Deadlock Prevention

 Do not allow one of the four conditions to occur.

No preemption:

a)  Release any resource already being held if the process can't get an additional resource.

b)  Allow preemption - if a needed resource is held by another process, which is also waiting on some resource, steal it. Otherwise wait.

Circular wait:

 Number resources and only request in ascending order.

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EACH of these prevention techniques may cause a decrease in utilization and/or resources. For this reason, prevention isn't necessarily the best technique.

Prevention is generally the easiest to implement.

Do not allow one of the four conditions to occur.

 Do not allow one of the four conditions to occur.

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Mutual exclusion:

a)   Automatically holds for printers and other non-sharables.

b)   Shared entities (read only files) don't need mutual exclusion (and aren’t susceptible to deadlock.)

c)   Prevention not possible, since some devices are intrinsically non-sharable.

Hold and wait:

a)   Collect all resources before execution.

b)   A particular resource can only be requested when no others are being held.  A sequence of resources is always collected beginning with the same one.

c)   Utilization is low, starvation possible.

DEADLOCKS

Mutual exclusion

One or more than one resource must be held by a process in a non-sharable (exclusive) mode.

Hold and Wait

A process holds a resource while waiting for another resource.

No Preemption

There is only voluntary release of a resource - nobody else can make a process give up a resource.

Circular Wait

Process A waits for Process B waits for Process C .... waits for Process A.

Multiprocessor Operating Systems

•Consists of a set of processors that share a set of physical memory blocks & clock over an interconnection network.

•Controls & manages HW & SW resources such that users view it as a uniprocessor system.

•Design issues same as traditional system.

•Practical issues: increased complexity of synchronization, scheduling, memory management, protection and security.

Functions of an OS

•Resource Management:

–Time management - CPU and disk scheduling

–Space management - main and secondary storage allocation

–Synchronization and deadlock handling (Controlled Sharing) - IPC, critical section, coordination

–Accounting and status information - resource usage tracking

•User Environment - OS layer transforms bare hardware machine into higher level abstractions

–Execution environment - process management, file manipulation, interrupt handling, I/O operations, language.

–Error detection and handling

–Protection and security

–Fault tolerance and failure recovery

•User Friendly Interface

computer systems

•Hardware and software combine to solve specific problems

–Software: Application logic providing a service or solves some problem: entertainment, information management, scientific problem solving, system control, forwarding packets in a router, etc.
Although strictly speaking many solutions can be designed and implemented entirely in hardware but this is a course on operating systems.

–Hardware: provides the basic computing resources (Processor(s), Memory, System Bus and I/O modules).

•Software is divided into two categories:

–System software: simplifies application programming by creating convenient to use programming and run-time environments.

•Resource Management: time and space multiplexing of system resources

•Extended virtual machine: standardized interfaces and abstractions simplify programming and system use

–Application software: used directly by user (person, another program or computer system) to solve some problem.

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Mesotheliomo: Mesotheliomo

Mesotheliomo: Mesotheliomo: "mesotheliomo , more precisely malignant mesotheliomo , is a rare form of cancer that develops from the protective lining that covers ma..."

Mesotheliomo

mesotheliomo , more precisely malignant mesotheliomo, is a rare form of cancer that develops from the protective lining that covers many of the body's internal organs, the mesothelium. It is usually caused by exposure to asbestos.

Its most common site is the pleura (outer lining of the lungs and internal chest wall), but it may also occur in the peritoneum (the lining of the abdominal cavity), the pericardium (a sac that surrounds the heart), or the tunica vaginalis (a sac that surrounds the testis).

Most people who develop mesotheliomo have worked on jobs where they inhaled asbestos and glass particles, or they have been exposed to asbestos dust and fiber in other ways. It has also been suggested that washing the clothes of a family member who worked with asbestos or glass can put a person at risk for developing mesotheliomo. Unlike lung cancer, there is no association between mesothelioma and smoking, but smoking greatly increases the risk of other asbestos-induced cancers. Those who have been exposed to asbestos have collected damages for asbestos-related disease, including mesotheliomo. Compensation via asbestos funds or lawsuits is an important issue in law practices regarding mesotheliomo (see asbestos and the law).

The symptoms of mesotheliomo include shortness of breath due to pleural effusion (fluid between the lung and the chest wall) or chest wall pain, and general symptoms such as weight loss. The diagnosis may be suspected with chest X-ray and CT scan, and is confirmed with a biopsy (tissue sample) and microscopic examination. A thoracoscopy (inserting a tube with a camera into the chest) can be used to take biopsies. It allows the introduction of substances such as talc to obliterate the pleural space (called pleurodesis), which prevents more fluid from accumulating and pressing on the lung. Despite treatment with chemotherapy, radiation therapy or sometimes surgery, the disease carries a poor prognosis. Research about screening tests for the early detection of mesotheliomo is ongoing

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