I need lock a function from another function in java. In example above, I call slave function to print counter. And I need when that if master function called, all threads which calls slave function must be wait master functions to be ended.
How can I do that?
int counter = 0;
private void slave()
{
System.out.println(counter);
}
private void master()
{
lockSlave();
counter ++;
unlockSlave();
}
Take a look at JDK ReentrantReadWriteLock.
private final ReadWriteLock lock = new ReentrantReadWriteLock();
private void slave()
{
lock.readLock().lock();
try {
System.out.println(counter);
...
} finally {
lock.readLock().unlock();
}
}
private void master()
{
lock.writeLock().lock();
try {
counter ++;
...
} finally {
lock.writeLock().unlock();
}
}
counter++, it doesn't need to be thread-save nor volatileUse a ReentrantReadWriteLock. Also make your variable volatile so changes can be seen by all threads.
ReadWriteLock m_lock = new ReentrantReadWriteLock();
Lock m_readLock = m_lock.readLock();
Lock m_writeLock = m_lock.writeLock();
volatile int counter = 0;
private void slave() {
m_readLock.lock();
try {
System.out.println(counter);
} finally {
m_readLock.unlock();
}
}
private void master(){
m_writeLock.lock();
try {
counter ++;
} finally {
m_writeLock.unlock();
}
}
try, not inside it, see: docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/… As .lock() itself may throw, after which you'll get an exception in finallyUse synchronized word, is what is for, you can synchronize the full method, so only one thread will be able to run at once.
AtomicIntegerorLongAdder