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Parallel.javaAPI DocApache Ant 1.7015759Wed Dec 13 06:16:20 GMT 2006org.apache.tools.ant.taskdefs

Parallel

public class Parallel extends org.apache.tools.ant.Task implements org.apache.tools.ant.TaskContainer
Executes the contained tasks in separate threads, continuing once all are completed.

New behavior allows for the ant script to specify a maximum number of threads that will be executed in parallel. One should be very careful about using the waitFor task when specifying threadCount as it can cause deadlocks if the number of threads is too small or if one of the nested tasks fails to execute completely. The task selection algorithm will insure that the tasks listed before a task have started before that task is started, but it will not insure a successful completion of those tasks or that those tasks will finish first (i.e. it's a classic race condition).

since
Ant 1.4
ant.task
category="control"

Fields Summary
private Vector
nestedTasks
Collection holding the nested tasks
private final Object
semaphore
Semaphore to notify of completed threads
private int
numThreads
Total number of threads to run
private int
numThreadsPerProcessor
Total number of threads per processor to run.
private long
timeout
The timeout period in milliseconds
private volatile boolean
stillRunning
Indicates threads are still running and new threads can be issued
private boolean
timedOut
Indicates that the execution timedout
private boolean
failOnAny
Indicates whether failure of any of the nested tasks should end execution
private TaskList
daemonTasks
The dameon task list if any
private StringBuffer
exceptionMessage
Accumulation of exceptions messages from all nested tasks
private int
numExceptions
Number of exceptions from nested tasks
private Throwable
firstException
The first exception encountered
private org.apache.tools.ant.Location
firstLocation
The location of the first exception
Constructors Summary
Methods Summary
public voidaddDaemons(org.apache.tools.ant.taskdefs.Parallel$TaskList daemonTasks)
Add a group of daemon threads

param
daemonTasks The tasks to be executed as daemon.


                        
        
        if (this.daemonTasks != null) {
            throw new BuildException("Only one daemon group is supported");
        }
        this.daemonTasks = daemonTasks;
public voidaddTask(org.apache.tools.ant.Task nestedTask)
Add a nested task to execute in parallel.

param
nestedTask Nested task to be executed in parallel

        nestedTasks.addElement(nestedTask);
public voidexecute()
Execute the parallel tasks

exception
BuildException if any of the threads failed.

        updateThreadCounts();
        if (numThreads == 0) {
            numThreads = nestedTasks.size();
        }
        spinThreads();
private intgetNumProcessors()
Determine the number of processors. Only effective on later VMs

return
the number of processors available or 0 if not determinable.

        try {
            Class[] paramTypes = {};
            Method availableProcessors =
                Runtime.class.getMethod("availableProcessors", paramTypes);

            Object[] args = {};
            Integer ret = (Integer) availableProcessors.invoke(Runtime.getRuntime(), args);
            return ret.intValue();
        } catch (Exception e) {
            // return a bogus number
            return 0;
        }
private voidprocessExceptions(org.apache.tools.ant.taskdefs.Parallel$TaskRunnable[] runnables)

        if (runnables == null) {
            return;
        }
        for (int i = 0; i < runnables.length; ++i) {
            Throwable t = runnables[i].getException();
            if (t != null) {
                numExceptions++;
                if (firstException == null) {
                    firstException = t;
                }
                if (t instanceof BuildException
                    && firstLocation == Location.UNKNOWN_LOCATION) {
                    firstLocation = ((BuildException) t).getLocation();
                }
                exceptionMessage.append(StringUtils.LINE_SEP);
                exceptionMessage.append(t.getMessage());
            }
        }
public voidsetFailOnAny(boolean failOnAny)
Control whether a failure in a nested task halts execution. Note that the task will complete but existing threads will continue to run - they are not stopped

param
failOnAny if true any nested task failure causes parallel to complete.

        this.failOnAny = failOnAny;
public voidsetPollInterval(int pollInterval)
Interval to poll for completed threads when threadCount or threadsPerProcessor is specified. Integer in milliseconds.; optional

param
pollInterval New value of property pollInterval.
public voidsetThreadCount(int numThreads)
Statically determine the maximum number of tasks to execute simultaneously. If there are less tasks than threads then all will be executed at once, if there are more then only threadCount tasks will be executed at one time. If threadsPerProcessor is set and the JVM is at least a 1.4 VM then this value is ignored.; optional

param
numThreads total number of threads.

        this.numThreads = numThreads;
public voidsetThreadsPerProcessor(int numThreadsPerProcessor)
Dynamically generates the number of threads to execute based on the number of available processors (via java.lang.Runtime.availableProcessors()). Requires a J2SE 1.4 VM, and it will overwrite the value set in threadCount. If used in a 1.1, 1.2, or 1.3 VM then the task will defer to threadCount.; optional

param
numThreadsPerProcessor Number of threads to create per available processor.

        this.numThreadsPerProcessor = numThreadsPerProcessor;
public voidsetTimeout(long timeout)
Sets the timeout on this set of tasks. If the timeout is reached before the other threads complete, the execution of this task completes with an exception. Note that existing threads continue to run.

param
timeout timeout in milliseconds.

        this.timeout = timeout;
private voidspinThreads()
Spin up required threads with a maximum number active at any given time.

exception
BuildException if any of the threads failed.

        final int numTasks = nestedTasks.size();
        TaskRunnable[] runnables = new TaskRunnable[numTasks];
        stillRunning = true;
        timedOut = false;

        int threadNumber = 0;
        for (Enumeration e = nestedTasks.elements(); e.hasMoreElements();
             threadNumber++) {
            Task nestedTask = (Task) e.nextElement();
            runnables[threadNumber]
                = new TaskRunnable(nestedTask);
        }

        final int maxRunning = numTasks < numThreads ? numTasks : numThreads;
        TaskRunnable[] running = new TaskRunnable[maxRunning];

        threadNumber = 0;
        ThreadGroup group = new ThreadGroup("parallel");

        TaskRunnable[] daemons = null;
        if (daemonTasks != null && daemonTasks.tasks.size() != 0) {
            daemons = new TaskRunnable[daemonTasks.tasks.size()];
        }

        synchronized (semaphore) {
            // When we leave this block we can be sure all data is really
            // stored in main memory before the new threads start, the new
            // threads will for sure load the data from main memory.
            //
            // This probably is slightly paranoid.
        }

        synchronized (semaphore) {
            // start any daemon threads
            if (daemons != null) {
                for (int i = 0; i < daemons.length; ++i) {
                    daemons[i] = new TaskRunnable((Task) daemonTasks.tasks.get(i));
                    Thread daemonThread =  new Thread(group, daemons[i]);
                    daemonThread.setDaemon(true);
                    daemonThread.start();
                }
            }

            // now run main threads in limited numbers...
            // start initial batch of threads
            for (int i = 0; i < maxRunning; ++i) {
                running[i] = runnables[threadNumber++];
                Thread thread =  new Thread(group, running[i]);
                thread.start();
            }

            if (timeout != 0) {
                // start the timeout thread
                Thread timeoutThread = new Thread() {
                    public synchronized void run() {
                        try {
                            wait(timeout);
                            synchronized (semaphore) {
                                stillRunning = false;
                                timedOut = true;
                                semaphore.notifyAll();
                            }
                        } catch (InterruptedException e) {
                            // ignore
                        }
                    }
                };
                timeoutThread.start();
            }

            // now find available running slots for the remaining threads
            outer:
            while (threadNumber < numTasks && stillRunning) {
                for (int i = 0; i < maxRunning; i++) {
                    if (running[i] == null || running[i].isFinished()) {
                        running[i] = runnables[threadNumber++];
                        Thread thread =  new Thread(group, running[i]);
                        thread.start();
                        // continue on outer while loop to get another
                        // available slot
                        continue outer;
                    }
                }

                // if we got here all slots in use, so sleep until
                // something happens
                try {
                    semaphore.wait();
                } catch (InterruptedException ie) {
                    // doesn't java know interruptions are rude?
                    // just pretend it didn't happen and go about out business.
                    // sheesh!
                }
            }

            // are all threads finished
            outer2:
            while (stillRunning) {
                for (int i = 0; i < maxRunning; ++i) {
                    if (running[i] != null && !running[i].isFinished()) {
                        //System.out.println("Thread " + i + " is still alive ");
                        // still running - wait for it
                        try {
                            semaphore.wait();
                        } catch (InterruptedException ie) {
                            // who would interrupt me at a time like this?
                        }
                        continue outer2;
                    }
                }
                stillRunning = false;
            }
        }

        if (timedOut) {
            throw new BuildException("Parallel execution timed out");
        }

        // now did any of the threads throw an exception
        exceptionMessage = new StringBuffer();
        numExceptions = 0;
        firstException = null;
        firstLocation = Location.UNKNOWN_LOCATION;
        processExceptions(daemons);
        processExceptions(runnables);

        if (numExceptions == 1) {
            if (firstException instanceof BuildException) {
                throw (BuildException) firstException;
            } else {
                throw new BuildException(firstException);
            }
        } else if (numExceptions > 1) {
            throw new BuildException(exceptionMessage.toString(),
                                     firstLocation);
        }
private voidupdateThreadCounts()
Determine the number of threads based on the number of processors

        if (numThreadsPerProcessor != 0) {
            int numProcessors = getNumProcessors();
            if (numProcessors != 0) {
                numThreads = numProcessors * numThreadsPerProcessor;
            }
        }