What is Starvation? What is a Livelock?

Starvation and livelock are much less common a problem than deadlock, but are still problems that every designer of concurrent software is likely to encounter.

LiveLock

Livelock occurs when all threads are blocked, or are otherwise unable to proceed due to unavailability of required resources, and the non-existence of any unblocked thread to make those resources available. In terms of Java API, thread livelock can occur in following conditions:

• When all the threads in a program execute Object.wait(0) on an object with zero parameter. The program is live-locked and cannot proceed until one or more threads call Object.notify() or Object.notifyAll() on the relevant objects. Because all the threads are blocked, neither call can be made.
• When all the threads in a program are stuck in infinite loops.

Starvation

Starvation describes a situation where a thread is unable to gain regular access to shared resources and is unable to make progress. This happens when shared resources are made unavailable for long periods by "greedy" threads. For example, suppose an object provides a synchronized method that often takes a long time to return. If one thread invokes this method frequently, other threads that also need frequent synchronized access to the same object will often be blocked. Starvation occurs when one thread cannot access the CPU because one or more other threads are monopolizing the CPU. In Java, thread starvation can be caused by setting thread priorities inappropriately. A lower-priority thread can be starved by higher-priority threads if the higher-priority threads do not yield control of the CPU from time to time.

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What is the difference between sleep(), suspend() and wait()?

Ans:Thread.sleep() sends the current thread into the "Not Runnable" state for some amount of time. The thread keeps the monitors it has aquired -- i.e. if the thread is currently in a synchronized block or method no other thread can enter this block or method. If another thread calls t.interrupt() it will wake up the sleeping thread. Note that sleep is a static method, which means that it always affects the current thread (the one that is executing the sleep method). A common mistake is to call t.sleep() where t is a different thread; even then, it is the current thread that will sleep, not the t thread. t.suspend() is deprecated. Using it is possible to halt a thread other than the current thread. A suspended thread keeps all its monitors and since this state is not interruptable it is deadlock prone. object.wait() sends the current thread into the "Not Runnable" state, like sleep(), but with a twist. Wait is called on a object, not a thread; we call this object the "lock object." Before lock.wait() is called, the current thread must synchronize on the lock object; wait() then releases this lock, and adds the thread to the "wait list" associated with the lock. Later, another thread can synchronize on the same lock object and call lock.notify(). This wakes up the original, waiting thread. Basically, wait()/notify() is like sleep()/interrupt(), only the active thread does not need a direct pointer to the sleeping thread, but only to the shared lock object.

Q:What are native operating system threads?

Ans: Native operating system threads are those provided by the computer operating system that plays host to a Java application, be it Windows, Mac or GNU/Linux. Operating system threads enable computers to run many programs simultaneously on the same central processing unit (CPU) without clashing over the use of system resources or spending lots of time running one program at the expense of another. Operating system thread management is usually optimised to specific microprocessor architecture and features so that it operates much faster than Java green thread processing.

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What is ThreadLocal class? How can it be used?

Ans:Below are some key points about ThreadLocal variables

• A thread-local variable effectively provides a separate copy of its value for each thread that uses it.
• ThreadLocal instances are typically private static fields in classes that wish to associate state with a thread
• In case when multiple threads access a ThreadLocal instance, separate copy of Threadlocal variable is maintained for each thread.
• Common use is seen in DAO pattern where the DAO class can be singleton but the Database connection can be maintained separately for each thread. (Per Thread Singleton) ThreadLocal variable are difficult to understand and I have found below reference links very useful in getting better understanding on them

Q:When InvalidMonitorStateException is thrown? Why?

Ans: This exception is thrown when you try to call wait()/notify()/notifyAll() any of these methods for an Object from a point in your program where u are NOT having a lock on that object.(i.e. u r not executing any synchronized block/method of that object and still trying to call wait()/notify()/notifyAll()) wait(), notify() and notifyAll() all throw IllegalMonitorStateException. since This exception is a subclass of RuntimeException so we r not bound to catch it (although u may if u want to). and being a RuntimeException this exception is not mentioned in the signature of wait(), notify(), notifyAll() methods.

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Folder Option Not Visible In Tools Menu

Want to change your windows folder options such as Show hidden files or Hide extensions for know file types.

But my folder options is not visible. How to make folder options visible under tools menu.

Here is the solution:

Step 1 : Goto Start Menu and Select Run otpion.

Step 2 : Type gpedit.msc in run dialog box. Group Policy dialog box will be displayed.

Step 3 : In Group Policy dialog box in the left pane select

user configuration->administrative templates->windows components->windows explorer

Step 4 : In left pane double click on "Removes the folder options menu item from the tools menu".

Step 5 : Change its setting to disabled.

Step 6 : Close the Group Policy Dialog box.

Step 7 : Check tools menu in windows explorer.

enjoy.............

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How do Java threads make the environment asynchrnous?

Ans: The thread mechanism in Java begins with the main entry point thread the runtime environment creates to start a Java program. When you use that initial thread create secondary threads, each one runs independently of the other. The Java virtual machine manages the execution of the threads so they behave as if they all run at the same time, in fact each thread briefly takes turns at execution.

In its simplest form there may be no communication or synchronization between multiple threads in a Java program and they each run to completion independently of each other. In this respect Java threads are fundamentally asynchronous, there is no master clock that governs when threads will run and when they synchronize variables to “catch-up” with each other.

It is often necessary and more useful if threads do check ready states before progressing, synchronize read and write access to shared variables and call-back to each other when their work is done. This is where the synchronized keyword and the various sleep(), wait() and notify() methods are used to more closely schedule the interaction between asynchronous threads.

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Power On Your Computer With Mouse

Want to power on your computer?


Press Power Button on cabinet.


Is there any other way?


Yah...


Double Click with your mouse.


But for that you need to make some settings.


Here goes the settings.


Step 1 Restart your computer.


Step 2 Press DEL button (F2 in some motherboards) to goto the BIOS settings.


Step 3 Select Integrated Peripherals from main menu.


Step 4 If PS/2 mouse power on disabled, activate it by press page up/ page down key it will became Double-Click.


Step 5 Press Esc key to exit.


Step 6 Press F10 to save and exit Power off your PC.


Step 7 Now double-click the left mouse button,
.. Your PC will turn on


This trick may not work with some motherboards.

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