs)

	// Diagnose common mistakes people make,
	// since there is no apifmt to format these files.
	// The missing final newline is important for the
	// final release step of cat next/*.txt >go1.X.txt.
	// If the files don't end in full lines, the concatenation goes awry.
	if strings.Contains(s, "\r") {
		log.Printf("%s: contains CRLFs", filename)
		exitCode = 1
	}

the number of items in the channel corresponds to the number of active uses,
the capacity of the channel corresponds to the maximum number of simultaneous uses,
sending an item acquires the semaphore, and receiving an item releases
the semaphore.
This is a common idiom for limiting concurrency.
</p>

<p>
This program starts a goroutine for every entry in the work list, but the