reactor-core/src/main/java/reactor/core/publisher/ParallelFlux.java
public final ParallelFlux<T> log(@Nullable String category,
			Level level,
			boolean showOperatorLine,
			SignalType... options) {
		return onAssembly(new ParallelLog<>(this, new SignalLogger<>(this, category, level, showOperatorLine, options)));
	}
public final ParallelFlux<T> log(@Nullable String category,
			Level level,
			boolean showOperatorLine,
			SignalType... options) {
		return onAssembly(new ParallelLog<>(this, new SignalLogger<>(this, category, level, showOperatorLine, options)));
	}
Observe Reactive Streams signals matching the passed filter {@code options} and use
{@link Logger} support to handle trace implementation. Default will use the passed
{@link Level} and java.util.logging. If SLF4J is available, it will be used
instead.
<p>
Options allow fine grained filtering of the traced signal, for instance to only
capture onNext and onError:
<pre>
ParallelFlux.log("category", Level.INFO, SignalType.ON_NEXT,
SignalType.ON_ERROR)

<p>
<img class="marble" src="doc-files/marbles/logForFlux.svg" alt="">

@param category to be mapped into logger configuration (e.g. org.springframework
.reactor). If category ends with "." like "reactor.", a generated operator
suffix will complete, e.g. "reactor.ParallelFlux.Map".
@param level the {@link Level} to enforce for this tracing ParallelFlux (only
FINEST, FINE, INFO, WARNING and SEVERE are taken into account)
@param showOperatorLine capture the current stack to display operator
class/line number.
@param options a vararg {@link SignalType} option to filter log messages

@return a new unaltered {@link ParallelFlux}