Synchronized problem - I have a real challenge!

Question

Hi,
I have a real synchronized problem. Please see the code and the output below and tell me what is wrong. It seens that synchronized is not working properly.
---> CODE:
public synchronized void publish(LogRecord record) {
if (!isLoggable(record)) {
return;
System.out.println("AutoPushMemoryHandler in - buffer index: " + count +
" lgth " + buffer.length +
" ts " + System.currentTimeMillis() +
" trd " + Thread.currentThread().getName());
try {
buffer[count] = record;
catch (ArrayIndexOutOfBoundsException ex) {
System.out.println("AutoPushMemoryHandler ArrayIndexOutOfBoundsException - buffer index: " + count +
" lgth " + buffer.length +
" ts: " + System.currentTimeMillis() +
" trd " + Thread.currentThread().getName());
return;
count++;
if ((record.getLevel().intValue() >= pushLevel.intValue()) ||
(count == buffer.length)) {
// we don't want to lost any log, so it's time to push
push();
System.out.println("AutoPushMemoryHandler out - buffer index: " + count +
" lgth " + buffer.length +
" ts " + System.currentTimeMillis() +
" trd " + Thread.currentThread().getName());
public synchronized void push() {
for (int i = 0; i < count; i++) {
LogRecord record = buffer;
target.publish(record);
// empty the buffer.
System.out.println("AutoPushMemoryHandler - push() executed" +
" trd " + Thread.currentThread().getName());
count = 0;
---> OUTPUT:
AutoPushMemoryHandler in - buffer index: 998 lgth 1000 ts 1035858336618 trd RequestProcessor[10]
AutoPushMemoryHandler out - buffer index: 999 lgth 1000 ts 1035858336618 trd RequestProcessor[10]
AutoPushMemoryHandler in - buffer index: 999 lgth 1000 ts 1035858336618 trd RequestProcessor[10]
AutoPushMemoryHandler in - buffer index: 1000 lgth 1000 ts 1035858340039 trd RequestProcessor[12]
AutoPushMemoryHandler ArrayIndexOutOfBoundsException - buffer index: 1000 lgth 1000 ts: 1035858340040 trd RequestProcessor[12]
QUESTION:
How is possible the thread RequestProcessor[12] enter in the method publish() if the RequestProcessor[10] did not leave the meyhod yet????? Note that publish() is synchronized!!!

Answer 1

You probably have several object instances, from looking at the code it calls target.push or target.publish. Synchronized only blocks other instances of the same object from concurrently executing synchronized code. If you truly need to lock the CLASS, not the INSTANCE of class, then you need to synchronize on another object, such as {YourClass}.class