For languages which support concurrent execution the OpenTelemetry APIs provide specific guarantees and safeties. Not all of API functions are safe to be called concurrently. Function and method documentation must explicitly specify whether it is safe or no to make concurrent calls and in what situations.
The following are general recommendations of concurrent call safety of specific subsets of the API.
Tracer - all methods are safe to be called concurrently.
SpanBuilder - It is not safe to concurrently call any methods of the same SpanBuilder instance. Different instances of SpanBuilder can be safely used concurrently by different threads/coroutines, provided that no single SpanBuilder is used by more than one thread/coroutine.
Span - All methods of Span are safe to be called concurrently.
Link - same as SpanData.