I am depending on libraries that hang for certain errors, which I cannot fix! The offenders are currently StackOverflowError and OutOfMemoryError but there might be more.
I am trying to upgrade the unrecoverable hang to an exit/abort. However, I cannot figure out how to pass multiple different errors to the -XX:AbortVMOnException as only the latest argument is active in:
JAVA_OPTS="-XX:+UnlockDiagnosticVMOptions -XX:AbortVMOnException=java.lang.StackOverflowError -XX:java.lang.OutOfMemoryError" foo
There can be only one value for AbortVMOnException option.
JVM does a substring search when checking if the exception class matches AbortVMOnException value. E.g. -XX:AbortVMOnException=Error will cause the VM to abort on any throwable with Error in its name: java.lang.StackOverflowError, java.lang.OutOfMemoryError, java.lang.NoClassDefFoundError, etc.
To add a custom callback on the desired exception types, you may use the JVM TI approach described in this answer. You'd only need to replace
if (strcmp(class_name + 1, fatal_error_class) == 0) {
with
if (strstr(fatal_error_class, class_name + 1) != NULL) {
and then it will be possible to specify multiple exceptions types that cause VM exit:
java -agentpath:/path/to/libabort.so=java/lang/StackOverflowError,java/lang/OutOfMemoryError ...
Related
I am using Gradle 7.5, Quarkus 2.12.3 and mockk 1.13.3. When I try to run quarkusDev task from command line and then start continuous testing (by pressing r), then all tests pass OK.
However, when I do the same as from IntelliJ (as gradle run configuration), all tests fail with error:
java.lang.NoClassDefFoundError: Could not initialize class io.mockk.impl.JvmMockKGateway
How can I fix that?
Masked thrown exception
After much debugging I found the problem. The thrown exception actually originates in HotSpotVirtualMachine.java and is thrown during attachment of ByteBuddy as a java agent. Here is the relevant code;
// The tool should be a different VM to the target. This check will
// eventually be enforced by the target VM.
if (!ALLOW_ATTACH_SELF && (pid == 0 || pid == CURRENT_PID)) {
throw new IOException("Can not attach to current VM");
}
Turning check off
So the check can be turned off by setting ALLOW_ATTACH_SELF constant to true. The constant is set from a system property named jdk.attach.allowAttachSelf:
String s = VM.getSavedProperty("jdk.attach.allowAttachSelf");
ALLOW_ATTACH_SELF = "".equals(s) || Boolean.parseBoolean(s);
So, in my case, I simply added the following JVM argument to my gradle file and tests started to pass:
tasks.quarkusDev {
jvmArgs += "-Djdk.attach.allowAttachSelf"
}
I'm trying to write a script to test all DataSources of a WebSphere Cell/Node/Cluster. While this is possible from the Admin Console a script is better for certain audiences.
So I found the following article from IBM https://www.ibm.com/support/knowledgecenter/en/SSAW57_8.5.5/com.ibm.websphere.nd.multiplatform.doc/ae/txml_testconnection.html which looks promising as it describles exactly what I need.
After having a basic script like:
ds_ids = AdminConfig.list("DataSource").splitlines()
for ds_id in ds_ids:
AdminControl.testConnection(ds_id)
I experienced some undocumented behavior. Contrary to the article above the testConnection function does not always return a String, but may also throw a exception.
So I simply use a try-catch block:
try:
AdminControl.testConnection(ds_id)
except: # it actually is a com.ibm.ws.scripting.ScriptingException
exc_type, exc_value, exc_traceback = sys.exc_info()
now when I print the exc_value this is what one gets:
com.ibm.ws.scripting.ScriptingException: com.ibm.websphere.management.exception.AdminException: javax.management.MBeanException: Exception thrown in RequiredModelMBean while trying to invoke operation testConnection
Now this error message is always the same no matter what's wrong. I tested authentication errors, missing WebSphere Variables and missing driver classes.
While the Admin Console prints reasonable messages, the script keeps printing the same meaningless message.
The very weird thing is, as long as I don't catch the exception and the script just exits by error, a descriptive error message is shown.
Accessing the Java-Exceptions cause exc_value.getCause() gives None.
I've also had a look at the DataSource MBeans, but as they only exist if the servers are started, I quickly gave up on them.
I hope someone knows how to access the error messages I see when not catching the Exception.
thanks in advance
After all the research and testing AdminControl seems to be nothing more than a convinience facade to some of the commonly used MBeans.
So I tried issuing the Test Connection Service (like in the java example here https://www.ibm.com/support/knowledgecenter/en/SSEQTP_8.5.5/com.ibm.websphere.base.doc/ae/cdat_testcon.html
) directly:
ds_id = AdminConfig.list("DataSource").splitlines()[0]
# other queries may be 'process=server1' or 'process=dmgr'
ds_cfg_helpers = __wat.AdminControl.queryNames("WebSphere:process=nodeagent,type=DataSourceCfgHelper,*").splitlines()
try:
# invoke MBean method directly
warning_cnt = __wat.AdminControl.invoke(ds_cfg_helpers[0], "testConnection", ds_id)
if warning_cnt == "0":
print = "success"
else:
print "%s warning(s)" % warning_cnt
except ScriptingException as exc:
# get to the root of all evil ignoring exception wrappers
exc_cause = exc
while exc_cause.getCause():
exc_cause = exc_cause.getCause()
print exc_cause
This works the way I hoped for. The downside is that the code gets much more complicated if one needs to test DataSources that are defined on all kinds of scopes (Cell/Node/Cluster/Server/Application).
I don't need this so I left it out, but I still hope the example is useful to others too.
It may happen that data that enters Flink job triggers exception either due to bug in code or lack of validation.
My goal is to provide consistent way of exception handling that our team could use within Flink jobs that won't cause any downtime in production.
Restart strategies do not seem to be applicable here as:
simple restart won't fix issue and we fall into restart loop
we cannot simply skip event
they can be good for OOME or some transient issues
we cannot add custom one
try/catch block in "keyBy" function does not fully help as:
there's no way to skip event in "keyBy" after exception is handled
Sample code:
env.addSource(kafkaConsumer)
.keyBy(keySelector) // must return one result for one entry
.flatMap(mapFunction) // we can skip some entries here in case of errors
.addSink(new PrintSinkFunction<>());
env.execute("Flink Application");
I'd like to have ability to skip processing of event that caused issue in "keyBy" and similar methods that are supposed to return exactly one result.
Beside the suggestion of #phanhuy152 (which seems totally legit to me) why not filter before keyBy?
env.addSource(kafkaConsumer)
.filter(invalidKeys)
.keyBy(keySelector) // must return one result for one entry
.flatMap(mapFunction) // we can skip some entries here in case of errors
.addSink(new PrintSinkFunction<>());
env.execute("Flink Application");
Can you reserve a special value like "NULL" for the keyBy to return in such case? Then your flatMap function can skip when encounter such value?
Having:
Velocity template or macro
some object
How to validate the object (#if) and fail (stop further processing) in a way that is easily tracable to the place of failure (like throwing exception in Java).
I am looking for something like this:
#if ( ! $context.treasureMap.containsKey('gold'))
#fail('no golden treasure here')
#end
Background
I am writing a maven site page. The velocity context is injected by maven and contains POM information. I want to test existence of some information from effective pom. When the information is not available, I want to fail.
Requirements
fail Velocity processing > fail site generation > fail maven build.
error message should lead to the place of failure so the site should be fixed
preferably no configuration (no extensions, just constructs/tools contained in plain Velocity)
Tried
Strict Reference Mode
Unwanted configuration, do not want to fail on every occasion.
#evaluate('#end') aka syntax error
(Chose #end as most descriptive to my intent) Basically what I want. Fails the processing and maven build but the error message does not lead back to failure location:
ParseException: Encountered "#end" at line 1, column 1..
You need to make a method call which produce exception.See explanation:
The only place where one could run into trouble within Velocity is if there is a call to a method which throws an exception during runtime. For example, this VTL defines a String $foo and then attempts to call its substring() method on it would throw an IndexOutOfBoundsException:
#set ($foo = "bar")
#set ($bar = $foo.substring(0,10))
When the exception is thrown, the parser will stop processing and throw that exception up the stack tree where it can be caught in the method that caused the parser to execute. At that point, the exception can be handled gracefully.
I forked Codeception/Codeception and added a Command module check that throws an exception.
When testing, this exception causes the test to fail but I'm running a test to force the exception and failure, to make sure it catches it.
Here's the edit to src/Codeception/Command/GenerateSuite.php
if ($this->containsInvalidCharacters ($suite)) {
throw new \Exception("Suite name '{$suite}' contains invalid characters. ([A-Za-z0-9_]).");
}
When updating tests/cli/GenerateSuiteCept.php when I run the command $I->executeCommand('generate:suite invalid-suite'); it fails because I'm throwing the exception in src/Codeception/Command/GenerateSuite.php in the first place.
Here is the addition to tests/cli/GenerateSuiteCept.php:
$I->executeCommand('generate:suite invalid-dash-suite');
When I run it, it says it failed. However, I want it to pass because I'm deliberately adding the dash to verify it catches invalid characters. What is the best way to do that? I'm wary of a try/catch block in these tests. I'm not sure if that is the best way to do that.
After looking at the other Codeception tests, I found this to be a better way than throwing an exception:
if ($this->containsInvalidCharacters ($suite)) {
$output->writeln("<error>Suite name '{$suite}' contains invalid characters. ([A-Za-z0-9_]).</error>");
return;
}
So I modified the test to:
$I->expect ('suite is not created due to dashes');
$I->executeCommand('generate:suite invalid-dash-suite');
$I->seeInShellOutput('contains invalid characters');