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    • io.bdeploy.common.TaskSynchronizer Maven / Gradle / Ivy

    package io.bdeploy.common;

import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Performs tasks. When *another* Thread wants to perform the *same* operation, it instead waits for the first Thread to complete
 * the task.
 */
public class TaskSynchronizer {

    private static final Logger log = LoggerFactory.getLogger(TaskSynchronizer.class);

    @SuppressWarnings("unchecked")
    private final Map, Future> tasks = new TreeMap<>((a, b) -> {
        if (a == null && b == null) {
            return 0;
        }

        if (a == null || b == null) {
            return a == null ? 1 : -1;
        }

        String clsAName = a.getClass().getName();
        String clsBName = b.getClass().getName();

        int x = clsAName.compareTo(clsBName);

        if (x != 0) {
            return x;
        }

        // only if SAME classes.
        return ((Comparable) a).compareTo(b);
    });

    /**
     * @param key the key to check
     * @return whether the given task key is currently associated with a running task.
     */
    public synchronized boolean isPerforming(Comparable key) {
        return tasks.containsKey(key);
    }

    /**
     * Performs the operation or waits until an existing operation with the same key is done
     *
     * @param key the task key.
     * @param task the task to be performed if not already running.
     */
    @SuppressWarnings("unchecked")
    public  T perform(Comparable key, Callable task) {
        if (key == null) {
            // accept for compat but write warning log.
            log.warn("Null key not allowed in future", new IllegalStateException("Null key, task: " + task));
        }

        Future existing;
        CompletableFuture tracker = null;
        synchronized (this) {
            existing = (Future) tasks.get(key);

            if (existing == null) {
                tracker = new CompletableFuture<>();
                tasks.put(key, tracker);
            }
        }

        if (existing != null) {
            try {
                return existing.get(); // just wait for the existing one.
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                throw new IllegalStateException("Task interrupted", e);
            } catch (ExecutionException e) {
                throw new IllegalStateException("Task failed", e);
            }
        } else {
            try {
                T result = task.call();
                tracker.complete(result);
                return result;
            } catch (RuntimeException e) {
                tracker.completeExceptionally(e);
                throw e;
            } catch (Exception e) {
                tracker.completeExceptionally(e);
                throw new RuntimeException(e);
            } finally {
                synchronized (this) {
                    tasks.remove(key);
                }
            }
        }
    }

}
    
    
    
    

    




    
    
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