A semaphore is a blocking synchronisation primitive. Describe how they work with the aid of pseudo-code. You can assume the existance of a thread_block() and a...

A semaphore is a blocking synchronisation primitive. Describe how they work with the
aid of pseudo-code. You can assume the existance of a thread_block() and a thread_wakeup()
function

---

Semaphores work by blocking processes with P, calling thread_block(), waiting for a resource if it is not
available, then being put into a queue of processes that want to access this resource. This is more
efficient than other solutions because we avoid busy waiting – other processes can do other things while
blocked ones are in the queue! When a resource is released, V is run, which calls thread_wakeup() to
signal the next thread to use it. See:

---

Titany answered the question on April 26, 2022 at 05:35

Exams With Marking Schemes

• Grade 1
• Grade 2
• Grade 3
• Grade 4
• Grade 5
• Grade 6
• Grade 7
• Grade 8
• Grade 9
• PP1
• PP2
• Playgroup
• Form 1
• Form 2
• Form 3
• Form 4

Related Questions

---

• What is the producer consumer problem? Give an example of its occurrence in operating systems (Solved)
  

  What is the producer consumer problem? Give an example of its occurrence in operating systems

  Date posted: April 26, 2022 .    Answers (1)

• Interrupt disabling and enabling is a common approach to implementing mutual exclusion, what are its advantages and disadvantages? (Solved)
  

  Interrupt disabling and enabling is a common approach to implementing mutual exclusion,
  what are its advantages and disadvantages?

  Date posted: April 26, 2022 .    Answers (1)

• Why is turn passing a poor solution to the critical sections problem? (Solved)
  

  Why is turn passing a poor solution to the critical sections problem?

  Date posted: April 26, 2022 .    Answers (1)

• What are three requirements of any solution to the critical sections problem? Why are the requirements needed? (Solved)
  

  What are three requirements of any solution to the critical sections problem? Why are the
  requirements needed?

  Date posted: April 26, 2022 .    Answers (1)

• What is a critical region? How do they relate to controlling access to shared resources? (Solved)
  

  What is a critical region? How do they relate to controlling access to shared resources?

  Date posted: April 26, 2022 .    Answers (1)

• What is a race condition? Give an example (Solved)
  

  What is a race condition? Give an example

  Date posted: April 26, 2022 .    Answers (1)

• Context switching between two threads of execution within the operating system is usually performed by a small assembly language function. In general terms, what does this small... (Solved)
  

  Context switching between two threads of execution within the operating system is
  usually performed by a small assembly language function. In general terms, what does this
  small function do internally?

  Date posted: April 26, 2022 .    Answers (1)

• Enumerate the advantages and disadvantages of supporting multi-threaded applications with kernel-level threads (Solved)
  

  Enumerate the advantages and disadvantages of supporting multi-threaded applications
  with kernel-level threads

  Date posted: April 26, 2022 .    Answers (1)

• Why are user-level threads packages generally cooperatively scheduled? (Solved)
  

  Why are user-level threads packages generally cooperatively scheduled?

  Date posted: April 26, 2022 .    Answers (1)

• Name some advantages and disadvantages of user-level threads (Solved)
  

  Name some advantages and disadvantages of user-level threads

  Date posted: April 26, 2022 .    Answers (1)

• Describe how a multi-threaded application can be supported by a user-level threads package. It may be helpful to consider (and draw) the components of such... (Solved)
  

  Describe how a multi-threaded application can be supported by a user-level threads package. It may be helpful to consider (and draw) the components of such a package, and the function they perform

  Date posted: April 26, 2022 .    Answers (1)

• What is a process? What are attributes of a process? (Solved)
  

  What is a process? What are attributes of a process?

  Date posted: April 26, 2022 .    Answers (1)

• Multi-programming (or multi-tasking) enables more than a single process to apparently execute simultaneously. How is this achieved on a uniprocoessor? (Solved)
  

  Multi-programming (or multi-tasking) enables more than a single process to apparently execute simultaneously. How is this achieved on a uniprocoessor?
  

  Date posted: April 25, 2022 .    Answers (1)

• Describe the three state process model, describe what transitions are valid between the three states, and describe an event that might cause such a transition (Solved)
  

  Describe the three state process model, describe what transitions are valid between the
  three states, and describe an event that might cause such a transition
  

  Date posted: April 25, 2022 .    Answers (1)

• Is putting security checks in the C library a good or a bad idea? Why? (Solved)
  

  Is putting security checks in the C library a good or a bad idea? Why?
  

  Date posted: April 25, 2022 .    Answers (1)

• Why must the operating system be more careful when accessing input to a system call (or producing the result) when the data is in memory... (Solved)
  

  Why must the operating system be more careful when accessing input to a system call (or
  producing the result) when the data is in memory instead of registers?

  Date posted: April 25, 2022 .    Answers (1)

• Describe the two general roles of an operating system, and elaborate why these roles are important (Solved)
  

  Describe the two general roles of an operating system, and elaborate why these roles are
  important

  Date posted: April 25, 2022 .    Answers (1)

• Name three non electronic tools that were used before the invention of electronic computers. (Solved)
  

  Name three non electronic tools that were used before the invention of electronic computers.

  Date posted: July 23, 2021 .    Answers (1)

• Write the following acronyms in full. i. ICT ii. CPU iii. VLSI iv. UPS (Solved)
  

  Write the following acronyms in full.
  i. ICT
  ii. CPU
  iii. VLSI
  iv. UPS

  Date posted: July 23, 2021 .    Answers (1)

• Define the term troubleshooting as used in operating systems. (Solved)
  

  Define the term troubleshooting as used in operating systems.

  Date posted: July 23, 2021 .    Answers (1)