MappedByteBuffer and corrupted data

[John]

Hi,
i've been experiencing somme corruption of data with MappedByteBuffer. My serialisations are pretty simples. I've put "magic" byte for the debug, and some time, the byte i read is not equal to the "magic" value.

So i'm wondering if somebody has already experienced this kind of troubles. If it's not a bug in Java, what can it be ?

TIA

 

[EJP]

If it's not a bug in Java, what can it be ?

A bug in your code?

 

[Lew]

A bug in your code?

John, without your code as an SSCCE
<http://www.physci.org/codes/sscce.html>
we cannot answer your question, although in general terms EJP's answer is most
likely the correct one.

 

[Daniele Futtorovic]

Hi,
i've been experiencing somme corruption of data with MappedByteBuffer.
My serialisations are pretty simples. I've put "magic" byte for the
debug, and some time, the byte i read is not equal to the "magic" value.

So i'm wondering if somebody has already experienced this kind of
troubles. If it's not a bug in Java, what can it be ?

TIA

Post a code example (sscce) if you want precise answers.

As a guess, it might be you're trying to compare signed bytes with
unsigned byte values and get entangled in promotions and widening
conversions. Careful addition of 0xFF masks might solve it.

df.

 

[John]

Lew a écrit :

John, without your code as an SSCCE
<http://www.physci.org/codes/sscce.html>
we cannot answer your question, although in general terms EJP's answer
is most likely the correct one.

Yes it is a concurency issue

 

[Lew]

Lew a écrit :

Yes it is a concurency issue

One of the top three authors on Java concurrency:
<http://www.briangoetz.com/pubs.html>

Reading /Java Concurrency in Practice/ taught me that a quarter century of
concurrent programming experience has not made me an expert yet.

 

[Daniele Futtorovic]

Post a code example (sscce) if you want precise answers.

As a guess, it might be you're trying to compare signed bytes with
unsigned byte values and get entangled in promotions and widening
conversions. Careful addition of 0xFF masks might solve it.

To illustrate my point:
public static void main(String[] ss) {
int MAGIC = 0xFA;

byte b = (byte) MAGIC;

System.out.println(b == MAGIC);
System.out.println((b & 0xFF) == MAGIC);
}

Yields:
false
true

Likewise:
public static void main(String[] ss) throws Exception {
final byte MAGIC = (byte) 0xFA;

PipedOutputStream pos = new PipedOutputStream();
PipedInputStream pis = new PipedInputStream(pos);

pos.write(MAGIC);

int read = pis.read();

System.out.println(read == MAGIC);
System.out.println(read == (MAGIC & 0xFF));
}

Yields:
false
true

Conclusion: Mind two's complement arithmetic, especially when doing IO!
In Java, bytes are signed, but the "bytes" you read off an InputStream
are unsigned.

df.

 

[pcspecialist9]

Post a code example (sscce) if you want precise answers.

As a guess, it might be you're trying to compare signed bytes with
unsigned byte values and get entangled in promotions and widening
conversions. Careful addition of 0xFF masks might solve it.

To illustrate my point:
     public static void main(String[] ss) {
         int MAGIC = 0xFA;

         byte b = (byte) MAGIC;

         System.out.println(b == MAGIC);
         System.out.println((b & 0xFF) == MAGIC);
     }

Yields:
  false
  true

Likewise:
     public static void main(String[] ss) throws Exception {
         final byte MAGIC = (byte) 0xFA;

         PipedOutputStream pos = new PipedOutputStream();
         PipedInputStream pis = new PipedInputStream(pos);

         pos.write(MAGIC);

         int read = pis.read();

         System.out.println(read == MAGIC);
         System.out.println(read == (MAGIC & 0xFF));
     }

Yields:
  false
  true

Conclusion: Mind two's complement arithmetic, especially when doing IO!
In Java, bytes are signed, but the "bytes" you read off an InputStream
are unsigned.

df.

I am a beginner in Java and this kind of troubles and solutions is
what I need to read. Thanks to the great people here.

www.ljaranet.com