The Art of Multiprocessor Programming, Revised Reprint

8

Monitors and Blocking Synchronization

8.1 Introduction

Monitors are a structured way of combining synchronization and data. A class encapsulates both data and methods in the same way that a monitor combines data, methods, and synchronization in a single modular package.

Here is why modular synchronization is important. Let us imagine our application has two threads, a producer and a consumer, that communicate through a shared FIFO queue. We could have the threads share two objects: an unsynchronized queue, and a lock to protect the queue. The producer looks something like this:

mutex.lock();

try {

 queue.enq(x)

} finally {

 mutex.unlock();

}

This is no way to run a railroad. Suppose the queue is bounded, meaning that an attempt to add an item ...