![]() The construct uses a variable known as a counter that controls access over the shared resource. In Java, it is a thread synchronization construct. ![]() Public synchronized void notifyToWakeup() Public synchronized void waitForNotify() throws InterruptedException Let's see the implementation of the counting semaphores. For example, consider the following code snippet. Hence to overcome this problem we use counting semaphore. The counting semaphores are used to resolve the situation in which more than one process wants to execute in the critical section, simultaneously. There are four types of semaphores, which are as follows: Let's understand the working of semaphore with the help of a flow chart. If counter = 0, the thread does not get permission to access the shared resource.If another thread is waiting for acquiring a resource, the thread will acquire a permit at that time.After releasing the resource, the counter value incremented by 1. When the execution of the thread is completed then there is no need for the resource and the thread releases it.Else, the thread will be blocked until a permit can be acquired.If counter > 0, the thread gets permission to access the shared resource and the counter value is decremented by 1.It contains a value either greater than 0 or equal to 0. Semaphore controls over the shared resource through a counter variable. We can implement semaphore using the test operation and interrupts, and we use the file descriptors for executing it.It holds a value that may either greater than zero or equal to zero. The semaphore does not contain a negative value.Hence, provides a low-level synchronization mechanism. It decreases the level of synchronization.It provides synchronization among the threads.There are the following characteristics of a semaphore: Therefore, semaphore grants permission to threads to share a resource. In short, the counter keeps tracking the number of permissions it has given to a shared resource. If counter = 0, access to shared resources is denied.If counter > 0, access to shared resources is provided.A mechanism in which a thread is waiting on a semaphore can be signaled by other threads. In other words, it is a non-negative variable that is shared among the threads known as a counter. What is a semaphore?Ī Semaphore is used to limit the number of threads that want to access a shared resource. After knowing all about it, we will move to the Java semaphore programs. We will discuss it later in this section.īefore moving ahead in this section, first, we will understand what is semaphore, types of semaphore, how it works, and how to implement semaphore. Java also provides a Semaphore class that contains constructors and various methods to control access over the shared resource. It is used to control access to a shared resource that uses a counter variable. In Java, we use semaphore in the thread synchronization. ![]()
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