Transcript IPC - Inter-process Communication

Interprocess Communication
Race Conditions
Two processes want to access shared memory at same time
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Critical Regions (1)
Four conditions to provide mutual exclusion
1.
2.
3.
4.
No two processes simultaneously in critical region
No assumptions made about speeds or numbers of CPUs
No process running outside its critical region may block
another process
No process must wait forever to enter its critical region
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Critical Regions (2)
Mutual exclusion using critical regions
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Mutual Exclusion with Busy Waiting (1)
Proposed solution to critical region problem
(a) Process 0.
(b) Process 1.
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Mutual Exclusion with Busy Waiting (2)
Peterson's solution for achieving mutual exclusion
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Mutual Exclusion with Busy Waiting (3)
Entering and leaving a critical region using the
TSL instruction
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Sleep and Wakeup
Producer-consumer problem with fatal race condition7
What is a Semaphore?
•A mechanism that provides concurrency among processes.
•Facilitates synchronization among processes.
•Usually implemented with a struct, including an int as well
as other information fields, and a queue to ensure mutual
exclusion to a shared resource.
•Requires two operations (functions):
•sleep() or down()
•wakeup() or up()
•A new type of variable that saves the number of pending
wakeups.
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Semaphores
The producer-consumer problem using semaphores
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Mutexes
Implementation of mutex_lock and mutex_unlock
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