non-blocking mutual exclusion

[Giambattista Bloisi]

Hi,
In your opinion there is a faster way to implement a non-blocking
multual exclusion than:

Object sem = new Object();
int count = 0;

void mutex_activity() {
synchronized(sem) {
if(count > 0)
return;
count++;
}

//... activity

synchronized(sem) {
count--;
}
}

I tryed with the following, but it seems to not work properly.

volatile int count = 0;

void mutex_activity() {
if(++count > 1) {
--count;
return;
}

//activity...

--count;
}

Regards,
Giambattista

 

[Matt Humphrey]

Hi,
In your opinion there is a faster way to implement a non-blocking
multual exclusion than:

The performance of locking really depends on how it is implemented in the
underlying JVM. If your locking is correct (a big task to begin with) try
profiling your code to see if that's where the problem is. Otherwise you'll
be optimizing the wrong thing.

I tryed with the following, but it seems to not work properly.

volatile int count = 0;

void mutex_activity() {
if(++count > 1) {
--count;
return;
}

//activity...

--count;
}

Regards,
Giambattista

From p. 97 of Doug Lea's book "In particular, composite read/write
operations such as the "++" operation on volatile variables are not
performed atomically." Try looking up java.util.concurrent.atomic.

Cheers,