fix: NPE fix when signal not found from model

[ikaakkola]

In some rare cases the BpmnModel can change between the call to "containsSignalId" and the call to get the signal, causing an NPE if the signal was no longer available on the model.

Due to the way containsSignalId is implemented, the call to it is entirely unnecessary in these cases.

[dbmalkovsky]

Please do not change the ordering of the imports from the standards for this project. See for example the top of this file: https://github.com/flowable/flowable-engine/blob/main/ide-settings/idea/idea-code-style-configuration.xml

[ikaakkola]

👍 thanks for the link, will update to match project code style.

[filiphr]

@ikaakkola can you please provide some tests cases for this NPE? We would like to see why it fails.

[ikaakkola]

@ikaakkola can you please provide some tests cases for this NPE? We would like to see why it fails.

I have not been able to reproduce this in unit tests, but have witnessed NPE in production for this ; that is, the BpmnModel signals were changed by another thread between the two calls (bpmnModel.containsSignalId() and the subsequent bpmnModel.getSignal() call) which is entirely possible as there is no synchronization of any sorts here.

The change simply removes the entirely unnecessary step of getting the signal twice - containsSignalId() calls provide no additional functionality as opposed to simply getting the signal and then checking if it was not null before using the signal.

It is very difficult to get this to happen in a junit test due to the fact that the BpmnModel needs to be changed between two subsequent function calls, but that doesn't mean it cannot happen.

[ikaakkola]

Here is a stack trace showing this happen (Flowable 6.7.2) , the in-house ExtendedProcessRuntimeService.java parts are not really relevant here, the failure happens after calling org.flowable.engine.impl.RuntimeServiceImpl.startProcessInstanceById(using RuntimeService interface, not the Impl directly).

https://github.com/flowable/flowable-engine/blob/flowable-6.7.2/modules/flowable-engine/src/main/java/org/flowable/engine/impl/util/ProcessInstanceHelper.java#L415 (signal.getName() throws as signal is null)

Exception in thread "ProcessExecutor-1" org.flowable.common.engine.api.FlowableException: Exception during command execution
	at org.flowable.common.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:138)
	at org.flowable.common.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:30)
	at org.flowable.common.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:56)
	at org.flowable.common.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:51)
	at org.flowable.engine.impl.RuntimeServiceImpl.startProcessInstanceById(RuntimeServiceImpl.java:162)
	at com.qvantel.flex.bpmn.executor.service.process.ExtendedProcessRuntimeService.lambda$queueProcessWithId$6(ExtendedProcessRuntimeService.java:370)
	at org.flowable.engine.impl.interceptor.CommandInvoker$1.run(CommandInvoker.java:67)
	at org.flowable.engine.impl.interceptor.CommandInvoker.executeOperation(CommandInvoker.java:140)
	at org.flowable.engine.impl.interceptor.CommandInvoker.executeOperations(CommandInvoker.java:114)
	at org.flowable.engine.impl.interceptor.CommandInvoker.execute(CommandInvoker.java:72)
	at org.flowable.engine.impl.interceptor.BpmnOverrideContextInterceptor.execute(BpmnOverrideContextInterceptor.java:26)
	at org.flowable.common.engine.impl.interceptor.TransactionContextInterceptor.execute(TransactionContextInterceptor.java:53)
	at org.flowable.common.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:105)
	at org.flowable.common.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:30)
	at org.flowable.common.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:56)
	at org.flowable.common.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:51)
	at com.qvantel.flex.bpmn.executor.service.process.ExtendedProcessRuntimeService.command(ExtendedProcessRuntimeService.java:156)
	at com.qvantel.flex.bpmn.executor.service.process.ExtendedProcessRuntimeService.lambda$queueProcessWithId$7(ExtendedProcessRuntimeService.java:365)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.base/java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
	at org.flowable.engine.impl.util.ProcessInstanceHelper.handleSignalEventSubscription(ProcessInstanceHelper.java:415)
	at org.flowable.engine.impl.util.ProcessInstanceHelper.processEventSubProcess(ProcessInstanceHelper.java:348)
	at org.flowable.engine.impl.util.ProcessInstanceHelper.processAvailableEventSubProcesses(ProcessInstanceHelper.java:299)
	at org.flowable.engine.impl.util.ProcessInstanceHelper.startProcessInstance(ProcessInstanceHelper.java:280)
	at org.flowable.engine.impl.util.ProcessInstanceHelper.createAndStartProcessInstanceWithInitialFlowElement(ProcessInstanceHelper.java:257)
	at org.flowable.engine.impl.util.ProcessInstanceHelper.createProcessInstance(ProcessInstanceHelper.java:109)
	at org.flowable.engine.impl.cmd.StartProcessInstanceCmd.startProcessInstance(StartProcessInstanceCmd.java:239)
	at org.flowable.engine.impl.cmd.StartProcessInstanceCmd.execute(StartProcessInstanceCmd.java:128)
	at org.flowable.engine.impl.cmd.StartProcessInstanceCmd.execute(StartProcessInstanceCmd.java:53)
	at org.flowable.engine.impl.interceptor.CommandInvoker$1.run(CommandInvoker.java:67)
	at org.flowable.engine.impl.interceptor.CommandInvoker.executeOperation(CommandInvoker.java:140)
	at org.flowable.engine.impl.interceptor.CommandInvoker.executeOperations(CommandInvoker.java:114)
	at org.flowable.engine.impl.interceptor.CommandInvoker.execute(CommandInvoker.java:72)
	at org.flowable.engine.impl.interceptor.BpmnOverrideContextInterceptor.execute(BpmnOverrideContextInterceptor.java:26)
	at org.flowable.common.engine.impl.interceptor.TransactionContextInterceptor.execute(TransactionContextInterceptor.java:53)
	at org.flowable.common.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:105)
	... 20 more