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<p class="MsoNormal">I’ve just started to use Drools Flow in anger and I’m really struggling to understand the correct way to use it and think I am missing something.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is what I want to achieve:<o:p></o:p></p>
<p class="MsoNormal">The app code executes a StartProcess command and waits for the process to return (1 main process per session, 1 session per thread).<o:p></o:p></p>
<p class="MsoNormal">The process either succeeds, or it fails with a result.<o:p></o:p></p>
<p class="MsoNormal">A process could be complicated so I want to split it up into a parent process calling subprocesses.<o:p></o:p></p>
<p class="MsoNormal">I want to minimize boilerplate code (particularly in the ruleflow files) and keep the workflows as simple and maintainable as possible.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">It sounds simple enough and doesn’t seem to be particularly unusual.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Issue 1: startProcess is semi-synchronous. It starts the process, runs through as many nodes as it can until it gets to a non-synchronous task (rules, long lived customer work item etc) at which point it returns – or it returns when the
entire process has been completed.<o:p></o:p></p>
<p class="MsoNormal">Challenge 1a: How to detect when the process has finished and use it in a synchronous manner.<o:p></o:p></p>
<p class="MsoNormal">Solution: A ProcessEventListener which completes a countdown latch when teh process has completed.<o:p></o:p></p>
<p class="MsoNormal">Challenge 1b: Subprocesses also trigger process events<o:p></o:p></p>
<p class="MsoNormal">Solution: Have the latch track the first process that started (the parent) and only return when that process completes.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Issue 2: Drools Flow is littered with error checking code which just prints to System.err and either carrys on or just stop. Eg if a work item handler isn’t registered the process just stalls with a message.<o:p></o:p></p>
<p class="MsoNormal">Solution: Make sure code is perfectly written and doesn’t have any bugs... hope that it doesn’t happen in production ... complain on mailing list and add TODO to raise issue.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Issue 3: Fault nodes seem to be the correct way to say that something has gone wrong and the process should terminate.<o:p></o:p></p>
<p class="MsoNormal">Challenge: How does the calling code actually work out what the fault was and get the variable? The guide talks very very briefly about exception handlers but from what I can understand this is a way for the process to define what to do
in this conditions. I want the process to be aborted and the calling application to be informed of this and the details.<o:p></o:p></p>
<p class="MsoNormal">Solution: Add an event listener which detects when a fault node is being entered and extracts the details – seems like a big hack surely there is a better way.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Issue 4: If a child process executes a fault node it is aborted. The parent process is set to wait for completion and has the child node as not being independent so I would expect that the parent process should also be marked as aborted.<o:p></o:p></p>
<p class="MsoNormal">Challenge: The parent process isn’t marked as complete – it still has a status of Executing. However the process is stalled. Looking at subprocessNodeInstance internalTrigger (line 117) if the node returns a state of completed then trigger
completed is called, otherwise it just adds a process listener – which will never be called as the process has already aborted. The parent process just stalls left in the state of active forever. <o:p></o:p></p>
<p class="MsoNormal">Sollution: ?? Hack my fault listener to work round the issue and update the parent process, make the processEventListener assert that if a child process is aborted then we should return? Ask on the mailing list to get me out of a blind
alley and point me to the correct drools way of doing it...<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thomas<o:p></o:p></p>
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