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Module: stdgo.internal.godebug

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Overview

Package godebug makes the settings in the $GODEBUG environment variable available to other packages. These settings are often used for compatibility tweaks, when we need to change a default behavior but want to let users opt back in to the original. For example GODEBUG=http2server=0 disables HTTP/2 support in the net/http server.

In typical usage, code should declare a Setting as a global and then call Value each time the current setting value is needed: 

	var http2server = godebug.New("http2server")
	func ServeConn(c net.Conn) {
		if http2server.Value() == "0" {
			disallow HTTP/2
			...
		}
		...
	}

Each time a non-default setting causes a change in program behavior, code should call [Setting.IncNonDefault] to increment a counter that can be reported by [runtime/metrics.Read]. Note that counters used with IncNonDefault must be added to various tables in other packages. See the [Setting.IncNonDefault] documentation for details.

Index

Variables

import stdgo.internal.godebug.Godebug
var _cache:stdgo.sync.Map_

cache is a cache of all the GODEBUG settings, a locked map[string]*atomic.Pointer[string].

All Settings with the same name share a single *atomic.Pointer[string], so that when GODEBUG changes only that single atomic string pointer needs to be updated.

A name appears in the values map either if it is the name of a Setting for which Value has been called at least once, or if the name has ever appeared in a name=value pair in the $GODEBUG environment variable. Once entered into the map, the name is never removed.

name string -\> value *atomic.Pointer[string] 

var _empty:stdgo.internal.godebug.T_value
var _stderr:stdgo.internal.godebug.T_runtimeStderr
var _updateMu:stdgo.sync.Mutex

Functions

import stdgo.internal.godebug.Godebug

function _lookup

function _lookup(_name:stdgo.GoString):stdgo.Ref<stdgo.internal.godebug.T_setting>

lookup returns the unique *setting value for the given name.

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function _newIncNonDefault

function _newIncNonDefault(_name:stdgo.GoString):():Void

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function _parse

function _parse(_did:stdgo.GoMap<stdgo.GoString, Bool>, _s:stdgo.GoString):Void

parse parses the GODEBUG setting string s, which has the form k=v,k2=v2,k3=v3. Later settings override earlier ones. Parse only updates settings k=v for which did[k] = false. It also sets did[k] = true for settings that it updates. Each value v can also have the form v#pattern, in which case the GODEBUG is only enabled for call stacks matching pattern, for use with golang.org/x/tools/cmd/bisect.

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function _registerMetric

function _registerMetric(_name:stdgo.GoString, _read:():stdgo.GoUInt64):Void

registerMetric is provided by package runtime. It forwards registrations to runtime/metrics. 

go:linkname registerMetric

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function _setNewIncNonDefault

function _setNewIncNonDefault(_newIncNonDefault:()):Void

setNewIncNonDefault is provided by package runtime. The runtime can do 

	inc := newNonDefaultInc(name)

instead of 

	inc := godebug.New(name).IncNonDefault

since it cannot import godebug. 

go:linkname setNewIncNonDefault

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function _setUpdate

function _setUpdate(_update:(:stdgo.GoString, :stdgo.GoString):Void):Void

setUpdate is provided by package runtime. It calls update(def, env), where def is the default GODEBUG setting and env is the current value of the $GODEBUG environment variable. After that first call, the runtime calls update(def, env) again each time the environment variable changes (due to use of os.Setenv, for example). 

go:linkname setUpdate

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function _update

function _update(_def:stdgo.GoString, _env:stdgo.GoString):Void

update records an updated GODEBUG setting. def is the default GODEBUG setting for the running binary, and env is the current value of the $GODEBUG environment variable.

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function _write

function _write(_fd:stdgo.GoUIntptr, _p:stdgo.unsafe.UnsafePointer, _n:stdgo.GoInt32):stdgo.GoInt32

Since we cannot import os or syscall, use the runtime's write function to print to standard error. 

go:linkname write runtime.write

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function new_

function new_(_name:stdgo.GoString):stdgo.Ref<stdgo.internal.godebug.Setting>

New returns a new Setting for the $GODEBUG setting with the given name.

GODEBUGs meant for use by end users must be listed in ../godebugs/table.go, which is used for generating and checking various documentation. If the name is not listed in that table, New will succeed but calling Value on the returned Setting will panic. To disable that panic for access to an undocumented setting, prefix the name with a #, as in godebug.New("#gofsystrace"). The # is a signal to New but not part of the key used in $GODEBUG.

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Classes

import stdgo.internal.godebug.*

class Setting

A Setting is a single setting in the $GODEBUG environment variable. 

var _name:stdgo.GoString
var _once:stdgo.sync.Once
var _setting:stdgo.Ref<stdgo.internal.godebug.T_setting>

Setting function new

function new(?_name:stdgo.GoString, ?_once:stdgo.sync.Once, ?_setting:stdgo.Ref<stdgo.internal.godebug.T_setting>):Void

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Setting function _register

function _register():Void

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Setting function incNonDefault

function incNonDefault():Void

IncNonDefault increments the non-default behavior counter associated with the given setting. This counter is exposed in the runtime/metrics value /godebug/non-default-behavior/\:events.

Note that Value must be called at least once before IncNonDefault.

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Setting function name

function name():stdgo.GoString

Name returns the name of the setting.

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Setting function string

function string():stdgo.GoString

String returns a printable form for the setting: name=value.

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Setting function undocumented

function undocumented():Bool

Undocumented reports whether this is an undocumented setting.

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Setting function value

function value():stdgo.GoString

Value returns the current value for the GODEBUG setting s.

Value maintains an internal cache that is synchronized with changes to the $GODEBUG environment variable, making Value efficient to call as frequently as needed. Clients should therefore typically not attempt their own caching of Value's result.

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