SemaphoreThe underlying implementation principle of the class involves more complex thread synchronization and operating system-related mechanisms, and is implemented based on the underlying counters and thread waiting queues.
In Java, Semaphoreclasses use an inner Syncclass to implement synchronization and thread waiting mechanisms. Specifically, Semaphorethe class uses AQS (AbstractQueuedSynchronizer)a subclass of to manage the thread's permission state and wait queue.
AQSIt is a key class in the Java concurrency package, which is used to implement the basic framework of locks and synchronizers. It represents the number of permits through an integer counter, and manages the threads waiting to obtain permits through an internal waiting queue. AQSProvides basic implementations of atomic operations and thread wait queues.
For Semaphorethe class , Syncthe class inherits from AQSand overrides some of its methods to implement license acquisition and release operations. Specifically, Syncthe class overrides tryAcquireSharedthe and tryReleaseSharedmethods to implement the permission acquisition and release logic. tryAcquireSharedThe method is used to try to obtain a license. If the number of licenses is greater than zero, the acquisition is successful; otherwise, a negative value is returned to indicate that the acquisition failed and enter the waiting queue. tryReleaseSharedThe method is used to release the license, increase the number of licenses by one, and wake up the threads in the waiting queue.
Through AQSthe internal mechanism of , Semaphorethe class can realize the acquisition and release of the license, and correctly manage the threads in the waiting queue to ensure the synchronization and mutual exclusion of the threads.
It should be noted that Semaphorethe underlying implementation principles of classes may vary with different Java versions and specific implementations. The above description is a common implementation. The actual implementation details may vary between different implementations of the JVM.