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8 Cards in this Set
- Front
- Back
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concurrency what ,why ,how |
running multiple threads to do part of a work in prallel , To do fast work , increase throughput, reduce time by running multiple threads to do parts of job, async work |
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process/Threads what are they , differences |
process is a running programe thread is lighweight process as uses shared memory of process , once process can have multi thread thread has it's own call stack , but reads from process shared memory as well |
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advantage and disadvantage of concurrency or multiThreaded environment , emphasise on multi Thread word |
fast work , less time , use of multi core cpu access , visibility are the issues , access --> two thread wants to access the same variable , race condition deadlock visibility -- changes done by one thread not visible to other threads |
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how to get rid / reduce of disadvantages , |
use of synchronized block for a code block(with a lock object) or for a method,ensure with lock public synchronized void critial() { // some thread critical stuff // here} is a sync method |
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what's a volatile qualifier |
the volatile keyword in Java is used as an indicator to Java compiler and Thread that do not cache value of this variable and always read it from main memory , used as a form of synchronization |
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properties of volatile keyword , advantages , how to use , when to use |
1)values will always be read from main memory, no thread will cache it 2)read/write becomes atomic , as every thread has to read from one variable 3)only in multi thread environment you should use , there only make sense |
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Special uses of volatile , what can be done so great , with that atomicity , synchronisation |
1)read of long and double can be atomic as 64 bit . 32 bit platform can read/write only 32 bit at once so advantageous over there 2) visibility can be achieved as all has to read same variable 3)advantageous over sync keyword as no wait , lock etc fast and easy to use |
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example of volatile |
public class Singleton{ private static volatile Singleton _instance; //volatile variable public static Singleton getInstance(){ if(_instance == null){ synchronized(Singleton.class){ if(_instance == null) _instance = new Singleton(); } } return _instance; } |
