Synchronization- Semaphore

Provide a scenario that shows the following policy gives priority to writers. In your scenario, you should have two readers and a writer.

reader() { while(TRUE) { ; P(writePending); P(readBlock); P(mutex1); readCount++; if(readCount == 1) P(writeBlock); V(mutex1); V(readBlock); V(writePending); access(resource); P(mutex1); readCount--; if(readCount == 0) V(writeBlock); V(mutex1); } } int readCount = 0, writeCount = 0; semaphore mutex1 = 1, mutex2 = 1; semaphore readBlock = 1, writeBlock = 1, writePending = 1; fork(reader, 0);/* could be many */ fork(writer, 0);/* could be many */

writer() { while(TRUE) { ; P(mutex2); writeCount++; if(writeCount == 1) P(readBlock); V(mutex2); P(writeBlock); access(resource); V(writeBlock); P(mutex2) writeCount--; if(writeCount == 0) V(readBlock); V(mutex2); } }

Time Action Result

0 Reader 1 arrives

1 Reader 1 executes P (writePending) writePending = 0

2 Reader 1 executes P (readBlock) readBlock = 0

Fill in the rest of the operations steps

(the answers i have so far

3 Reader 1 executes P (mutex)_ m1=0

4 Reader 1 executes readcount++ rc=1

5 Reader 1 executes p(write block) wb=0

6 Reader 1 executes v(mutex1) m1=1

7 Reader 1 executes v(read block rb=1

8 Reader 1 executes v(write pending) wp=1

9 Reader 1 executes access(resource)

10 Reader 1 is interrupted

11 W1 arrrives

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