auxtestlib

Class ThreadFlag

java.lang.Object

auxtestlib.ThreadFlag

public class ThreadFlag
extends Object

Class used to control running threads. A flag keeps a marker whether threads should or not continue and keeps record of which threads have reached the flag. It is essentially an implementation of a barrier.

Using this class several threads may keep a synchronization point. Lets suppose we have a process that divides into three phases, A, B and C and we want several threads in parallel to execute phase A. We want all threads to move to phase B when all have finished A. When all finish phase B we want all to start phase C. In order to do this we create two flags, one representing the end of phase A and the other the end of phase B. Each thread is now:

 public void process(ThreadFlag flagA, ThreadFla flagB) {
        doSomethingInPhazeA();
        flagA.reach();
        doSomethingInPhazeB();
        flagB.reach();
        doSomethingInPhazeC();
 }
 

The method reach will block the current thread until someone invokes the allowContinue method. So, if there were 20 threads running, we could use a subclass of ThreadFlag to start all threads into the next phase:

 public class MyStartAllAtOnceFlag extends ThreadFlag {
        public int count = 0;
 
        public void threadReached(List l) {
                if (l.size() == 20) {
                        // All threads have arrived.
                        allowContinue();
                }
        }
 }
 

Constructor Summary

Constructors

Constructor and Description
ThreadFlag() Creates a new flag.

Method Summary

Modifier and Type	Method and Description
void	allowContinue() Starts all threads currently stopped at the flag.
void	reach() Invoked by a thread to mark that it has reached the flag.
List<Thread>	reached() Obtains the list of all threads that have reached the flag.
void	threadReached(List<Thread> l) A thread has reached the flag.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ThreadFlag

public ThreadFlag()

Creates a new flag.

Method Detail

reach

public void reach()

Invoked by a thread to mark that it has reached the flag. This method will block the thread until it receives an order to continue. If the flag has been marked to continue (the allowContinue() method has been called) this method returns immediately.

allowContinue

public void allowContinue()

Starts all threads currently stopped at the flag.

threadReached

public void threadReached(List<Thread> l)

A thread has reached the flag. This method does nothing and may be overridden by subclasses.

Parameters:

l - the list of threads that have reached the flag

reached

public List<Thread> reached()

Obtains the list of all threads that have reached the flag.

Returns:

the list of threads