What is Process State Diagram?

In the systems where multiple processors or multitasking is involved, a process has to go through a number of states. In this article we shall discuss about these states. 

The kernel of the operating system may not recognize these states distinctly but still for the understanding of how the processes are executed they act as useful abstractions. 

These various states can be looked up in a process state diagram for a systematic view. This diagram shows the transitions of the process between various states with arrows. Processes can be stored both in the secondary or virtual memory and in the main memory as per the situation.

Process States

- The primary process states occur in all types of the systems. 

- Processes in these states are usually stored in the main memory. 

Basically there are 5 major states of any process as discussed below:

Ø  Created: 

- It is also known as the ‘new’ state. 

- A process occupies this state up on it creation. 

- While waiting for being admitted to the next ready state this process lies in this state. 

- The admission scheduler will decide whether to admit the process to next state or to delay it on a short or long term. 

- However, this admission is approved in an automatic way in most of the desktop computers. 

- But in the systems with real time operating systems this is not true. 

- Here, the admission might be delayed by a certain amount of time.

- If too many states are admitted to the ready state in a real time operating system, condition of over contention and over saturation might occur disabling the system to meet its deadlines.

Ø  Ready or Waiting: 

- This state is taken up a process when it has been loaded in to the physical memory of the system and is waiting to be executed by the processor or precisely waiting to be context switched by the dispatcher. 

- At any instant of time there might be a number of processes waiting for their execution. 

- Here the processes have to wait in a queue called the run queue out of which only one process will be taken up by a processor. 

- Processes that are waiting for obtaining input from some event are not put in to this ready queue.

Ø  Running: 

- When a process is selected by the CPU for execution, its state is changed to running. 

- One of the processors executes the instructions of the process one by one. 

- Only one process can be run by the process at a time.

Ø Blocked: 

- When a process is blocked because of some event such as I/O operations is put in to the blocked state. 

- Another reason for a process being a blocked state can be its running out of the CPU time allocated to it.

Ø  Terminated: 

- Termination of a process may occur when either its execution is complete or it has been explicitly killed.

- This state is called the terminated or halted. 

- This process is called a zombie process if after coming in the terminated state it is not removed from the main memory. 

There are two additional states for supporting the virtual memory. In these states the process is usually stored in the secondary memory of the system:

Ø Swapped out or Waiting: 

- A process is said to be swapped out when it is removed from the primary memory and placed in the secondary memory. 

- This is done by the mid - term scheduler. 

- After this the state of this process changes to waiting.  

Ø  Swapped out and Blocked:

- In some cases, the processes that were in blocked state might be swapped out. 

- The same process might be again swapped in providing the conditions remain the same.

What are features of Hyper-Threading technology?

The HT technology or the hyper–threading technology is a proprietary SMT (simultaneous multi–threading) implementation developed by Intel in order to make improvements in the pluralization of the computations that are carried out by the microprocessors in PC. It was first included in the Xeon server processes and then in Pentium 4 processors, atom, Itanium, core I series etc. Two logical or virtual cores are addressed by the operating system for each physical processor core present. The workload is shared among these two whenever required and possible.

Features of Hyper Threading Technology

1. Hyper–threading technology reduces the number of instructions in the pipeline that are dependent in nature. This is also its main purpose.
2. Architecture: The hyper – threading technology is based on the super scalar architecture. This kind of architecture is capable of operate multiple instructions in parallel with separate data. It appears as if there are two processors, thus letting the OS operate with two processes simultaneously.
3. Resource sharing: The same resources can be shared by the two or more processors available. Re–allocation of the resources can be done up on the failure of one of the processes.
4. Support for SMT: Hyper–threading implies the support for SMT through an OS that is SMT supportable. The OS needs to be specially optimized for this technology. It is recommended by Intel to disable the HTT if the OS have not been optimized for HTT.
5. Two processors: Certain processor sections are duplicated by the HTT. These are the sections in which the architectural states are stored. The main execution resources are not duplicated. Because of this, the HT processor appears as two processors to the OS namely, the physical and the logical processor. So the OS is able to process two threads at the same time without messing up. When a current task is not using the execution resources and the HTT and when the processor is stalled (because of data dependency, cache miss or branch mis-prediction), those resources can be used by the HT processor in execution of some other task scheduled earlier.
6. Support for SMP: SMP stands for symmetric multiprocessing which is mandatory for taking full advantage of the hyper – threading processing.
7. Transparency: There is a lot of transparency between the OS, its programs and this technology.
8. Easy optimization: HTT allows easy optimization of the behavior of the OS on HTT capable systems running on multiprocessors.
9. Provides support for multi–threaded code thus improving both the response time and reaction.
10. Application – dependent performance: It works well in improving the performance of most of the MPI applications. The improvement in the performance depends largely on the nature of the running application and its cluster configuration. The performance gain can also be negative. Using performance tools would be beneficial for understanding the factors contributing to performance gain and degradation.
11. Security: A timing attack can be used by some malicious thread for monitoring the other thread’s memory access patterns. This is nothing but the stealing of the cryptographic info. This can be avoided by changing the cache eviction strategy of the processor. 

The hyper – threading technology has been criticized heavily for being energy inefficient. It has been stated by ARM that power consumption in SMT is more than in the dual – core designs by a margin of 46%. It was also claimed that cash thrashing is also increased by a margin of 42% in SMT when compared to a 37% decrease in the case of dual core processors. However, on the other side, Intel has claimed the HTT to be highly efficient since it puts the ideal resources to use. 

What are different aspects of distributed testing?

We have heard a lot about different kinds of testing such as regression testing, scalability testing, web testing, unit testing, visual testing, and performance testing and so on. But do you know what is distributed testing? Ever heard about it? No? Then this piece of writing is certainly for you!

This type of testing usually receives very less coverage and that’s why most of the people are not familiar with it. Here I have attempted to explain what is meant by distributed testing and how it compares with its non distributive counterpart.

Non distributed testing can be defined as the tests that run or execute only on a single computer and usually do not involve any kind of interaction with the other computer systems. I used the word “usually” here because there exist some tests that are executed from a host machine to test the target device which holds an embedded or a real time operating system. Non distributed test cases can be configured very easily.

Non distributed testing is further divided into two sub categories namely local testing and remote testing. They have been discussed in details below:

- Local Testing
This kind of testing involves running the test cases on a local computer system. The tests used are called local tests. For performing local test you don’t have to be connected to a network connection.

- Remote Testing
This kind of testing requires a network connection so that you can run a test on a remote computer system to which you don’t have local access. This is very comfortable since you can work right from your desk and you also get the results right on your desk. Remote tests can be performed on several computer systems at a time. The best about thing about remote testing is that no matter how many software systems are under the distributed testing, there is no interference between the processors of different CPUs.

Now that you have got the idea of how non distributed testing is like, it will be easy for you to understand distributed testing is like.
- A distributed test case consists of many parts that interact with each other.
- Each part of the test case is executed on different computer system.
- The interaction of the different parts of the distributed testing sets it apart from non distributed testing.
- If you notice the testing is all about testing the interaction between different computer systems.
- All of the test cases being processed on different processors have a common aim irrespective of the system on which they are performed.
- Distributed testing is not to be confused with simultaneous testing since in simultaneous testing there is no interaction between the different tests.
- Platform proves to be one of the great challenges to the distributed testing.
- The testing environment should be capable of working on all the platforms involved effectively.
- After setting up of your testing environment, you need to make a test plan or say that you need to describe how you want to carry out distributed testing.
- This can be done via a test scenario.
- A test scenario lists all the test cases and also describes how they are to carried out on the computer systems.
- The description of the test cases is provided in the form of a formal directive.
- Test scenario is an effective way to describe test cases.
- For distributed testing we use distributed directives and for non distributed testing we use remote directives.