CODEWITHSUNDEEP
javamultithreading
digoferra
digoferra

Reputation: 1001

Separate hashset to run the list at several threads

I googled and search here for this question and did not find anything similar to what I´m looking for.

I populated a HashSet with few objects called Person, I need to set four or five threads to search these Person in a huge text, thread seems to be the best solution for the better usage from the hardware.

The doubt is, how can I separate this HashSet and start 4 threads? I tried to create a new HashSet list and start a new thread with this new hashset divided in 4.

It seems to be a good solution but, is there a better way to do it? How can I separate the hashset and send at pieces to 4 or 5 new threads?

Upvotes: 4

Views: 726

Answers (4)

Tudor
Tudor

Reputation: 62459

You can implement a producer-consumer scheme: have a single thread read the values from the hash set one by one and put them in a queue which is then processesed by several worker threads. You can use the ExecutorService class to manage the workers.

Edit: Here's what you can do:

Define your worker class:

public class Worker implements Runnable {
    private Person p;

    public Worker(Person p) {
        this.p = p;
    }      

    public void run() {
        // search for p
    }
}

In the main thread:

ExecutorService s = Executors.newCachedThreadPool();
for(Person p: hashSet) {
    s.submit(new Worker(p));
}

Upvotes: 2

Peter Lawrey
Peter Lawrey

Reputation: 533660

Access to a HashSet is O(1) so if you split it across multiple threads, it won't go any faster. You are better off attempting to split the file of searching is expensive. However if its efficient enough, one thread will be optimal.

It is worth remembering that using all the cores on your machine can mean your program is slower. If you just want to use up all the CPU on you machine, you can create a thread pool which does nothing but use up all the CPU on your machine.

Upvotes: 2

mevada.yogesh
mevada.yogesh

Reputation: 1128

You cane iterate through the hash set using Iterator. & while iterating fetch the value and create a thread and fire it.

Else

you can use ExecutorService API where simultaneous tasks can be run in parallel.

Upvotes: 1

Francis Upton IV
Francis Upton IV

Reputation: 19443

A couple of things to consider:

1) You could use the same HashSet, but you will need to synchronize it (wrap the calls to it with a synchronized block. But if all you are doing is looking up things in the hash, being multi-threaded will not buy you much.

2) If you want to split the HashSet, then you can consider a split on key ranges. So for example if you are searching for a name, names that start with A-F go in HashSet1, G-L HashSet2, etc. This way your searches can be completely parallel.

Upvotes: 1

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