Advanced Java: Multi-threading Part 12 - Semaphores

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How to use Semaphores in multi-threaded Java code. Semaphores allow you to control how many threads can access a resource simultaneously; you can also use them as locks if the mood takes you, with the advantage that you can release (unlock) them from threads other than where you locked them.
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[neoforu]

Countless online tutorials and failed attempts at reading tedious documentation later I finally understand multithreading. Absolute gem. Thanks a lot.

[zam]

Reviewing for an Operating Systems exam and came across this video during my studies. Extremely well done, it was a delight to watch. Liked and subscribed :)

[neux]

Finally, a video which provides an up-to-date use of semaphores in concurrency that I can understand. Thank you so much.

[caveofprogramming]

It's Beethoven, Piano Concert 4, played by Debbie Hu. Actually no, I find music distracting. These days I don't really do much programming apart from the occasional burst, but sometimes I used to listen to trance. It's an acquired taste ... most trance is tacky and vile, but some is really quite delicious. Many of my colleagues felt they could program really well while listening to Internet radio.

[caveofprogramming]

Cheers, that sounds like a good idea. I'll keep it in mind when I get round to re-doing this one. This one is a bit unnecessarily complex, I see that now.

[workless]

Hey, i'm new to multi-threading, but i thought your connection example with semaphores was perfect. Everything was very well presented. Fantastic job!
kesten

[caveofprogramming]

I'm in the process of remaking these videos with a better mic, so if you have any suggestions, I'd like to hear them.

[caveofprogramming]

@DaSilentLprince Haha, yes I can see how it would be confusing, now you mention it! There's a Connection class; it has a connect() method, and it counts the number of things that are currently 'connected'. I should have called the class "Server" really.

[JackMelon]

Excellent explanation. If i didnt get it wrong, when you call sem.acquire() if the object "sem" doesnt have a permit available the code below that sentence will not execute till a permit is realease and that could happen in the same or another thread if the threads share the same semaphore object. Is that right?

[ufo]

I like your  Multi-threading Tutorials. but in this case you make its so much harder to understand with the static method...

[dorkendr]

love your start music, gets me into the video instantly

[dosenmarko]

Well i like your tutorials, but when you are adding new stuff to program like Semaphore here, try to use it on something rly simple. You could explain how semaphore multy threading work on simple displaying of String vector. and limit how many of them u want to display with semaphore.

[xthmath]

Will the JSP and Swings will use these Multithreading techniques to a Wide Range?

[RaviKumar-cwvl]

When to use Semaphore? I am unable to link this example with real time multithreading scanerio.

[eilay]

I'm a little confused here. Isn't semaphone acquire and release like synchronized. Why do we need synchronized(this) after acquireing a semaphore?

[keithscull]

QUESTION: Can you invoke the semaphore upon regular threads? as in thread t1 = new Thread(new Runnable(){
public void run(){

}
}); ??

[grandmaatemysweater]

Should the release be inside the catch block of the acquire? I.E. what happens if the exception is thrown on the acquire, and then a release is called?

[bautrey]

Do you listen to any music while programming? From your intro, I would guess piano. Also what is the name of your intro piano song?

[bluex]

So the point seems to be to put a thread.sleep() right OUTSIDE of the synchronized block, I see that. BUT, I don't understand WHY since we're calling the entire METHOD 200 times via the ExecutorService, why wouldn't that thread.sleep be executing within EVERY iteration of the loop constantly?

[MrJonnis]

Is there any necessity of making the Connection class, Singleton ?