Please implement client switch in 64-bit server JDK 14 builds
youngty1997 at gmail.com
Fri Jul 19 02:46:06 UTC 2019
I'm requesting that the long unimplemented "client" java switch be
implemented in Java 14.
(Note: this entire request is based on the assumption that a JVM with
-client is equivalent to a client JVM variant. If this is wrong, I
apologies. There isn't much documentation to go on.)
Since there aren't many google results or any kind of mention of this
feature/ability even existing, i'll give an explanation to the best of
my knowledge and personal observations:
A "client" JVM variant is geared towards graphical end-user
applications. According to a URL link found in the man entry for java
this supposedly results in faster startups. While this *may* be true, a
much larger and more important benefit is a massive committed memory
reduction in the range of about 25% to 50% when running a JavaFX
application. At minimum with similar heap sizes, that is a 75 MB memory
savings at 300MB (a somewhat typical peak usage with JavaFX
applications) with a typical server JVM. That's huge.
The downside to this however is that at most, the maximum amount of
(committed?) memory that a client JVM variant can use is somewhere
around 300MB by default. For the intended purpose of the client JVM
switch/variant this is *probably* fine. Server JVM variants only seems
to allocate more memory to boost performance, which really isn’t that
much of a difference with the intended use case of the client JVM
switch/variant… especially considering the more appealing memory savings.
So why should this be implemented?
The answer is simple: using more memory then is necessary is bad, angers
users, and frustrates developers who want to be responsible by not
wanting to eat up their users's memory when it isn't needed.
Even if you've have never heard anyone complain about Java's memory
usage, you've most likely heard someone complain about a similar
cross-platform software: Electron. People hate Electron applications for
their absurd memory usage and will actively avoid them by using
alternatives if possible.
For reference, Etcher, an Electron application that allows users to
easily create bootable USB drives on Windows, Linux, and probably Mac OS
uses around 298 MB just at launch on Linux. Electron is both comparable
in both goals(cross-platform solutions, JavaFX vs. Electron) and in
Java may not be a native language and there may be *some* unavoidable
penalty for that but being wasteful and consuming resources where not
necessary is, well, unnecessary. This can help reduce the amount of
memory a java application uses significantly when used.
With that all said, since JEPs include risks/impact/problems, it's best
to mention some that come to mind:
Because of the default lower memory limit, applications which go beyond
this will fail. The easiest and best workaround would be to simply make
the client JVM switch/variant opt-in. This would allow all existing Java
applications to continue to work as expected.
The only other issue that I can think of is people launching
applications with -client without knowing the limitations of it and
filing bogus bug reports to app developers. This can be mitigated with
better documentation and awareness in places like the man page for Java.
Since no one seems to really have used or knew about it before it's more
likely end developers that will be passing the switch to their
applications via scripts then end users will be.
All in all, this is pretty safe as long as server JVM switch/variant
remains the default. Maybe others can think of other risks/impacts/problems.
And finally addressing the two questions/comments I imagine someone at
some point are going to ask/say:
Why not just compile a client JVM variant from source and use jLink?
If heap and garbage collection is healthy, who cares?
For the first one, yes, this is a route that could be taken. It has some
problems however, namely:
- You have to be the developer or have source code access to use jLink.
- jLink -from my understanding- requires a **fully** modular Java
application. Some used libraries may not be modular yet.
- A full JDK source code compile is required - something that is really
easy to do under Linux but might not be under Windows and takes
considerable CPU power to do. No one that I’m aware of (on Linux anyway)
provides client JVM variant builds. Presumably This is because the
server JVM variant is the most versatile.
and as for the second: just because there is say, 5.8GB out of 8GB
available doesn't mean you should or have the right to use it as you see
fit. People do more than use Java applications. If you are running a web
browser with lots of tabs open, a Java application could realistically
cause major system stuttering as memory is moved to swap/pagefile. While
I used 300MB above as an easy realistic example, i've seen JavaFX
applications consume as much as 700MB and even 1GB committed memory.
Just opening Scene Builder and playing around with the GUI consumes
400MB easily on a server JVM variant(Oracle JDK/JRE 10 to be exact).
While memory usage may never be as good as native, the current amount of
memory being consumed is insane and any normal user with standard amount
of memory(6-8GB) *will* feel this. Adding this switch could potentially
help a lot here and give Java a slight edge over similar software solutions.
Can this feature please be implemented? Likewise, could the
documentation on what a "client" JVM and other JVM variants be updated
More information about the jdk-dev