teven Stewart-Gallus wrote:
>
> Okay I have an idea.
> I can't shake the idea you could do fun tricks with thread local
> executable pages.
>
> The theoretically fastest way of safepoint polling is inserting a trap
> instruction. But icache overheads dominate. If the icache is
Okay I have an idea.
I can't shake the idea you could do fun tricks with thread local executable
pages.
The theoretically fastest way of safepoint polling is inserting a trap
instruction. But icache overheads dominate. If the icache is based on physical
addresses and not virtual ones then it sh
; On Thu, May 7, 2020 at 14:47, Steven Stewart-Gallus <
> stevensele...@gmail.com > wrote:
>
>> Hi,
>>
>> Just going to update this thread with a link to the repo I am asking this
>> question for which I finally see fit to share
>> https://github.com/sstewar
t;. Are there public benchmarks on real world
software? Has anything changed on recent hardware? It seems the obviously
fastest way to cause a fault but what if it is not?
Thanks
Steven Stewart-Gallus
On Mon., May 18, 2020, 9:04 a.m. Gil Tene, wrote:
> This is an evolving and ever-explored field...
&g
Hi
As I understand it most VMs poll for safepoints by using memory management
tricks to page fault polling threads. A page is set aside to read from and
whenever a safepoint is desired the page is set to be unreadable.
But can't a number of other hardware traps be used instead
https://wiki.osde
some of you might be interested in this kind of bytecode spinning
stuff.
On Sunday, April 26, 2020 at 9:36:07 AM UTC-7, Steven Stewart-Gallus wrote:
>
> I'm spinning a lot of classes dynamically for an interpreter.
> I'm not sure the best way to load the classes into the VM.
>
>
pathy" >
> *Envoyé: *Dimanche 26 Avril 2020 19:11:53
> *Objet: *Re: Best way to dynamically spin Java classes?
>
> In Java 15 we will have hidden classes, which seem like the right model
> for what you are trying to do.
>
> On Sun, 26 Apr 2020 at 19:36, Steven Stewa
resolve(MethodHandles.Lookup lookup) throws
ReflectiveOperationException {
if (null == result) {
result = desc.resolveConstantDesc(lookup);
}
return result;
}
}
On Thursday, April 30, 2020 at 6:57:19 PM UTC-7, Steven Stewart-Gallus
wrote:
>
> Hello,
&g
ivate finals in
lambda objects to do this but I'm not quite certain that would work.
Thanks
Steven Stewart-Gallus
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I'm spinning a lot of classes dynamically for an interpreter.
I'm not sure the best way to load the classes into the VM.
Aside from Unsafe's defineAnonymousClass what's the best way to load classes
into the VM?
I believe I could create a new classloader for each spun class but IIRC
classloaders
Couldn't you do a compare and compare and swap? With VarHandles something
like
if (ACTION.getOpaque(this) != expected) return false;
return compareAndExchange(this, expected, newValue) == expected;
Not sure I got this correct
On Saturday, September 14, 2019 at 11:29:00 AM UTC-7, Vitaly Davidovi
Figured out something bizarre about combining lambdas just the other day.
Code like
static EqualsSupport makeEquals(Set> getters) {
EqualsSupport equals = (a, b) -> true;
for (var getter : getters) {
if (getter instanceof ObjectGetter) {
var g = (ObjectGetter) getter;
Hi,
For a long while, I couldn't think of what to reply with.
I just don't feel the problem of grouping fields together deserves to
distort the API that much.
I guess part of the problem is Java doesn't support a syntax for field
references (even though VarHandleDesc are already implemented.)
It
'd
inevitably end up needing more support methods such as a toString method.
On Friday, April 26, 2019 at 8:13:17 AM UTC-7, Remi Forax wrote:
>
>
>
> --------------
>
> *De: *"Steven Stewart-Gallus" >
> *À: *"mechanical-sympathy"
1. Why
public abstract class ObjectSupport {
public abstract boolean equals(Object self, Object other);
public abstract int hashCode();
public static ObjectSupport of(Lookup lookup, String... fields) {
// impl details
}
// impl details
}
and not something like?
interf
I feel like this is just a bug in the JDK that should be patched.
Couldn't this all be solved by replacing UNSAFE.copyMemory with a call to a
different method that isn't a HotSpot intrinsic?
https://hg.openjdk.java.net/jdk/jdk/file/235883996bc7/src/java.base/share/classes/java/nio/Direct-X-Buffe
Ahah!
I believe I might have a possible hacky workaround!
Instead of doing:
static void mul(int[] accum, int accumOffset, int[] src, int srcOffset, int
n) {
for (int ii = 0; ii < n; ++ii) {
accum[ii + accumOffset] *= src[ii + srcOffset];
}
}
do
static void mul(int[] accum, int
I found a much more complete reference (also by Vladimir Ivanov it seems)
but it may be out of date (it's from 2017.)
http://cr.openjdk.java.net/~vlivanov/talks/2017_Vectorization_in_HotSpot_JVM.pdf
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I see, so the same doesn't apply to read only workflow though right?
private static int dot(int[] heap, int n, int a, int b) {
var sum = 0;
for (var ii = 0; ii < n; ++ii) {
sum += heap[a + ii] * heap[b + ii];
}
return sum;
}
And one last question.
Can VarHandle byte arra
You can use a MutableCallSite with MethodHandles.constant if you really
need to to create "mostly final" variables. In addition null checks are
heavily optimised by the JVM to use segmentation faults and so can be
slightly faster than boolean checks sometimes. As well, JVM inlining handle
this
I'm really confused.
You're talking about putting the data into sqlite which suggests there
really isn't so much log data and it could be filtered with a hacky shell
script. But then you're talking about a lot of heavy optimisation which
suggests you really may need to put in custom effort. Pre
It is well known that compilers can't optimise things as well if values may
alias. Because src and dest may overlap:
public static void multiply(int[] accum, int accumOffset, int[] src, int
srcOffset, int n){
for (var ii = 0; ii < n; ++ii) {
dest[ii] *= src[ii];
}
}
does not hav
Seriously no. Just use a VarHandle fence
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On Friday, January 18, 2019 at 5:37:58 AM UTC-8, Rémi Forax wrote
>
> no, CHA only works on class, not on interface.
>
> You're probably know better than me. I seem to remember there's something
like that for interfaces but very limited such as if you ever only have
ever one implementation. I s
I think what you want is something like the mincore system call on Linux so
your thread can write directly if the page is mapped but offload the work
to another thread if it is not mapped. I don't have any experience with the
system call though.
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Is there any reason you can't just manually pack the bytes together?
public int getInt(byte[]buf, int ix){
return buf[ix] | buf[ix + 1] << 8 | buf[ix + 2] << 16 | buf[ix + 3] <<
24;
}
It should be kind of slow but probably less so than a bunch of allocations
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I've been working on similar issues trying to optimise something
heavily. I made a similar class to this one (I even had a similar
API) but I found I called it MostlyFinal instead.
private static final MostlyConstant FOO = new MostlyConstant<>(42,
int.class);
private static final IntSupplier F
There are more than a few ways to Denial of Service other threads and or
cores on most personal computers today.
Of which the most common way encountered is to probably use up too much
memory causing the system to swap to the hard drive.
This is partly a feature not a bug. You wouldn't like a s
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