The operators P and V

1
The operators P and V

• P (request)
• P (sem)
• Sem - -
• If Sem lt 0
• Block on Sem
• V (sem)
• Sem
• If Sem lt 0
• Wake up next process

2
Types of Semaphores

• Binary semaphore maximum value of 1
• Counting semaphore maximum value other than 1

3
Producer/Consumer Problem

• Set of 10 buffers
• Producer fills a buffer with information
• Consumer empties the buffer when it is full

4
Producer/Consumer Problem

• Producer
• P (empty)
• P (mutex)
• ltCSgt
• V (mutex)
• V (full)

• Consumer
• P (full)
• P (mutex)
• ltCSgt
• V (mutex)
• V (empty)