Why does DataOutputStream write Boolean as 1 Byte?

Im trying to conserve space in a file storing booleans.
why does dataoutputstream write booleans as a byte?
is there a way to write a bit only?
thanks!

Hi,
A boolean does even allocate at least 8 bits when it is declared in the code.
From the VM spec:
"3.2.4 There Is No boolean Type
Although Java defines a boolean type, the Java Virtual Machine does not
have instructions dedicated to operations on boolean values. Instead, a
Java expression that operates on boolean values is compiled to use the int
data type to represent boolean variables.
Although the Java Virtual Machine has support for the creation of arrays of
type boolean (see the description of the newarray instruction), it does not
have dedicated support for accessing and modifying elements of boolean
arrays. Arrays of type boolean are accessed and modified using the byte
array instructions.1
For more information on the treatment of boolean values in the Java Virtual
Machine, see Chapter 7, "Compiling for the Java Virtual Machine.""http://java.sun.com/docs/books/vmspec/html/Overview.doc.html#22909
/Kaj

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Why does VISA write vi get a clock symbol added?

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What is this clock symbol doing there, when it wasn't on the functions panel version of the VISA write vi?
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Thx.

The little clock symbol means to do I/O asynchronously. If you right click on the function, you'll see the option to do it synchronously. Select that and the clock will disappear.
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Hi Steve,
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Justin D
Applications Engineer
National Instruments
http://www.ni.com/support/

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Why does the Java API use int instead of short or byte?

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Using Disk Utility, try an re-partition the drive into two partitions, making the second partition very small (a megabyte or two), then see if you can format the first partition normally. Leave the second partition alone.
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RE: (HLS) Why does Verilog pointer requires two clocks to get updated??

In HLS (2015.2), I created a simple comparator circuit. The HLS C-simulation worked fine. The HLS C-function compares
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bus matches the sequence of bytes in the stored array, a match is detected.
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chip Verilog code, and attempted a Modelsim simulation. It did not work!!
The HLS generated Verilog file has the ports below:
ap_clk
ap_rst
ap_start
ch(7:0) <--- This is the incoming 8-bit data bus.
ch_valid   <----   This is an input that indicates the ch(7:0) data bus has valid data.
ap_return <--- This is the match signal.
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due to the ModelSim simulation. In the C-code below, the fixed array is "pattern0", while the pointer is "check0."
int compare (uint8_t ch, int ch_valid, int sop)
uint8_t pattern0[24] = {0xaa, 0xbb, 0xcc, 0xdd, 0x12, 0x34, 0x56, 0x78, 0x11, 0x11, 0x22, 0x22, \
                                0x33, 0x33, 0x44, 0x44, 0x22, 0x22, 0x33, 0x33, 0x44, 0x44, 0x55, 0x55};
static int prematch0 = 0, check0 = 0, match0 = 0;
int j;
if (ch_valid == 1) {
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            prematch0 = 1;
            check0 = check0+1;
         else {
             prematch0 = 0;
             check0 = 0;
     else if ((check0 == sizeof(pattern0)) && (prematch0 == 1)) {
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          match0 = 1;
          prematch0 = 1;
     else {
          check0 = check0;
          match0 = match0;
          prematch0 = prematch0;
else {
       check0 = check0;
       match0 = match0;
       prematch0 = prematch0;
return (match0);
If I write this code manually in Verilog, the check0 pointer is updated in one clock cycle.
Questions:
Why does HLS need two clock cycles to update the check0 pointer?
Do I need to set an HLS directive to cause the verilog code to be generated in a different way?
Does the C-code need to be written differently?
Thanks,
Roy

Hi Debraj,
Thanks for the response. I have another question.
I quicly took the C-code above and added a Verilog clock statement. The code below would execute in one clock.
Is there any way I can re-write the C-code to reduce the 2cc down to 1cc, or is this not possible?
always @(posedge ap_clk) {
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       if(check0 < sizeof(pattern0)){
            if(ch == pattern0[check0]) {
                prematch0 = 1;
                check0 = check0+1;
            else {
                prematch0 = 0;
                check0 = 0;
       else if ((check0 == sizeof(pattern0)) && (prematch0 == 1)) {
            check0 = check0;
            match0 = 1;
            prematch0 = 1;
       else {
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            match0 = match0;
            prematch0 = prematch0;
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       check0 = check0;
       match0 = match0;
       prematch0 = prematch0;
Thanks,
Roy

Why does performance decrease as cache size increases?

Hi,
We have some very serious performance problems with our
database. I have been trying to help by tuning the cache size,
but the results are the opposite of what I expect.
To create new databases with my data set, it takes about
8200 seconds with a 32 Meg cache. Performance gets worse
as the cache size increases, even though the cache hit rate
improves!
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32 Meg does not seem like such a large cache that it would
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Here are some stats from db_stat -m
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160MB 1KB 900B Total cache size
1 Number of caches
1 Maximum number of caches
160MB 8KB Pool individual cache size
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0 Current dirty page count
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11 The longest hash chain searched for a page
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1 Number of caches
1 Maximum number of caches
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36104 Pages created in the cache
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20024 Current clean page count
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1 Number of caches
1 Maximum number of caches
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10M Pages read into the cache (10808327)
9200273 Pages written from the cache to the backing file
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0 Dirty pages written by trickle-sync thread
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0 Current dirty page count
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vmstat says that a few minutes into the test, the box is
spending 80-90% of its time in iowait. That worsens as
the test continues.
System and test info follows
We have 10 databases (in 10 files) sharing a database
environment. We are using a hash table since we expect
data accesses to be pretty much random.
We are using the default cache type: a memory mapped file.
Using DB_PRIVATE did not improve performance.
The database environment created with these flags:
DB_CREATE | DB_THREAD | DB_INIT_CDB | DB_INIT_MPOOL
The databases are opened with only the DB_CREATE flag.
There is only one process accessing the db. In my tests,
only one thread access the db, doing only writes.
We do not use transactions.
My data set is about 550 Meg of plain ASCII text data.
13 million inserts and 2 million deletes. Key size is
32 bytes, data size is 4 bytes.
BDB 4.6.21 on linux.
1 Gig of RAM
Filesystem = ext3 page size = 4K
The test system is not doing anything else while I am
testing.

Surprising result: I tried closing the db handles with DB_NOSYNC and performance
got worse. Using a 32 Meg cache, it took about twice as long to run my test:
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40MB 1KB 900B Total cache size
1 Number of caches
1 Maximum number of caches
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10M Requested pages not found in the cache (10811882)
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118M Total number of hash chain entries checked for page (118169805)
It looks like not flushing the cache regularly is forcing a lot more
dirty pages (and fewer clean pages) from the cache. Forcing a
dirty page out is slower than forcing a clean page out, of course.
Is this result reasonable?
I suppose I could try to sync less often than I have been, but more often
than never to see if that makes any difference.
When I close or sync one db handle, I assume it flushes only that portion
of the dbenv's cache, not the entire cache, right? Is there an API I can
call that would sync the entire dbenv cache (besides closing the dbenv)?
Are there any other suggestions?
Thanks,
Eric

Why does this make *nix crash ?

why does
:(){ :|:& };:
make my system crash ?
* Don`t try it if you don`t want to crash your box

:(){:|:&};:
can also be viewed as
function(){
function|function&
Does this look more familiar? It's basically a standard bash function. The code you posted, called a forkbomb, creates a bash function called ":" which calls itself recursively twice through a pipe and sends the recursion call to the background. Basically, this causes the process to fork (or split) itself forever. This creates a huge number of processes which overrun your CPU, causing your precious computer to freeze/crash/whatever.
Sending the second function call to the background causes the calling function to not wait until the call returns. Since there is no stop condition for this recursion, the function would wait forever allowing you to kill it and all its children with ^C. Since the recursion call is running in the background, the calling function will complete immediately making it damn near impossible to kill its child processes.
So why call it twice? Because of the recursive call in the background, the calling process dies as soon as it makes the recursive call. Hence, if we only call it once it will always have one process replacing its parent, defeating the purpose of a forkbomb.
What's the point? It's a denial of service attack, plain and simple.
Various other type of forkbombs...
Windows
%0|%0
-or-
:s
start %0
%0|%0
goto :s
Perl
fork while fork
Haskell
import Control.Monad
import System.Posix.Process
forkBomb = forever $ forkProcess forkBomb
Python
import os
while True:
os.fork()
Ruby
loop { fork }
C/C++
#include <unistd.h>
int main(void)
while(1)
fork();
return 0;
NASM
section .text
global _start ;Call start
_start:
push byte 2 ;syscall to Linux fork
pop eax ;set EAX argument for fork to NULL [So it works in strings]
int 0x80 ;Execute syscall with fork & the EAX [null, above] argument
jmp short _start ;Go back to beginning, causing a fork bomb
Lisp
(defmacro wabbit () ;; A program that writes code.
(let ((fname (gentemp 'INET)))
`(progn
(defun ,fname () ;; Generate.
nil)
(wabbit))))
(wabbit) ;; Start multiplying.
* Disclaimer: It's not my fault if you fuck up your system trying these out.
** Edit: Wow... in the time it took me to write that up a crapload of people answered the question... oh well.
Last edited by Ghost1227 (2009-06-21 14:02:55)

Why does my card reader not work on my iPad since upgrade?

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No but I was just trying to find a way in to your help desk. I didn't find
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Douglas Whiteley
In a message dated 10/05/2012 20:43:50 GMT Daylight Time, [email protected]
writes:
Re: why does my adobe reader not work
created by Claudio González
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Why does iTunes fail to see that I am a customer

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Why have I ended up with two iTunes account instead of just one?
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The Apple Support Communities are an international user to user technical support forum. As a man from Mexico my first language is Spanish. I do not speak English, however I do write in English with the aid of the Mac OS X spelling and grammar checks. I also live in a culture perhaps very very different from your own. When offering advice in the ASC, my comments are not meant to be anything more than helpful and certainly not to be taken as insults.
Have you ever actually bought anything from the Mac App Store? Have you created an iTunes account in the past? Do you have a bank card from a bank in the country where you live with a local billing address?

Why does opening and closing FPGA references increase Windows XP handles by 3?

Hello.
We run a test system here that uses TestStand to communicate
to a number of Labview VI modules which in turn communicates to a
PXI-7833R FPGA. Everything has been working fine except after a long time running Labview would get an out of memory error. I discovered
after a particular VI was run 100,000 times, the number of handles in Windows XP Task
Manager grew to about 370,000. The number of threads and processes remains stable and normal. Closing Labview removes all the excessive handles.
I tried an experiment to create a standalone VI (ie: no TestStand) which simply opens the FPGA VI reference then closes the reference. This is repeated 4 times in the same VI. The number of handles in Windows XP Task
Manager increased by 12 each time the VI was run. No errors. This indicates closing the FPGA reference might not be working.
Why does this happen? Is there a way to avoid it? The version of Labview is 8.5.1.
Appreciate any help here. Thanks.
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could be related to this known issue--
FPGA FIFO reset behavior—When you use an FPGA target
emulator, FPGA FIFOs reset when the VI is stopped and then started
again. When you use an FPGA target with Interactive Front Panel
Communication, FPGA FIFOs do not reset when the FPGA VI is stopped and
then started again. To reset the FIFO, right-click the FPGA target in
the Project Explorer window and select Download
from the shortcut menu. When you control an FPGA VI using Programmatic
FPGA Interface Communication, use the Close FPGA VI Reference function
with the Close and Reset shortcut menu option selected or the Invoke Method with the Reset method selected to reset FPGA FIFOs
see Knowledgebase
Also remeber to load the FPGA Read/Write VI's dynamically from testStand and dump them after. Thechange to the data type causes the vi to need to recompile so it can't stay in memory if you need different types of data.
Message Edited by Jeff Bohrer on 10-27-2009 02:21 PM
Jeff

Why does you tube prevent music video downloads?

I have figured out that music companies do not want you tube users to download videos to their hard drives or jump drives. Well, I want to. All the other videos work fine. I am using Firefox 18.0 with video download helper, and every time I download a music video, it says zero bytes. Zero byte download files, zero byte music video file. So I found the workaround to this problem to be save vid dot com, where I can enter the url to the music video I want to download and save it to my disk. Why does Firefox not allow this. Why does you tube not allow this. Money must be involved. Like I said, there must be some stupid reason why they don't want us to download their music videos. What's their problem. I just want to watch the video when I am offline, and save vid has saved me from getting angry again.
All the other videos that do not have major sponsors download just fine, and it's sad that we have to find workarounds to stupid problems. Save vid allows you to save the you tube video without loading a spybot plugin that changes your home page and peppers you with ads, I'm glad they have it. I hope to save someone else the trouble.

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Why does DataOutputStream write Boolean as 1 Byte?

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