Producer Consumer Problem
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The document describes the producer-consumer problem where a producer produces items that are inserted into a shared buffer and a consumer removes items from the buffer. There must be careful synchronization between the producer and consumer so that the consumer does not try to remove an item from an empty buffer or the producer inserts into a full buffer. A typical solution uses a shared count variable and puts the producer or consumer to sleep if the buffer is full or empty, respectively, waking the other process up when it is possible for it to proceed.
Producer Consumer Problem
- 1. Problematic Scenario -Count is initially 0 Consumer reads the count- -Producer produces the item, inserts it, and increments count to 1 -Producer executes wakeup, but there is no waiting consumer (at this point) PRODUCER CONSUMER PROBLEM
- 2. -Consumer continues its execution and goes to sleep -Consumer stays blocked forever unnecessarily -Main problem: wakeup was lost
- 3. THE PRODUCER/CONSUMER PROBLEM WITH DIAGRAM from time to time, the producer places an item in the buffer the consumer removes an item from the buffer careful synchronization required the consumer must wait if the buffer empty the producer must wait if the buffer full producer process consumer process P buffe r C
- 4. typical solution would involve a shared variable count also known as the Bounded Buffer problem Example: in UNIX shell eqn myfile.t | troff
- 5. 5 OVERVIEW OF SOLUTIONS Low-level (for mutual exclusion) Interrupt disabling Using read/write instructions Using powerful instructions (Test-and-set, Compare-and Swap…) OS-level support (mutual exclusion and synchronization) Special variables: Semaphores, Mutexes Message passing primitives (send and receive) High-level Synchronization Primitives Monitors (Hoare, Brinch-Hansen) Synchronized method in Java Idealized Problems Producer-Consumer Dining Philosophers Readers-Writers
- 6. 6 SLEEP/WAKEUP SOLUTION TO PRODUCER-CONSUMER PROBLEM bounded buffer (of size N) producer writes to it, consumer reads from it Solution using sleep/wakeup synchronization int count = 0 /* number of items in buffer */ Producer code: while (TRUE) { /* produce */ if (count == N) sleep; /* add to buffer */ count = count + 1; if (count == 1) wakeup(Consumer); } Consumer code: while (TRUE) { if (count==0) sleep; /* remove from buffer */ count = count -1; if (count == N-1) wakeup(Producer); /* consume */ }