CentralizedSampling will not work with instrumentor

[praetp]

When using XRay SDK 2.0.1, we see every 5 seconds:

java.lang.NullPointerException: null
	at com.amazonaws.xray.handlers.TracingHandler.beforeExecution(TracingHandler.java:138) ~[aws-xray-recorder-sdk-aws-sdk-2.0.1.jar:?]
	at com.amazonaws.AmazonWebServiceClient.beforeClientExecution(AmazonWebServiceClient.java:723) ~[aws-java-sdk-core-1.11.398.jar:?]
	at com.amazonaws.services.xray.AWSXRayClient.getSamplingRules(AWSXRayClient.java:538) ~[aws-java-sdk-xray-1.11.398.jar:?]
	at com.amazonaws.xray.strategy.sampling.pollers.RulePoller.pollRule(RulePoller.java:53) ~[aws-xray-recorder-sdk-core-2.0.1.jar:?]
	at com.amazonaws.xray.strategy.sampling.pollers.RulePoller.lambda$start$0(RulePoller.java:41) ~[aws-xray-recorder-sdk-core-2.0.1.jar:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_152]
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [?:1.8.0_152]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_152]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [?:1.8.0_152]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_152]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_152]

This is caused by the TracingHandler being created when the globalrecorder has not yet finished initialization. Then the recorder of the TracingHandler will be null. See stacktrace below. The globalrecorder is in the process of being created but AWSXray.globalRecorder has not been assigned yet.

When just getting the globalRecorder, you will trigger this problem:

  at com.amazonaws.xray.AWSXRay.getGlobalRecorder(AWSXRay.java:28)
	  at com.amazonaws.xray.handlers.TracingHandler.<init>(TracingHandler.java:94)
	  at sun.reflect.NativeConstructorAccessorImpl.newInstance0(NativeConstructorAccessorImpl.java:-1)
	  at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	  at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	  at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	  at java.lang.Class.newInstance(Class.java:442)
	  at com.amazonaws.handlers.HandlerChainFactory.createRequestHandler(HandlerChainFactory.java:113)
	  at com.amazonaws.handlers.HandlerChainFactory.getGlobalHandlers(HandlerChainFactory.java:74)
	  at com.amazonaws.services.xray.AWSXRayClient.init(AWSXRayClient.java:283)
	  at com.amazonaws.services.xray.AWSXRayClient.<init>(AWSXRayClient.java:256)
	  at com.amazonaws.services.xray.AWSXRayClientBuilder.build(AWSXRayClientBuilder.java:61)
	  at com.amazonaws.services.xray.AWSXRayClientBuilder.build(AWSXRayClientBuilder.java:27)
	  at com.amazonaws.client.builder.AwsSyncClientBuilder.build(AwsSyncClientBuilder.java:46)
	  at com.amazonaws.xray.strategy.sampling.XRayClient.newClient(XRayClient.java:31)
	  at com.amazonaws.xray.strategy.sampling.CentralizedSamplingStrategy.<init>(CentralizedSamplingStrategy.java:40)
	  at com.amazonaws.xray.strategy.sampling.DefaultSamplingStrategy.<init>(DefaultSamplingStrategy.java:5)
	  at com.amazonaws.xray.AWSXRayRecorder.<init>(AWSXRayRecorder.java:87)
	  at com.amazonaws.xray.AWSXRayRecorderBuilder.build(AWSXRayRecorderBuilder.java:145)
	  at com.amazonaws.xray.AWSXRayRecorderBuilder.defaultRecorder(AWSXRayRecorderBuilder.java:78)
	  at com.amazonaws.xray.AWSXRay.<clinit>(AWSXRay.java:18)

Setting the samplingStrategy to CentralizedSampling again later, is a workaround.

        AWSXRay.getGlobalRecorder().setSamplingStrategy(new DefaultSamplingStrategy());

[haotianw465]

This issue is fixed as part of 2.1.0 release. See CHANGELOG for details.