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How can you solve consumer producer problem by using wait() and notify() method?
Java Interview Questions and Answers (part 4)
(Continued from previous question...)
17. How can you solve consumer producer problem by using wait() and notify() method?
Here come the time to answer very very important question from interview perspective. Interviewers tends to check how sound you are in threads inter communication. Because for solving this problem we got to use synchronization blocks, wait() and notify() method very cautiously. If you misplace synchronization block or any of the method, that may cause your program to go horribly wrong. So, before going into this question first i’ll recommend you to understand how to use synchronized blocks, wait() and notify() methods.
Key points we need to ensure before programming :
>Producer will produce total of 10 products and cannot produce more than 2 products at a time until products are being consumed by consumer.
Example> when sharedQueue’s size is 2, wait for consumer to consume (consumer will consume by calling remove(0) method on sharedQueue and reduce sharedQueue’s size). As soon as size is less than 2, producer will start producing.
>Consumer can consume only when there are some products to consume.
Example> when sharedQueue’s size is 0, wait for producer to produce (producer will produce by calling add() method on sharedQueue and increase sharedQueue’s size).
As soon as size is greater than 0, consumer will start consuming.
Explanation of Logic >
We will create sharedQueue that will be shared amongst Producer and Consumer. We will now start consumer and producer thread.
Note: it does not matter order in which threads are started (because rest of code has taken care of synchronization and key points mentioned above)
First we will start consumerThread >
consumerThread.start();
consumerThread will enter run method and call consume() method. There it will check for sharedQueue’s size.
-if size is equal to 0 that means producer hasn’t produced any product, wait for producer to produce by using below piece of code-
synchronized (sharedQueue) {
while (sharedQueue.size() == 0) {
sharedQueue.wait();
}
}
-if size is greater than 0, consumer will start consuming by using below piece of code.
synchronized (sharedQueue) {
Thread.sleep((long)(Math.random() * 2000));
System.out.println("consumed : "+ sharedQueue.remove(0));
sharedQueue.notify();
}
Than we will start producerThread >
producerThread.start();
producerThread will enter run method and call produce() method. There it will check for sharedQueue’s size.
-if size is equal to 2 (i.e. maximum number of products which sharedQueue can hold at a time), wait for consumer to consume by using below piece of code-
synchronized (sharedQueue) {
while (sharedQueue.size() == maxSize) { //maxsize is 2
sharedQueue.wait();
}
}
DETAILED DESCRIPTION with program : Solve Consumer Producer problem by using wait() and notify() methods in multithreading.
Another illustration with program : How to solve Consumer Producer problem by using wait() and notify() methods, where consumer can consume only when production is over.
(Continued on next question...)
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