Lesson 6 - Multithreading in Java - Semaphore
In the previous lesson, Multithreading in Java - Useful components for parallelism, we summarized other available techniques for parallel programming. Today, we're going to show the first of the advanced classes for parallel programming - the semaphore.
Before describing individual synchronization primitives, we'll explain what exactly a critical section is. In the previous lessons, we mentioned it briefly, but didn't explain it in detail. Let's fix that.
A critical section is where concurrency occurs, i.e. where common data is being accessed.
Our goal is to ensure that only one process/thread works with the critical section at a time.
Each critical section refers to specific data being accessed in
s1, ...). We
try to not lock everything but only specific critical
places where the data is shared.
We've already introduced one synchronization primitive: monitor.
Monitor support must be implemented directly in the programming language. In
Java, the monitor is implemented using the
Now let's move on to other primitives.
The Semaphore in C
To understand the principles of the semaphore, we'll show a short abstract implementation in the C language. Dijkstra (1962/1963) designed a primitive that simplifies
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