# Annotation Interface Period

@Retention(RUNTIME) @Inherited @Target(TYPE) public @interface Period
Event annotation, specifies the default setting value for a periodic event.

The following example shows how the `Period` annotation can be used to emit events at different intervals.

    @Period("1 s")
    @Name("Counter")
    class CountEvent extends Event {
        int count;
    }
    @Period("3 s")
    @Name("Fizz")
    class FizzEvent extends Event {
    }
    @Period("5 s")
    @Name("Buzz")
    class BuzzEvent extends Event {
    }

    var counter = new AtomicInteger();
    FlightRecorder.addPeriodicEvent(CountEvent.class, () -> {
        CountEvent event = new CountEvent();
        event.count = counter.incrementAndGet();
        event.commit();
    });
    FlightRecorder.addPeriodicEvent(FizzEvent.class, () -> {
        new FizzEvent().commit();
    });
    FlightRecorder.addPeriodicEvent(BuzzEvent.class, () -> {
        new BuzzEvent().commit();
    });

    var sb = new StringBuilder();
    var last = new AtomicInteger();
    var current = new AtomicInteger();
    try (var r = new RecordingStream()) {
        r.onEvent("Counter", e -> current.set(e.getValue("count")));
        r.onEvent("Fizz", e -> sb.append("Fizz"));
        r.onEvent("Buzz", e -> sb.append("Buzz"));
        r.onFlush(() -> {
            if (current.get() != last.get()) {
                System.out.println(sb.isEmpty() ? current : sb);
                last.set(current.get());
                sb.setLength(0);
            }
        });
        r.start();
    }

Since:
  9

## Field Summary

Fields
Modifier and Type
Field
Description
`static final String`
`NAME`
Settings name `"period"` for configuring periodic events

## Optional Element Summary

Optional Elements
Modifier and Type
Optional Element
Description
`String`
`value`
Returns the default setting value for a periodic setting.

## Field Details

### NAME

static final String NAME
Settings name `"period"` for configuring periodic events

See Also:
  - Constant Field Values

## Element Details

### value

String value
Returns the default setting value for a periodic setting.

String representation of a positive `Long` value followed by an empty space and one of the following units:
`"ns"` (nanoseconds)
`"us"` (microseconds)
`"ms"` (milliseconds)
`"s"` (seconds)
`"m"` (minutes)
`"h"` (hours)
`"d"` (days)

Example values: `"0 ns"`, `"10 ms"`, and `"1 s"`.

A period may also be `"everyChunk"` to specify that it occurs at least once for every recording file. The number of events that are emitted depends on how many times the file rotations occur when data is recorded.

Returns:
  the default setting value, not `null`

Default:
  `"everyChunk"`