Inconsistent global set behavior

[MrAlias]

Description

The global TextMapPropagator, MeterProvider, and TracerProvider can be set as many times as the user wants to call the appropriate set method.

opentelemetry-go/internal/global/state.go

Line 62 in fd9de7e

globalTracer.Store(tracerProviderHolder{tp: tp})

opentelemetry-go/internal/metric/global/metric.go

Line 53 in fd9de7e

globalMeter.Store(meterProviderHolder{mp: mp})

opentelemetry-go/internal/global/state.go

Line 85 in fd9de7e

globalPropagators.Store(propagatorsHolder{tm: p})

The global ErrorHandler can only be set once. Subsequent calls to SetErrorHandler are ignored.

opentelemetry-go/handler.go

Lines 73 to 84 in fd9de7e

	// SetErrorHandler sets the global ErrorHandler to be h.
	func SetErrorHandler(h ErrorHandler) {
	delegateErrorHandlerOnce.Do(func() {
	current := GetErrorHandler()
	if current == h {
	return
	}
	if internalHandler, ok := current.(*loggingErrorHandler); ok {
	internalHandler.setDelegate(h)
	}
	})
	}

Expected behavior

This inconsistent behavior needs to be made consistent.

[pellared]

My opinion: we should allow setting as many times as the user wants to call the appropriate set method.

Why? Even for the sake of unit testing. Example: https://github.com/open-telemetry/opentelemetry-go-contrib/blob/00f202e858996b1600131b021e810d17f93fb6d6/instrumentation/github.com/emicklei/go-restful/otelrestful/restful_test.go#L149-L176

Just to confirm. Is it possible to get a "current" value to be able to make some set+revert logic?

[MrAlias]

Just to confirm. Is it possible to get a "current" value to be able to make some set+revert logic?

Yes. There should be a corresponding Get* function for any Set* function (e.g. this)