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本文主要研究一下flink的AscendingTimestampExtractor

AscendingTimestampExtractor

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/timestamps/AscendingTimestampExtractor.java

/*** A timestamp assigner and watermark generator for streams where timestamps are monotonously* ascending. In this case, the local watermarks for the streams are easy to generate, because* they strictly follow the timestamps.** @param <T> The type of the elements that this function can extract timestamps from*/
@PublicEvolving
public abstract class AscendingTimestampExtractor<T> implements AssignerWithPeriodicWatermarks<T> {private static final long serialVersionUID = 1L;/** The current timestamp. */private long currentTimestamp = Long.MIN_VALUE;/** Handler that is called when timestamp monotony is violated. */private MonotonyViolationHandler violationHandler = new LoggingHandler();/*** Extracts the timestamp from the given element. The timestamp must be monotonically increasing.** @param element The element that the timestamp is extracted from.* @return The new timestamp.*/public abstract long extractAscendingTimestamp(T element);/*** Sets the handler for violations to the ascending timestamp order.** @param handler The violation handler to use.* @return This extractor.*/public AscendingTimestampExtractor<T> withViolationHandler(MonotonyViolationHandler handler) {this.violationHandler = requireNonNull(handler);return this;}// ------------------------------------------------------------------------@Overridepublic final long extractTimestamp(T element, long elementPrevTimestamp) {final long newTimestamp = extractAscendingTimestamp(element);if (newTimestamp >= this.currentTimestamp) {this.currentTimestamp = newTimestamp;return newTimestamp;} else {violationHandler.handleViolation(newTimestamp, this.currentTimestamp);return newTimestamp;}}@Overridepublic final Watermark getCurrentWatermark() {return new Watermark(currentTimestamp == Long.MIN_VALUE ? Long.MIN_VALUE : currentTimestamp - 1);}//......
}
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• AscendingTimestampExtractor抽象类实现AssignerWithPeriodicWatermarks接口的extractTimestamp及getCurrentWatermark方法，同时声明抽象方法extractAscendingTimestamp供子类实现
• AscendingTimestampExtractor适用于elements的时间在每个parallel task里头是单调递增(timestamp monotony)的场景，extractTimestamp这里先是调用子类实现的extractAscendingTimestamp方法从element提取newTimestamp，然后返回，对于违反timestamp monotony的，这里调用MonotonyViolationHandler进行处理
• getCurrentWatermark方法在currentTimestamp不为Long.MIN_VALUE时返回Watermark(currentTimestamp - 1)

MonotonyViolationHandler

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/timestamps/AscendingTimestampExtractor.java

 /*** Interface for handlers that handle violations of the monotonous ascending timestamps* property.*/public interface MonotonyViolationHandler extends java.io.Serializable {/*** Called when the property of monotonously ascending timestamps is violated, i.e.,* when {@code elementTimestamp < lastTimestamp}.** @param elementTimestamp The timestamp of the current element.* @param lastTimestamp The last timestamp.*/void handleViolation(long elementTimestamp, long lastTimestamp);}/*** Handler that does nothing when timestamp monotony is violated.*/public static final class IgnoringHandler implements MonotonyViolationHandler {private static final long serialVersionUID = 1L;@Overridepublic void handleViolation(long elementTimestamp, long lastTimestamp) {}}/*** Handler that fails the program when timestamp monotony is violated.*/public static final class FailingHandler implements MonotonyViolationHandler {private static final long serialVersionUID = 1L;@Overridepublic void handleViolation(long elementTimestamp, long lastTimestamp) {throw new RuntimeException("Ascending timestamps condition violated. Element timestamp "+ elementTimestamp + " is smaller than last timestamp " + lastTimestamp);}}/*** Handler that only logs violations of timestamp monotony, on WARN log level.*/public static final class LoggingHandler implements MonotonyViolationHandler {private static final long serialVersionUID = 1L;private static final Logger LOG = LoggerFactory.getLogger(AscendingTimestampExtractor.class);@Overridepublic void handleViolation(long elementTimestamp, long lastTimestamp) {LOG.warn("Timestamp monotony violated: {} < {}", elementTimestamp, lastTimestamp);}}
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• MonotonyViolationHandler继承了Serializable，它定义了handleViolation方法，这个接口内置有三个实现类，分别是IgnoringHandler、FailingHandler、FailingHandler
• IgnoringHandler的handleViolation方法不做任何处理；FailingHandler的handleViolation会抛出RuntimeException；LoggingHandler的handleViolation方法会打印warn日志
• AscendingTimestampExtractor默认使用的是LoggingHandler，也可以通过withViolationHandler方法来进行设置

实例

    @Testpublic void testWithFailingHandler() {AscendingTimestampExtractor<Long> extractor = (new AscendingTimestampExtractorTest.LongExtractor()).withViolationHandler(new FailingHandler());this.runValidTests(extractor);try {this.runInvalidTest(extractor);Assert.fail("should fail with an exception");} catch (Exception var3) {;}}private void runValidTests(AscendingTimestampExtractor<Long> extractor) {Assert.assertEquals(13L, extractor.extractTimestamp(13L, -1L));Assert.assertEquals(13L, extractor.extractTimestamp(13L, 0L));Assert.assertEquals(14L, extractor.extractTimestamp(14L, 0L));Assert.assertEquals(20L, extractor.extractTimestamp(20L, 0L));Assert.assertEquals(20L, extractor.extractTimestamp(20L, 0L));Assert.assertEquals(20L, extractor.extractTimestamp(20L, 0L));Assert.assertEquals(500L, extractor.extractTimestamp(500L, 0L));Assert.assertEquals(9223372036854775806L, extractor.extractTimestamp(9223372036854775806L, 99999L));}private void runInvalidTest(AscendingTimestampExtractor<Long> extractor) {Assert.assertEquals(1000L, extractor.extractTimestamp(1000L, 100L));Assert.assertEquals(1000L, extractor.extractTimestamp(1000L, 100L));Assert.assertEquals(999L, extractor.extractTimestamp(999L, 100L));}private static class LongExtractor extends AscendingTimestampExtractor<Long> {private static final long serialVersionUID = 1L;private LongExtractor() {}public long extractAscendingTimestamp(Long element) {return element;}}
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• 这里使用withViolationHandler设置了violationHandler为FailingHandler，在遇到999这个时间的时候，由于比之前的1000小，因而会调用MonotonyViolationHandler.handleViolation方法

小结

• flink为了方便开发提供了几个内置的Pre-defined Timestamp Extractors / Watermark Emitters，其中一个就是AscendingTimestampExtractor
• AscendingTimestampExtractor抽象类实现AssignerWithPeriodicWatermarks接口的extractTimestamp及getCurrentWatermark方法，同时声明抽象方法extractAscendingTimestamp供子类实现
• AscendingTimestampExtractor适用于elements的时间在每个parallel task里头是单调递增的，对于违反timestamp monotony的，这里调用MonotonyViolationHandler的handleViolation方法进行处理；MonotonyViolationHandler继承了Serializable，它定义了handleViolation方法，这个接口内置有三个实现类，分别是IgnoringHandler、FailingHandler、FailingHandler

doc

• Pre-defined Timestamp Extractors / Watermark Emitters