Readers_Writers_SlideShare_Style.Sa.pptx

1. First Problem – Reader Priority
2. Second Problem – Writer Priority
3. Third Problem – No Starvation (Fair)

1. Reader Writer Problem Operating Systems By Rinku Monani

2. Introduction • A problem that deals with synchronization. • Involves a data set shared among concurrent processes. • Two types of processes: readers and writers. • Readers only read; writers update or write. • Important to maintain data consistency.

3. Sharing of Data • Allow multiple readers simultaneously. • Only one writer at a time. • A writer must have exclusive access.

4. Active Readers and Writers • If one writer is writing, no other process (reader or writer) can access the data. • If one or more readers are reading, no writer can access the data. • Multiple readers can read simultaneously.

5. Types of Reader Writer Problem 1. Reader Priority 2. Writer Priority

6. Reader Priority • Multiple readers can read at the same time. • Writer must wait until readers finish. • Problem: Writer starvation.

7. Writer Priority • Writers given priority over readers. • Once a writer is waiting, no new readers are allowed. • Problem: Reader starvation.

8. Semaphores • Semaphore is a synchronization tool. • Can be used to control access to shared resources.

9. Semaphore Definitions • readcount – number of readers currently reading. • mutex – controls access to readcount. • wrt – allows writers exclusive access to the data.

10. Structure of Reader Process // Reader wait(mutex) readcount++; if (readcount == 1) wait(wrt); signal(mutex) [Reading is performed] wait(mutex) readcount--; if (readcount == 0) signal(wrt); signal(mutex)

11. Structure of Writer Process // Writer wait(wrt) [Writing is performed] signal(wrt)

12. End Thank you!