# readBlocking and timeout exception

**URL:** <https://forum.inductiveautomation.com/t/readblocking-and-timeout-exception/38921>\
**Category:** Ignition\
**Tags:** ignition80, scripting\
**Created:** [September 22, 2020, 8:44am UTC](https://forum.inductiveautomation.com/t/readblocking-and-timeout-exception/38921 "2020-09-22T08:44:28Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![steiger](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@steiger](https://forum.inductiveautomation.com/u/steiger)\
**Post date:** [September 22, 2020, 8:44am UTC](https://forum.inductiveautomation.com/t/readblocking-and-timeout-exception/38921/1 "2020-09-22T08:44:28Z")

</div>

Dear community,

I am not able to catch a timeout exception from system.tag.readBlocking.

My tag event script looks as follows:

```auto
from java.util.concurrent import TimeoutException
logger = system.util.getLogger("blnWriteBlockingTimeoutTest.TagChangeEvent")
	
try:
	result = system.tag.writeBlocking(
		["[GLT_PROD_INTERNAL]ENE/BETDRG00UG/BHKW/intSumPowerJZD"], [570], 100)
	
	logger.info("result=%s" % result)

except TimeoutException:
	logger.warn("TimeoutException for tag path=%s" % tagPath)
except Exception as e:
	logger.warn("Unexpected Error for tag path=%s; Exception=%s" % (tagPath, e))

```

In the gateway log I see the following exception:

```auto
INFO | jvm 1 | 2020/09/22 10:30:41 | E [Scripting[system_util_tag] ] [08:30:41]: Error during blocking write of tags through scripting.
INFO | jvm 1 | 2020/09/22 10:30:41 | java.util.concurrent.TimeoutException: null
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.util.concurrent.CompletableFuture.timedGet(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.util.concurrent.CompletableFuture.get(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.gateway.script.GatewayTagUtilities.writeBlockingImpl(GatewayTagUtilities.java:234)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.common.script.builtin.AbstractTagUtilities.writeBlocking(AbstractTagUtilities.java:397)
INFO | jvm 1 | 2020/09/22 10:30:41 | at jdk.internal.reflect.GeneratedMethodAccessor133.invoke(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.lang.reflect.Method.invoke(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyReflectedFunction. __call__ (PyReflectedFunction.java:188)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.common.script.ScriptManager$ReflectedInstanceFunction. __call__ (ScriptManager.java:524)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyObject. __call__ (PyObject.java:515)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyObject. __call__ (PyObject.java:519)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.pycode._pyx1595.valueChanged$1(<tagevent:valueChanged>:14)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.pycode._pyx1595.call_function(<tagevent:valueChanged>)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyTableCode.call(PyTableCode.java:171)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyBaseCode.call(PyBaseCode.java:308)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyFunction.function ___call__ (PyFunction.java:471)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyFunction. __call__ (PyFunction.java:466)
INFO | jvm 1 | 2020/09/22 10:30:41 | at org.python.core.PyFunction. __call__ (PyFunction.java:461)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.common.script.ScriptManager.runFunction(ScriptManager.java:822)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.common.script.ScriptManager.runFunction(ScriptManager.java:806)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.gateway.project.ProjectScriptLifecycle$TrackingProjectScriptManager.runFunction(ProjectScriptLifecycle.java:687)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.gateway.tags.scripting.TagScriptManagerImpl$FunctionInvokerImpl.run(TagScriptManagerImpl.java:527)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.gateway.tags.scripting.events.AbstractTagScript.invoke(AbstractTagScript.java:34)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.gateway.tags.scripting.TagScriptManagerImpl$Task.invoke(TagScriptManagerImpl.java:476)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.gateway.tags.scripting.TagScriptManagerImpl$TagScriptDispatcher.run(TagScriptManagerImpl.java:439)
INFO | jvm 1 | 2020/09/22 10:30:41 | at com.inductiveautomation.ignition.common.execution.impl.BasicExecutionEngine$ThrowableCatchingRunnable.run(BasicExecutionEngine.java:518)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | at java.base/java.lang.Thread.run(Unknown Source)
INFO | jvm 1 | 2020/09/22 10:30:41 | I [b.TagChangeEvent] [08:30:41]: result=[Error_Exception]

```

As you can see, the two defined exception handlers (TimeoutException, Exception) are not called. But Ignition raises still a java.util.concurrent.TimeoutException.

Does any body know how I can gracefully handle the timeout exception?

---

<div class="post-metadata">

**Author:** ![JordanCClark](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/jordancclark/32/83362_2.png) [@JordanCClark](https://forum.inductiveautomation.com/u/JordanCClark)\
**Post date:** [September 22, 2020, 11:55am UTC](https://forum.inductiveautomation.com/t/readblocking-and-timeout-exception/38921/2 "2020-09-22T11:55:07Z")

</div>

This might help:

> [@Using Try/Except to Dummy Proof & Check if SQL Tables/Columns Exist](http://forum.inductiveautomation.com/t/using-try-except-to-dummy-proof-check-if-sql-tables-columns-exist/26140/4):
>
> Ah, missed that. A bare “except” block doesn’t necessarily catch java exceptions. Use a structure like this: import java.lang.Exception try: # some code that can throw either java exceptions or python exceptions except java.lang.Exception, e: # Handle the java exception in 'e', possibly using e.cause to drill into the nesting except Exception, e: # Handle the python exception in 'e'. Note that python doesn't need to import its native exception

---

<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [September 22, 2020, 12:20pm UTC](https://forum.inductiveautomation.com/t/readblocking-and-timeout-exception/38921/3 "2020-09-22T12:20:24Z")

</div>

If the error was a direct throw of that TimeoutException, your `except` clause would work. But it is being wrapped in some other throwable (the TimeoutException add as the cause). I recommend this structure for this case:

```auto
import java.lang.Throwable

def someFunction():
	try:
		system.tag.writeBlocking(.....)
	except java.lang.Throwable, t:
		# do something, including looking at t.cause
	except Exception, e:
		# do something with other python problems.

```

---

<div class="post-metadata">

**Author:** ![steiger](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@steiger](https://forum.inductiveautomation.com/u/steiger)\
**Post date:** [September 22, 2020, 1:34pm UTC](https://forum.inductiveautomation.com/t/readblocking-and-timeout-exception/38921/4 "2020-09-22T13:34:47Z")

</div>

Thanks for the recommendations. I tried to catch the error with

```auto
except java.lang.Throwable, t:

```

but it did not work. I did not wrap it in a function but I think that’s not an issue.  
If I put the same code in the Script Console the exception is caught even with java.util.concurrent.TimeoutException. Why does it not work inside the tag change event?

---

<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [September 22, 2020, 2:50pm UTC](https://forum.inductiveautomation.com/t/readblocking-and-timeout-exception/38921/5 "2020-09-22T14:50:48Z")

</div>

It is likely that it is simply not being thrown in your thread. system.tag.readBlocking & .writeBlocking are documented to return a list that contains the operation results. That implies that exceptions thrown are converted to status codes and delivered in the list. But logged for forensic follow-up.