Answers inline.
On 9/3/19 4:01 PM, Till Rohrmann wrote:
How so? Does your REPL add the generated classes to the system class
loader? I assume the system class loader is used to load the Flink classes.
No, it does not. It cannot on JDK >= 9 (or would have to hack into
jdk.internal.loader.ClassLoaders, which I don't want to :)). It just
creates another class loader, and is able to create a jar from generated
files. The jar is used for remote execution.
Ideally, what you would like to have is the option to provide the parent
class loader which is used load user code to the LocalEnvironment. This one
could then be forwarded to the TaskExecutor where it is used to generate
the user code class loader. But this is a bigger effort.
I'm not sure how this differs from using context classloader? Maybe
there is subtle difference in that this is a little more explicit. On
the other hand, users normally do not modify class loaders, so the
practical impact is IMHO negligible. But maybe this opens another
possibility - we probably could add optional ClassLoader parameter to
LocalEnvironment, with default value of
FlinkRunner.class.getClassLoader()? That might be a good compromise.
The downside to this approach is that it requires you to create a jar file
and to submit it via a REST call. The upside is that it is closer to the
production setting.
Yes, a REPL has to do that anyway to support distributed computing, so
this is not an issue.
Jan
Cheers,
Till
On Tue, Sep 3, 2019 at 3:47 PM Jan Lukavský <je...@seznam.cz> wrote:
On the other hand, if you say, that the contract of LocalEnvironment is
to execute as if it had all classes on its class loader, then it
currently breaks this contract. :-)
Jan
On 9/3/19 3:45 PM, Jan Lukavský wrote:
Hi Till,
hmm, that sounds it might work. I would have to incorporate this
(either as default, or on demand) into Apache Beam. Would you see any
disadvantages of this approach? Would you suggest to make this default
behavior for local beam FlinkRunner? I can introduce a configuration
option to turn this behavior on, but that would bring additional
maintenance burden, etc., etc.
Jan
On 9/3/19 3:38 PM, Till Rohrmann wrote:
I see the problem Jan. What about the following proposal: Instead of
using
the LocalEnvironment for local tests you always use the
RemoteEnvironment
but when testing it locally you spin up a MiniCluster in the same
process
and initialize the RemoteEnvironment with `MiniCluster#getRestAddress`.
That way you would always submit a jar with the generated classes and,
hence, not having to set the context class loader.
The contract of the LocalEnvironment is indeed that all classes it is
supposed t execute must be present when being started.
Cheers,
Till
On Tue, Sep 3, 2019 at 2:27 PM guaishushu1...@163.com <
guaishushu1...@163.com> wrote:
guaishushu1...@163.com
From: guaishushu1...@163.com
Date: 2019-09-03 20:25
To: dev
Subject: Re: Re: ClassLoader created by BlobLibraryCacheManager is not
using context classloader
guaishushu1...@163.com
From: guaishushu1...@163.com
Date: 2019-09-03 20:23
To: dev
Subject: Re: Re: ClassLoader created by BlobLibraryCacheManager is not
using context classloader
guaishushu1...@163.com
From: Jan Lukavský
Date: 2019-09-03 20:17
To: dev
Subject: Re: ClassLoader created by BlobLibraryCacheManager is not
using
context classloader
Hi Till,
the use-case is pretty much simple - I have a REPL shell in groovy,
which generates classes at runtime. The actual hierarchy is therefore
system class loader -> application classloader -> repl classloader
(GroovyClassLoader actually)
now, when a terminal (sink) operation in the shell occurs, I'm able to
build a jar, which I can submit to remote cluster (in distributed
case).
But - during testing - I run the code using local flink. There is no
(legal) way of adding this new runtime generated jar to local flink. As
I said, I have a hackish solution which works on JDK <= 8, because it
uses reflection to call addURL on the application classloader (and
thefore "pretends", that the generated jar was there all the time from
the JVM startup). This breaks on JDK >= 9. It might be possible to work
around this somehow, but I think that the reason why
LocalEnvironment is
not having a way to add jars (as in case of RemoteEnvironment) is that
is assumes, that you actually have all of the on classpath when using
local runner. I think that this implies that it either has to use
context classloader (to be able to work on top of any classloading user
might have), or is wrong and would need be fixed, so that
LocalEnvironment would accept files to "stage" - which would mean
adding
them to a class loader (probably URLClassLoader with the application
class loader as parent).
Or, would you see any other option?
Jan
On 9/3/19 2:00 PM, Till Rohrmann wrote:
Hi Jan,
I've talked with Aljoscha and Stephan offline and we concluded that we
would like to avoid the usage of context class loaders if possible.
The
reason for this is that using the context class loader can easily
mess up
an otherwise clear class loader hierarchy which makes it hard to
reason
about and to debug class loader issues.
Given this, I think it would help to better understand the exact
problem
you are trying to solve by using the context class loader. Usually the
usage of the context class loader points towards an API deficiency
which
we
might be able to address differently.
Cheers,
Till
On Mon, Sep 2, 2019 at 11:32 AM Aljoscha Krettek <aljos...@apache.org
wrote:
I’m not saying we can’t change that code to use the context class
loader.
I’m just not sure whether this might break other things.
Best,
Aljoscha
On 2. Sep 2019, at 11:24, Jan Lukavský <je...@seznam.cz> wrote:
Essentially, the class loader of Flink should be present in parent
hierarchy of context class loader. If FlinkUserCodeClassLoader
doesn't
use
context class loader, then it is actually impossible to use a
hierarchy
like this:
system class loader -> application class loader ->
user-defined class
loader (defines some UDFs to be used in flink program)
Flink now uses the application class loader, and so the UDFs fail to
deserialize on local flink, because the user-defined class loader is
bypassed. Moreover, there is no way to add additional classpath
elements
for LocalEnvironment (as opposed to RemoteEnvironment). I'm able
to hack
this by calling addURL method on the application class loader
(which is
terribly hackish), but that works only on JDK <= 8. No sensible
workaround
is available for JDK >= 9.
Alternative solution would be to enable adding jars to class loader
when
using LocalEnvironment, but that looks a little odd.
Jan
On 9/2/19 11:02 AM, Aljoscha Krettek wrote:
Hi,
I actually don’t know whether that change would be ok.
FlinkUserCodeClassLoader has taken
FlinkUserCodeClassLoader.class.getClassLoader() as the parent
ClassLoader
before my change. See:
https://github.com/apache/flink/blob/release-1.2/flink-runtime/src/main/java/org/apache/flink/runtime/execution/librarycache/FlinkUserCodeClassLoader.java
<
https://github.com/apache/flink/blob/release-1.2/flink-runtime/src/main/java/org/apache/flink/runtime/execution/librarycache/FlinkUserCodeClassLoader.java
.
I have the feeling that this might be on purpose because we want to
have the ClassLoader of the Flink Framework components be the parent
ClassLoader, but I could be wrong. Maybe Stephan would be most
appropriate
for answering this.
Best,
Aljoscha
On 30. Aug 2019, at 16:28, Till Rohrmann <trohrm...@apache.org>
wrote:
Hi Jan,
this looks to me like a bug for which you could create a JIRA
and PR
to fix it. Just to make sure, I've pulled in Aljoscha who is the
author
of
this change to check with him whether we are forgetting something.
Cheers,
Till
On Fri, Aug 30, 2019 at 3:44 PM Jan Lukavský <je...@seznam.cz
<mailto:
je...@seznam.cz>> wrote:
Hi,
I have come across an issue with classloading in Flink's
MiniCluster.
The issue is that when I run local flink job from a thread,
that has
a
non-default context classloader (for whatever reason), this
classloader
is not taken into account when classloading user defined
functions.
This
is due to [1]. Is this behavior intentional, or can I file a
JIRA and
use Thread.currentThread.getContextClassLoader() there? I have
validated
that it fixes issues I'm facing.
Jan
[1]
https://github.com/apache/flink/blob/ce557839d762b5f1ec92aa1885fd3d2ae33d0d0b/flink-runtime/src/main/java/org/apache/flink/runtime/execution/librarycache/BlobLibraryCacheManager.java#L280
<
https://github.com/apache/flink/blob/ce557839d762b5f1ec92aa1885fd3d2ae33d0d0b/flink-runtime/src/main/java/org/apache/flink/runtime/execution/librarycache/BlobLibraryCacheManager.java#L280
