In my app there are 2 phases, one download some big data, and the other manipulates it. so i created 2 classes which implements runnable: ImageDownloader and ImageManipulator, and they share a downloadedBlockingQueue:
public class ImageDownloader implements Runnable {
private ArrayBlockingQueue<ImageBean> downloadedImagesBlockingQueue;
private ArrayBlockingQueue<String> imgUrlsBlockingQueue;
public ImageDownloader(ArrayBlockingQueue<String> imgUrlsBlockingQueue, ArrayBlockingQueue<ImageBean> downloadedImagesBlockingQueue) {
this.downloadedImagesBlockingQueue = downloadedImagesBlockingQueue;
this.imgUrlsBlockingQueue = imgUrlsBlockingQueue;
}
@Override
public void run() {
while (!this.imgUrlsBlockingQueue.isEmpty()) {
try {
String imgUrl = this.imgUrlsBlockingQueue.take();
ImageBean imageBean = doYourThing(imgUrl);
this.downloadedImagesBlockingQueue.add(imageBean);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
public class ImageManipulator implements Runnable {
private ArrayBlockingQueue<ImageBean> downloadedImagesBlockingQueue;
private AtomicInteger capacity;
public ImageManipulator(ArrayBlockingQueue<ImageBean> downloadedImagesBlockingQueue,
AtomicInteger capacity) {
this.downloadedImagesBlockingQueue = downloadedImagesBlockingQueue;
this.capacity = capacity;
}
@Override
public void run() {
while (capacity.get() > 0) {
try {
ImageBean imageBean = downloadedImagesBlockingQueue.take(); // <- HERE I GET THE DEADLOCK
capacity.decrementAndGet();
} catch (InterruptedException e) {
e.printStackTrace();
}
// ....
}
}
}
public class Main {
public static void main(String[] args) {
String[] imageUrls = new String[]{"url1", "url2"};
int capacity = imageUrls.length;
ArrayBlockingQueue<String> imgUrlsBlockingQueue = initImgUrlsBlockingQueue(imageUrls, capacity);
ArrayBlockingQueue<ImageBean> downloadedImagesBlockingQueue = new ArrayBlockingQueue<>(capacity);
ExecutorService downloaderExecutor = Executors.newFixedThreadPool(3);
for (int i = 0; i < 3; i++) {
Runnable worker = new ImageDownloader(imgUrlsBlockingQueue, downloadedImagesBlockingQueue);
downloaderExecutor.execute(worker);
}
downloaderExecutor.shutdown();
ExecutorService manipulatorExecutor = Executors.newFixedThreadPool(3);
AtomicInteger manipulatorCapacity = new AtomicInteger(capacity);
for (int i = 0; i < 3; i++) {
Runnable worker = new ImageManipulator(downloadedImagesBlockingQueue, manipulatorCapacity);
manipulatorExecutor.execute(worker);
}
manipulatorExecutor.shutdown();
while (!downloaderExecutor.isTerminated() && !manipulatorExecutor.isTerminated()) {
}
}
}
The deadlock happens because this scenario: t1 checks capacity its 1.
t2 checks its 1.
t3 checks its 1.
t2 takes, sets capacity to 0, continue with flow and eventually exits. t1 and t3 now on deadlock, cause there will be no adding to the downloadedImagesBlockingQueue.
Eventually i want something like that: when the capacity is reached && the queue is empty = break the "while" loop, and terminate gracefully.
to set "is queue empty" as only condition won't work, cause in the start it is empty, until some ImageDownloader puts a imageBean into the queue.
