Introduction to Synchronization

Introduction to Synchronization Synchronization is a mechanism which helps to use shared memory resources in an operating system. In the current world, most of the computers are multi-tasking computers. So these computers can do more than one process at the same time. And the networking technology is has become one of the most modern and developed technologies in the current worlds. So both these computer and network technologies work together in order to achieve common goals. While working together these technologies have to share resources such as memory at the same time. While sharing memory, there can be many problems. To avoid these problems synchronization mechanisms were implemented. Concurrency As it is mentioned above, operating systems share memory in order to achieve common goals. The data can be shared among two processes in one operating system or two operating systems over a network. However there are sometimes that the shared data can be accessed by only one process at a time. As a real life example, shared bathroom can be taken. A shared bathroom can be used by many people but it can be used by only one person at the time. If someone is using the bathroom, others have to wait until that person to come out. Then the one of the waited people can use the bathroom. Another real life example for this is shared streets or junctions. In shared streets, people can use only one direction at one time. If the shared street is used by any direction, people from other direction have to wait till others to stop using the shared street. Otherwise there can be clashes and a lot of problems. Like these, when the operating systems use shared memory, sometimes only one process can acc ess the data at one time. So this is called concurrency. There must be some mechanisms to avoid this concurrency. In the above given two real life examples, the shared bathroom can use a lock in its door to make sure that only one person is using the bathroom at one time. In the shared streets, traffic lights can be used to make sure that only one direction is using the street and avoid the clashes. Like this, locking and synchronizations are the mechanisms that can be used to avoid concurrency in operating systems. Properties of systems with concurrency There are some properties of the systems with concurrency. Those properties are, multiple actors, shared resources and rules for accessing the resources. In the above given two real life examples, the multiple actors are people and vehicles while the shared resources become bathroom and street. The rules for accessing these shared resources are one person at one time for the bathroom and one direction for one time for the shared streets. When talking about these three properties in relating to the operating systems, it can be explained like this. Here, the multiple actors are processes within the operating system or threads in processes. Shared memory, global variables and shared devices can be taken as the examples for the shared resources property while locking and semaphores techniques become the rules for accessing the shared resources in operating systems. These are the three properties of the systems with concurrency and it helps to understand what the concurrency is. Situations with no risk of concurrency In the current computer technology, there are some situations that there is no risk of concurrency but the shared resources are accessed by more than one processes or threads at the same time. Those situations are as follows, No shared memory or communication :- Here, the processes or threads do not have shared memory or communication. So those processes or threads work only with its private memory. Shared memory with read-only access :- Here, the shared memory can be accessed by one or more processes or threads at the same time. But in this situation, the shared memory is only available for processes or threads to read-only. So the shared memory cannot be modified in this situation. Copy-on-Write (COW) :- Here, the shared memory is accessed by one or more processes or threads at the same time and each process or thread has a separate copy of the shared memory. So each process is accessing its own copy of the shared memory and there is no risk of concurrency. Situation with risk of concurrency As well as the situations with no risk of concurrency, there are some situations with risk of concurrency in the current operating systems. Those situations can be explained as follows, Using of shared memory without any synchronization :- Here, if the shared memory is accessed by more than one processes or threads at the same time without and synchronization (without having any separate copy for each process or threads), there is a risk of concurrency. Any modification to the shared memory :- If the shared memory is accessed by more than one processes or threads, and at least one of the processes or threads makes any changes to the shared memory, then there is a risk of concurrency. These are the situations with risk of concurrency. If one of these happens, then there is a risk of concurrency in the system. If a concurrency is happened, then there may be a lot of problems in the system. And the risk of happening the concurrency is known as race condition. Race condition Under this topic, the race conditions is discussed by using an example. Here, an example of a bank account is taken to discuss the race condition. In this example, there are two peoples and a bank account. Execution of the code of this example as follows, account.balance =  £200; int withdraw (account, amount =  £50){ balance = account.balance; balance -= amount; int deposit (account, amount= £100){ balance = account.balance; balance += amount; account.balance = balance; return balance; } account.balance = balance; return balance; } For this example, the two persons are named as person1 and person2. The code executed by the person1 is coloured with blue colour while the code executed by the person2 is coloured with red colour. This is a sketch of the programme but not coded with any programming language. In the very first line, the balance of the account is set to  £200. The rest of the code is explained as follows, Line 1 :- person1 starts executing the code and calls the withdraw() by giving the account and  £50 of amount as the parameters. Line 2 :- person1 reads the balance from the account class and assigns the value of balance variable in account class to his balance variable in his withdraw(). Line 3 :- person1 modifies the value of the balance variable in his withdraw() by subtracting the value of amount. So the value of the balance variable in his withdraw() becomes  £150. Line 4 :- In this line, the person2 starts executing the code by calling his deposit() by parsing account and  £100 of amount as the parameters. Line 5 :- Here, person2 reads the value of the balance variable in account class and assigns it to the balance variable in his deposit(). Here, still the value of balance variable in account class is  £200 as the person1 has not updated the balance in account class. Line 6 :- Person2 modifies the value of the balance variable by adding the value of amount variable to it. So the value of balance variable in deposit() becomes  £300. Line 7 :- person1 updates the value of the balance variable in the account class as  £150. Line 8 :- person 1 returns the value of the balance variable in withdraw() Line 9 :- person2 updates the value of the balance variable in the account class as  £300 Line 10 :- person2 returns the value of the balance variable in his deposit() After executing this code 2 peoples complete their transactions by leaving the final value of the balance variable in account class as  £300 while the real value of the balance variable in account class has to be  £250. So there is clear error in the final output of the process and this is called as the race condition. Manage concurrency Manage Synchronization means, use synchronization mechanism programs to write rues for control concurrency situations. One of these rules are as follows: Atomicity Atomicity allows one threat to access data to manipulate at a single situation. In another way, will allows no other threats to change data while one is running. This will either will lock the threat is in progress of manipulating the record or let other records to be waiting while one record access record. The other rule is conditional synchronization In this explain threats will be in a particular order to access the record. When threats arrives to access record rule will check the order and add to the queue and let wait until the turn of the threat to access the records. All above access methods will be easy to implement when can identify which is the critical part of the process should allow to access at a time. i.e. When Person A accessing account balance person B not allows to access balance at the same time. If extract further as bellow. 1.int withdraw (account, amount) { 2.int balance = account.balance; 3.balance -= amount; 4.account.balance = balance; 5.return balance; 6.} Line 1: will initialize threat and pass external parameter values into the threat withdraw as account and amount in this situation. Line 2: will declare balance variable locally to retrieve stored account balance from the database for threat to process and pass account balance in the account table account.balance. Line 3: will manipulate balance variable value (in this situation, we will deduct since it is withdrawal) from the amount has been pass form external parameter. -= notation for the deduction. Line 4: will update database with new balance value after withdrawal amount deducted from original balance. balance which is a local variable holding the new balance transfer to the account.balance and update record with new balance value. Line 5: will return new balance value to the screen if necessary Line 6: will terminate the process of withdraw by } There will be no concurrent when two threat access lines 1, 5 and 6. But if any threat try to access lines 2, 3 and 4 will be given incorrect information for one of the threats. Therefore from line 2 to 4 is very critical to let access only for one threat at any given time of the process as explain bellow. int withdraw (account, amount) { int balance = account.balance; balance -= amount;Critical Section account.balance = balance; return balance; } This identified sections will call as a critical section in another word, no other threats will allows to access while one threat is using at any given time because data will be manipulate when access line 2, 3 and 4. Critical section Critical section is set of codes access shared resources and there are several ways of developing critical section such as: Locks, Semaphores, Monitors and Messages. In this report will describe locks and semaphores how behave and how priority will work. Locks in synchronization First method of synchronization is locks. Locking is a very primitive system been used. Lock will lock the threat in the critical section while it is processing the record. Mainly lock has two stats Held and Not Held. At the Held state, one threat is in the critical section and at the Not Held state no threats in the critical section and can prioritised threats to have access. Also locks having two operations Acquire and Release. Which threat will request the lock to be held to access critical section and once threat previously use critical section release the lock acquired thread will get a chance and change the state as held. When threat finish it process in the critical section must release the lock to use by the other threats which are waiting in the queue. Figure The above figure has explain how acquire and release will behave at the critical section access, i.e. threats A, B and C request access permission to critical section at the same time by Acquire operation and threat A will grant access with the lock Held state enable. Once threat complete the process will call release operation to change the lock state to Not Held and lock will change state to Held with threat B and so on will be proceed to complete different threat request at the critical section. By using previous example take a look where to use Acquire and Release operations threat. int withdraw (account, amount) { acquire (lock); // Request lock to held to access critical section int balance = account.balance; balance -= amount;Critical Section account.balance = balance; release (lock); // Release lock after complete critical section access return balance; } With further explanation considering previous withdraw and deposit situation Figure 2. Overcome concurrency situation had occurred while both people access same account balance to manipulate the amount. Figure When implement locks use Boolean variable to check is lock held TRUE or FALSE? Acquire operation will keep other threats in the waiting state while lock held values is TRUE. If lock held VALUE is false, will change to TRUE with requested threat. When the threat completed process in critical section will call release operation and change lock held value as FALSE to make lock available for other threats will show in below construct. First create a global Boolean type variable held values TRUE or FALSE to check is lock holding by a threat or not and by default lock will not hold by any threat and value will be FALSE. structure lock { bool held; // initial value FALSE } Construct acquire by requesting a lock to be held and if lock à ¯Ã†â€™Ã‚  held value TRUE request threat will wait in the queue for lock to be released. If lock à ¯Ã†â€™Ã‚  held is FALSE and by acquire change value of lock à ¯Ã†â€™Ã‚  held to TRUE and take the control of the critical section access. void acquire (lock) { while (lock à ¯Ã†â€™Ã‚   held) ; // Hold other threats in the wait queue lock à ¯Ã†â€™Ã‚   held = TRUE; // Once get the lock, change lock value to TRUE } Construct release operation simply will change the start of lock à ¯Ã†â€™Ã‚  held value to false and allows other threat to access critical section for the next process. void release (lock) { lock à ¯Ã†â€™Ã‚   held = FALSE; // When complete process in the critical section, change lock value to FALSE } Semaphores in synchronization This is the second method of synchronization. This method is a very basic and powerful mechanism but difficult Implementation method and use blocking threats to access critical section instead of locking threats while using critical section. Semaphores has two operations and they are: wait (semaphore) or P() First of all as soon as threat request access permission P() or wait (semaphore) will decrease the counter values which is 1 by default. Then check is counter value become 0 or signal (semaphore) or V() Once a threat complete process in the critical section will call V() or signal (semaphore) and will increase counter value by 1. i.e. if a P() had decrease counter value 0 while it was in critical section and no other threats can access, but second threat has decreased to -1 while requesting permission to access critical section and waited. Also since second threat is still waiting to get permission it goes to sleep mode, hence V() will wake up threat in a sleep to start it process in critical section explains in Figure à ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦. Figure à ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦Ãƒ ¢Ã¢â€š ¬Ã‚ ¦.. Figure Readers/Writers synchronization This is another powerful method of synchronization. In this method, the data is accessed by two different ways. Those two ways are, readers and writers. Here, the readers only read files and writers update file contents or data. There are four (4) rules while using the readers/writers synchronization methods and they are as follows, If any reader(s) read the file and no writer is pending, the next reader can read the file without waiting. Writers have to wait till the reader(s) finish reading file. After readers finish reading, writer(s) will can start writing. If any writer is writing to the file, acquiring readers have to wait till writer finish writing. If one writer is writing to the file and if both readers and writers are waiting, at this situation priority will be given for writers who are waiting. Therefore readers will wait till all writers to compete writing and then readers will start reading. So readers can read most updated file. Future trends of synchronization In the current situation, locks and semaphores are widely used in order to prevent the concurrency. So it is very important to deal with the codes in critical section as otherwise there will be a lot of problems with the reliability of information systems. However using of systems with the locks are not time efficiency. So in the current situation of the computer technology, there is a trend of implementing lock free systems. According to the previous example of shared street, the shared street has to be controlled by using traffic lights. So on the shared streets, only one direction is allowed at one time. So the other directions are blocked at the same time. But there is a technique that does not need of using any traffic lights on the shared street. Here, fly over technique can be used and avoid blocking the directions. So all the directions on the shared street can be used at once without having any problem. But here, this technique may has some more waiting time as the length of the street can be increased while using fly over technique. Like in this example, lock free systems can be implemented in information systems. Semaphore method can be taken as an example for lock free system. But here as well, the processes have to wait sometimes as in the give example of fly over technique on shared streets. The weakness of this method is that lock free and wait free features cannot be implemented in the same information system. So only one of these methods (lock free or wait free) can be implemented in information system.

Formalistic and Dialogic Analysis of The Descent of Odin :: Descent of Odin Essays

Formalistic and Dialogic Analysis of The Descent of Odin Poems are more that words on a piece of paper, it is a grand "play" with different "characters" strewn onto the pages. "The Descent of Odin" is a poem with a story with a rich vein of conversation embedded into it. By using the formalistic and dialogic method, I plan on showing you these jewels that I found while reading this poem. The first voice that is found in the poem is the voice of the Narrator. When using the Dialogical Method, the reader notices that the voice is obviously an older person. Now, when the poem is turned to Formalistic, see how the point of view of the Narrator is like a mediator at the beginning at the poem. There he is looking out during the vocal transitions between Odin and the Prophetess, then relays it back to the reader (HCAL, Dialogics pg 349,P.O.V. pg. 87, Voice: pg, 89). His speech is very sensual and symbolic, which adds to the darkness of the poem. The first example of this is the beginning of the poem where you can read it (HCAL pg 85). Up rose the king of men with speed, And saddled straight his coal-black steed; Down the yawning steep he rode, That leads to Hela's drear abode ("The Descent of Odin", Lines 1-4). Look the wording that he uses for the color of the steed: coal-black, the slope of the steep. It causes the reader to take another glance at the poem to visualize wh at is going on with their mind and imagine that they are there watching "The king of men" ride his horse to Hela's abode. The second example is found in the second paragraph. Right against the eastern gate, By the moss-grown pile he sate; Where long of yore to sleep was laid the dust of the prophetic maid ("Odin", lines 17-20). Now we take a glance at the voice of Odin, the mighty god of war. Fix onto the lines of Odin when he first speaks. His voice is not induced with flowery language; instead it is very plain with even tones. The voice of Odin causes the reader to be pulled back to earth (HCAL pg 87). The voice seems to say, "Look at me, listen to me!† Now look at how he converses with the Prophetess: Yet a while my call obey; Prophetess awake, and say.

Journey to Become a Nurse Essay

I like to help and nurture people back to health, so why not join a career which includes that? Nursing goes along well with what I’m best at, it could be the perfect career for me. Where I can enjoy helping people and taking care of them to make them feel better. If they are sick, I want to help figure out what is causing them to feel that way or what the symptoms are of the possible illnesses. I’m also a very social person and can talk to anybody, which is something needed if you want to become a nurse. But what does it take? Will the money spent going to school be reimbursed or more by the career I have chosen? Well we’re about to find out! Before you decide what career to choose for life, you need to look at everything. Where to go, what school has the best programs, would it be better to get a degree, what benefits it has for family matters, how much it pays, can it support the lifestyle you’re looking for in life, and how much time you can get off. There are so many more but how can you think through all of them in such a short period of time? Even two to three years won’t be good enough to think of all the questions. But what I am going to do is answer the most important questions that you should consider in the period of time leading up to the time you need to choose the occupation you will be doing for the rest of your life or for a majority of your life. One of the most important questions you need to consider would be, what do you enjoy to do the most in your life? If you consider being a nurse as one the possibilities you could be happy doing for fifty years or so, then pick it. I’ve read quite a few articles online and they all talk about how most nurses wish that they never went into that profession in the first place. Though it does have flexible hours and family friendly time off, you have to constantly be on your feet running around all over the place, keep track of many doctors patients and paper work, and work really long hours maybe even graveyard shifts. But some say, how much you enjoy being a registered nurse is your attitude towards all the rush and stress. A lot enjoy their jobs and a lot don’t enjoy it as well. It all depends on your outlook on the job. You must also consider where you want to go. Find out where the best place to go would be, and who has the greatest nursing programs. If you can afford a really good college then go there, but if you are working on a low income and have a family and house to take care of then it may not be the best idea to go somewhere out of your budget. Also, consider whether you want to go out of state or stay close to home? Some colleges and universities that are considered to have the best nursing programs in the country, as of 2011, are Columbia University, University of Pennsylvania, and Duke University. They are most selective, meaning they are very hard schools to get into. The top schools in Utah that have the best nursing programs are University of Utah, Westminster College, and Western Governors University. They all are located in Salt Lake City, 4-year program schools, and offer Bachelor’s and Master’s degrees in nursing. Back in 2011, the average salary of a registered nurse was $65,950 annually and the average hourly wage was $34.71. There are many opportunities and advancements you can take advantage of from being a nurse or going to nursing school. You could become a doctor, a nurse practitioner, pediatrician, and a lot more. Some nurses may start their career off as a hospital nurse, but when they are there long enough and have experience, they can be promoted to assistant unit manager or even head nurse. For those nurses who want to go back to school to get a Master’s or a Doctorate’s degree have even greater opportunities. Such as nurse practitioners, nurse midwives, or nurse anesthetist. Experts are saying that the job opportunities for nurses will nearly double the expected average rate for all occupations between the years of 2011 and 2020. This is expected because the medical industry is expanding quickly and the demand for medical personnel will be exceptionally high. Next you want to consider what nurses do on an average day at work. They go around feeding the patients, checking the patients to see how they are doing, be a friend to them and their families, etc. An average nurse’s day is consisted of recording a patient’s history and symptoms on their medical charts, discuss their patients with other nurses and doctors, change the dressings on the wounds so they don’t get infected, observe the patients to  see if they are progressing in health or declining, give them their medications, and talk with their families to discuss what is happening or what is expected. Let’s go a step further, think about the average day of an ER nurse. Their days must be so hectic. I’ve gone to the ER a couple times and what I see there amazes me. There are numerous crazy stories from ER nurses and doctors. For example, one man came in saying he has abdominal pain and he had a rash on his stomach. When they administered an abdomina l exam, they discovered a turkey sandwich that has been there for over a month. Never underestimate a day in the life of a nurse. Learning about nursing, what it takes to become one, what their average day is like, and what to expect for nursing has been informational. There are numerous sources which gives information on what to look forward to. I found out the average wage is $34.71 and the annual salary is $65,950, what schooling you need to participate in before starting a career as a nurse. Becoming a nurse may seem difficult, but it’s all worth it in the end.

What Are A Calendar - 867 Words

Chapter Forty What is research? Research is searching and gathering of information to answer a question. Long hours are spent on research, it is not something that could be done overnight. There are many sources available for gathering information. It can range from books, articles from magazines and newspapers, countless sources from the Web, and information gathered from experiments and field research. With much information easily available, it is easy to get drowned in more than what is needed. There are strategies you can follow in order to avoid an overwhelming research, A research could be done smoothly and with less stress if it is planned and done in an organized manner. Before starting a research, make sure you†¦show more content†¦Make sure to always keep a record of every source encountered even when you think you will not need it for later. This will help you save time just in case you need to revisit a source. Chapter Forty-one There are three different types of resources. These are the libraries, informational databases and indexes, and the Internet. In the library you will find books, journals, newspapers, and other printed materials. Librarians can help you locate and evaluate sources. There are also services such as EBSCohost, InfoTrac, and LexisNexis that provide abstracts or full versions of articles in journals, magazines, and newspapers. These are examples of online databases and indexes. And then there is the Web. You can find endless source of information just by using search engines such as Google and Bing. Be careful with the information gathered on the internet, they are not always the best of quality. When working with these different type of resources you need to learn its full capacity in doing research using each tool. Learn to use the library catalog. It can tell you if the library has the item you need, its location on the shelves, and its availability. You c an search an item by its author, title, subject, keywords, and call number. If you are unable to go to a library another excellent option is to use a research guide. These are