On Thursday, October 27, 2016, Brunoais <brunoa...@gmail.com
<mailto:brunoa...@gmail.com>> wrote:
Did you read the C code?
I looked at the Linux code in the JDK.
Have you got any idea how many functions Windows or Linux (nearly
all flavors) have for the read operation towards a file?
I do.
I have already done that homework myself. I may not have read
JVM's source code but I know well that there's functions on both
Windows and Linux that provide such interface I mentioned although
they require a slightly different treatment (and different constants).
You should read the JDK (native) source code instead of
guessing/assuming. On Linux, it doesn't use aio facilities for
files. The kernel io scheduler may issue readahead behind the scenes,
but there's no nonblocking file io that's at the heart of your premise.
On 27/10/2016 00:06, Vitaly Davidovich wrote:
On Wednesday, October 26, 2016, Brunoais <brunoa...@gmail.com
<mailto:brunoa...@gmail.com>> wrote:
It is actually based on the premise that:
1. The first call to ReadableByteChannel.read(ByteBuffer)
sets the OS
buffer size to fill in as the same size as ByteBuffer.
Why do you say that? AFAICT, it issues a read syscall and that
will block if the data isn't in page cache.
2. The consecutive calls to
ReadableByteChannel.read(ByteBuffer)
orders
the JVM to order the OS to execute memcpy() to copy
from its memory
to the shared memory created at ByteBuffer
instantiation (in
java 8)
using Unsafe and then for the JVM to update the
ByteBuffer fields.
I think subsequent reads just invoke the same read syscall,
passing the current file offset maintained by the file channel
instance.
3. The call will not block waiting for I/O and it won't
take longer
than the JNI interface if no new data exists. However,
it will
block
waiting for the OS to execute memcpy() to the shared
memory.
So why do you think it won't block?
Is my premise wrong?
If I read correctly, if I don't use a DirectBuffer, there
would be
even another intermediate buffer to copy data to before
giving it
to the "user" which would be useless.
If you use a HeapByteBuffer, then there's an extra copy from
the native buffer to the Java buffer.
On 26/10/2016 11:57, Pavel Rappo wrote:
I believe I see where you coming from. Please correct
me if
I'm wrong.
Your implementation is based on the premise that a call to
ReadableByteChannel.read()
_initiates_ the operation and returns immediately. The
OS then
continues to fill
the buffer while there's a free space in the buffer
and the
channel hasn't encountered EOF.
Is that right?
On 25 Oct 2016, at 22:16, Brunoais
<brunoa...@gmail.com>
wrote:
Thank you for your time. I'll try to explain it. I
hope I
can clear it up.
First of it, I made a meaning mistake between
asynchronous
and non-blocking. This implementation uses a
non-blocking
algorithm internally while providing a blocking-like
algorithm on the surface. It is single-threaded
and not
multi-threaded where one thread fetches data and
blocks
waiting and the other accumulates it and provides to
whichever wants it.
Second of it, I had made a mistake of going after
BufferedReader instead of going after
BufferedInputStream.
If you want me to go after BufferedReader it's ok
but I
only thought that going after BufferedInputStream
would be
more generically useful than BufferedReaderwhen I
started
the poc.
On to my code:
Short answers:
• The sleep(int) exists because I don't
know how
to wait until more data exists in the buffer which
is part
of read()'s contract.
• The ByteBuffer gives a buffer that is
filled by
the OS (what I believe Channels do) instead of getting
data only by demand (what I believe
Streams do).
Full answers:
The blockingFill(boolean) method is a method for a
busy
wait for a fill which is used exclusively by the
read()
method. All other methods use the version that
does not
sleep (fill(boolean)).
blockingFill(boolean)'s existance like that is only
because the read() method must not return unless
either:
• The stream ended.
• The next byte is ready for reading.
Additionally, statistically, that while loop will
rarely
evaluate to true as reads are in chunks so readPos
will be
behind writePos most of the time.
I have no idea if an interrupt will ever happen, to be
honest. The main reasons why I'm using a sleep is
because
I didn't want a hog onto the CPU in a full thread
usage
busy wait and because I didn't find any way of doing a
thread sleep in order to wake up later when the buffer
managed by native code has more data.
The Non-blocking part is managed by the buffer the OS
keeps filling most if not all the time. That
buffer is the
field
ByteBuffer readBuffer
That's the gaining part against the plain old Buffered
classes.
Did that make sense to you? Feel free to ask
anything else
you need.
On 25/10/2016 20:52, Pavel Rappo wrote:
I've skimmed through the code and I'm not sure
I can
see any asynchronicity
(you were pointing at the lack of it in
BufferedReader).
And the mechanics of this is very puzzling to
me, to
be honest:
void blockingFill(boolean forced) throws
IOException {
fill(forced);
while (readPos == writePos) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// An interrupt may mean more
data is
available
}
fill(forced);
}
}
I thought you were suggesting that we should
utilize
the tools which OS provides
more efficiently. Instead we have something
that looks
very similarly to a
"busy loop" and... also who and when is
supposed to
interrupt Thread.sleep()?
Sorry, I'm not following. Could you please
explain how
this is supposed to work?
On 24 Oct 2016, at 15:59, Brunoais
<brunoa...@gmail.com>
wrote:
Attached and sending!
On 24/10/2016 13:48, Pavel Rappo wrote:
Could you please send a new email on
this list
with the source attached as a
text file?
On 23 Oct 2016, at 19:14, Brunoais
<brunoa...@gmail.com>
wrote:
Here's my poc/prototype:
http://pastebin.com/WRpYWDJF
I've implemented the bare minimum
of the
class that follows the same
contract of
BufferedReader while signaling all
issues
I think it may have or has in
comments.
I also wrote some javadoc to help
guiding
through the class.
I could have used more fields from
BufferedReader but the names were so
minimalistic that were confusing me. I
intent to change them before
sending this
to openJDK.
One of the major problems this has
is long
overflowing. It is major because it is
hidden, it will be extremely rare
and it
takes a really long time to reproduce.
There are different ways of
dealing with
it. From just documenting to actually
making code that works with it.
I built a simple test code for it
to have
some ideas about performance and
correctness.
http://pastebin.com/eh6LFgwT
This doesn't do a through test if
it is
actually working correctly but I
see no
reason for it not working
correctly after
fixing the 2 bugs that test found.
I'll also leave here some conclusions
about speed and resource
consumption I found.
I made tests with default buffer
sizes,
5000B 15_000B and 500_000B. I noticed
that, with my hardware, with the 1
530 000
000B file, I was getting around:
In all buffers and fake work:
10~15s speed
improvement ( from 90% HDD speed
to 100%
HDD speed)
In all buffers and no fake work: 1~2s
speed improvement ( from 90% HDD
speed to
100% HDD speed)
Changing the buffer size was giving
different reading speeds but both were
quite equal in how much they would
change
when changing the buffer size.
Finally, I could always confirm
that I/O
was always the slowest thing while
this
code was running.
For the ones wondering about the file
size; it is both to avoid OS cache
and to
make the reading at the main use-case
these objects are for (large
streams of
bytes).
@Pavel, are you open for
discussion now
;)? Need anything else?
On 21/10/2016 19:21, Pavel Rappo
wrote:
Just to append to my previous
email.
BufferedReader wraps any
Reader out there.
Not specifically FileReader. While
you're talking about the case
of effective
reading from a file.
I guess there's one existing
possibility to provide exactly
what
you need (as I
understand it) under this method:
/**
* Opens a file for reading,
returning a {@code
BufferedReader} to
read text
* from the file in an efficient
manner...
...
*/
java.nio.file.Files#newBufferedReader(java.nio.file.Path)
It can return _anything_ as
long as it
is a BufferedReader. We can do
it, but it
needs to be investigated not
only for
your favorite OS but for other
OSes as
well. Feel free to prototype
this and
we can discuss it on the list
later.
Thanks,
-Pavel
On 21 Oct 2016, at 18:56,
Brunoais
<brunoa...@gmail.com>
wrote:
Pavel is right.
In reality, I was
expecting such
BufferedReader to use only a
single buffer and have
that Buffer
being filled
asynchronously, not
in a different Thread.
Additionally, I don't have the
intention of having a larger
buffer than before unless
stated
through the API (the
constructor).
In my idea, internally, it is
supposed to use
java.nio.channels.AsynchronousFileChannel
or equivalent.
It does not prevent having two
buffers and I do not intent to
change BufferedReader
itself. I'd
do an BufferedAsyncReader
of sorts
(any name suggestion is
welcome as
I'm an awful namer).
On 21/10/2016 18:38, Roger
Riggs
wrote:
Hi Pavel,
I think Brunoais
asking for a
double buffering scheme in
which the
implementation of
BufferReader fills (a
second
buffer) in parallel
with the
application reading
from the
1st buffer
and managing the swaps and
async reads transparently.
It would not change
the API
but would change the
interactions between the
buffered reader
and the underlying
stream. It
would also increase memory
requirements and
processing
by introducing or using a
separate thread and the
necessary synchronization.
Though I think the formal
interface semantics
could be
maintained, I have doubts
about compatibility
and its
unintended consequences on
existing subclasses,
applications and
libraries.
$.02, Roger
On 10/21/16 1:22 PM, Pavel
Rappo wrote:
Off the top of my
head, I
would say it's not
possible to change the
design of an
_extensible_ type
that has
been out there for
20 or
so years. All
these I/O
streams from
java.io <http://java.io>
<http://java.io> were
designed for simple
synchronous use case.
It's not that
their design
is flawed in some way,
it's that they
doesn't seem to
suit your needs.
Have you
considered using
java.nio.channels.AsynchronousFileChannel
in your applications?
-Pavel
On 21 Oct 2016, at
17:08, Brunoais
<brunoa...@gmail.com>
wrote:
Any feedback
on this?
I'm really
interested
in
implementing such
BufferedReader/BufferedStreamReader
to allow
speeding up
my applications
without having to
think in an
asynchronous
way or
multi-threading while
programming
with it.
That's why I'm
asking
this here.
On 13/10/2016
14:45,
Brunoais wrote:
Hi,
I looked at
BufferedReader
source
code for
java 9
long with
the source
code of
the
channels/streams
used. I
noticed
that, like
in java
7,
BufferedReader
does not
use an
Async API
to load
data from
files,
instead,
the data
loading is all
done
synchronously
even when
the OS
allows
requesting
a file to
be read
and getting a
warning
later when
the file is
effectively read.
Why Is
BufferedReader not
async while
providing
a sync API?
<BufferedNonBlockStream.java><Tests.java>
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