On Thursday, October 27, 2016, Brunoais
<brunoa...@gmail.com
<javascript:_e(%7B%7D,'cvml','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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