Why does the memory usage remain high for more than ten minutes when occasionally stuck in waitResult?

[alinlky]

When calling the fillReport method in JasperReports, the data volume is not very large, only about a thousand records. Occasionally, it gets stuck in waitResult for more than ten minutes, and memory usage is high. What could be the reason?
the Version is 6.20.0

[alinlky]

at java.lang.Object.wait(Native Method)
at java.lang.Object.wait(Object.java:502)
at net.sf.jasperreports.engine.fill.AbstractThreadSubreportRunner.waitResult(AbstractThreadSubreportRunner.java:84)
at net.sf.jasperreports.engine.fill.AbstractThreadSubreportRunner.start(AbstractThreadSubreportRunner.java:55)
at net.sf.jasperreports.engine.fill.JRFillSubreport.prepare(JRFillSubreport.java:943)
at net.sf.jasperreports.components.table.fill.FillTableSubreport.prepareSubreport(FillTableSubreport.java:182)
at net.sf.jasperreports.components.table.fill.FillTable.prepare(FillTable.java:427)
at net.sf.jasperreports.engine.fill.JRFillComponentElement.prepare(JRFillComponentElement.java:152)
at net.sf.jasperreports.engine.fill.JRFillElementContainer.prepareElements(JRFillElementContainer.java:542)
at net.sf.jasperreports.engine.fill.JRFillBand.fill(JRFillBand.java:453)
at net.sf.jasperreports.engine.fill.JRFillBand.fill(JRFillBand.java:428)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillColumnBand(JRVerticalFiller.java:2709)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillDetail(JRVerticalFiller.java:836)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReportStart(JRVerticalFiller.java:275)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:119)
at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:622)
at net.sf.jasperreports.engine.fill.BaseReportFiller.fill(BaseReportFiller.java:433)
at net.sf.jasperreports.engine.fill.JRFiller.fill(JRFiller.java:162)
at net.sf.jasperreports.engine.JasperFillManager.fill(JasperFillManager.java:651)
at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:1020)

[alinlky]

@teodord

[teodord]

Difficult to say what happens if we do not have a reproduceable case that we could verify on our side.
Maybe you can provide a thread dump so that we can see what is the subreport thread doing while the main report thread waits.

[teodord]

Also, uploading here the JRXML files involved would not hurt.