Consider the following two programs in a shared address space. Remember that semaphores are signals (like the flags and lights that railroads use) item buffer [5]; semaphore full (0); semaphore empty (5); semaphore mutex; while (1) { // produce next item to store wait (empty); wait (mutex); // add item to item_buffer signal (mutex); signal (full); while (1) { wait (full); wait (mutex); // remove item from item_buffer; signal (mutex); signal (empty); 11 consume the item } Why must "wait(mutex)" be the last wait performed? • Why does the program on the left wait on the "empty" semaphore, but signal the "full" semaphore? • Why was the "mutex" semaphore added? (What is its purpose?)

Consider the following two programs in a shared address space. Remember that semaphores are signals (like the flags and lights that railroads use) item buffer [5]; semaphore full (0); semaphore empty (5); semaphore mutex; while (1) { // produce next item to store wait (empty); wait (mutex); // add item to item_buffer signal (mutex); signal (full); while (1) { wait (full); wait (mutex); // remove item from item_buffer; signal (mutex); signal (empty); 11 consume the item } Why must "wait(mutex)" be the last wait performed? • Why does the program on the left wait on the "empty" semaphore, but signal the "full" semaphore? • Why was the "mutex" semaphore added? (What is its purpose?)

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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