[bugfix] Downstep otel to fix freebsd compile issue (#1773)

https://github.com/open-telemetry/opentelemetry-go/issues/4076

vendor/go.opentelemetry.io/otel/handler.go

@@ -15,16 +15,58 @@
 package otel // import "go.opentelemetry.io/otel"
 
 import (
-	"go.opentelemetry.io/otel/internal/global"
+	"log"
+	"os"
+	"sync/atomic"
+	"unsafe"
 )
 
 var (
-	// Compile-time check global.ErrDelegator implements ErrorHandler.
-	_ ErrorHandler = (*global.ErrDelegator)(nil)
-	// Compile-time check global.ErrLogger implements ErrorHandler.
-	_ ErrorHandler = (*global.ErrLogger)(nil)
+	// globalErrorHandler provides an ErrorHandler that can be used
+	// throughout an OpenTelemetry instrumented project. When a user
+	// specified ErrorHandler is registered (`SetErrorHandler`) all calls to
+	// `Handle` and will be delegated to the registered ErrorHandler.
+	globalErrorHandler = defaultErrorHandler()
+
+	// Compile-time check that delegator implements ErrorHandler.
+	_ ErrorHandler = (*delegator)(nil)
+	// Compile-time check that errLogger implements ErrorHandler.
+	_ ErrorHandler = (*errLogger)(nil)
 )
 
+type delegator struct {
+	delegate unsafe.Pointer
+}
+
+func (d *delegator) Handle(err error) {
+	d.getDelegate().Handle(err)
+}
+
+func (d *delegator) getDelegate() ErrorHandler {
+	return *(*ErrorHandler)(atomic.LoadPointer(&d.delegate))
+}
+
+// setDelegate sets the ErrorHandler delegate.
+func (d *delegator) setDelegate(eh ErrorHandler) {
+	atomic.StorePointer(&d.delegate, unsafe.Pointer(&eh))
+}
+
+func defaultErrorHandler() *delegator {
+	d := &delegator{}
+	d.setDelegate(&errLogger{l: log.New(os.Stderr, "", log.LstdFlags)})
+	return d
+}
+
+// errLogger logs errors if no delegate is set, otherwise they are delegated.
+type errLogger struct {
+	l *log.Logger
+}
+
+// Handle logs err if no delegate is set, otherwise it is delegated.
+func (h *errLogger) Handle(err error) {
+	h.l.Print(err)
+}
+
 // GetErrorHandler returns the global ErrorHandler instance.
 //
 // The default ErrorHandler instance returned will log all errors to STDERR
@@ -34,7 +76,9 @@ var (
 //
 // Subsequent calls to SetErrorHandler after the first will not forward errors
 // to the new ErrorHandler for prior returned instances.
-func GetErrorHandler() ErrorHandler { return global.GetErrorHandler() }
+func GetErrorHandler() ErrorHandler {
+	return globalErrorHandler
+}
 
 // SetErrorHandler sets the global ErrorHandler to h.
 //
@@ -42,7 +86,11 @@ func GetErrorHandler() ErrorHandler { return global.GetErrorHandler() }
 // GetErrorHandler will send errors to h instead of the default logging
 // ErrorHandler. Subsequent calls will set the global ErrorHandler, but not
 // delegate errors to h.
-func SetErrorHandler(h ErrorHandler) { global.SetErrorHandler(h) }
+func SetErrorHandler(h ErrorHandler) {
+	globalErrorHandler.setDelegate(h)
+}
 
 // Handle is a convenience function for ErrorHandler().Handle(err).
-func Handle(err error) { global.Handle(err) }
+func Handle(err error) {
+	GetErrorHandler().Handle(err)
+}