Exercises 1-6

Answers:

1.A deadlock is a problem occuring when the resources needed by some jobs to finish execution are held by other jobs, which, in turn, are waitingfor other resources to become available...Or a situation wherein two or more competing actions are waiting for the other to finish, and thus neither ever does.Also called deadly embrace. A Starvation is the result of conservative allocation of resources in which a single job is prevented from execution because it's kept waiting for resources that never become available. Similar in effect to deadlock. Two or more programs become deadlocked together, when each of them wait for a resource occupied by another program in the same set. On the other hand, one or more programs are in starvation, when each of them is waiting for resources that are occupied by programs, that may or may not be in the same set that are starving. While a race is a synchronozation problem between two processes vying for the same resources.

2. Real-life example of deadlock is the traffic.Real-life example of starvation is in the staircase, when two people meet at the opposing side. The staircase can be accomodated by one person.Real-life example of Race is when two people arrived at the same time on the same door.

3. Four Necessary Conditions for Deadlock:The presence of deadlock in a systems is characterized by these four necessary conditions. The term necessary means that if there is deadlock then all four must be present.
a. Mutual exclusive resource access - A resource acquired is held exclusively, i.e., it is not shared by other processes.
b. No preemption - A process' resources cannot be taken away from it. Only the process can give up its resources.
c. Hold and Wait - A process has some resources and is blocked requesting more.
d. Circularity - This means that there is a circular chain of two or more processes in which the resources needed by one process are held by the next process.

4. Algorithm for prevention of deadlock and starvation:

public boolean tryAcquire( int n0, int n1, ... ) { if ( for all i: ni ≤ availi ) { // successful acquisition availi -= ni for all i; return
true; // indicate success } else return false; // indicate failure}

init) Semaphore s = new Semaphore(1,1);

Thread A Thread B

-------- --------

s.acquire(1,0); s.acquire(0,1);
s.acquire(0,1); s.acquire(1,0);
Thread B--------
while(true) {
s.acquire(0,1);
if ( s.tryAcquire(1,0) ) // if second acquisition succeeds
break; // leave the loop
else {
s.release(0,1); // release what is held
sleep( SOME_AMOUNT); // pause a bit before trying again
}
}
run action s.value--- ------ -------
(1,1)A s.acquire(1,0) (0,1)B s.acquire(0,1) (0,0)A s.acquire(0,1)
A blocks on secondB s.tryAcquire(1,0) => falseB s.release(0,1) (0,1)A s.acquire(0,1) (0,0) A succeeds on second

5.a. Deadlock can occur when the bridge is destroyed.
b. When there are no traffic lights.
c. To prevent deadlock make all the road to be one-way direction.

6. Figure 5.17
a. This is not a deadlocked.
b. There is no blocked processes.
c. P2 can freely request on R1 and R2.
d. P1 can freely request on R1 and R2.
e. Both P1 and P2 have requested R2.
1. P1 will wait after the request of P2.
2. P2 will wait after the request of P1.

the reasons why a regional bank might decide to buy six server computer instead of one supercomputer

• The regional bank can save investments with six servers computers.
  
• And avoid any lost or damage with only one computer running.
  
• The regional bank can have at least 3 or 4 computers running when 2 or 3 computers have its maintenance.


• Supercomputer systems are very expensive both to purchase and maintain, with prices varying depending upon computational power from . Physically they can occupy a substantial amount of space and need controlled environments in terms of cooling and air conditioning. Software for larger supercomputer installations is usually custom written and can be difficult to design, develop and maintain.
• have backups for their important files when the other computers have errors or experiencing problems.

Operating System News

Apple Mac OS X on x86: a first test

Back in June, when Apple boss Steve Jobs announced the platform change to the x86 architecture, some Apple-watchers could not believe their ears. Had Jobs not preached for years that Intel's architecture was much too slow? But Apple's slogan is not 'Think Different' for nothing. Its decision to support the x86 architecture lies in the unsatisfactory performance of the incumbent PowerPC processors -- particularly in the lucrative and growing notebook market, where the IBM/Motorola-designed PowerPC chips clearly lag behind Intel's CPUs.
Mac OS X will not be available on any old x86 PC, though, as Apple wants to retain control over its hardware platform. From the company's point of view, this is an understandable position, as the margins on Apple-branded computers are much higher than is usual for standard x86 PCs.
Were Apple to put the x86 version of its operating system on general release, Dell would begin to manufacture Apple clones. This would put enormous pressure on the price of Apple's own computers -- something the company is naturally keen to avoid. Apple would prefer to manufacture and sell its own high-margin Macs, while denying companies like Dell the chance to endanger its hardware business. This is the motivation behind Apple's decision to restrict the x86 version of Mac OS X to its own hardware.
When Steve Jobs announced the platform change, he publicly demonstrated Apple computers with Intel processors running an x86 version of Mac OS X. The OS is bound directly to the hardware by a special security chip. However, some developers have succeeded in circumventing this coupling, allowing the operating system to be installed on any x86 system, as this test report shows.

Source: http://reviews.zdnet.co.uk/