A virtual thread cannot be unmounted during a blocking operation, including executing code inside a synchronized block or method. Why is this the case and how does a semaphore fit into this equation?
The Solutions:
Solution 1: Compare-and-Swap (CAS) vs. Thread Blocking
The difference between synchronized blocks and semaphores lies in their synchronization mechanisms.
Synchronized Blocks:
Use a spin lock, which means the thread continues executing instructions while waiting.
Block the thread in case of contention.
Semaphores:
Use non-blocking CAS (Compare-and-Swap) technique.
Yield after a few failed CAS attempts.
Key Distinctions:
CAS techniques do not block the thread, whereas synchronized blocks do.
ReentrantLock and AQS (which is used by semaphores) also use CAS, but they may still block the thread using LockSupport.park.
Virtual Threads cannot be unmounted during blocking operations. Since synchronized blocks block the thread, they require a semaphore to prevent Virtual Thread unmounting.
Q&A
Is a synchronized block a spin lock?
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Yes, a synchronized block is implemented as a spin lock in Java.
What is the difference between a synchronized block and a semaphore?
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A synchronized block is a non-blocking synchronization primitive, while a semaphore is a blocking synchronization primitive.
Video Explanation:
The following video, titled "Loom is Blooming by José Paumard & Remi Forax - YouTube", provides additional insights and in-depth exploration related to the topics discussed in this post.
These virtual threads can be block at almost no cost. These new ... Java 21 new feature: Virtual Threads #RoadTo21. Java•45K views · 51:52.
