I have a BlockingQueue which is being populated by a thread with put(). But I am confused on how to do take() for the BlockingQueue. Currently I implemented it this way:
String link;
try {
while(!(link = links.take()).isEmpty()) {
System.out.println(link);
}
} catch(InterruptedException ex) {
ex.printStackTrace();
}
Is that right? How is it possible to loop the queue and assign the string variable if not within the conditional statement?
If I have understood correctly, you have asked for a way to take outside of the condition? Well, it's not that hard:
while (!links.isEmpty()) {
try {
String link = links.take();
// Do stuff.
} catch (InterruptedException e) {
// Exception handling.
}
}
Your current condition !(link = links.take()).isEmpty() checks if the return value—a string—is empty (length equals 0), not the queue.
Anyhow, please bear in mind that the code above is not atomic, so there's no guarantee that nothing else happens between links.isEmpty() and links.take().
EDIT: You can handle race conditions during the startup with a flag:
BlockingQueue<Integer> numbers = new ArrayBlockingQueue<>(10);
AtomicBoolean flag = new AtomicBoolean(true);
// Producer.
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
numbers.put(i);
} catch (InterruptedException e) { /* NOP */ }
}
flag.set(false);
}).start();
// Consumer.
while (flag.get() || !numbers.isEmpty()) {
try {
System.out.println(numbers.take());
} catch (InterruptedException e) { /* NOP */ }
}
The AtomicBoolean is not necessary here, but it might become handy if you have multiple producers and/or consumers. It's also part of java.util.concurrent which you definitely should checkout.
n items to be consumed, then you can create a ArrayBlockingQueue with a capacity of n. put only blocks if there's not enough space in the queue, so your producer is able to fire and forget.take from the consumer will make space, and the producer would continue putting into the queue, so it does only pauses the producer but I want it to stop completely once the consumer processes up to a number of items.put in a for loop that terminates after n iterations. This way your producer will exactly submit n items. The consumers can take independently.put into links, thus skipping the while loop altogether. What should I do to make the while loop waits for something to be inserted into the queue?My understanding is that you are asking on how to terminate a BlockingQueue in a good way. There are two scenarios I can think of. In any case you have a Message producer A and message consumer B.
