How do virtual threads differ from platform threads in Java?

Explains cheap JVM-scheduled threads, blocking-I/O throughput, carrier pinning, ThreadLocal cost, and unchanged downstream limits.

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A platform thread is typically backed by an operating-system thread for its lifetime. A virtual thread is a lightweight Java thread scheduled by the JVM over a smaller set of carrier platform threads. When a virtual thread blocks in supported operations, the JVM can usually unmount it so the carrier runs other work. This improves throughput for many blocking I/O tasks; it does not make CPU-bound work execute faster than available cores.

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Modern Java concurrency judgment without treating virtual threads as faster CPU threads.

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Virtual threads make thread-per-task blocking code scalable for suitable workloads by decoupling Java task count from platform-thread count.
A platform thread is typically backed by an operating-system thread for its lifetime. A virtual thread is a lightweight Java thread scheduled by the JVM over a smaller set of carrier platform threads. When a virtual thread blocks in supported operations, the JVM can usually unmount it so the carrier runs other work. This improves throughput for many blocking I/O tasks; it does not make CPU-bound work execute faster than available cores.
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Virtual threads are intended to be created per task rather than pooled. A semaphore or downstream pool should limit scarce resources such as database connections or provider concurrency. Some operations can pin a virtual thread to its carrier, and library or native behavior must be checked on the target JDK. Thread-local values can become expensive when the application creates very many virtual threads.

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Pooling virtual threads.
Using them as a CPU speedup.
Removing downstream concurrency limits.

How do virtual threads differ from platform threads in Java?

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