问外部共享资源(智能卡)的Java并发模式

EN

public void setMaximumPoolSize(int maximumPoolSize)

public void setCorePoolSize(int corePoolSize)

Core and maximum pool sizes:

 ExecutorService executor = Executors.newFixedThreadPool(6);

import java.util.*;
import java.util.concurrent.*;

/**
 * A resource pool that expects shared resources 
 * to be added and removed from the pool by an external process
 * (i.e. not done by the pool itself, see {@link #add(Object)} and {@link #remove(Object)}.
 * <br>A {@link ResourcePoolValidator} can optionally be used. 
 * @param <T> resource type handed out by the pool.
 */
public class ResourcePool<T> {

    private final Set<T> registered = Collections.newSetFromMap(new ConcurrentHashMap<T, Boolean>()); 
    /* Use a linked list as FIFO queue for resources to lease. */
    private final List<T> available = Collections.synchronizedList(new LinkedList<T>()); 
    private final Semaphore availableLock = new Semaphore(0, true); 

    private final ResourcePoolValidator<T> validator;

    public ResourcePool() {
        this(null);
    }

    public ResourcePool(ResourcePoolValidator<T> validator) {
        super();
        this.validator = validator;
    }

    /**
     * Add a resource to the pool.
     * @return true if resource is not already in the pool.
     */
    public synchronized boolean add(T resource) {

        boolean added = false;
        if (!registered.contains(resource)) {
            registered.add(resource);
            available.add(resource);
            availableLock.release();
            added = true;
        }
        return added;
    }

    /**
     * Removes a resource from the pool.
     * The resource might be in use (see {@link #isLeased(Object)})
     * in which case {@link ResourcePoolValidator#abandoned(Object)} will be called 
     * when the resource is no longer used (i.e. released). 
     * @return true if resource was part of the pool and removed from the pool.
     */
    public synchronized boolean remove(T resource) {

        // method is synchronized to prevent multiple threads calling add and remove at the same time 
        // which could in turn bring the pool in an invalid state.
        return registered.remove(resource);
    }

    /**
     * If the given resource is (or was, see also {@link #remove(Object)} part of the pool,
     * a returned value true indicates the resource is in use / checked out.
     * <br>This is a relative expensive method, do not call it frequently.
     */
    public boolean isLeased(T resource) {
        return !available.contains(resource);
    }

    /**
     * Try to get a shared resource for usage. 
     * If a resource is acquired, it must be {@link #release(Object)}d in a finally-block.
     * @return A resource that can be exclusively used by the caller.
     * @throws InterruptedException When acquiring a resource is interrupted.
     * @throws TimeoutException When a resource is not available within the given timeout period.
     */
    public T tryAcquire(long timeout, TimeUnit tunit) throws InterruptedException, TimeoutException {

        T resource = null;
        long timeRemaining = tunit.toMillis(timeout);
        final long tend = System.currentTimeMillis() + timeRemaining;
        do {
            if (availableLock.tryAcquire(timeRemaining, TimeUnit.MILLISECONDS)) {
                resource = available.remove(0);
                if (registered.contains(resource)) {
                    boolean valid = false;
                    try {
                        valid = (validator == null ? true : validator.isValid(resource));
                    } catch (Exception e) {
                        // TODO: log exception
                        e.printStackTrace();
                    }
                    if (valid) {
                        break; // return the "checked out" resource
                    } else {
                        // remove invalid resource from pool
                        registered.remove(resource);
                        if (validator != null) {
                            validator.abandoned(resource);
                        }
                    }
                }
                // resource was removed from pool, try acquire again
                // note that this implicitly lowers the maximum available resources
                // (an acquired permit from availableLock goes unused).
                // TODO: retry puts us at the back of availableLock queue but should put us at the front of the queue
                resource = null;
            }
            timeRemaining = tend - System.currentTimeMillis();
        } while (timeRemaining > 0L);
        if (resource == null) {
            throw new TimeoutException("Unable to acquire a resource within " + tunit.toMillis(timeout) + " ms.");
        }
        return resource;
    }

    /**
     * This method must be called by the caller / client whenever {@link #tryAcquire(long, TimeUnit)}
     * has returned a resource. If the caller has determined the resource is no longer valid,
     * the caller should call {@link #remove(Object)} before calling this method.
     * @param resource no longer used.
     */
    public void release(T resource) {

        if (resource == null) {
            return;
        }
        if (registered.contains(resource)) {
            available.add(resource);
            availableLock.release();
        } else {
            if (validator != null) {
                validator.abandoned(resource);
            }
        }
    }

    /** An array (copy) of all resources registered in the pool. */
    @SuppressWarnings("unchecked")
    public T[] getRegisteredResources() {
        return (T[]) registered.toArray(new Object[registered.size()]);
    }

}

import java.util.concurrent.TimeUnit;

/**
 * Used by a {@link ResourcePool} to validate a resource before handing it out for lease
 * (see {@link #isValid(Object)} and signal a resource is no longer used (see {@link #abandoned(Object)}). 
 */
public class ResourcePoolValidator<T> {

    /**
     * Overload this method (this method does nothing by default) 
     * to validate a resource before handing it out for lease.
     * If this method returns false or throws an exception (which it preferably should not do), 
     * the resource is removed from the pool.
     * @return true if the resource is valid for leasing
     */
    public boolean isValid(T resource) {
        return true;
    }

    /**
     * Called by the {@link ResourcePool#release(Object)} method when a resource is released by a caller 
     * but the resource was previously removed from the pool and in use.
     * <br>Called by {@link ResourcePool#tryAcquire(long, TimeUnit)} if a resource if not valid 
     * (see {@link #isValid(Object)}.
     * <br>Overload this method (this method does nothing by default) to create a notification of an unused resource,
     * do NOT do any long period of processing as this method is called from a caller (client) thread.
     */
    public void abandoned(T resource) {
        // NO-OP
    }

}